It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track shorts unless you are very careful with your soldering. The gain of a virtual-earth stage was too high, so I altered some resistor values to
cut it down.
As this was a stereo system, I experimented with one channel first and
then switched off and replaced the equivalent resistors in the second
channel (one of the other op-amps in the same chip).
The input signal was a 6 Kc/s sinwave at about -10 dBu. After the modification, the volume control, which was in a feedback loop, didnt
seem to make much difference. Then I realised that applying the signal
to the left channel gave a distorted version of it in the right channel
and vice-versa. Obviously I had shorted two tracks somewhere - but
where?
Things got even worse when I realised that the input signal was
appearing on the virtual earth input of each op-amp, this definitely
can't happen! I decided it was time to switch off the power supply and
go and ponder the problem over a cup of tea.
That was the point where I discovered I hadn't switched the power supply
on in the first place.
It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track >shorts unless you are very careful with your soldering. The gain of a >virtual-earth stage was too high, so I altered some resistor values to
cut it down.
As this was a stereo system, I experimented with one channel first and
then switched off and replaced the equivalent resistors in the second
channel (one of the other op-amps in the same chip).
The input signal was a 6 Kc/s sinwave at about -10 dBu. After the >modification, the volume control, which was in a feedback loop, didnt
seem to make much difference. Then I realised that applying the signal
to the left channel gave a distorted version of it in the right channel
and vice-versa. Obviously I had shorted two tracks somewhere - but
where?
Things got even worse when I realised that the input signal was
appearing on the virtual earth input of each op-amp, this definitely
can't happen! I decided it was time to switch off the power supply and
go and ponder the problem over a cup of tea.
That was the point where I discovered I hadn't switched the power supply
on in the first place.
On Tue, 10 Sep 2024 10:31:37 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track >>shorts unless you are very careful with your soldering. The gain of a >>virtual-earth stage was too high, so I altered some resistor values to
cut it down.
Show us a pic of your breadboard!
As this was a stereo system, I experimented with one channel first and
then switched off and replaced the equivalent resistors in the second >>channel (one of the other op-amps in the same chip).
The input signal was a 6 Kc/s sinwave at about -10 dBu. After the >>modification, the volume control, which was in a feedback loop, didnt
seem to make much difference. Then I realised that applying the signal
to the left channel gave a distorted version of it in the right channel
and vice-versa. Obviously I had shorted two tracks somewhere - but
where?
Things got even worse when I realised that the input signal was
appearing on the virtual earth input of each op-amp, this definitely
can't happen! I decided it was time to switch off the power supply and
go and ponder the problem over a cup of tea.
That was the point where I discovered I hadn't switched the power supply
on in the first place.
Sometimes people note that a CMOS circuit works properly with no power >supply, because some ESD diodes are rectifying a logic input.
I never use those dreadful Veroboard or plastic block plugin things.
Try this:
https://www.dropbox.com/scl/fi/f3redjl7umja5v8tsi2p5/Z382_1.JPG?rlkey=epclqs4lkx2cmdakne390bbae&raw=1
https://www.dropbox.com/scl/fi/ydvcds95zvzjq56bzeimr/Z412_Proto.JPG?rlkey=hyejukxbbnk3573engf0if4zt&raw=1
Get artistic!
It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track shorts unless you are very careful with your soldering. The gain of a virtual-earth stage was too high, so I altered some resistor values to
cut it down.
As this was a stereo system, I experimented with one channel first and
then switched off and replaced the equivalent resistors in the second
channel (one of the other op-amps in the same chip).
The input signal was a 6 Kc/s sinwave at about -10 dBu. After the modification, the volume control, which was in a feedback loop, didnt
seem to make much difference. Then I realised that applying the signal
to the left channel gave a distorted version of it in the right channel
and vice-versa. Obviously I had shorted two tracks somewhere - but
where?
Things got even worse when I realised that the input signal was
appearing on the virtual earth input of each op-amp, this definitely
can't happen! I decided it was time to switch off the power supply and
go and ponder the problem over a cup of tea.
That was the point where I discovered I hadn't switched the power supply
on in the first place.
It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track >shorts unless you are very careful with your soldering. The gain of a >virtual-earth stage was too high, so I altered some resistor values to
cut it down.
As this was a stereo system, I experimented with one channel first and
then switched off and replaced the equivalent resistors in the second
channel (one of the other op-amps in the same chip).
The input signal was a 6 Kc/s sinwave at about -10 dBu. After the >modification, the volume control, which was in a feedback loop, didnt
seem to make much difference. Then I realised that applying the signal
to the left channel gave a distorted version of it in the right channel
and vice-versa. Obviously I had shorted two tracks somewhere - but
where?
Things got even worse when I realised that the input signal was
appearing on the virtual earth input of each op-amp, this definitely
can't happen! I decided it was time to switch off the power supply and
go and ponder the problem over a cup of tea.
That was the point where I discovered I hadn't switched the power supply
on in the first place.
A cuppa Tea solves EVERYTHING!
On 9/10/2024 12:38 PM, John Robertson wrote:
A cuppa Tea solves EVERYTHING!
Sadly, it takes time to prepare (boil water, steep,
cool to drinking temperature).
I'm debating buying an "electric kettle" so I can
buy *two* and always have one that is ready to
stand in for the one that is just emptying...
On Tue, 10 Sep 2024 10:31:37 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track
shorts unless you are very careful with your soldering. The gain of a
virtual-earth stage was too high, so I altered some resistor values to
cut it down.
Show us a pic of your breadboard!
As this was a stereo system, I experimented with one channel first and
then switched off and replaced the equivalent resistors in the second
channel (one of the other op-amps in the same chip).
The input signal was a 6 Kc/s sinwave at about -10 dBu. After the
modification, the volume control, which was in a feedback loop, didnt
seem to make much difference. Then I realised that applying the signal
to the left channel gave a distorted version of it in the right channel
and vice-versa. Obviously I had shorted two tracks somewhere - but
where?
Things got even worse when I realised that the input signal was
appearing on the virtual earth input of each op-amp, this definitely
can't happen! I decided it was time to switch off the power supply and
go and ponder the problem over a cup of tea.
That was the point where I discovered I hadn't switched the power supply
on in the first place.
Sometimes people note that a CMOS circuit works properly with no power supply, because some ESD diodes are rectifying a logic input.
until all the inputs are low, then it only works until the bypass cap is discharged ;)
seem to remember seeing a boost converter made from just a cmos gate and an inductor, using the output as input and the supply pins as output via the ESD diodes, but I can't find it again, but I found this
https://www.edn.com/efficient-voltage-doubler-is-made-from-generic-cmos-inverters/
On 9/10/24 16:47, john larkin wrote:
On Tue, 10 Sep 2024 10:31:37 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track >>> shorts unless you are very careful with your soldering. The gain of a
virtual-earth stage was too high, so I altered some resistor values to
cut it down.
Show us a pic of your breadboard!
As this was a stereo system, I experimented with one channel first and
then switched off and replaced the equivalent resistors in the second
channel (one of the other op-amps in the same chip).
The input signal was a 6 Kc/s sinwave at about -10 dBu. After the
modification, the volume control, which was in a feedback loop, didnt
seem to make much difference. Then I realised that applying the signal
to the left channel gave a distorted version of it in the right channel
and vice-versa. Obviously I had shorted two tracks somewhere - but
where?
Things got even worse when I realised that the input signal was
appearing on the virtual earth input of each op-amp, this definitely
can't happen! I decided it was time to switch off the power supply and
go and ponder the problem over a cup of tea.
That was the point where I discovered I hadn't switched the power supply >>> on in the first place.
Sometimes people note that a CMOS circuit works properly with no power
supply, because some ESD diodes are rectifying a logic input.
until all the inputs are low, then it only works until the bypass cap is >discharged ;)
seem to remember seeing a boost converter made from just a cmos gate and
an inductor, using the output as input and the supply pins as output via
the ESD diodes, but I can't find it again, but I found this
https://www.edn.com/efficient-voltage-doubler-is-made-from-generic-cmos-inverters/
Don Y <blockedofcourse@foo.invalid> wrote:
On 9/10/2024 12:38 PM, John Robertson wrote:
A cuppa Tea solves EVERYTHING!
Sadly, it takes time to prepare (boil water, steep,
cool to drinking temperature).
I find little tasks that can be done whilst waiting for the tea to
cool. The problem is that I sometimes get so engrossed in them that I
don't remember the tea until it is nearly cold.
I'm debating buying an "electric kettle" so I can
buy *two* and always have one that is ready to
stand in for the one that is just emptying...
I habitually top up the kettle straight after pouring from it. This is
a habit I acquired when using a wood-fired Kelly Kettle (AKA Storm
Kettle) to make tea for outdoor work parties. If you didn't top it up immediately, there was a risk of burning it out.
On 9/10/24 16:47, john larkin wrote:
On Tue, 10 Sep 2024 10:31:37 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track >>> shorts unless you are very careful with your soldering. The gain of a >>> virtual-earth stage was too high, so I altered some resistor values to
cut it down.
Show us a pic of your breadboard!
As this was a stereo system, I experimented with one channel first and
then switched off and replaced the equivalent resistors in the second
channel (one of the other op-amps in the same chip).
The input signal was a 6 Kc/s sinwave at about -10 dBu. After the
modification, the volume control, which was in a feedback loop, didnt
seem to make much difference. Then I realised that applying the signal >>> to the left channel gave a distorted version of it in the right channel
and vice-versa. Obviously I had shorted two tracks somewhere - but
where?
Things got even worse when I realised that the input signal was
appearing on the virtual earth input of each op-amp, this definitely
can't happen! I decided it was time to switch off the power supply and >>> go and ponder the problem over a cup of tea.
That was the point where I discovered I hadn't switched the power supply >>> on in the first place.
Sometimes people note that a CMOS circuit works properly with no power
supply, because some ESD diodes are rectifying a logic input.
until all the inputs are low, then it only works until the bypass cap is discharged ;)
seem to remember seeing a boost converter made from just a cmos gate and
an inductor, using the output as input and the supply pins as output via
the ESD diodes, but I can't find it again, but I found this
https://www.edn.com/efficient-voltage-doubler-is-made-from-generic-cmos-inverters/
On 11/09/2024 23:59, Lasse Langwadt wrote:
On 9/10/24 16:47, john larkin wrote:
On Tue, 10 Sep 2024 10:31:37 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track >>>> shorts unless you are very careful with your soldering. The gain of a >>>> virtual-earth stage was too high, so I altered some resistor values to >>>> cut it down.
Show us a pic of your breadboard!
As this was a stereo system, I experimented with one channel first and >>>> then switched off and replaced the equivalent resistors in the second
channel (one of the other op-amps in the same chip).
The input signal was a 6 Kc/s sinwave at about -10 dBu. After the
modification, the volume control, which was in a feedback loop, didnt
seem to make much difference. Then I realised that applying the signal >>>> to the left channel gave a distorted version of it in the right channel >>>> and vice-versa. Obviously I had shorted two tracks somewhere - but
where?
Things got even worse when I realised that the input signal was
appearing on the virtual earth input of each op-amp, this definitely
can't happen! I decided it was time to switch off the power supply and >>>> go and ponder the problem over a cup of tea.
That was the point where I discovered I hadn't switched the power supply >>>> on in the first place.
Sometimes people note that a CMOS circuit works properly with no power
supply, because some ESD diodes are rectifying a logic input.
until all the inputs are low, then it only works until the bypass cap is
discharged ;)
seem to remember seeing a boost converter made from just a cmos gate and
an inductor, using the output as input and the supply pins as output via
the ESD diodes, but I can't find it again, but I found this
https://www.edn.com/efficient-voltage-doubler-is-made-from-generic-cmos-inverters/
It is possible you were remembering my posting this in April 2016:
<https://www.dropbox.com/scl/fi/8n4fz5o0r79rkmbn05j1a/micropowerBoost.pdf?rlkey=v1w9vm0his1pzd3lwd93dsm3v&st=5x8irpk6&raw=1>
All power flows through the inductor. The ESD diodes are only involved
during startup, once oscillator running the output stage n-fet is the
boost switch and the p-fet is the synchronous rectifier. A version built >using 74HC132 was in a successful product which needed micropower 5V
from 2-3V input.
piglet
On Tue, 10 Sep 2024 10:31:37 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track >shorts unless you are very careful with your soldering. The gain of a >virtual-earth stage was too high, so I altered some resistor values to
cut it down.
Show us a pic of your breadboard!
john larkin <jlarkin_highland_tech> wrote:
On Tue, 10 Sep 2024 10:31:37 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track >>> shorts unless you are very careful with your soldering. The gain of a
virtual-earth stage was too high, so I altered some resistor values to
cut it down.
Show us a pic of your breadboard!
I've posted circuit diagrams and a picture at:
http://www.poppyrecords.co.uk/other/Turntables/parallel-tracker.htm
It was the headphone amplifier that caused the mystery. So simple, yet
so confusing when you aren't expecting simple things to go wrong.
Liz Tuddenham <liz@poppyrecords.invalid.invalid> wrote:
john larkin <jlarkin_highland_tech> wrote:
On Tue, 10 Sep 2024 10:31:37 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
It's always the stupid things that cause the most trouble:
I was working on a fairly straightforward experimental audio circuit
using TL074 op-amps laid out on Veroboard, which is prone to inter-track >>> shorts unless you are very careful with your soldering. The gain of a >>> virtual-earth stage was too high, so I altered some resistor values to >>> cut it down.
Show us a pic of your breadboard!
I've posted circuit diagrams and a picture at:
http://www.poppyrecords.co.uk/other/Turntables/parallel-tracker.htm
It was the headphone amplifier that caused the mystery. So simple, yet
so confusing when you aren't expecting simple things to go wrong.
Thanks, interesting headphones volume setting.
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