Minimoog discrete VCA

[Sound]

hello , I found in Marjan Urekar page http://members.tripod.com/urekarm/ the schematics of a Minimoog discrete VCA.

http://members.tripod.com/urekarm/synth/minivca.pdf

I see that there is an "440 Hz AUDIO IN". I see that is different that the other VCA audio in.

What is it?




Many thanks.

[Pehr]

Is it for tuning the oscillators?

[Tim Servo]

The Minimoog has a built-in 440Hz reference oscillator. This is merely a dedicated input for that osc, and can be left off if you're building a stand alone Mini VCA.

The (Mini me) Servo

[mono-poly]

Ooow Tim = Minime

[Tim Servo]

Oh no, I'm not Minime the used synth seller. I was just making a Minimoog reference/joke/sig/thingy. Gotta admit, Minime seems to get to play with a LOT of cool gear though. Still, I'm just Servo (and half of Magic Smoke).

Tim (dad/husband/engineer/idiot) Servo

[mono-poly]

Hehehe i was just kidding Tim.
I knew you were a different person.

[Sound]

I see. It is an non CV audio IN.

I'm trying to understand the circuit. After that, It will be my first DIY PCB.

Thanks,

[GlassX]

Also notice there's actually two-VCAs-in-one on the Minimoog. One for Envelope and one for External Control... It's a very simple (and well designed) circuit when you look at it

[Sound]

Thanks GlassX,

Why he designed two VCA, one for each CV input?

It is not more usual mix the two VC signals and send it to one VCA?

[ian-s]

[Sound]

I understand... VC2 affects the signal after it pass through VC1...

I have some questions more

What function have parts marked 1,2 and 3 in the following picture?

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[GlassX]

[Sound]

Thanks, Your explantion and the link of yusynth helps me a lot.

Other question is ... If I would put another output in the leg that I marked in the following picture... I would achieve a negative output? I meant 180º output of the actual output.

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[yusynth]

Yes it will be a negative output, that's what is done in the Moog 902 VCA module.

[Sound]

Very interesting Yusson!

I add the pdf that I found here http://www.hylander.com/moogschematics.html the complete minimoog schematics. Maybe any of you are interested in.

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[yusynth]

If you want to know more about the minimoog VCA check the excellent site by Jorgen BERGFORS :
http://hem.bredband.net/bersyn/minimoog%20VCA.htm
There is also a very interesting comparison of various VCA designs:
http://hem.bredband.net/bersyn/vca.htm

[Sound]

Yes! It is an amazing website. I like it very much. But I didn't understand one thing... In his schematics he applies the envelope to the second VCA. So... It will work if the first VCA is closed?

From http://hem.bredband.net/bersyn/VCA%20Minimoog.GIF

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[softfin]

Last year I made (and tested) a PCB layout for a dual Bergfors' 13600/13700 VCA. I can post it if there's any interest...

[yusynth]

[Sound]

Can the VCA2 close the signal of the CVA1?... Definitely I need to breadboard it I have alredy orered the BC550 &BC560. Waiting for them.

Softfin, of course! post your experience!!!

[softfin]

Ok I'll submit it ín another post so I don't have to risk hijacking this thread .