[sdiy] Bernie Hutchins CA3080 VCA

[Magnus Danielson]

From: eq927 at freenet.carleton.ca
Subject: Re: [sdiy] Bernie Hutchins CA3080 VCA 
Date: Wed, 19 Dec 2001 18:23:51 -0500

> Is this similar to the technique used by W. Jung (see Journal of Audio 
> Engineering Society, April 1975, Vol.23, No.3)? The normal PNP + op amp 
> current source is not used here - instead, the OTA is put in the 
> feedback loop of an op amp. Positive control voltages feed a resistor 
> connected to op amp (-) input, op amp output connects to OTA Vcc- (pin 
> 4), while OTA Iabc (pin 5) is connected to op amp (-) input. This forces 
> a current linearly proportional to the control voltage into the Iabc 
> pin. A diode clamp is used for reverse polarity protection.

I don't have the article (Pleeeease ;O) but I was hinted to a
schematic using the "right" style and indeed, this seems correctly
wired. The ASM-1 VCA is of the same style.

I happend to think it is a bit odd.

Your description matches the schematic at least.

Cheers,
Magnus