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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.<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of A.M. Barrio via Synth-diy <synth-diy@synth-diy.org><br>
<b>Sent:</b> 19 February 2023 13:45<br>
<b>To:</b> synth-diy@synth-diy.org <synth-diy@synth-diy.org><br>
<b>Subject:</b> [sdiy] Signals leaking into the PSU?</font>
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<div>Hello, <br>
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<div>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:</div>
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<div>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. <br>
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<div>That would be: <b>without connecting the clock or the LFO anywhere</b>, 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.</div>
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<div>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:</div>
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