Category Archives: Electronic projects

Debugging MFOS SLMS

I made some scope measurements to help understand and debug faulty MFOS SLMS in SMT version.
My scope is not very accurate and the tested unit is far from perfect, but at least, it gives a pretty good idea of expected signals on the Test Points.


First signal to check is VCO1 (TP201). Put VCO1 Frequency pot in middle position (50%), LFO and AR switches on Off position:

VCO1 Test Point (TP201) shows a Clean Sawtooth, from 0 to 4V.

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MFOS SoundLab MiniSynth in SMT

Ray Wilson was the guy behind Music From Outer Space. He was a huge contributor to the Synth DIY scene. He designed a lot of cool projects, offered kits, schematics and a huge amount of tips and tricks for beginners. He even wrote a book on how to build an Analog Synth. MFOS kits and PCBs are still available through various resellers (see synthcube).

Eurorack MFOS SLMS clone

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Ground is Not your Negative Rail

Unfortunately, the PSU you just bought isn’t adequate for your Eurorack system?
It’s common to be confused by the “-V” label.


Yes, “-V” on a PSU is a “negative” output, but only compared to the positive output. Your synth needs more!

So, what is the difference between “-V” and “ground”? How to select and use a proper power supply for your Synth?
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