From: sbhattac@sales.GBA.NYU.EDU (Shankar Bhattacharyya)
Newsgroups: rec.audio
Subject: Re: Corey Greenberg's Unity Gain Preamp.
Date: 16 Apr 92 23:20:27 GMT
Organization: NYU Stern School of Business

In article <12502@tamsun.tamu.edu> p0p4018@zeus.tamu.edu (PREMTHAMKORN, PRAKIT) writes:
>preamp?  I itchs to try it but the parts are not cheap (Buff-3J, millitary spec.
>cost $65 each, Welborne labs' PS-1 power supply costs $95, etc).  Is it worth 
>the investment?  Please comment.

Greenberg's buffer seems like a case of vast overkill, with design of the
"more is always better" variety. There was some followup on  his buffer
design in a later issue of Stereophile, by the way. PMI said that he seemed
to be running his buffers at the ragged edge, and could expect trouble. He
seems to have chosen the absolute highest bias he thought he could use
without leaving any room for tolerances. And one of the people who
designed the power supply he recommends, Jung or Galo, I think, wrote in to
express some difference of opinion as well. If you do build this buffer,
look for the followups. I don't remember the details. I just skimmed the
letters at a friend's place a couple of months ago.

Greenberg also has this attitude that there's all this bandwidth available,
let's use it all, and let's get the most expensive way we can find to solve
the problem.

It is also not obvious to me that you need as much power supply as he wants
you to use. It may be that you do need that much, but I would not take that
on faith. His article makes cheerful assumptions. The style suggests to me,
and that is just my opinion, either that Greenberg does not build, or that
he is writing for people who don't. I can certainly believe the latter,
since I presume that the readership of Stereophile is mostly the buying
population, as against the solder rats.

If you do decide to build, there is not a whole lot of reason to buy
everything from some high price establishment. A major part of the cost of
a power supply is the transformer. Good toroidal transformers from the
premium sources like Wellborne cost $35 and up. Tanner Electronics, at
214-242-8702, has (or had, anyway) Avel-Lindberg 3021 toroidals,
two 22 V secondaries, 3 amps each, for $16, which is a steal. That should
be $35-40 directly from Avel-Lindberg, and I  have no idea how much more
from the premium places.

That should be enough to power everything in most full-blown preamps that
don't need higher voltages..

For a rather cheaper solution I would suggest the Linear Technologies
LT1010 buffer. It costs $4 a piece, and needs four resistors, and a couple
of fets in addition, and should do just fine. Total parts cost per channel
should be well under $10, not counting the supply.

I have not used the 1010, but I expect to. I'm just mentioning what seems
like a very attractive, and much less expensive option.

If anyone has designed with the 1010, by the way, I'd like to exchange
messages. At my level of electronic competence I can use lots of advice.

Linear Technologies is at 408-432-1900, or 800-637-5545.

Their Application Notes 4 and 16 deal with the 1010. A circuit using the
buffer was published in Electronic Design, Vol. 37, # 5, March 9, 1989.

If someone has a copy, I'd like one. I've only seen the reference, not the
article.

The circuit diagram was reproduced in  Audio Amateur in issue 2 of 1990,
page 48. There's good stuff in that Audio Amateur article, by the way, for
those who are not offended by the very thought of an op amp.

- Shankar