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

[Richie Burnett]

I would have said that those strange squeaking sounds were likely beating 
between the high-frequency BBD clocks in the chorus section, but you said 
it's audible on the audio before if goes into the effects section.  The 
squeaking sound just sounds similar to the swooshing that you can sometimes 
hear at a very low-level in the noise-floor of a normal BBD chorus.

Definitely sounds like a loose connection somewhere though from all the 
cracking.  Are Polysix synths particularly prone to battery leakage damage? 
I have a friend who is also currently grappling with some really quite 
extensive corrosion issues due to a leaked battery in a Polysix!

Out of interest have you looked on the positive and negative supply rails in 
that area of the circuit?  You said there were glitches visible on various 
clock signals as well as the audio when you hear the crackles.  Just 
wondered if there is a bad power supply rail connection somewhere.

-Richie,



-----Original Message----- 
From: Jimmy Moore via Synth-diy
Sent: Saturday, March 28, 2026 9:00 PM
To: Adam (synthDIY)
Cc: synth-diy mailing list
Subject: Re: [sdiy] diagnosing polysix output noise (fwd from AH)


Great catch, I hadn't listened too critically back to back. Here are two 
recordings where you can clearly hear that the noisehas higher frequencies 
when the note is playing

Not playing: 
https://drive.google.com/file/d/1eYx_YXt7WBBX25fwzZ2FOYc6I9fTDbf0/view?usp=drivesdk

Droning note: 
https://drive.google.com/file/d/1Rp-peon3I2BJ0aEmvOlD7LLR-jI8AMf4/view?usp=drivesdk

In both cases resonance was at zero and cutoff was about 25%

I don't know the signal path or how it corresponds to stages of the 
schematic, maybe someone can help out here. But would this imply that the 
noise source could be between the filter and envelope generator?








On Fri, Mar 27, 2026, 3:34 PM Adam (synthDIY) <synthdiy at adambaby.com> wrote:





On 28 Mar 2026, at 00:50, Jimmy Moore <jamoore84 at gmail.com> wrote:
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.



But you'll agree that in your example recording, the noise has more high 
frequency content when the note is playing, than later when the note dies 
away?
If not affected by the filter directly, then there may be some relationship 
with the note envelope




On Thu, Mar 26, 2026, 11:35 PM Adam (synthDIY) <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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