[sdiy] pin 5 3080

[Don Tillman]

   Date: Thu, 15 Mar 2001 12:53:41 +0000 (GMT)
   From: =?iso-8859-1?q?Ken=20MacBeth?= <macbeth2600 at yahoo.co.uk>

   On some circuits I see a 3080 used as an op amp. For instance in
   the micro/multi moog schemos, filter section, one is used in the
   regeneration loop. Pin 5 has a resistor tied to the supply. I've
   seen this also in other circuits. I thought the whole point of the
   OTA was to vary the current/gain. Please help put me right!

The 3080 is not being used as an opamp in the MicroMoog -- it's being
used as an instrumentation amp.  Very different.

The "opamp equivalent" would be two voltage followers to buffer the
signals off the ladder and a third opamp connected as a difference
amp.  The OTA approach is far more elegant and doesn't require closely
matched resistors.

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com