Re: Op-amp mystery

From	Jan Panteltje <alien@comet.invalid>
Newsgroups	sci.electronics.design
Subject	Re: Op-amp mystery
Date	2024-09-10 15:05 +0000
Message-ID	<vbpn8h$2foq$1@solani.org> (permalink)
References	<1qznz5d.1m219rjmrzni6N%liz@poppyrecords.invalid.invalid> <rhm0ejtf032lq1g2q7kkvl20081gsd1v8r@4ax.com>

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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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Thread

Op-amp mystery liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2024-09-10 10:31 +0100
  Re: Op-amp mystery Don Y <blockedofcourse@foo.invalid> - 2024-09-10 05:27 -0700
  Re: Op-amp mystery john larkin <jlarkin_highland_tech> - 2024-09-10 07:47 -0700
    Re: Op-amp mystery Jan Panteltje <alien@comet.invalid> - 2024-09-10 15:05 +0000
    Re: Op-amp mystery Lasse Langwadt <llc@fonz.dk> - 2024-09-12 00:59 +0200
      Re: Op-amp mystery Don Y <blockedofcourse@foo.invalid> - 2024-09-11 19:00 -0700
      Re: Op-amp mystery john larkin <JL@gct.com> - 2024-09-11 19:10 -0700
      Re: Op-amp mystery piglet <erichpwagner@hotmail.com> - 2024-09-12 08:27 +0100
        Re: Op-amp mystery Jan Panteltje <alien@comet.invalid> - 2024-09-12 10:12 +0000
    Re: Op-amp mystery liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2024-09-12 13:21 +0100
      Re: Op-amp mystery piglet <erichpwagner@hotmail.com> - 2024-09-12 14:34 +0000
        Re: Op-amp mystery liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2024-09-12 18:03 +0100
  Re: Op-amp mystery John Robertson <jrr@flippers.com> - 2024-09-10 12:38 -0700
    Re: Op-amp mystery Don Y <blockedofcourse@foo.invalid> - 2024-09-11 12:15 -0700
      Re: Op-amp mystery liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2024-09-11 21:35 +0100
        Re: Op-amp mystery Don Y <blockedofcourse@foo.invalid> - 2024-09-11 18:37 -0700
  Re: Op-amp mystery legg <legg@nospam.magma.ca> - 2024-09-11 09:29 -0400

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