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YuSynth moog VCF noisy on the same PSU as Nozori 68
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author YuSynth moog VCF noisy on the same PSU as Nozori 68
Hey folks, bit of a head-scratcher here. I've been playing around with my new Nozoid Nozori 68 and noticed that my YuSynth minimoog VCF eurorack filter outputs a bunch of noise whenever the Nozori is on (sounds like a digital clock signal ringing the filter). My MFOS VCO also seems to get a bit noisier when the module is plugged in. I've noticed the same issue when powering an arduino and broadboard from the same supply.

I'm using a MFOS diy +/-12v power supply with a Jameco 12V AC brick. My suspicion is that the yusynth doesn't have adequate noise filtering on the power supply input and the nozori has somewhat inadequate capacitance. What I don't really know is how to fix it, since I know very little about analog electronics and power supplies.

My first though is to build a power supply filtering daughterboard for the VCF, with some inline ferrite beads and an array of capacitors. If this would work I'm not sure but it would be relatively easy. Another idea is to build a similar filter board for the Nozori, which uses an arduino due as its backpack board.

The Nozori passes its +12v signal through a small fuse(?) to the Vin of the Due, which uses an AMS1117 3.3v linear regulator.

I suppose the problem could also be in my synth power supply (inadequate current) or wiring (homemade busboards) but since only these 2 modules misbehave I somehow doubt that.

Has anyone else had noise/line sensitivity issues with the YuSynth VCF or other modules? How did you address?
Scot Solida
Has anyone else had noise/line sensitivity issues with the YuSynth VCF or other modules? How did you address?

I have. I spent ages trying to track down a non-existent problem in a YuSynth Steiner filter circuit, only to find that the trouble was that the YuSynth module didn't like the power supply I was using - a QPS2. When powering the module from the QPS1 or QPS3, the noise went away.

I think the trouble was due to the fact that the cheaper QPS2 was a switching power supply. (note that the QPS2 powers the modules just fine, with no noise).
I remember seeing a post somewhere that the power supply noise rejection of the Yu MM VCF is really low so you need big filters at the power input. Or a PSU with lower noise.

My solution (i have both the MM and the Steiner by Yusynth) was to get a linear PSU and a big, low ESR filter cap at the power rails of the these VCFs.

For the 10 ohm resistor at the power rails i choose a 470uF cap, these have the -3db point at 33hz, good enough to filter out a lot of audio range stuff.

On the other hand you cant use a lot of these big caps everywhere because their large transient current draw when you turn on your PSU can mess with your PSU.
Thanks a bunch for the ideas! Have been considering one of those meanwell multi-output supplies instead of the MFOS - may make the switch and see if it helps. The MFOS has LM2940/LM2840 regulators but I don't really if they're up to the task.

Good info on the caps! Will try with the biggest ones I have around (100uF i think) and see if it helps any. One thing I've learned by osmosis is that decoupling caps need physical proximity to be effective so hoping it's as simple as beefing up the input filtering.
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