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From: bill@crystal.UUCP
Newsgroups: net.audio
Subject: Re: Adding a buffer amp
Message-ID: <392@crystal.UUCP>
Date: Fri, 11-Jan-85 19:52:29 EST
Article-I.D.: crystal.392
Posted: Fri Jan 11 19:52:29 1985
Date-Received: Mon, 14-Jan-85 02:45:30 EST
References: <38@angband.UUCP>
Distribution: net
Organization: U of Wisconsin CS Dept
Lines: 37

> 
> At any rate, one article about putting a buffer between a preamp output
> and your cables appears in issue 4 of the 1977 Audio Amateur magazine.
> Unfortunately, you must buy the entire year of 4 back issues for $10
> (Box 176, Peterborough, NH 03458, USA). The same people, wearing a
> different hat, also sell for $17.50 a kit KH-8 called the "Morrey Super
> Buffer", including parts and board, but not the instructions, which
> appear only in the original magazine article (Old Colony Kits, Box 243,
> Peterborough, NH 03458; VISA, MC 603 924-6526).
> 
The Audio Amateur (TAA) is an interesting mag for anyone interested in how to
put audio equipment together (with or without taking it apart first -- they
do a lot of rebuild articles).  I highly recommend it.

The Morrey super buffer uses a 531 op amp, I believe.  TAA ran Walt Jung's
articles on op-amp selection for critical audio uses; he thinks the 531 is
a stinker.  It also requires an output transistor.

I would suggest building a simple non-inverting buffer, with a voltage gain
of 3, using an NE5534 (single) or NE5532(dual) op amp -- it directly
drives 600 ohm lines, and is very quiet.  (Signetics or TI; the 553[24]A version
is a low-noise selected version, but the non-A ones are usually about as good)
Jameco or DigiKey sells the TI version, I believe.  Runs $3 - $5, depending
on the usual things.  I have several friends who use these for pro-audio
stuff, and swear by them (and the '071, below).  Walt Jung's Audio IC Op Amp
book (Sams) has lots of circuits, but apparently not all of them are very
good.

Another choice would be the TI bifet op amps, the TL071 family (low-noise),
available for around 75cents from Action Electronics (see ads in
Radio-Electronics).  Need an output transistor, however.
-- 
	William Cox
	Computer Sciences Department
	University of Wisconsin, Madison WI
	bill@uwisc
	...{ihnp4,seismo,allegra}!uwvax!bill