[sdiy] diagnosing polysix output noise (fwd from AH)

[el macaco]

Hi Jimmy,

Not familiar with these circuits, but if the corrosion traveled up the traces to other boards I’ve read that it is very difficult to remove and if I remember correctly someone made new boards to replace corrosion damaged ones.

If the 324 is an amplifying stage it could be that the noise is coming from further up and just boosted at this stage.

Best of luck, these kinds if problems are always a tricky thing requiring much patience.

I hope your aha moment comes soon!

Ed

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________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Jimmy Moore via Synth-diy <synth-diy at synth-diy.org>
Sent: Friday, March 27, 2026 9:50:56 AM
To: Adam (synthDIY) <synthdiy at adambaby.com>
Cc: synth-diy mailing list <synth-diy at synth-diy.org>
Subject: Re: [sdiy] diagnosing polysix output noise (fwd from AH)

I can't wait when I figure out where it's coming from so I can figure out how to patch it in as a reliable effect haha!

Florian and a few others on AH said it sounded like a flaky transistor or BBD chip.

Modifying the filter cutoff or resonance does NOT change the noise timbre. There may be a slight relationship between changing the resonance and that triggering the the noise. But only very slight. Florian called out that this out:

Does it depend on the on/off-setting of the effect section? If not then there are only a few parts that remain as suspects.

And just as remark: many people forget, that there is a VCA on the effect board that is controlled by the resonance setting. So, if the noise depends on the resonance setting, you can narrow down the source quite well.

 Curious if that helps localize things any.


I've had the synth droning this morning and it took about 20mins before the noise emerged. I can get another recording of people want, but it's more of the same. It appears independent of the effects section being engaged or not. The resonance setting does not appear to influence its prevalence.


On Thu, Mar 26, 2026, 11:35 PM Adam (synthDIY) <synthdiy at adambaby.com<mailto:synthdiy at adambaby.com>> wrote:
Interesting noise!

Sounds to me like the noise is being affected by the filter - would you agree? If so, it's not coming from the Effect Board BBD

A
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