MFOS Dual VCA

[matrix12x]

I'm new here and I just started building the MFOS Dual VCA using the Bridechamber front panel. What is the best op amp to use in this for using my VCA primarily for audio?

[DETOX]

[matrix12x]

I have also use my VCAs in the past for CV attenuation

[falafelbiels]

I have used TL084 as in the schematic and it works as expected. I'd almost add another "...as expected".

[matrix12x]

Thanks. I did not know if the TL074's lower noise figure was any help in this type of application.

[fluxmonkey]

for audio levels typically found in modular synths (+/-5v), i've never heard a difference between TL074 or TL084... mic level audio might be a different story, but you'd have lots of other factors there, like powersupply and shielding, that would probably be more significant than the opamps.

[sonicwarrior]

If I understand the schematic correctly the TL084 is not in the audio path and processes the CV only.

@matrix12x:

I'm using the Bridechamber front, too. Did you build it in the meantime?
I'm wondering were I have to install the Gain potentiometer as it is not mentioned in the MFOS description/schematics.
Or is it the offset potentiometer without a connection to V- and instead connecting that point to ground?

[matrix12x]

I put mine between R17 pin 2 and J3 pin 1.

[sonicwarrior]

That's the output level, not gain. Gain is the base amplification. E.g. if you want a constant signal without any CV input you raise the gain knob to the needed level.

[matrix12x]

I know, I was just lazy about it.

[matrix12x]

A voltage at R11 or R33 would change gain though.

[sonicwarrior]

I'll try that then. Thanks for helping.

[slacker]

On the schematic here http://www.musicfromouterspace.com/mfosweb/navigate.action?MAINTAB=SYNTHDIY&PROJARG=DUALVCA/DLLVCA001.html the "Offset Adjust" pots are the gain controls. They do this "...you want a constant signal without any CV input you raise the gain knob to the needed level."

[matrix12x]

Yeah, I just rewired mine in that manner last night.

[sonicwarrior]

[sonicwarrior]

[nyd]

Anyone tried wiring a pot instead of a switch to adjust the LIN/LOG response of the VCA? I'm thinking in lines of mimicing the uVCA from Intellijel that has a pot to adjust the response.

Would it work?

[sonicwarrior]

Yes, should work. Intellijel did also just put a pot between these two instead of a switch. The circuit developer Dr Sketch n Etch explained that @Muffwiggler in a thread about the DIY variant of the uVCA.