VCO pcb worries

Tony Allgood oakley at
Sat Mar 11 18:47:23 CET 2000

>Or does unwanted sync things has more to do with porely
regultated/filtered power than "badly" placed components .

Hi Per and all,

This was one thing that scared the living daylights out of me when I
designed my minimoog VCO board. I had heard so many times how the mini's
VCOs would lock up with a clean power supply line. Probably the second
issue mini VCO design , and mine's the final one, but when you put
120UKP into getting just four PCBs made, you have to cross your fingers

So I went over the top on decoupling, even having two different power
supply lines for different parts of the same VCO. I was mighty relieved
when it didn't soft sync at all with neighbouring VCOs. Pheww!!

The other thing to watch out for is 50Hz/60Hz modulation. The high
impedance areas of your circuit are prone to stray pick up, and that
means you get unwanted FM, usually very subtle. The most susceptible
part is probably the timing cap itself. Keep those lines short.

Hopefully, I should have some photos of the PCB and bits on my site by
next week.


Tony Allgood  Penrith, Cumbria, UK

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