Path: utzoo!mnetor!uunet!husc6!rutgers!mcnc!uvaarpa!umd5!mimsy!aplcen!osiris!phil
From: phil@osiris.UUCP (Philip Kos)
Newsgroups: sci.electronics
Subject: Re: Voltage Controlled Amplifier IC
Message-ID: <1512@osiris.UUCP>
Date: 28 Jan 88 18:01:30 GMT
References: <341@gaia.UUCP> <975@neoucom.UUCP>
Lines: 36
Summary: OTA

In addition to the Solid State Music SSM2013 and Signetics NE570 and
NE572 (I think the 572 is either the low-noise version or stereo
version of the 570, but I'm not sure), just about any OTA (Operational
Transconductance Amplifier, ~= VCA) circuit, like the RCA CA3080 and
others, should work with a little glue.  You may have to check data
sheets to find quiet enough versions.

I expect the SSM2013 has lots of peripheral circuitry designed to do
stuff that you may not need.  I know the NE570/NE572 do; they were
designed to make building companders (like dbx noise-reduction boxes)
easier, which is why they contain the extra circuitry (log amp, etc.)
Bill Mayhew mentioned.

A section in Walter Jung's "Audio IC Op Amp Applications" (TAB books,
I think) contains a low-noise high-stability VCA designed around a
3080.  It includes some pretty involved (to my mind, at least)
temperature compensating elements, suggesting that the older OTA ICs
like the 3080 aren't particularly stable, but it might be a good
starting point if you want to brew your own.  3080s are cheap.

In other news, Radio-Electronics recently ran a couple of quick blurbs
(one in the New Products section, the other in Don Lancaster's new
"hacker" column) on a "solid-state pot" IC which may be an attractive
alternative to using an OTA.

Serious electron heads out there: if I've said anything blatantly
wrong, please be gentle.  It's been awhile since I've seen most of this
stuff.  Also, I'm tracking this discussion.. if you have anything to
add to it, either post it to the net or cc: me a mail copy.  Thanks in
advance....


                                                                 Phil Kos
...!decvax!decuac!\                                   Information Systems
  ...!uunet!mimsy!aplcen!osiris!phil           The Johns Hopkins Hospital
...!allegra!/                                               Baltimore, MD