Simple VCA Amplitude?????

[mrmrshoes]

I've just built the Simple VCA and it seems to be working, I think, But I haven't done any serious configuring yet apart from trimming A2 to mute input signal when the gain control is in a CCW position. When this is configured the amplitude on the output of the VCA is about ¼ of the input amplitude. Is this normal? I haven't matched the transistor pair yet just used two from the same batch for basic tests.

I know you can change the gain of the VCA with R10 & R11. I'm thinking I’ve got a working board and just need to configure these. Has anyone experienced the same behaviour?

I've check all component values on the board as well as for other problems like Shorts/Opens/Cold Joints and everything looks good.

The VCA is set-up for AC operation.

Any input would ready help me out.

Cheers

mrmrshoes

[Benjamin AM]

Curious what the control input voltage is.

[mrmrshoes]

I have figured out my problem man. I spent a couple of days checking over the board, replacing parts and looking for Shorts and opens. All the wiring looked good as-well, so I was pretty stumped.

When I was testing the VCA I had all the pots and nanner sockets attached to my panel. When I eventually remove the gain pot from the panel I realized that I had the wrong value pot (10K) instead of 100k. This explains the lack of amplitude when trimming A2 trim pot.

I feel pretty stupid. Well you can't win them all.

[Benjamin AM]

You shouldn't be to embarrassed, it happens to everyone.

[gdavis]

If it makes you feel any better, I just realized my LFO wasn't working because I put the TL074's in backwards

[AlanP]

Hah, when I was trying to dial in my Minimoog VCF, I couldn't work out why adjusting T1 did nothing to the voltage on Q1... until I noticed the resistor attached to it was 100K, not 1k8.