VCAs, and Noise reduction for NE571

[Paul R. Higgins]

In his excellent handbook "Making Music with the NE570 Compander", Thomas Henry 
(of Midwest Analog Products) makes this suggestion, to replace the internal 
opamp with an external one.  The internal opamp in the 570/571 is essentially 
the same as a 741; not really superlative performance, but more than adequate 
for applications such as a compander in analog delay lines, etc.  Replacing the 
internal opamp is a trivial matter.

Apropos, years ago I built the Craig Anderton "Hyperflange and Chorus", which 
uses the horribly noisy (but great-sounding) SAD1024 IC.  A 571 is used as a 
compander and performs very well in this application.  Any 571 device noise is 
completely swamped by the delay line garbage.  I think that my demands on S/N 
performance are pretty severe, as my entire studio is digital except for a 
little-used cassette deck.  My only regret about the Hyperflange is that I 
didn't build more than one.  As long as you keep the signal pretty hot through 
the Hyperflange, noise is masked very well.

By the way, the app notes for the 570/571 claim >90 dB S/N, low THD, etc.  The 
notes also show how to build a (supposedly) high performance VCA.  I've never 
built the VCA, so I can't comment.

Speaking of the NE572, does anyone know where to find these?  Jameco Electronics
only stocks the 570/571.

Thanks,
PRH


> 	>Believe me a 3080 is a whole lot quieter than
> 	>the 571.
> 
> Are you sure this is not just because of the shitty internal opamp ?
> There is a recommendation to replace it with an external opamp and
> only use the variable gain cell. This is mainly to get a reasonable
> slew rate, but probably also to improove the SNR. Don't know, it's
> too long since I've played with these.



Paul Higgins
email: higg0008 at tc.umn.edu
University College, University of Minnesota