• Op-amp mystery

    From Liz Tuddenham@21:1/5 to All on Tue Sep 10 10:31:37 2024
    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.

    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

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  • From Don Y@21:1/5 to Liz Tuddenham on Tue Sep 10 05:27:28 2024
    On 9/10/2024 2:31 AM, 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.

    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.

    Too funny!

    Reminds me of a remote display/control device I made for one
    of our products in the 70's. All designed with CMOS and other
    low power technologies as it had to sit at the end of a long
    cable (e.g., for use on a flying bridge).

    I got the prototype board assembled and debugged properly.
    Then, discovered the power switch (an alternate acting pushbutton)
    had been OFF the whole time! The circuit was able to run off
    power derived from the data signals.

    Hmmm... now, how do I make it LOOK like it's "off" vs. "on"?

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  • From john larkin @21:1/5 to Liz Tuddenham on Tue Sep 10 07:47:46 2024
    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!

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  • From Jan Panteltje@21:1/5 to All on Tue Sep 10 15:05:53 2024
    On a sunny day (Tue, 10 Sep 2024 07:47:46 -0700) it happened john larkin <jlarkin_highland_tech> wrote in <rhm0ejtf032lq1g2q7kkvl20081gsd1v8r@4ax.com>:

    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!

    Veroboard is nice, all .1 inch specing, easy soldering, easy mounting connectors, no drilling required:
    https://panteltje.online/pub/PMT_HV_generator_solder_side_img_3172.jpg
    https://panteltje.nl/pub/test_board_component_side_1_IMG_3911.GIF
    that one is about 1.5 GHz out..
    etc etc...

    https://panteltje.nl/pub/test_board_wiring_side_IMG_3921.GIF

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  • From John Robertson@21:1/5 to Liz Tuddenham on Tue Sep 10 12:38:30 2024
    On 2024-09-10 2:31 a.m., 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.

    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!

    John :-#)#

    --
    (Please post followups or tech inquiries to the USENET newsgroup)
    John's Jukes Ltd.
    #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
    (604)872-5757 (Pinballs, Jukes, Video Games)
    www.flippers.com
    "Old pinballers never die, they just flip out."

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  • From legg@21:1/5 to Liz Tuddenham on Wed Sep 11 09:29:09 2024
    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.

    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.


    Stupid op amps!

    RL

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  • From Don Y@21:1/5 to John Robertson on Wed Sep 11 12:15:42 2024
    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...

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  • From Liz Tuddenham@21:1/5 to Don Y on Wed Sep 11 21:35:30 2024
    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.

    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

    --- SoupGate-Win32 v1.05
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  • From Lasse Langwadt@21:1/5 to john larkin on Thu Sep 12 00:59:58 2024
    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/

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  • From Don Y@21:1/5 to Lasse Langwadt on Wed Sep 11 19:00:06 2024
    On 9/11/2024 3:59 PM, Lasse Langwadt wrote:
    until all the inputs are low, then it only works until the bypass cap is discharged ;)

    Never a problem when your Vcc looks like a 2 ohm load and you've only got
    a handful of TTL I/Os to/from your "source"!

    Problem is when you're given an interface that was *designed* to
    connect one board to another INSIDE an instrument and then told to
    extend it a couple of feet OUTSIDE the instrument (so the device
    can be hidden to reduce clutter on the bridge).

    THEN, told to make that *30* ft and denied a power supply at
    the remote end of the cable!

    "We won't be able to use PGDs because we can't deliver that
    much power FROM THE INSTRUMENT. And, all of the control logic
    draws way too much current for the functionality it provides.
    And, drop-in CMOS counterparts aren't available. And, there's
    way too much C in the cable for those TTL signals. And you've
    already committed to the aluminum castings for the case. And..."

    [The idea/feasability of using an MCU for such a function, back
    then, was just plain silly!]

    That's what happens when a company lets "sales/marketing" drive
    their product development, unconditionally. You need "adults"
    that can make them understand the consequences of their fantasies!

    OTOH, the salesman who boasted he could sell hundreds of these
    "if you could extend the cable to 30 ft" was never heard from,
    again!

    [Valuable lesson learned. There and at all subsequent employers
    and clients, I did my own market research USING THEIR SALES RECORDS
    to argue against the inevitable "kitchen sink" requirements lists
    that invariably came along. "Yeah, I know you, as a salesman,
    don't want to lose ANY sale because of some missing capability.
    BUT, you have to realize that these capabilities come with costs;
    figure out the ESSENTIAL features and then learn how to spin those
    to your customers!"]

    So, I turned lemons into lemonade: left the hardware run continuously (eliminating the start-up delay necessary to "acquire signal") and
    just turned the power switch into a "display blank" and "controls
    inhibit" function.

    But, the prototype board -- instead of being ready for production
    for the previous design requirements -- had to be completely
    redone (we had a small etch tank so we could print 2 layer protos
    in-house so this was just an annoyance).

    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/




    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to All on Wed Sep 11 19:10:11 2024
    On Thu, 12 Sep 2024 00:59:58 +0200, Lasse Langwadt <llc@fonz.dk>
    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/



    This will drive a blue or whatever LED from a low voltage supply.

    https://www.dropbox.com/scl/fi/w3km774qoq5979eeh0uhg/LED_boost.JPG?rlkey=mvar3ydo8pjsgd6f04ggybfls&raw=1

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  • From Don Y@21:1/5 to Liz Tuddenham on Wed Sep 11 18:37:35 2024
    On 9/11/2024 1:35 PM, Liz Tuddenham wrote:
    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.

    The bigger problem is having to wait/watch while the kettle boils.
    And, then while the tea steeps. Steeping for too long with Pu'er
    will almost stain *glass*!

    I boil half a gallon of water and then let the tea steep in a
    large thermos. After it's steeped, I seal the thermos and dispense
    12 oz at a time over the course of the next 6 hours.

    Then, repeat the process for a second batch. (this usually gets me
    through to bedtime)

    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.

    The thermos will keep the tea hot for ~20 hours -- i.e., steaming
    hot even as I pour the last cup. (When I work away from home, I
    bring the thermos with me as my "hydration source") So, no need
    to keep "hot water" available from which to make more.

    ["Tea" is just a beverage, for me]

    I have a second (identical) thermos (bought to address the
    inevitability of this one breaking/failing) but having TWO in
    use just means having to MAKE two when they are both empty.

    An electric kettle seems like it wold cut down on wear-and-tear
    on the (electric) stove -- boilovers are a PITA to clean -- as
    well as easing the requirement for me to stand over it waiting
    for it to boil.

    [I would just use the kettle to boil the water and still steep
    it in the thermos]

    Having a third tap -- hot, cold, tea -- at the sink would be
    ideal!

    --- SoupGate-Win32 v1.05
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  • From piglet@21:1/5 to Lasse Langwadt on Thu Sep 12 08:27:36 2024
    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

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  • From Jan Panteltje@21:1/5 to erichpwagner@hotmail.com on Thu Sep 12 10:12:41 2024
    On a sunny day (Thu, 12 Sep 2024 08:27:36 +0100) it happened piglet <erichpwagner@hotmail.com> wrote in <vbu558$4nm1$1@dont-email.me>:

    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

    Interesting!

    Classic voltage doubler is the Villard circuit:
    https://josepheoff.github.io/posts/diode-capacitors-volts-pt1

    And if you need more low power voltage:
    https://panteltje.online/pub/PMT_regulated_power_supply_diagram_img_3182.jpg
    https://panteltje.nl/pub/PMT_HV_supply_componet_side_img_3180.jpg
    https://panteltje.nl/pub/PMT_HV_generator_size_img_3174.jpg
    has been working for decades now...
    also all battery powered
    https://panteltje.nl/pub/gamma_spectrometer_plus_probe_plus_geiger_counter_2_IMG_4185.JPG
    https://panteltje.nl/pub/gamma_spectrometer_supply_side_MG_6578.JPG

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  • From Liz Tuddenham@21:1/5 to All on Thu Sep 12 13:21:00 2024
    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 ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

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  • From piglet@21:1/5 to Liz Tuddenham on Thu Sep 12 14:34:15 2024
    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.


    --
    piglet

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  • From Liz Tuddenham@21:1/5 to piglet on Thu Sep 12 18:03:54 2024
    piglet <erichpwagner@hotmail.com> wrote:

    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.

    I was originally just going to copy the circuit of the headphone
    amplifier in a Marantz CD player (why bother to re-invent the wheel?),
    then I spotted that they used a 100-ohm resistor in series with the
    headphone socket. This would remove the damping, so that headphones
    with any unwanted resonances wouldn't give as good sound quality as they
    would have been capable of if they had been fed from a low impedance.

    To keep the output impedance low, I took the feedback from the output terminals.and put the 100-ohm resistors in the collector circuit, where
    they would still limit the output current to a safe value that wouldn't
    destroy the headphones.

    The volume control circuit was derived from a Doug Self design in which
    he used a unity-gain buffer to minimise the loading on the pot wiper. I
    had a bagfull of 5k twin-gang pots, so I decided that I could omit the
    buffer as long as the feedback resistors around the op-amp were high
    compared with the pot itself. The pot is linear but the scale is
    approximately in dB, which works a lot better than trying to make two logarithmic pots track accurately together (or buying some exotic and
    expensive controls).

    Originally I was aiming for similar gain characteristics to the line
    driver amplifier (pot half-way up = 0dBm output) but I found that was
    far too much gain and the volume control never needed to go beyond a
    quarter of a turn. The input signals going into all the output stages
    are around -10dBu with a cartridge giving around -45dBu on an 'average'
    record; this allows 30dB headroom before the volume control, which is
    necessary to avoid clipping the crackles from a damaged 78.

    The circuit I finished up with actually generates a loss, rather than a
    gain, but that gives a more favourable pot setting for comfortable
    listening. Despite not workoing quite as Doug Self intended, it
    manages to produce a smooth transition across the middle of the scale,
    without 'crowding' near the top ot the bottom.


    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

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