Opinions on the CA3080 ???

[Don Tillman]

   Date: Sun, 11 Jun 2000 21:47:27 -0400
   From: Harry Bissell <harrybissell at prodigy.net>

   I've been playing with the CA3080  (old RCA).  I tried it as a
   preamp for a guitar pickup (hex fuzz idea) with voltage variable
   gain. 

   What I found was that the unit was prone to oscillation (using the
   inverting input) when the coil of the guitar had some series resistance
   with it (guitar volume 1/2 way down... usually thats a 250K pot). I got
   rid of most of the oscillation with a 20pF feedback cap.

Three things:

 The problems you report really suggest a grounding or ground loop
 problem.  

 The CA3080 is not recommended for this sort of thing because it
 doesn't have a noise spec.  The LM13600 and CA3280, on the other
 hand, both have respectable noise specs.

 I don't think the CA3080 is going to work for high input impedance
 circuits due to the input bias current requirements.  I would use a
 source follower buffer stage first.

  -- Don

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