Op-amp heresy.....

Don Tillman don at till.com
Sun Jan 26 20:00:21 CET 1997


   Date: Fri, 24 Jan 1997 21:07:02 GMT
   From: Chris Crosskey <chrisc at zetnet.co.uk>

     I've been thinking about op-amps, mostly because of the thread running
   at the moment, and a thought struck me from a few years ago. Back then 
   my friend Paul (currently re-creating a Moog 55 by himself) had built a 
   fairly large Penfold system, half a dozen VCO's etc, and he was unhappy
   with the tuning stability and linearity of the oscillators. I had a look
   at the circuit and suggested using a TL071 in place of the 741 in the 
   lin-log converter stage. He did and the improvement was massive. He then
   went through the rest of the modules over the course of the next month
   or so doing it to all the 741's in there. There was one module where he put
   the 741's back though. The audio mixers. He reckoned that with a TL071 it
   was just a bit too clinical whereas with 741's it became somehow warmer.
   That has got to be some sort of distortion effect, but it was a marked 
   effect, you could hear it on tape easily. Maybe we shouldn't be in too much
   of a hurry to bin the old horrors after all. 

I've used to a bunch of commercial mixers, and some of the differences
in sound are truly obvious.  And I've noticed that all the cheap
models (Peavy's, Yamahas, off-brands) sound horribly thin and tinny
and use 741's/1458's, while the nicer units (like the Mackies) sound
warm and rich and use better quality opamps.

The Moog Modular, by the way, uses a discrete mixer.  Heck, the Moog
Modular has almost no opamps in the audio path.

I guess what I'm saying is that if I was going to be introducing
distortion in a mixer I'd never choose 741 opamp distortion.

  -- Don



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