[sdiy] Signals leaking into the PSU?

[Mike Bryant]

Bypass every IC with 100nF.  And as you are building your own circuits, consider adding a capacitance multiplier on the positive and negative supplies.  Costs a few cents and you lose a little headroom but does wonders for noise reduction.
________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of A.M. Barrio via Synth-diy <synth-diy at synth-diy.org>
Sent: 19 February 2023 13:45
To: synth-diy at synth-diy.org <synth-diy at synth-diy.org>
Subject: [sdiy] Signals leaking into the PSU?

Hello,
I'm having an issue where the frequency of my VCO is being affected by the operation of other modules. I'll give a a broader explanation:

I'm a beginner on synth DIY, right now I have my home made case, a PSU, two VCOs, an LFO, a clock module and an amplifier/speaker (built in the case, not externally). Everything has been arranged by me, I haven't purchased any module yet. The clock and the LFO are the latest modules I have built (pretty much both at the same time), and when I tested them on their own, they worked just fine. However I noticed that when they are powered, the frequency of the VCO would stutter following the operation of the clock and the LFO.

That would be: without connecting the clock or the LFO anywhere, just having them powered up, whenever the clock is up or down, or the waves generated by the LFO reset, the frequency of the VCO varies a tiny bit. It gets more noticeable the higher the pitch of the VCO.

After some head scratching I've realised that the signals generated by any of the modules I have (both VCOs, the clock and the LFO) are somehow leaking into the +12 and -12 rails of my PSU. Measuring any of the rails on my scope (on AC mode, so only the noise is shown), I can see that the waves generated by the modules I mentioned above are there as well in the form of noise (around 20mVpp each of them). That explains the little variations in frequency of the VCO. However I have no idea why this is happening or how to fix it. I have tried with different PSUs I have around:


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20230219/cf0455ea/attachment.htm>