Simple VCA troubleshoot

will0000 · Joined: Apr 02, 2015 Posts: 4 Location: bay of fundy

I've built the Simple VCA, and have it mostly working in my 12v system. I have trimmed it according to the instructions, and everything is OK except that the whole thing is very quiet, almost inaudible. If I adjust A2 (init. level) to bring up the volume the CV input no longer does anything. I've checked the component values several times and I can't find anything wrong. Hoping for some help.

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

Check your wiring as well.
Post hires photos of your PCB (component and track faces) so we can check your build.

will0000 · Joined: Apr 02, 2015 Posts: 4 Location: bay of fundy

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So what is happening is when I set A2 (initial level) so that I get envelope response from CV1 input, the volume is way too low. If i turn A2 to raise the overall level, I no longer get any envelope response, just constant volume level. I hope this is clear. I don't have an oscilloscope so I can't trim according to the instructions but I understand the idea, I think.

will0000 · Joined: Apr 02, 2015 Posts: 4 Location: bay of fundy

will0000 · Joined: Apr 02, 2015 Posts: 4 Location: bay of fundy

I should add also: the transistor pair is a matched pair of BC548C. I have been experimenting with the values of R10 and R11, it seems the smaller I make them, the closer it gets to working normally (right now they are 4.7K). Besides that everything is true to the original Yusynth schematic.