MFOS Dual Log/Lin VCA - value changes for +/- 15 V?

Bodo1967 · Joined: Aug 10, 2016 Posts: 14 Location: Germany

Hi everyone,

I'd like to add a few more VCAs to my system (completely DIY including cases and PSUs), which is kind of hybrid and has both +/- 12 and 15 V PSUs.

I'll add another 5U case in which I'd like to integrate one of the MFOS VCA modules. However, I't prefer to install only one PSU there, and that'll have to be a +/- 15 V one.

In the description, Ray writes somewhat vaguely:
"If you are using +/-15 volt supplies you will probably need to mess with some values to get this to work for you."

Did anyone here ever build a 15 V version, and if so, which values actually need to be replaced with which other values?

I'd like to spare myself the trial & error part, to be honest Laughing

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jeephour · Joined: Dec 23, 2014 Posts: 3 Location: Sheffield

Hi

I think I got a 15v version.
Still need an answer?

Bodo1967 · Joined: Aug 10, 2016 Posts: 14 Location: Germany

johans121 · Posted: Thu Dec 24, 2020 10:25 am Post subject:

Just out of curiosity, did you ever make any changes to your VCA for +/- 15V operation? I just got through putting one together. It works as it should. The problem is that it seems that the gain is relatively low as compared to my other 15V VCAs.

If I have the gain offset set to where I can not hear any audio when no CV is applied and then apply 10VPP input signal (say from a MOTM LFO) the output is indeed amplified but not to where I want it to be. In order to get the levels I want the gain offset needs to be boosted quite a bit but then there is a lot of input bleed through in the output.

Any help is appreciated.