Howard Stone's experience with the Radford amp brought this on, so please forgive the rant-like process here.from minimally annoying to spectacularly annoying to genuinely dangerous to life and property.
Guys and Gals:
When introducing a new piece of equipment to the system, please take NOTHING for granted, not even it it is brand-new, fresh from the box. And if it is used, or, much worse, vintage-used please be exceedingly cautious. Equipment failure can be anything
I have no problems running my 56 year old tube system in my office, and leaving it unattended for hours at a time. It has been through my bench, sat for hours on a metered variac, and I created a temperature-table using a heat-gun such that if I seechanges over time, I have a pretty good idea where to look for trouble. But when it came to me, I had no such faith.
In all seriousness, if one is going to pursue this hobby at more than an occasional level, one should obtain the basic tools necessary to do so safely both for the equipment and the real-estate. This is not to suggest that such would have preventedHoward's experience - but he very probably would have seen it coming in time to prevent the special effects.
If there is a consensus, I would be glad to take a picture of my (very basic) bench, and (very basic) tooling, with an explanation for each item and the purpose(s) it services.
Thoughts?
Almost the entire reason for a hobby is to be able to indulge in pointless behavior without consequence.
I don’t think Trevor, that the problem was caused by the fact that it’s a tube amp. I mean, in principle valve amps are as robust as SS aren’t they - apart from the fact that the tubes wear out,
My aim was to find an amp which I liked, regardless of whether or was valve or SS - the fact that the Radford has valves seemed an implementation detail which I would learn with,
Anyway, I’d like to hear a list of your favourite amps Trevor. Since I still don’t have my Radford!
OK, OK, I will bite! Minor rant to follow:voltages and so forth. Other than moving parts (CD player), the newest component in my office system was made in 1963. The system runs 9 hours per day, 5 days per week. Oh, and the tubes are original as well.
Tube vs. Solid State on reliability:
There are not so very many 60-year old components in operation these days unmodified since-new. My oldest tube item turned 100 this year and likely works better than when it was new based on a better understanding of antenna systems, optimum tube
On the other hand, and given my hobby, I see a large number of SS components that have blown transistors, exploded capacitors and much worse, irrespective of age and source. The well made, well designed stuff is serviceable, distinguishing it from therest of the garbage out there.
I would make a fairly apt comparison: A tube amplifier is much like a mid-last-century Mercedes or VW - few things were self-adjusting, and they required regular and attentive care-and-feeding. With such, they were good for several hundred thousandmiles of reliable service. A contemporary Ford, Cadillac, Plymouth would be considered remarkable were it to survive 100,000 miles without heroic measures. Might run very nicely when running, but that would be your basic solid-state device in comparison.
Put simply, they are different beasts designed with different things in mind, but for the same basic purpose. That one is or is not "BETTER" than the other is not relevant to the purpose in either case.rolled on the thighs of virgins on Walpurgis Night...
Now, when I here things like "Zero global NFB" and "Critically matched components", I can smell the snake-oil from a great distance, even the 10,000 miles from here to Australia. I am sure that process also contains descriptives of "interconnects"
Note that even "critically matched" solid-state components drift after a very short period of time in-service. All of them, such that that "less than 1%" is meaningful for perhaps 12 hours or so.
Being as this is a hobby for me, I get to try things that are otherwise unproductive, unprofitable or impractical. Such as shotgunning a device with single-value capacitors and then comparing it to the same device with carefully screened and matchedcaps. Or matching driver and output transistors and comparing to a similar device with disparate values. Guys and gals - you would be seriously shocked to discover how little difference some things make that the ALL-SEEING, ALL-KNOWING gurus will tell
OK, OK, I will bite! Minor rant to follow:voltages and so forth. Other than moving parts (CD player), the newest component in my office system was made in 1963. The system runs 9 hours per day, 5 days per week. Oh, and the tubes are original as well.
Tube vs. Solid State on reliability:
There are not so very many 60-year old components in operation these days unmodified since-new. My oldest tube item turned 100 this year and likely works better than when it was new based on a better understanding of antenna systems, optimum tube
On the other hand, and given my hobby, I see a large number of SS components that have blown transistors, exploded capacitors and much worse, irrespective of age and source. The well made, well designed stuff is serviceable, distinguishing it from therest of the garbage out there.
I would make a fairly apt comparison: A tube amplifier is much like a mid-last-century Mercedes or VW - few things were self-adjusting, and they required regular and attentive care-and-feeding. With such, they were good for several hundred thousandmiles of reliable service. A contemporary Ford, Cadillac, Plymouth would be considered remarkable were it to survive 100,000 miles without heroic measures. Might run very nicely when running, but that would be your basic solid-state device in comparison.
Put simply, they are different beasts designed with different things in mind, but for the same basic purpose. That one is or is not "BETTER" than the other is not relevant to the purpose in either case.rolled on the thighs of virgins on Walpurgis Night...
Now, when I here things like "Zero global NFB" and "Critically matched components", I can smell the snake-oil from a great distance, even the 10,000 miles from here to Australia. I am sure that process also contains descriptives of "interconnects"
Note that even "critically matched" solid-state components drift after a very short period of time in-service. All of them, such that that "less than 1%" is meaningful for perhaps 12 hours or so.caps. Or matching driver and output transistors and comparing to a similar device with disparate values. Guys and gals - you would be seriously shocked to discover how little difference some things make that the ALL-SEEING, ALL-KNOWING gurus will tell
Being as this is a hobby for me, I get to try things that are otherwise unproductive, unprofitable or impractical. Such as shotgunning a device with single-value capacitors and then comparing it to the same device with carefully screened and matched
OK... getting down to basics:necessarily be slower than multiple smaller capacitors in parallel, all other things being equal. The limiting factor being real-estate in most cases.
Electrolytic capacitors are essentially chemical engines. The materials developed over the last 20 years have greatly improved along with longevity and reliability, but they remain chemical engines. A single very large capacitor will, therefore,
Generally, I try to run multiple caps in parallel where real-estate permits, with a small-value, high-voltage film cap across each as a snubber. This is a preference, not a requirement.faster transient than a single very large cap. NOTE: If you are going to have the capacity (pun intended) to overdrive your output devices for these transients, you might need to install some sort of speaker protection. Solid-state devices often do not
For something as brute-force as a power-supply for audio purposes, the difference(s) will be manifest only at or near clipping, or when the amps are fed signal with extreme Peak-to-Average content. A cap bank will be able to deliver a *marginally*
Peter Wieck
Melrose Park, PA
On 10/09/2019 11:54 PM, Peter Wieck wrote:
OK, OK, I will bite! Minor rant to follow:
Tube vs. Solid State on reliability:
There are not so very many 60-year old components in operation these
days unmodified since-new. My oldest tube item turned 100 this year
and likely works better than when it was new based on a better
understanding of antenna systems, optimum tube voltages and so forth.
Other than moving parts (CD player), the newest component in my office
system was made in 1963. The system runs 9 hours per day, 5 days per
week. Oh, and the tubes are original as well.
On the other hand, and given my hobby, I see a large number of SS
components that have blown transistors, exploded capacitors and much
worse, irrespective of age and source. The well made, well designed
stuff is serviceable, distinguishing it from the rest of the garbage
out there.
I would make a fairly apt comparison: A tube amplifier is much like a
mid-last-century Mercedes or VW - few things were self-adjusting, and
they required regular and attentive care-and-feeding. With such, they
were good for several hundred thousand miles of reliable service. A
contemporary Ford, Cadillac, Plymouth would be considered remarkable
were it to survive 100,000 miles without heroic measures. Might run
very nicely when running, but that would be your basic solid-state
device in comparison.
Put simply, they are different beasts designed with different things
in mind, but for the same basic purpose. That one is or is not
"BETTER" than the other is not relevant to the purpose in either case.
Now, when I here things like "Zero global NFB" and "Critically matched
components", I can smell the snake-oil from a great distance, even the
10,000 miles from here to Australia. I am sure that process also
contains descriptives of "interconnects" rolled on the thighs of
virgins on Walpurgis Night...
Note that even "critically matched" solid-state components drift after
a very short period of time in-service. All of them, such that that
"less than 1%" is meaningful for perhaps 12 hours or so.
Being as this is a hobby for me, I get to try things that are
otherwise unproductive, unprofitable or impractical. Such as
shotgunning a device with single-value capacitors and then comparing
it to the same device with carefully screened and matched caps. Or
matching driver and output transistors and comparing to a similar
device with disparate values. Guys and gals - you would be seriously
shocked to discover how little difference some things make that the
ALL-SEEING, ALL-KNOWING gurus will tell you are critical. Often no
difference at all.
Thanks for your input Peter. If I may ask, do you have an opinion on
'storage capacitors' on an amplifier power supply? What in your opinion
is 'better', a single (or few) very large caps or multiple smaller caps
to the same / similar capacitance?
I have a long term project building my own amp based on PCBs taken from
100w MOSFET (two pairs of J50 / K135 devices per amp) PA amps made by a
New Zealand company in the 1980s. (Craft, Gary Morrison's company before
he went on to become head designer at Plinius until 2005 when he left to
set up Pure Audio). I got my hands on a rack of four of these mono amps
and preliminary testing using a clean source and good speakers suggest
they will make a great stereo amp.
I need to put together a power supply to feed two of these and have some
new 10,000uF caps but was wondering if multiple smaller caps would be
better. (In the PA amps they only had 2,200uF but obviously weren't
called on to reproduce much bass.)
As it is I'll be using fly leads from the rectifier PCB to the caps,
then to the amps and I'm building my own case. I was thinking of maybe
using my 10,000uF caps as well as maybe some smaller ones, perhaps 1,000
in a bank, the best of both worlds. (There are also 100uF electros
across the rails on the amp PCBs that I'll be replacing.) That said I
could also just go to multiple
Cheers,
https://www.eeweb.com/tools/parallel-wire-inductanceactual inductance realized will be infinitesimal in "real life".
This website will allow you to calculate inductance by giving it the gauge, type and nature of the wire you are using. You will find, pretty quickly, that the distances involved in the typical component of say 40 cm (16") square are such that the
Again, getting to practical matters: there are common-sense applications and techniques for wiring electronics, much dependent on the nature and use intended. Part of my hobby is the restoration of vintage Zenith TransOceanic tube radios - and wirelocation/component location can be critical for high-band Short Wave sensitivity. It is common sense to shield power-supplies in pre-amplifiers, especially those that contain phono or NAB pre-amp sections. And, wire-dressing is always good practice. But
Now, Trevor clearly has a 'thing' about negative feedback, which is entirely his choice, and doubtless for sufficient and good reasons.
https://en.wikipedia.org/wiki/Negative-feedback_amplifier#Two-port_analysis_of_feedback
Go down to the "distortion" section. As brief as it is, it conveys some very good information.
In point-of-fact, part of the TIP-Mod for your 120 involved increasing capacitance within the feedback loop to reduce bass roll-off.
On 12/09/2019 12:17 am, ~misfit~ wrote:
On 10/09/2019 11:54 PM, Peter Wieck wrote:
OK, OK, I will bite! Minor rant to follow:
Tube vs. Solid State on reliability:
There are not so very many 60-year old components in operation these days unmodified since-new.
My oldest tube item turned 100 this year and likely works better than when it was new based on a
better understanding of antenna systems, optimum tube voltages and so forth. Other than moving
parts (CD player), the newest component in my office system was made in 1963. The system runs 9
hours per day, 5 days per week. Oh, and the tubes are original as well.
On the other hand, and given my hobby, I see a large number of SS components that have blown
transistors, exploded capacitors and much worse, irrespective of age and source. The well made,
well designed stuff is serviceable, distinguishing it from the rest of the garbage out there.
I would make a fairly apt comparison: A tube amplifier is much like a mid-last-century Mercedes
or VW - few things were self-adjusting, and they required regular and attentive
care-and-feeding. With such, they were good for several hundred thousand miles of reliable
service. A contemporary Ford, Cadillac, Plymouth would be considered remarkable were it to
survive 100,000 miles without heroic measures. Might run very nicely when running, but that
would be your basic solid-state device in comparison.
Put simply, they are different beasts designed with different things in mind, but for the same
basic purpose. That one is or is not "BETTER" than the other is not relevant to the purpose in
either case.
Now, when I here things like "Zero global NFB" and "Critically matched components", I can smell
the snake-oil from a great distance, even the 10,000 miles from here to Australia. I am sure
that process also contains descriptives of "interconnects" rolled on the thighs of virgins on
Walpurgis Night...
Note that even "critically matched" solid-state components drift after a very short period of
time in-service. All of them, such that that "less than 1%" is meaningful for perhaps 12 hours
or so.
Being as this is a hobby for me, I get to try things that are otherwise unproductive,
unprofitable or impractical. Such as shotgunning a device with single-value capacitors and then
comparing it to the same device with carefully screened and matched caps. Or matching driver and
output transistors and comparing to a similar device with disparate values. Guys and gals - you
would be seriously shocked to discover how little difference some things make that the
ALL-SEEING, ALL-KNOWING gurus will tell you are critical. Often no difference at all.
Thanks for your input Peter. If I may ask, do you have an opinion on 'storage capacitors' on an
amplifier power supply? What in your opinion is 'better', a single (or few) very large caps or
multiple smaller caps to the same / similar capacitance?
I have a long term project building my own amp based on PCBs taken from 100w MOSFET (two pairs of
J50 / K135 devices per amp) PA amps made by a New Zealand company in the 1980s. (Craft, Gary
Morrison's company before he went on to become head designer at Plinius until 2005 when he left
to set up Pure Audio). I got my hands on a rack of four of these mono amps and preliminary
testing using a clean source and good speakers suggest they will make a great stereo amp.
I need to put together a power supply to feed two of these and have some new 10,000uF caps but
was wondering if multiple smaller caps would be better. (In the PA amps they only had 2,200uF but
obviously weren't called on to reproduce much bass.)
As it is I'll be using fly leads from the rectifier PCB to the caps, then to the amps and I'm
building my own case. I was thinking of maybe using my 10,000uF caps as well as maybe some
smaller ones, perhaps 1,000 in a bank, the best of both worlds. (There are also 100uF electros
across the rails on the amp PCBs that I'll be replacing.) That said I could also just go to multiple
Cheers,
**Those old MOSFETs were pretty ordinary devices (not very linear). Evidenced by the fact that
Plinius amps have always used BJTs. As Peter has stated, multiple small value caps will usually
provide a superior, higher speed power supply. However, I would posit that those old MOSFETs are so
horrible (modern MOSFETs are far superior), that it may not be worth the effort.
Craft amps used
huge amounts of global NFB, required due to very low bias currents and the necessity to reduce the
huge levels of distortion caused by the 'knee' at low currents (A Class A, or high bias MOSFET amp
would have been much better). Anyway, the huge levels of global NFB means that PSRR (Power Supply
Rejection Ratio) will be quite high, thus the influence of power supply changes will be relatively
small.
One more thing: Decent amounts of capacitance placed close to the output devices is far more
influential than caps placed some distance away. In fact, long(ish) cables AFTER the main filter
caps can be a serious limiting factor on the effectiveness of a power supply in a Class A/B
amplifier. This is because the inductance of the wires can be a factor.
On 12/09/2019 10:18 PM, Trevor Wilson wrote:
On 12/09/2019 12:17 am, ~misfit~ wrote:
On 10/09/2019 11:54 PM, Peter Wieck wrote:
OK, OK, I will bite! Minor rant to follow:
Tube vs. Solid State on reliability:
There are not so very many 60-year old components in operation these
days unmodified since-new. My oldest tube item turned 100 this year
and likely works better than when it was new based on a better
understanding of antenna systems, optimum tube voltages and so
forth. Other than moving parts (CD player), the newest component in
my office system was made in 1963. The system runs 9 hours per day,
5 days per week. Oh, and the tubes are original as well.
On the other hand, and given my hobby, I see a large number of SS
components that have blown transistors, exploded capacitors and much
worse, irrespective of age and source. The well made, well designed
stuff is serviceable, distinguishing it from the rest of the garbage
out there.
I would make a fairly apt comparison: A tube amplifier is much like
a mid-last-century Mercedes or VW - few things were self-adjusting,
and they required regular and attentive care-and-feeding. With such,
they were good for several hundred thousand miles of reliable
service. A contemporary Ford, Cadillac, Plymouth would be considered
remarkable were it to survive 100,000 miles without heroic measures.
Might run very nicely when running, but that would be your basic
solid-state device in comparison.
Put simply, they are different beasts designed with different things
in mind, but for the same basic purpose. That one is or is not
"BETTER" than the other is not relevant to the purpose in either case. >>>>
Now, when I here things like "Zero global NFB" and "Critically
matched components", I can smell the snake-oil from a great
distance, even the 10,000 miles from here to Australia. I am sure
that process also contains descriptives of "interconnects" rolled on
the thighs of virgins on Walpurgis Night...
Note that even "critically matched" solid-state components drift
after a very short period of time in-service. All of them, such that
that "less than 1%" is meaningful for perhaps 12 hours or so.
Being as this is a hobby for me, I get to try things that are
otherwise unproductive, unprofitable or impractical. Such as
shotgunning a device with single-value capacitors and then comparing
it to the same device with carefully screened and matched caps. Or
matching driver and output transistors and comparing to a similar
device with disparate values. Guys and gals - you would be seriously
shocked to discover how little difference some things make that the
ALL-SEEING, ALL-KNOWING gurus will tell you are critical. Often no
difference at all.
Thanks for your input Peter. If I may ask, do you have an opinion on
'storage capacitors' on an amplifier power supply? What in your
opinion is 'better', a single (or few) very large caps or multiple
smaller caps to the same / similar capacitance?
I have a long term project building my own amp based on PCBs taken
from 100w MOSFET (two pairs of J50 / K135 devices per amp) PA amps
made by a New Zealand company in the 1980s. (Craft, Gary Morrison's
company before he went on to become head designer at Plinius until
2005 when he left to set up Pure Audio). I got my hands on a rack of
four of these mono amps and preliminary testing using a clean source
and good speakers suggest they will make a great stereo amp.
I need to put together a power supply to feed two of these and have
some new 10,000uF caps but was wondering if multiple smaller caps
would be better. (In the PA amps they only had 2,200uF but obviously
weren't called on to reproduce much bass.)
As it is I'll be using fly leads from the rectifier PCB to the caps,
then to the amps and I'm building my own case. I was thinking of
maybe using my 10,000uF caps as well as maybe some smaller ones,
perhaps 1,000 in a bank, the best of both worlds. (There are also
100uF electros across the rails on the amp PCBs that I'll be
replacing.) That said I could also just go to multiple
Cheers,
**Those old MOSFETs were pretty ordinary devices (not very linear).
Evidenced by the fact that Plinius amps have always used BJTs. As
Peter has stated, multiple small value caps will usually provide a
superior, higher speed power supply. However, I would posit that those
old MOSFETs are so horrible (modern MOSFETs are far superior), that it
may not be worth the effort.
I hooked a pair of them up to a preamp while still using their original
power supplies and was very pleased with the sound so decided to go
ahead with the build.
Craft amps used huge amounts of global NFB, required due to very low
bias currents and the necessity to reduce the huge levels of
distortion caused by the 'knee' at low currents (A Class A, or high
bias MOSFET amp would have been much better). Anyway, the huge levels
of global NFB means that PSRR (Power Supply Rejection Ratio) will be
quite high, thus the influence of power supply changes will be
relatively small.
Unfortunately I don't own a 'scope so am unable to check a lot of stuff.
When I listened to them with the original power supplies (designed for
PA use) they sounded sweet and clean at low and moderate volume levels
but seemed to run out of power at higher volumes, especially when there
was a lot of bass.
One more thing: Decent amounts of capacitance placed close to the
output devices is far more influential than caps placed some distance
away. In fact, long(ish) cables AFTER the main filter caps can be a
serious limiting factor on the effectiveness of a power supply in a
Class A/B amplifier. This is because the inductance of the wires can
be a factor.
Thanks. The fly-leads will only be 6" tops and I'll be using at least
1.5 square mm multistrand copper conductors. If space allows I'll put a ~1,000uF cap right at the amplifier PCB as well (or as large as I can
get away with). I may end up building a wooden case as I don't have a suitable metal one and wood's something I have experience and the tools
for.
I still haven't finalised my design yet. I might end up feeding them a
few more volts than they were getting from their original power supplies
(my only suitable toroidial transformer is 10v AC higher than original)
so may parallel up a third pair of output devices onto the heatsinks
using one of the other amps as a donor. I haven't decided yet, as I said
it's a long-term project and I'm learning as I go.
So, a little Ohm's Law should tell you if you are demanding more current
than the output devices are capable of delivering. 14 Amps is, by high
end audio standards, a relatively modest current ability for a (say) 100
Watt @ 8 Ohms amplifier. Provided the driver impedance is relatively
benign, you should be OK.
On 13/09/2019 8:02 pm, ~misfit~ wrote:
On 12/09/2019 10:18 PM, Trevor Wilson wrote:
On 12/09/2019 12:17 am, ~misfit~ wrote:
On 10/09/2019 11:54 PM, Peter Wieck wrote:
OK, OK, I will bite! Minor rant to follow:
Tube vs. Solid State on reliability:
There are not so very many 60-year old components in operation these days unmodified
since-new. My oldest tube item turned 100 this year and likely works better than when it was
new based on a better understanding of antenna systems, optimum tube voltages and so forth.
Other than moving parts (CD player), the newest component in my office system was made in
1963. The system runs 9 hours per day, 5 days per week. Oh, and the tubes are original as well.
On the other hand, and given my hobby, I see a large number of SS components that have blown
transistors, exploded capacitors and much worse, irrespective of age and source. The well
made, well designed stuff is serviceable, distinguishing it from the rest of the garbage out
there.
I would make a fairly apt comparison: A tube amplifier is much like a mid-last-century
Mercedes or VW - few things were self-adjusting, and they required regular and attentive
care-and-feeding. With such, they were good for several hundred thousand miles of reliable
service. A contemporary Ford, Cadillac, Plymouth would be considered remarkable were it to
survive 100,000 miles without heroic measures. Might run very nicely when running, but that
would be your basic solid-state device in comparison.
Put simply, they are different beasts designed with different things in mind, but for the same
basic purpose. That one is or is not "BETTER" than the other is not relevant to the purpose in
either case.
Now, when I here things like "Zero global NFB" and "Critically matched components", I can
smell the snake-oil from a great distance, even the 10,000 miles from here to Australia. I am
sure that process also contains descriptives of "interconnects" rolled on the thighs of
virgins on Walpurgis Night...
Note that even "critically matched" solid-state components drift after a very short period of
time in-service. All of them, such that that "less than 1%" is meaningful for perhaps 12 hours
or so.
Being as this is a hobby for me, I get to try things that are otherwise unproductive,
unprofitable or impractical. Such as shotgunning a device with single-value capacitors and
then comparing it to the same device with carefully screened and matched caps. Or matching
driver and output transistors and comparing to a similar device with disparate values. Guys
and gals - you would be seriously shocked to discover how little difference some things make
that the ALL-SEEING, ALL-KNOWING gurus will tell you are critical. Often no difference at all.
Thanks for your input Peter. If I may ask, do you have an opinion on 'storage capacitors' on an
amplifier power supply? What in your opinion is 'better', a single (or few) very large caps or
multiple smaller caps to the same / similar capacitance?
I have a long term project building my own amp based on PCBs taken from 100w MOSFET (two pairs
of J50 / K135 devices per amp) PA amps made by a New Zealand company in the 1980s. (Craft, Gary
Morrison's company before he went on to become head designer at Plinius until 2005 when he left
to set up Pure Audio). I got my hands on a rack of four of these mono amps and preliminary
testing using a clean source and good speakers suggest they will make a great stereo amp.
I need to put together a power supply to feed two of these and have some new 10,000uF caps but
was wondering if multiple smaller caps would be better. (In the PA amps they only had 2,200uF
but obviously weren't called on to reproduce much bass.)
As it is I'll be using fly leads from the rectifier PCB to the caps, then to the amps and I'm
building my own case. I was thinking of maybe using my 10,000uF caps as well as maybe some
smaller ones, perhaps 1,000 in a bank, the best of both worlds. (There are also 100uF electros
across the rails on the amp PCBs that I'll be replacing.) That said I could also just go to
multiple
Cheers,
**Those old MOSFETs were pretty ordinary devices (not very linear). Evidenced by the fact that
Plinius amps have always used BJTs. As Peter has stated, multiple small value caps will usually
provide a superior, higher speed power supply. However, I would posit that those old MOSFETs are
so horrible (modern MOSFETs are far superior), that it may not be worth the effort.
I hooked a pair of them up to a preamp while still using their original power supplies and was
very pleased with the sound so decided to go ahead with the build.
**I haven't listened to Craft (hi fi) amps in many years. What I heard back then was pleasing. Very
wide bandwidth (ca. 1MHz), as I recall.
Craft amps used huge amounts of global NFB, required due to very low bias currents and the
necessity to reduce the huge levels of distortion caused by the 'knee' at low currents (A Class
A, or high bias MOSFET amp would have been much better). Anyway, the huge levels of global NFB
means that PSRR (Power Supply Rejection Ratio) will be quite high, thus the influence of power
supply changes will be relatively small.
Unfortunately I don't own a 'scope so am unable to check a lot of stuff. When I listened to them
with the original power supplies (designed for PA use) they sounded sweet and clean at low and
moderate volume levels but seemed to run out of power at higher volumes, especially when there
was a lot of bass.
**That could be due to a number of factors. Including:
* Insufficient Voltage output.
* Insufficient current output.
* Insufficient power supply.
* An unreasonable speaker impedance.
Don't forget: Those meaty looking 2SJ50/2SK135 output devices are only rated for a meagre 7 Amps
each and 100 Watts PDiss. By comparison, a typical output BJT of the same time period was rated at
a far more respectable 20 Amps and 200 Watts PDiss (MJ15003/MJ15004). Present production variants
are rated at 25 Amps and 250 Watts.
So, a little Ohm's Law should tell you if you are demanding more current than the output devices
are capable of delivering. 14 Amps is, by high end audio standards, a relatively modest current
ability for a (say) 100 Watt @ 8 Ohms amplifier. Provided the driver impedance is relatively
benign, you should be OK. Fortunately, it is real hard to damage MOSFETs, by 'asking' them to
deliver more current than they are rated for.
One more thing: Decent amounts of capacitance placed close to the output devices is far more
influential than caps placed some distance away. In fact, long(ish) cables AFTER the main filter
caps can be a serious limiting factor on the effectiveness of a power supply in a Class A/B
amplifier. This is because the inductance of the wires can be a factor.
Thanks. The fly-leads will only be 6" tops and I'll be using at least 1.5 square mm multistrand
copper conductors. If space allows I'll put a ~1,000uF cap right at the amplifier PCB as well (or
as large as I can get away with). I may end up building a wooden case as I don't have a suitable
metal one and wood's something I have experience and the tools for.
**Wiring sounds good. And yeah, caps placed close to output devices is a very good thing. A wooden
case, not so much. Wood is an excellent thermal insulator, which means heat may not escape too easily.
I still haven't finalised my design yet. I might end up feeding them a few more volts than they
were getting from their original power supplies (my only suitable toroidial transformer is 10v AC
higher than original) so may parallel up a third pair of output devices onto the heatsinks using
one of the other amps as a donor. I haven't decided yet, as I said it's a long-term project and
I'm learning as I go.
**Well, the MOSFETs are rated for a decent 160 Volts, so a few more rail Volts should be OK. And
yes, more output devices won't hurt (refer to Ohm's Law as before). Pay attention to the drive
capabilities of the preceding stages though.
On Saturday, September 14, 2019 at 9:58:44 AM UTC-4, Trevor Wilson wrote:
So, a little Ohm's Law should tell you if you are demanding more current
than the output devices are capable of delivering. 14 Amps is, by high
end audio standards, a relatively modest current ability for a (say) 100
Watt @ 8 Ohms amplifier. Provided the driver impedance is relatively
benign, you should be OK.
Hmm, that's not what a little Ohm's law tells me.
100 Watts into 8 Ohms is a tad over 3.5 amps. Let's say it's a VERY
robust 100 watt amplifier, delivering 200 Watts into 4 Ohms requires
about 7 amps, and, let's pretend it has essentially ZERO output
impedance and an effectively limitless power supply, you're not reaching
14 amps until you're driving 400 watts into 2 ohms.
So, a couple of questions that Mr. Ohm may ask; what kind of loudspeaker presents a broadband 2 ohm impedance or, conversely, what kind of
musical content would generate that kind of power requirement over
the pretty narrow band of frequencies where a loudspeaker has the
kind of pathological impedance curve that would dip to as low as
2 ohms.
(Yes, there exist SOME rare examples of loudspeakers with
2 ohm impedance, but such are confined to a VERY narrow
band of frequencies)
Okay, let's pretend we have real examples of the above. Let's assume
such a speaker has a moderately low efficiency, say the equivalent
of, oh, 86 dB SPL/1W/1M. We're blowing in 400 watts that means the speaker
is putting out 112 dB 1 meter way, a stereo pair, assuming the two
channels are uncorrelated, that's 115 dB. Really? This is a serious requirement?
But wait, you explicitly stated:
"Provided the driver impedance is relatively benign"
and you specified 8 Ohms. So let's assume it's a nominal 8 ohm
impedance 3-way speaker using at least a 2nd-order crossover
network. The impedance will be around 6.5 ohms below system
cutoff (DC resistance of woofer voice coil), will rise to
perhaps 30 Ohms at and around system cutoff, then drop down
to perhaps 15% above the DC resistance above there, start
rising again until the woofer-midrange crossover starts working,
maybe betting to 10-12 ohms, then dip to perhaps 60% of the rated
impedance, so about 4.8 ohms, rise again to about 12 ohms or so
at the mid-tweeter crossover point, drop down to about 10-15% above
the tweeter DC resistance (which, for the purpose of argument, we'll
take to be a nominal 4 Ohm tweeter, so about 4.5 Ohms, after which
it starts rising again.
So, minimum impedance of about 4.8 ohms will occur over perhaps
a 2-octave band around 1 kHz, then about 4.5 ohms around 5 kHz.
Let's take your 14 amps, produce a musical signal where ALL the energy
is concentrated from about 500-2000 Hz and from about 4000-8000 Hz
ALONE, and see what 14 Amps does.
Well, since
P = I^R
And we'll assume the impedance at these points is largely resistive,
which is is, then:
P = 14^2 * 4.5
882 watts. And to do that, the amplifier must be capable of outputting
E = I R
E = 14 * 4.5
63 volts RMS.
Really?
Oh, wait! Everyone knows that under transient conditions, the loudspeaker impedance can actually go well below the lowest impedance of the
speaker for brief moments due to back EMF, Otala said so.
Oh, wait! Everyone who knows that is wrong and has yet to advance any confirmed data sowing this to be the case and, by the way, Otala DID
NOT say so: he basically said that the peak current requirement under
actual transient conditions is exactly what is expected from the actual measure steady state impedance, and the only thing he really said
that's even remotely like this is that the peak current requirements
are greater than predicted by the "nominal" impedance of the loudspeaker.
Give me a shovel, Mr. Ohm wants to go back to sleep.
On 15/09/2019 1:58 AM, Trevor Wilson wrote:
On 13/09/2019 8:02 pm, ~misfit~ wrote:
On 12/09/2019 10:18 PM, Trevor Wilson wrote:
On 12/09/2019 12:17 am, ~misfit~ wrote:
On 10/09/2019 11:54 PM, Peter Wieck wrote:
OK, OK, I will bite! Minor rant to follow:
Tube vs. Solid State on reliability:
There are not so very many 60-year old components in operation
these days unmodified since-new. My oldest tube item turned 100
this year and likely works better than when it was new based on a
better understanding of antenna systems, optimum tube voltages and >>>>>> so forth. Other than moving parts (CD player), the newest
component in my office system was made in 1963. The system runs 9
hours per day, 5 days per week. Oh, and the tubes are original as
well.
On the other hand, and given my hobby, I see a large number of SS
components that have blown transistors, exploded capacitors and
much worse, irrespective of age and source. The well made, well
designed stuff is serviceable, distinguishing it from the rest of
the garbage out there.
I would make a fairly apt comparison: A tube amplifier is much
like a mid-last-century Mercedes or VW - few things were
self-adjusting, and they required regular and attentive
care-and-feeding. With such, they were good for several hundred
thousand miles of reliable service. A contemporary Ford, Cadillac, >>>>>> Plymouth would be considered remarkable were it to survive 100,000 >>>>>> miles without heroic measures. Might run very nicely when running, >>>>>> but that would be your basic solid-state device in comparison.
Put simply, they are different beasts designed with different
things in mind, but for the same basic purpose. That one is or is
not "BETTER" than the other is not relevant to the purpose in
either case.
Now, when I here things like "Zero global NFB" and "Critically
matched components", I can smell the snake-oil from a great
distance, even the 10,000 miles from here to Australia. I am sure
that process also contains descriptives of "interconnects" rolled
on the thighs of virgins on Walpurgis Night...
Note that even "critically matched" solid-state components drift
after a very short period of time in-service. All of them, such
that that "less than 1%" is meaningful for perhaps 12 hours or so. >>>>>>
Being as this is a hobby for me, I get to try things that are
otherwise unproductive, unprofitable or impractical. Such as
shotgunning a device with single-value capacitors and then
comparing it to the same device with carefully screened and
matched caps. Or matching driver and output transistors and
comparing to a similar device with disparate values. Guys and gals >>>>>> - you would be seriously shocked to discover how little difference >>>>>> some things make that the ALL-SEEING, ALL-KNOWING gurus will tell
you are critical. Often no difference at all.
Thanks for your input Peter. If I may ask, do you have an opinion
on 'storage capacitors' on an amplifier power supply? What in your
opinion is 'better', a single (or few) very large caps or multiple
smaller caps to the same / similar capacitance?
I have a long term project building my own amp based on PCBs taken
from 100w MOSFET (two pairs of J50 / K135 devices per amp) PA amps
made by a New Zealand company in the 1980s. (Craft, Gary Morrison's
company before he went on to become head designer at Plinius until
2005 when he left to set up Pure Audio). I got my hands on a rack
of four of these mono amps and preliminary testing using a clean
source and good speakers suggest they will make a great stereo amp.
I need to put together a power supply to feed two of these and have
some new 10,000uF caps but was wondering if multiple smaller caps
would be better. (In the PA amps they only had 2,200uF but
obviously weren't called on to reproduce much bass.)
As it is I'll be using fly leads from the rectifier PCB to the
caps, then to the amps and I'm building my own case. I was thinking
of maybe using my 10,000uF caps as well as maybe some smaller ones,
perhaps 1,000 in a bank, the best of both worlds. (There are also
100uF electros across the rails on the amp PCBs that I'll be
replacing.) That said I could also just go to multiple
Cheers,
**Those old MOSFETs were pretty ordinary devices (not very linear).
Evidenced by the fact that Plinius amps have always used BJTs. As
Peter has stated, multiple small value caps will usually provide a
superior, higher speed power supply. However, I would posit that
those old MOSFETs are so horrible (modern MOSFETs are far superior),
that it may not be worth the effort.
I hooked a pair of them up to a preamp while still using their
original power supplies and was very pleased with the sound so
decided to go ahead with the build.
**I haven't listened to Craft (hi fi) amps in many years. What I heard
back then was pleasing. Very wide bandwidth (ca. 1MHz), as I recall.
Craft amps used huge amounts of global NFB, required due to very low
bias currents and the necessity to reduce the huge levels of
distortion caused by the 'knee' at low currents (A Class A, or high
bias MOSFET amp would have been much better). Anyway, the huge
levels of global NFB means that PSRR (Power Supply Rejection Ratio)
will be quite high, thus the influence of power supply changes will
be relatively small.
Unfortunately I don't own a 'scope so am unable to check a lot of
stuff. When I listened to them with the original power supplies
(designed for PA use) they sounded sweet and clean at low and
moderate volume levels but seemed to run out of power at higher
volumes, especially when there was a lot of bass.
**That could be due to a number of factors. Including:
* Insufficient Voltage output.
* Insufficient current output.
* Insufficient power supply.
* An unreasonable speaker impedance.
Don't forget: Those meaty looking 2SJ50/2SK135 output devices are only
rated for a meagre 7 Amps each and 100 Watts PDiss. By comparison, a
typical output BJT of the same time period was rated at a far more
respectable 20 Amps and 200 Watts PDiss (MJ15003/MJ15004). Present
production variants are rated at 25 Amps and 250 Watts.
So three pairs per side should be fine for a reasonably powerful amp?
I've studied the PCB and the output devices are paralleled (along with a resistor for each) so it wouldn't be hard to add a third device to each
(on very short flyleads - or even daughterboards - mounted to the same heatsink).
The speakers I'm intending to use with this are Sony SS-K90EDs.
Like these: <https://www.stereo.net.au/forums/topic/260972-fs-sony-ss-k90ed-speakers-rare/>
So, a little Ohm's Law should tell you if you are demanding more
current than the output devices are capable of delivering. 14 Amps is,
by high end audio standards, a relatively modest current ability for a
(say) 100 Watt @ 8 Ohms amplifier. Provided the driver impedance is
relatively benign, you should be OK. Fortunately, it is real hard to
damage MOSFETs, by 'asking' them to deliver more current than they are
rated for.
That's one of the things I like about MOSFETs.
One more thing: Decent amounts of capacitance placed close to the
output devices is far more influential than caps placed some
distance away. In fact, long(ish) cables AFTER the main filter caps
can be a serious limiting factor on the effectiveness of a power
supply in a Class A/B amplifier. This is because the inductance of
the wires can be a factor.
Thanks. The fly-leads will only be 6" tops and I'll be using at least
1.5 square mm multistrand copper conductors. If space allows I'll put
a ~1,000uF cap right at the amplifier PCB as well (or as large as I
can get away with). I may end up building a wooden case as I don't
have a suitable metal one and wood's something I have experience and
the tools for.
**Wiring sounds good. And yeah, caps placed close to output devices is
a very good thing. A wooden case, not so much. Wood is an excellent
thermal insulator, which means heat may not escape too easily.
I have a couple of big heatsinks for the amplifier modules that will sit either side of the case, fins outwards in free air. They'll easily
handle the power dissipation being 4x bigger than the 'sinks used on the
PA amp. Also I'll ventilate the top and bottom of the 'box' (if I end up going with wood).
I still haven't finalised my design yet. I might end up feeding them
a few more volts than they were getting from their original power
supplies (my only suitable toroidial transformer is 10v AC higher
than original) so may parallel up a third pair of output devices onto
the heatsinks using one of the other amps as a donor. I haven't
decided yet, as I said it's a long-term project and I'm learning as I
go.
**Well, the MOSFETs are rated for a decent 160 Volts, so a few more
rail Volts should be OK. And yes, more output devices won't hurt
(refer to Ohm's Law as before). Pay attention to the drive
capabilities of the preceding stages though.
Thanks for this Trevor, I have saved it for future reference. My 300 VA toroid that I'm thinking of using with this outputs 50v AC so +/- 70v DC
when rectified. The original PA transformers were 40v AC.
On 16/09/2019 11:43 am, ~misfit~ wrote:
On 15/09/2019 1:58 AM, Trevor Wilson wrote:
On 13/09/2019 8:02 pm, ~misfit~ wrote:
On 12/09/2019 10:18 PM, Trevor Wilson wrote:
On 12/09/2019 12:17 am, ~misfit~ wrote:
On 10/09/2019 11:54 PM, Peter Wieck wrote:
OK, OK, I will bite! Minor rant to follow:
Tube vs. Solid State on reliability:
There are not so very many 60-year old components in operation these days unmodified
since-new. My oldest tube item turned 100 this year and likely works better than when it was
new based on a better understanding of antenna systems, optimum tube voltages and so forth.
Other than moving parts (CD player), the newest component in my office system was made in
1963. The system runs 9 hours per day, 5 days per week. Oh, and the tubes are original as well.
On the other hand, and given my hobby, I see a large number of SS components that have blown
transistors, exploded capacitors and much worse, irrespective of age and source. The well
made, well designed stuff is serviceable, distinguishing it from the rest of the garbage out
there.
I would make a fairly apt comparison: A tube amplifier is much like a mid-last-century
Mercedes or VW - few things were self-adjusting, and they required regular and attentive
care-and-feeding. With such, they were good for several hundred thousand miles of reliable
service. A contemporary Ford, Cadillac, Plymouth would be considered remarkable were it to
survive 100,000 miles without heroic measures. Might run very nicely when running, but that
would be your basic solid-state device in comparison.
Put simply, they are different beasts designed with different things in mind, but for the
same basic purpose. That one is or is not "BETTER" than the other is not relevant to the
purpose in either case.
Now, when I here things like "Zero global NFB" and "Critically matched components", I can
smell the snake-oil from a great distance, even the 10,000 miles from here to Australia. I
am sure that process also contains descriptives of "interconnects" rolled on the thighs of
virgins on Walpurgis Night...
Note that even "critically matched" solid-state components drift after a very short period
of time in-service. All of them, such that that "less than 1%" is meaningful for perhaps 12
hours or so.
Being as this is a hobby for me, I get to try things that are otherwise unproductive,
unprofitable or impractical. Such as shotgunning a device with single-value capacitors and
then comparing it to the same device with carefully screened and matched caps. Or matching
driver and output transistors and comparing to a similar device with disparate values. Guys
and gals - you would be seriously shocked to discover how little difference some things make
that the ALL-SEEING, ALL-KNOWING gurus will tell you are critical. Often no difference at all.
Thanks for your input Peter. If I may ask, do you have an opinion on 'storage capacitors' on
an amplifier power supply? What in your opinion is 'better', a single (or few) very large
caps or multiple smaller caps to the same / similar capacitance?
I have a long term project building my own amp based on PCBs taken from 100w MOSFET (two
pairs of J50 / K135 devices per amp) PA amps made by a New Zealand company in the 1980s.
(Craft, Gary Morrison's company before he went on to become head designer at Plinius until
2005 when he left to set up Pure Audio). I got my hands on a rack of four of these mono amps
and preliminary testing using a clean source and good speakers suggest they will make a great
stereo amp.
I need to put together a power supply to feed two of these and have some new 10,000uF caps
but was wondering if multiple smaller caps would be better. (In the PA amps they only had
2,200uF but obviously weren't called on to reproduce much bass.)
As it is I'll be using fly leads from the rectifier PCB to the caps, then to the amps and I'm
building my own case. I was thinking of maybe using my 10,000uF caps as well as maybe some
smaller ones, perhaps 1,000 in a bank, the best of both worlds. (There are also 100uF
electros across the rails on the amp PCBs that I'll be replacing.) That said I could also
just go to multiple
Cheers,
**Those old MOSFETs were pretty ordinary devices (not very linear). Evidenced by the fact that
Plinius amps have always used BJTs. As Peter has stated, multiple small value caps will
usually provide a superior, higher speed power supply. However, I would posit that those old
MOSFETs are so horrible (modern MOSFETs are far superior), that it may not be worth the effort.
I hooked a pair of them up to a preamp while still using their original power supplies and was
very pleased with the sound so decided to go ahead with the build.
**I haven't listened to Craft (hi fi) amps in many years. What I heard back then was pleasing.
Very wide bandwidth (ca. 1MHz), as I recall.
Craft amps used huge amounts of global NFB, required due to very low bias currents and the
necessity to reduce the huge levels of distortion caused by the 'knee' at low currents (A
Class A, or high bias MOSFET amp would have been much better). Anyway, the huge levels of
global NFB means that PSRR (Power Supply Rejection Ratio) will be quite high, thus the
influence of power supply changes will be relatively small.
Unfortunately I don't own a 'scope so am unable to check a lot of stuff. When I listened to
them with the original power supplies (designed for PA use) they sounded sweet and clean at low
and moderate volume levels but seemed to run out of power at higher volumes, especially when
there was a lot of bass.
**That could be due to a number of factors. Including:
* Insufficient Voltage output.
* Insufficient current output.
* Insufficient power supply.
* An unreasonable speaker impedance.
Don't forget: Those meaty looking 2SJ50/2SK135 output devices are only rated for a meagre 7 Amps
each and 100 Watts PDiss. By comparison, a typical output BJT of the same time period was rated
at a far more respectable 20 Amps and 200 Watts PDiss (MJ15003/MJ15004). Present production
variants are rated at 25 Amps and 250 Watts.
So three pairs per side should be fine for a reasonably powerful amp?
**Again: It depends on the maximum Voltage output. 3 pairs allows for a peak current ability of 21
Amps.
I've studied the PCB and the output devices are paralleled (along with a resistor for each) so it
wouldn't be hard to add a third device to each (on very short flyleads - or even daughterboards -
mounted to the same heatsink).
**Sure. However, make certain the drive circuitry can cope.
The speakers I'm intending to use with this are Sony SS-K90EDs.
Like these:
<https://www.stereo.net.au/forums/topic/260972-fs-sony-ss-k90ed-speakers-rare/>
**OK.
So, a little Ohm's Law should tell you if you are demanding more current than the output devices
are capable of delivering. 14 Amps is, by high end audio standards, a relatively modest current
ability for a (say) 100 Watt @ 8 Ohms amplifier. Provided the driver impedance is relatively
benign, you should be OK. Fortunately, it is real hard to damage MOSFETs, by 'asking' them to
deliver more current than they are rated for.
That's one of the things I like about MOSFETs.
**Well, a properly designed BJT amp should demonstrate the same robustness and reliability.
One more thing: Decent amounts of capacitance placed close to the output devices is far more
influential than caps placed some distance away. In fact, long(ish) cables AFTER the main
filter caps can be a serious limiting factor on the effectiveness of a power supply in a Class
A/B amplifier. This is because the inductance of the wires can be a factor.
Thanks. The fly-leads will only be 6" tops and I'll be using at least 1.5 square mm multistrand
copper conductors. If space allows I'll put a ~1,000uF cap right at the amplifier PCB as well
(or as large as I can get away with). I may end up building a wooden case as I don't have a
suitable metal one and wood's something I have experience and the tools for.
**Wiring sounds good. And yeah, caps placed close to output devices is a very good thing. A
wooden case, not so much. Wood is an excellent thermal insulator, which means heat may not
escape too easily.
I have a couple of big heatsinks for the amplifier modules that will sit either side of the case,
fins outwards in free air. They'll easily handle the power dissipation being 4x bigger than the
'sinks used on the PA amp. Also I'll ventilate the top and bottom of the 'box' (if I end up going
with wood).
**OK.
I still haven't finalised my design yet. I might end up feeding them a few more volts than they
were getting from their original power supplies (my only suitable toroidial transformer is 10v
AC higher than original) so may parallel up a third pair of output devices onto the heatsinks
using one of the other amps as a donor. I haven't decided yet, as I said it's a long-term
project and I'm learning as I go.
**Well, the MOSFETs are rated for a decent 160 Volts, so a few more rail Volts should be OK. And
yes, more output devices won't hurt (refer to Ohm's Law as before). Pay attention to the drive
capabilities of the preceding stages though.
Thanks for this Trevor, I have saved it for future reference. My 300 VA toroid that I'm thinking
of using with this outputs 50v AC so +/- 70v DC when rectified. The original PA transformers were
40v AC.
**+/- 70VDC suggests a maximum power output of around 250 Watts @ 8 Ohms. If you plan on attempting
to obtain that much power (continuously), then you will need two of those toroids.
On 16/09/2019 9:53 PM, Trevor Wilson wrote:
On 16/09/2019 11:43 am, ~misfit~ wrote:
On 15/09/2019 1:58 AM, Trevor Wilson wrote:
On 13/09/2019 8:02 pm, ~misfit~ wrote:
On 12/09/2019 10:18 PM, Trevor Wilson wrote:
On 12/09/2019 12:17 am, ~misfit~ wrote:
On 10/09/2019 11:54 PM, Peter Wieck wrote:
OK, OK, I will bite! Minor rant to follow:
Tube vs. Solid State on reliability:
There are not so very many 60-year old components in operation >>>>>>>> these days unmodified since-new. My oldest tube item turned 100 >>>>>>>> this year and likely works better than when it was new based on >>>>>>>> a better understanding of antenna systems, optimum tube voltages >>>>>>>> and so forth. Other than moving parts (CD player), the newest
component in my office system was made in 1963. The system runs >>>>>>>> 9 hours per day, 5 days per week. Oh, and the tubes are original >>>>>>>> as well.
On the other hand, and given my hobby, I see a large number of >>>>>>>> SS components that have blown transistors, exploded capacitors >>>>>>>> and much worse, irrespective of age and source. The well made, >>>>>>>> well designed stuff is serviceable, distinguishing it from the >>>>>>>> rest of the garbage out there.
I would make a fairly apt comparison: A tube amplifier is much >>>>>>>> like a mid-last-century Mercedes or VW - few things were
self-adjusting, and they required regular and attentive
care-and-feeding. With such, they were good for several hundred >>>>>>>> thousand miles of reliable service. A contemporary Ford,
Cadillac, Plymouth would be considered remarkable were it to
survive 100,000 miles without heroic measures. Might run very
nicely when running, but that would be your basic solid-state
device in comparison.
Put simply, they are different beasts designed with different
things in mind, but for the same basic purpose. That one is or >>>>>>>> is not "BETTER" than the other is not relevant to the purpose in >>>>>>>> either case.
Now, when I here things like "Zero global NFB" and "Critically >>>>>>>> matched components", I can smell the snake-oil from a great
distance, even the 10,000 miles from here to Australia. I am
sure that process also contains descriptives of "interconnects" >>>>>>>> rolled on the thighs of virgins on Walpurgis Night...
Note that even "critically matched" solid-state components drift >>>>>>>> after a very short period of time in-service. All of them, such >>>>>>>> that that "less than 1%" is meaningful for perhaps 12 hours or so. >>>>>>>>
Being as this is a hobby for me, I get to try things that are
otherwise unproductive, unprofitable or impractical. Such as
shotgunning a device with single-value capacitors and then
comparing it to the same device with carefully screened and
matched caps. Or matching driver and output transistors and
comparing to a similar device with disparate values. Guys and
gals - you would be seriously shocked to discover how little
difference some things make that the ALL-SEEING, ALL-KNOWING
gurus will tell you are critical. Often no difference at all.
Thanks for your input Peter. If I may ask, do you have an opinion >>>>>>> on 'storage capacitors' on an amplifier power supply? What in
your opinion is 'better', a single (or few) very large caps or
multiple smaller caps to the same / similar capacitance?
I have a long term project building my own amp based on PCBs
taken from 100w MOSFET (two pairs of J50 / K135 devices per amp) >>>>>>> PA amps made by a New Zealand company in the 1980s. (Craft, Gary >>>>>>> Morrison's company before he went on to become head designer at
Plinius until 2005 when he left to set up Pure Audio). I got my
hands on a rack of four of these mono amps and preliminary
testing using a clean source and good speakers suggest they will >>>>>>> make a great stereo amp.
I need to put together a power supply to feed two of these and
have some new 10,000uF caps but was wondering if multiple smaller >>>>>>> caps would be better. (In the PA amps they only had 2,200uF but
obviously weren't called on to reproduce much bass.)
As it is I'll be using fly leads from the rectifier PCB to the
caps, then to the amps and I'm building my own case. I was
thinking of maybe using my 10,000uF caps as well as maybe some
smaller ones, perhaps 1,000 in a bank, the best of both worlds.
(There are also 100uF electros across the rails on the amp PCBs
that I'll be replacing.) That said I could also just go to multiple >>>>>>>
Cheers,
**Those old MOSFETs were pretty ordinary devices (not very
linear). Evidenced by the fact that Plinius amps have always used
BJTs. As Peter has stated, multiple small value caps will usually
provide a superior, higher speed power supply. However, I would
posit that those old MOSFETs are so horrible (modern MOSFETs are
far superior), that it may not be worth the effort.
I hooked a pair of them up to a preamp while still using their
original power supplies and was very pleased with the sound so
decided to go ahead with the build.
**I haven't listened to Craft (hi fi) amps in many years. What I
heard back then was pleasing. Very wide bandwidth (ca. 1MHz), as I
recall.
Craft amps used huge amounts of global NFB, required due to very
low bias currents and the necessity to reduce the huge levels of
distortion caused by the 'knee' at low currents (A Class A, or
high bias MOSFET amp would have been much better). Anyway, the
huge levels of global NFB means that PSRR (Power Supply Rejection
Ratio) will be quite high, thus the influence of power supply
changes will be relatively small.
Unfortunately I don't own a 'scope so am unable to check a lot of
stuff. When I listened to them with the original power supplies
(designed for PA use) they sounded sweet and clean at low and
moderate volume levels but seemed to run out of power at higher
volumes, especially when there was a lot of bass.
**That could be due to a number of factors. Including:
* Insufficient Voltage output.
* Insufficient current output.
* Insufficient power supply.
* An unreasonable speaker impedance.
Don't forget: Those meaty looking 2SJ50/2SK135 output devices are
only rated for a meagre 7 Amps each and 100 Watts PDiss. By
comparison, a typical output BJT of the same time period was rated
at a far more respectable 20 Amps and 200 Watts PDiss
(MJ15003/MJ15004). Present production variants are rated at 25 Amps
and 250 Watts.
So three pairs per side should be fine for a reasonably powerful amp?
**Again: It depends on the maximum Voltage output. 3 pairs allows for
a peak current ability of 21 Amps.
I've studied the PCB and the output devices are paralleled (along
with a resistor for each) so it wouldn't be hard to add a third
device to each (on very short flyleads - or even daughterboards -
mounted to the same heatsink).
**Sure. However, make certain the drive circuitry can cope.
I'm not exactly sure of how to do that?
The speakers I'm intending to use with this are Sony SS-K90EDs.
Like these:
<https://www.stereo.net.au/forums/topic/260972-fs-sony-ss-k90ed-speakers-rare/>
**OK.
So, a little Ohm's Law should tell you if you are demanding more
current than the output devices are capable of delivering. 14 Amps
is, by high end audio standards, a relatively modest current ability
for a (say) 100 Watt @ 8 Ohms amplifier. Provided the driver
impedance is relatively benign, you should be OK. Fortunately, it is
real hard to damage MOSFETs, by 'asking' them to deliver more
current than they are rated for.
That's one of the things I like about MOSFETs.
**Well, a properly designed BJT amp should demonstrate the same
robustness and reliability.
One more thing: Decent amounts of capacitance placed close to the
output devices is far more influential than caps placed some
distance away. In fact, long(ish) cables AFTER the main filter
caps can be a serious limiting factor on the effectiveness of a
power supply in a Class A/B amplifier. This is because the
inductance of the wires can be a factor.
Thanks. The fly-leads will only be 6" tops and I'll be using at
least 1.5 square mm multistrand copper conductors. If space allows
I'll put a ~1,000uF cap right at the amplifier PCB as well (or as
large as I can get away with). I may end up building a wooden case
as I don't have a suitable metal one and wood's something I have
experience and the tools for.
**Wiring sounds good. And yeah, caps placed close to output devices
is a very good thing. A wooden case, not so much. Wood is an
excellent thermal insulator, which means heat may not escape too
easily.
I have a couple of big heatsinks for the amplifier modules that will
sit either side of the case, fins outwards in free air. They'll
easily handle the power dissipation being 4x bigger than the 'sinks
used on the PA amp. Also I'll ventilate the top and bottom of the
'box' (if I end up going with wood).
**OK.
I still haven't finalised my design yet. I might end up feeding
them a few more volts than they were getting from their original
power supplies (my only suitable toroidial transformer is 10v AC
higher than original) so may parallel up a third pair of output
devices onto the heatsinks using one of the other amps as a donor.
I haven't decided yet, as I said it's a long-term project and I'm
learning as I go.
**Well, the MOSFETs are rated for a decent 160 Volts, so a few more
rail Volts should be OK. And yes, more output devices won't hurt
(refer to Ohm's Law as before). Pay attention to the drive
capabilities of the preceding stages though.
Thanks for this Trevor, I have saved it for future reference. My 300
VA toroid that I'm thinking of using with this outputs 50v AC so +/-
70v DC when rectified. The original PA transformers were 40v AC.
**+/- 70VDC suggests a maximum power output of around 250 Watts @ 8
Ohms. If you plan on attempting to obtain that much power
(continuously), then you will need two of those toroids.
I intend to use the system in my lounge so won't want crazy SPLs, the speakers likely wouldn't handle that much power anyway. I actually do
have two of the toroids but that would make for a big amplifier case -
and surely then I'd need to consider adding *two* more pairs of output MOSFETs per amplifier?
I was thinking that, as I don't listen to dubstep or extremely
bass-heavy music, using one toroid and a lot of capacitance (in the
region of 20,000 to 50,000 uF per rail) would be enough to handle
transients. If not then I might as well build a pair of monoblocks.
I've got a few coffee-cup sized Mepco/Electra 14,000 uF / 100v caps but they're not new... I also have 8 new 10,000 uF / 100v Elna caps that are
only about 1/4 of the size.
On 16/09/2019 7:49 am, dpierce.cartchunk.org@gmail.com wrote:
On Saturday, September 14, 2019 at 9:58:44 AM UTC-4, Trevor Wilson wrote:
So, a little Ohm's Law should tell you if you are demanding more current >> than the output devices are capable of delivering. 14 Amps is, by high
end audio standards, a relatively modest current ability for a (say) 100 >> Watt @ 8 Ohms amplifier. Provided the driver impedance is relatively
benign, you should be OK.
Hmm, that's not what a little Ohm's law tells me.
100 Watts into 8 Ohms is a tad over 3.5 amps. Let's say it's a VERY
robust 100 watt amplifier, delivering 200 Watts into 4 Ohms requires
about 7 amps, and, let's pretend it has essentially ZERO output
impedance and an effectively limitless power supply, you're not reaching
14 amps until you're driving 400 watts into 2 ohms.
**Well, no. The RMS current is certainly 3.5 Amps, but output devices
only 'care' about PEAK currents. The peak current is, of course, 3.5 X
1.414 ~ 5 Amps.
With a 4 Ohm load, the peak current required is 10 Amps. For 2 Ohms, it
is 20 Amps.
Assuming a 100 Watt amp. For a (say) 200 Watt amp, those peak current
figures become 7 Amps, 14 Amps and 28 Amps respectively. WAY past the
ability of two pairs of old Hitachi MOSFETs to deal with.
So, a couple of questions that Mr. Ohm may ask; what kind of loudspeaker presents a broadband 2 ohm impedance or, conversely, what kind of
musical content would generate that kind of power requirement over
the pretty narrow band of frequencies where a loudspeaker has the
kind of pathological impedance curve that would dip to as low as
2 ohms.
**I have a few here that are tougher than that. Some of the Peerless
XXLS drivers dip to the low 2 Ohm region. Most ESLs fall lower than that
at HF.
On 16/09/2019 11:01 pm, ~misfit~ wrote:
On 16/09/2019 9:53 PM, Trevor Wilson wrote:
**Sure. However, make certain the drive circuitry can cope.
I'm not exactly sure of how to do that?
**You need to examine the drive circuitry, the components used and then calculate if those
components can cope with the extra load caused by extra MOSFETs. It will PROBABLY be OK, but I
don't know.
I intend to use the system in my lounge so won't want crazy SPLs, the speakers likely wouldn't
handle that much power anyway. I actually do have two of the toroids but that would make for a
big amplifier case - and surely then I'd need to consider adding *two* more pairs of output
MOSFETs per amplifier?
**As Peter has correctly stated, provided you don't need the full continuous power capacity of the
amplifier at all times, then one transformer will likely be plenty. From my perspective, I am a
purist. If I am presented with an amplifier rated at (say) 200 Watts/channel, then that amplifier
needs to be able to deliver 200 Watts/channel INDEFINITELY and, possibly more importantly, it needs
to be able to deliver roughly 40% of it's maximum power without thermal distress. With one
transformer in your amplifier chassis, it would fail such a test. But, your amplifier is not a
commercial item. You can make it anything you want.
I was thinking that, as I don't listen to dubstep or extremely bass-heavy music, using one toroid
and a lot of capacitance (in the region of 20,000 to 50,000 uF per rail) would be enough to
handle transients. If not then I might as well build a pair of monoblocks.
**A worthy consideration.
I've got a few coffee-cup sized Mepco/Electra 14,000 uF / 100v caps but they're not new... I also
have 8 new 10,000 uF / 100v Elna caps that are only about 1/4 of the size.
**The amplifier I presently use has a 5.5kVA (yes, 5,500VA), split wound (one winding for each
channel), double C core power transformer, followed by 92 X 3,300uF filter capacitors.
The result
is to ensure that, under full power operation (at any impedance higher than 2 Ohms) ripple is kept
below 100mV. So, discussions of 10,000uF per rail doesn't excite me. It's what I expect to see in a
mass market product from Yamaha or NAD. However, as Peter and I have both suggested, in a high
global NFB amp, such as yours, huge lumps of filter capacitance will not be pivotal to performance.
Placing a decent amount near the output devices will be beneficial though.
While much of what you say below is, strictly speaking, technically
correct under some very specific cases, it's misleading and could well
not be applicable in reality.
I've not got a lot of time to spend on this, so let me just
take on a couple of your points.
On Monday, September 16, 2019 at 5:52:54 AM UTC-4, Trevor Wilson wrote:
On 16/09/2019 7:49 am, dpierce.cartchunk.org@gmail.com wrote:
On Saturday, September 14, 2019 at 9:58:44 AM UTC-4, Trevor Wilson wrote: >>>> So, a little Ohm's Law should tell you if you are demanding more current >>>> than the output devices are capable of delivering. 14 Amps is, by high >>>> end audio standards, a relatively modest current ability for a (say) 100 >>>> Watt @ 8 Ohms amplifier. Provided the driver impedance is relatively
benign, you should be OK.
Hmm, that's not what a little Ohm's law tells me.
100 Watts into 8 Ohms is a tad over 3.5 amps. Let's say it's a VERY
robust 100 watt amplifier, delivering 200 Watts into 4 Ohms requires
about 7 amps, and, let's pretend it has essentially ZERO output
impedance and an effectively limitless power supply, you're not reaching >>> 14 amps until you're driving 400 watts into 2 ohms.
**Well, no. The RMS current is certainly 3.5 Amps, but output devices
only 'care' about PEAK currents. The peak current is, of course, 3.5 X
1.414 ~ 5 Amps.
With a 4 Ohm load, the peak current required is 10 Amps. For 2 Ohms, it
is 20 Amps.
Assuming a 100 Watt amp. For a (say) 200 Watt amp, those peak current
figures become 7 Amps, 14 Amps and 28 Amps respectively. WAY past the
ability of two pairs of old Hitachi MOSFETs to deal with.
All of your calculations ASSUME several things, none of which are
likely to be true in real usage.
1. Your continuous-to-peak current calculations using a factor of
sqrt(2) ASUMMES that the excitation is pure sine. That's surely
not the case in real life, I'm sure you'd agree. Yes, the actual
crest fact may be greater than 3dB, but, again, you ASSUME that
in actual practice those peak current are REQUIRED> I suggest
they are not, in absence of any supporting evidence they are.
2. The comprehensive list of impedance curves is, yes, useful but
the interpretation of them as applied to your case ignores the
VERY important details and thus is overly simplistic and mis-
leading. Let me take just a couple of example from the list:
a. Westlake BBSM-6F
Yes, the impedance gets to 2 ohms, but look at the
broadband sensitivity 92dB/2.83V: less power is needed to
achieve a given sound pressure level, continuous, peak or
otherwise. It illustrates that you simply can't look at one
particular measurement in isolation.
And, not that it may be relevant, this is specifically
marketed towards studio use at high (deafening?:-) level.
b. The acoustat impedance curve you posted on the RageAudio
site: indeed, the impedance drops WAY down to under 1 Ohm.
BUT it does it over a VERY narrow bandwidth, and it does
it at 15 kHz. It's above 4 ohms over the entire audio range
from 10Hz to 9kHz. Exactly what kind of musical material
would require one to dump a LOT of power between 9 kHz and
20+kHz? Over the majority of the audio bandwidth, the impedance
is 6 ohms or higher. Even if you assume (quite unrealistically)
that the energy is distributed across the spectrum, equal
energy per octave, your impedance problems ar confined to about
1 octave out of 10, suggesting that if you need 100 watts in that
one octave, you'll need another 900! for everything else.
Ah, but what about short-term transients, you ask. Look at the
spectral distribution of such in actual music: sorry, you're
still NOT generating a lot of power over such a narrow bandwidth
(Sorry, Mr. Fourier, you can lay back down, we shan't be needing
you just yet).
So, a couple of questions that Mr. Ohm may ask; what kind of loudspeaker >>> presents a broadband 2 ohm impedance or, conversely, what kind of
musical content would generate that kind of power requirement over
the pretty narrow band of frequencies where a loudspeaker has the
kind of pathological impedance curve that would dip to as low as
2 ohms.
**I have a few here that are tougher than that. Some of the Peerless
XXLS drivers dip to the low 2 Ohm region. Most ESLs fall lower than that
at HF.
Yes, over VERY narrow bands and at high frequencies, where your
power requirements are not anywhere near as large as at significantly
lower frequencies.
On 17/09/2019 11:54 AM, Trevor Wilson wrote:
On 16/09/2019 11:01 pm, ~misfit~ wrote:
On 16/09/2019 9:53 PM, Trevor Wilson wrote:
**Sure. However, make certain the drive circuitry can cope.
I'm not exactly sure of how to do that?
**You need to examine the drive circuitry, the components used and then calculate if those
components can cope with the extra load caused by extra MOSFETs. It will PROBABLY be OK, but I
don't know.
I intend to use the system in my lounge so won't want crazy SPLs, the speakers likely wouldn't
handle that much power anyway. I actually do have two of the toroids but that would make for a
big amplifier case - and surely then I'd need to consider adding *two* more pairs of output
MOSFETs per amplifier?
[ Massively pruned of old quotes because your mod just
couldn't take it any more. --dsr ]
**Let me be very clear about several things:
* NFB is fine. In fact, NO audio amplifier can work without it.
* GLOBAL NFB is also fine. When properly applied.
* I have a personal preference for the amplifiers I use, which employ
lots of local NFB and no global NFB. Others may have a different opinion.
* As part of my education into the world of zero global NFB amplifiers,
I subjected myself to a couple of single (unfortunately) blind tests,
between two, otherwise identical, amplifiers. One employed zero GNFB and
one employed a modest amount of GNFB. I preferred the zero GNFB one.
Since that time, I subjected several (10) of my clients to the same test >(DBT). The zero GNFB models was preferred every time. Except one.
* Once more: I would posit that part of the reason why some listeners
prefer valve amplifiers, is due to the fact that global NFB levels are
very low, or non-existent.
But, again, in the real world, negative feedback, done properly, has
many more advantages than disadvantages.
**Again: No issue with NFB. In fact, no issue with GNFB, when done well.
On 12 Sep 2019 20:28:33 GMT, Trevor Wilson wrote:
<snip>
**Let me be very clear about several things:
* NFB is fine. In fact, NO audio amplifier can work without it.
* GLOBAL NFB is also fine. When properly applied.
* I have a personal preference for the amplifiers I use, which employ
lots of local NFB and no global NFB. Others may have a different opinion.
* As part of my education into the world of zero global NFB amplifiers,
I subjected myself to a couple of single (unfortunately) blind tests,
between two, otherwise identical, amplifiers. One employed zero GNFB and
one employed a modest amount of GNFB. I preferred the zero GNFB one.
Since that time, I subjected several (10) of my clients to the same test
(DBT). The zero GNFB models was preferred every time. Except one.
* Once more: I would posit that part of the reason why some listeners
prefer valve amplifiers, is due to the fact that global NFB levels are
very low, or non-existent.
But, again, in the real world, negative feedback, done properly, has
many more advantages than disadvantages.
**Again: No issue with NFB. In fact, no issue with GNFB, when done well.
How do modern switching amps (class D) stack up for HiFi use?
most PA systems now fully digital?
at the spec sheet of the TDA7492 it doesn't look like it. Do they
sound worse than a good analog amp?
The class-D amps typically have a series inductance between the
switching elements and the speakers, does that influence transients?
Even a tweeter has already 15-20 microHenry of inductance.
Mat Nieuwenhoven
Even a tweeter has already 15-20 microHenry of inductance.
On 14/10/2019 8:00 am, Mat Nieuwenhoven wrote:
Even a tweeter has already 15-20 microHenry of inductance.
**Not so. I haven't measured one in quite some time, but the EMIT HF
drivers, used in many Infinity speakers exhibit far lower inductance
figures than that. If I had to guess, I'd estimate the inductance figure
to be around 5 X 10^-6H. I'll see if I can locate one to measure. Then,
of course, is the sadly deleted Audax HD-3P Piezo HF driver. And any
number of ELS HF drivers.
On 14 Oct 2019 18:58:55 GMT, Trevor Wilson wrote:
On 14/10/2019 8:00 am, Mat Nieuwenhoven wrote:
Even a tweeter has already 15-20 microHenry of inductance.
**Not so. I haven't measured one in quite some time, but the EMIT HF >drivers, used in many Infinity speakers exhibit far lower inductance >figures than that. If I had to guess, I'd estimate the inductance figure
to be around 5 X 10^-6H. I'll see if I can locate one to measure. Then,
of course, is the sadly deleted Audax HD-3P Piezo HF driver. And any
number of ELS HF drivers.
Some data from the German magazine "Hobby Hifi", from various
manufacturers:
Omnes Audio AMT50 (Air Motion Transformer): 10 uH/20 kHz
Audaphon APR 1.0, band tweeter: 54 uH/20 kHz
Monacor DT-352NF, dome tweeter: 45 uH/20 kHz
SB Acoustics TW29B, dome tweeter: 18 uH/20 kHz
Scan Speak D3404-552000, elliptical dome tweeter: 18 uH/20 kHz
Tang Band 25-2234SD, inverse dome tweeter: 24 uH/20 kHz
Multiple have a copper covering in the magnetgap to reduce the
increase of impedance at the higher frequencies, and to reduce
distortion.
Do they actually use FB?
**EVERY amplifier uses NFB. Every single one. Regardless of technology
or claims from manufacturers.
If I look
at the spec sheet of the TDA7492 it doesn't look like it. Do they
sound worse than a good analog amp?
**I see a loop feedback mechanism in the block diagram. I see some
audibly significant problems with the amplifier. Max THD is cited aas
0.4% and the frequency response is poor, compared to even modest Class
A/B amplifiers. The low switching frequency ensures that low impedance
(<4 Ohms) loads are not well catered for.
On 13 Oct 2019 21:26:46 GMT, Trevor Wilson wrote:
<snip>
Do they actually use FB?
**EVERY amplifier uses NFB. Every single one. Regardless of technology
or claims from manufacturers.
If I look
at the spec sheet of the TDA7492 it doesn't look like it. Do they
sound worse than a good analog amp?
**I see a loop feedback mechanism in the block diagram. I see some
audibly significant problems with the amplifier. Max THD is cited aas
0.4% and the frequency response is poor, compared to even modest Class
A/B amplifiers. The low switching frequency ensures that low impedance
(<4 Ohms) loads are not well catered for.
The TDA7492 has a switching frequency of typically 310 kHz. How is
this related to bad handling of a 4 ohm load, and why is that
dependent on the load resistance? And this IC is specified for 4 ohm
or more.
The low frequency fall off is deliberate (page 24 of the ST spec),
easily fixed by increasing the input size capacitor. The
THD-versus-frequency plot is indeed not impressive, THD rises in
spots to 0.2 %. You don't happen to have a link to a similar plot
from a good quality analog amp? Also, a link for a similar FFT plot ?
I am curious.
The IC is also dirt cheap, on a board for less than 10 $. For that
price, it is superb value for money.
There is indeed a feedback path from the OUTx pins to the second amp
inside.
<snip>
For a professional product, see e.g. https://icepower.dk/products/other/a-series/ . Its datasheet is at https://icepower.dk/download/2414/ . It supports loads down to 2.7
ohm loads. Again I wonder what the switching frequency has to do with
load.
I wonder if the phase plot can be matched by any analog amp, or even
the output resistance of <50 mOhm .
Mat Nieuwenhoven
On 13 Oct 2019 21:26:46 GMT, Trevor Wilson wrote:
<snip>
Do they actually use FB?
**EVERY amplifier uses NFB. Every single one. Regardless of technology
or claims from manufacturers.
If I look
at the spec sheet of the TDA7492 it doesn't look like it. Do they
sound worse than a good analog amp?
**I see a loop feedback mechanism in the block diagram. I see some
audibly significant problems with the amplifier. Max THD is cited aas
0.4% and the frequency response is poor, compared to even modest Class
A/B amplifiers. The low switching frequency ensures that low impedance
(<4 Ohms) loads are not well catered for.
The TDA7492 has a switching frequency of typically 310 kHz. How is
this related to bad handling of a 4 ohm load, and why is that
dependent on the load resistance? And this IC is specified for 4 ohm
or more.
The low frequency fall off is deliberate (page 24 of the ST spec),
easily fixed by increasing the input size capacitor.
THD-versus-frequency plot is indeed not impressive, THD rises in
spots to 0.2 %. You don't happen to have a link to a similar plot
from a good quality analog amp? Also, a link for a similar FFT plot ?
I am curious.
The IC is also dirt cheap, on a board for less than 10 $. For that
price, it is superb value for money.
There is indeed a feedback path from the OUTx pins to the second amp
inside.
<snip>
For a professional product, see e.g. https://icepower.dk/products/other/a-series/ . Its datasheet is at https://icepower.dk/download/2414/ . It supports loads down to 2.7
ohm loads. Again I wonder what the switching frequency has to do with
load.
I wonder if the phase plot can be matched by any analog amp, or even
the output resistance of <50 mOhm .
On 20/10/2019 1:03 AM, Mat Nieuwenhoven wrote:
On 13 Oct 2019 21:26:46 GMT, Trevor Wilson wrote:
<snip>
Do they actually use FB?
**EVERY amplifier uses NFB. Every single one. Regardless of technology
or claims from manufacturers.
If I look
at the spec sheet of the TDA7492 it doesn't look like it. Do they
sound worse than a good analog amp?
**I see a loop feedback mechanism in the block diagram. I see some
audibly significant problems with the amplifier. Max THD is cited aas
0.4% and the frequency response is poor, compared to even modest Class
A/B amplifiers. The low switching frequency ensures that low impedance
(<4 Ohms) loads are not well catered for.
The TDA7492 has a switching frequency of typically 310 kHz. How is
this related to bad handling of a 4 ohm load, and why is that
dependent on the load resistance? And this IC is specified for 4 ohm
or more.
The low frequency fall off is deliberate (page 24 of the ST spec),
easily fixed by increasing the input size capacitor. The
THD-versus-frequency plot is indeed not impressive, THD rises in
spots to 0.2 %. You don't happen to have a link to a similar plot
from a good quality analog amp? Also, a link for a similar FFT plot ?
I am curious.
The IC is also dirt cheap, on a board for less than 10 $. For that
price, it is superb value for money.
There is indeed a feedback path from the OUTx pins to the second amp
inside.
<snip>
For a professional product, see e.g.
https://icepower.dk/products/other/a-series/ . Its datasheet is at
https://icepower.dk/download/2414/ . It supports loads down to 2.7
ohm loads. Again I wonder what the switching frequency has to do with
load.
I wonder if the phase plot can be matched by any analog amp, or even
the output resistance of <50 mOhm .
Mat Nieuwenhoven
So would it be worth my while to buy one or two of these and play with
them?
<https://www.aliexpress.com/item/32796154933.html> I have a few ~100w
laptop power bricks around that I could use to feed power to them (that
I could supplement with a large local capacitor...).
I realise it's in a different class to the links you provided but I
don't have a big budget. That said I don't have money to waste either...
Cheers,
On 20/10/2019 1:07 pm, ~misfit~ wrote:
On 20/10/2019 1:03 AM, Mat Nieuwenhoven wrote:
On 13 Oct 2019 21:26:46 GMT, Trevor Wilson wrote:
<snip>
Do they actually use FB?
**EVERY amplifier uses NFB. Every single one. Regardless of technology >>>> or claims from manufacturers.
If I look
at the spec sheet of the TDA7492 it doesn't look like it. Do they
sound worse than a good analog amp?
**I see a loop feedback mechanism in the block diagram. I see some
audibly significant problems with the amplifier. Max THD is cited aas
0.4% and the frequency response is poor, compared to even modest Class >>>> A/B amplifiers. The low switching frequency ensures that low impedance >>>> (<4 Ohms) loads are not well catered for.
The TDA7492 has a switching frequency of typically 310 kHz. How is
this related to bad handling of a 4 ohm load, and why is that
dependent on the load resistance? And this IC is specified for 4 ohm
or more.
The low frequency fall off is deliberate (page 24 of the ST spec),
easily fixed by increasing the input size capacitor. The
THD-versus-frequency plot is indeed not impressive, THD rises in
spots to 0.2 %. You don't happen to have a link to a similar plot
from a good quality analog amp? Also, a link for a similar FFT plot ?
I am curious.
The IC is also dirt cheap, on a board for less than 10 $. For that
price, it is superb value for money.
There is indeed a feedback path from the OUTx pins to the second amp
inside.
<snip>
For a professional product, see e.g.
https://icepower.dk/products/other/a-series/ . Its datasheet is at
https://icepower.dk/download/2414/ . It supports loads down to 2.7
ohm loads. Again I wonder what the switching frequency has to do with
load.
I wonder if the phase plot can be matched by any analog amp, or even
the output resistance of <50 mOhm .
Mat Nieuwenhoven
So would it be worth my while to buy one or two of these and play with them? >> <https://www.aliexpress.com/item/32796154933.html> I have a few ~100w laptop power bricks around
that I could use to feed power to them (that I could supplement with a large local capacitor...).
I realise it's in a different class to the links you provided but I don't have a big budget. That
said I don't have money to waste either...
Cheers,
**Depends on what you are trying to achieve. For 4 Bucks, it represents very good value for money,
for an amplifier that can make some noise. It ain't 'proper' hi fi, but it will certainly
outperform many highly prized (and very expensive) valve amps. It cannot hope to perform as well as
any competently designed Class A/B solid state amp though. Still, it is FOUR BUCKS!
a) Argument-by-exception is, generally, fallacious.
b) Anything including a coil that carries current will be inductive.
c) Most well-designed speakers using conventional drivers that include voice-coils will account for this in their design.
d) Many crossover designs include inductors of various natures typed.
e) And those well-designed speakers that incorporate the exceptions
will also account for those option.
Comes down to the question of: Does driver/speaker inductance
in *this* particular speaker coupled with *that* particular
amplifier matter at *this* range of frequencies and volumes?
Theory is all well and good, but how things operate in the real
world at the living/listening room level are, or at least should,
be the primary issue.
a) Argument-by-exception is, generally, fallacious.
b) Anything including a coil that carries current will be inductive.
c) Most well-designed speakers using conventional drivers that include voice-coils will account for this in their design.
d) Many crossover designs include inductors of various natures typed.
e) And those well-designed speakers that incorporate the exceptions
will also account for those option.
Comes down to the question of: Does driver/speaker inductance
in *this* particular speaker coupled with *that* particular
amplifier matter at *this* range of frequencies and volumes?
Theory is all well and good, but how things operate in the real
world at the living/listening room level are, or at least should,
be the primary issue.
a) Argument-by-exception is, generally, fallacious.
b) Anything including a coil that carries current will be inductive.
c) Most well-designed speakers using conventional drivers that include voice-coils will account for this in their design.
d) Many crossover designs include inductors of various natures typed.
e) And those well-designed speakers that incorporate the exceptions
will also account for those option.
Comes down to the question of: Does driver/speaker inductance
in *this* particular speaker coupled with *that* particular
amplifier matter at *this* range of frequencies and volumes?
Theory is all well and good, but how things operate in the real
world at the living/listening room level are, or at least should,
be the primary issue.
| Sysop: | Keyop |
|---|---|
| Location: | Huddersfield, West Yorkshire, UK |
| Users: | 296 |
| Nodes: | 16 (2 / 14) |
| Uptime: | 20:43:05 |
| Calls: | 6,646 |
| Calls today: | 1 |
| Files: | 12,190 |
| Messages: | 5,327,412 |