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From: jgk@osc.COM (Joe Keane)
Newsgroups: rec.audio,sci.electronics
Subject: VCAs
Summary: How to build one?
Keywords: FET, OTA, VCA, CIA
Message-ID: <3747@osc.COM>
Date: 1 Sep 90 01:10:40 GMT
Reply-To: jgk@osc.COM (Joe Keane)
Followup-To: rec.audio
Organization: Object Sciences Corp., Menlo Park, CA
Lines: 14

I'm interested in building a bunch of voltage-controlled amplifiers, and i'd
like to know what are the best ways of doing this.  My requirements are that
it have low noise, high linearity with respect to the input voltage, and
reasonable linearity with respect to the control voltage.

The techniques i've seen include: FETs as variable resistances; four-quadrant
multiplier ICs; opto-isolators as variable resistances; OTAs (operational
transconductance amplifiers); balanced modulators using non-linear devices;
and probably some more i can't think of right now.

I'd like to know if any of you have an opinion about the pros and cons of
these or other techniques, or know how this is usually done in stereo
equipment or analog synthesizers.  E-mail to me and i'll summarize, and thanks
in advance for your help.