how to get cv out of this theremin circuit

Posted: 6/12/2011 7:37:41 AM

Joined: 6/12/2011

Hey there,
i built the volume control part of this theremin :

It works so far that I can change the pitch of the oscillator mix with my hand.
But I actually try to make an theremin controller. I built the whole Volume control part and put an voltage where it says "from point A" .

It doesnt work.
Do you guys have an idea on how I could get a control voltage(0-5V or 0-10V) which is more or less steady when my hand is steady, out of this circuit?

Posted: 6/16/2011 1:46:17 AM

From: Colmar, France

Joined: 12/31/2007

Point A has the raw pitch signal which is not yet controlled by the volume circuit. The volume cv can be picked up just before the 100k resistor which goes to the gate of the vca transistor 2N 3819, at the output of the 4-diode bridge behind the TLE 2027. It should give a voltage from almost 0 to about -2.5V and will need buffering, voltage shifting and an adjustable amplification by factor 2 to 4 with another OP amp in order to get 0 to 5V or 0 to 10V.
Posted: 7/26/2011 4:48:19 AM

Joined: 6/12/2011

Hey Thierry,
Thank you for the answer, I also thought that it works like that.

But at the moment nothing works. There is no voltage varying about 2.5V it is not even 0.1 V.

I am checking the high frequency oscillators at the moment and I recognized that the Outputwaveforms arent perfect sines and have an offset voltage to zero.

I used polarized capcitors for the 1µF after the JFET3189 and the other 1µF.

Could this be the mistake?

i also used other transistors and JFETS:

PNP = BC141

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