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From: brian@america.Telebit.COM (Brian Lloyd)
Newsgroups: rec.audio.high-end
Subject: Re: Tube pre-amps <$1000
Message-ID: <12580@uwm.edu>
Date: 29 May 91 12:53:26 GMT
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Approved: tjk@csd4.csd.uwm.edu
Originator: tjk@csd4.csd.uwm.edu

strong@tc.fluke.COM (Norm Strong) writes:

>In article <12346@uwm.edu> stiv@rice.edu (david n stivers) writes:
>}Any suggestion for new/used? I think that I may decide to get one eventually
>}(key word, eventually; see my other posting on Angelus and amplification) 
>}because I like the quality of the soundstage that they seem to offer, as well
>}as their smoothness. Of course, I wouldn't mind a good silicon amp, but
>}the ones that I've heard don't seem to be quite as good with these.
>}
>}The quality of the phono stage is a priority.

>A low level amplifier is the LAST place I would want to use vacuum tubes.
>They are much, much noisier than transistors.  In fact, it is usually
>necessary to use a transformer to couple an MC cartridge to a vacuum tube
>preamp, even if the cartridge is one of the high output types.

About 14 years ago I pioneered the use of passive EQ phono stages
while working at Audio Dimensions in San Diego.  In order to provide
reasonable support for MC cartridges with tubes I started using a
hybrid FET/triode cascode as the first stage of the phono preamp.  (My
approach was quite different from the approach that David Berning took
with his preamps in that I operated the triode and FET at a different
operating point so that the entire cascode operated as a
transconductance rather than a transresistance amplifier).  The bottom
line is that it sounded like tubes but was as quiet as the FET --
quite a tasty combination.

If anyone is interested in rolling their own (I make my living
designing routers and building networks now :-), I would be happy
posting my notes and even partial schematics for the phono stages.

-- 
Brian Lloyd, WB6RQN                              Telebit Corporation
Network Systems Architect                        1315 Chesapeake Terrace 
brian@napa.telebit.com                           Sunnyvale, CA 94089-1100
voice (408) 745-3103                             FAX (408) 734-3333