stiv@rice.edu (david n stivers) (05/22/91)
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. Comments on the below and additions would be appreciated: VTL Musical Reference Cary Audio Design conrad-johnson Audio Research -- david n stivers stiv@rice.edu
strong@tc.fluke.COM (Norm Strong) (05/24/91)
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. -- Norm Strong (strong@tc.fluke.com) 2528 31st S. Seattle WA 98144 USA
brian@america.Telebit.COM (Brian Lloyd) (05/29/91)
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
brian@america.Telebit.COM (Brian Lloyd) (06/03/91)
I have received NUMEROUS responses to my posting. It seems that there
is a great deal of interest in my old technology. What I thought that
I would do is to describe how I came to create the different preamp
architectures that I did (and that I am learing that others have been
copying) and how to build your own INEXPENSIVE vacuum tube and solid-
state preamps. Heck, I designed a solid-state preamp for Dennison
Electrostatics that was an ARC SP6A killer in its day. Parts cost was
about $20 (more if you put it in a box). It was low tech but it
sounded quite good (musical -- I personally don't care too much about
"accuracy" because who knows how the instrument(s) were played or
recorded, I just want to be able to listen to my recordings again and
again and again and not get tired of the sound).
Brian Lloyd's Rules of Amplifier Design
Actually, building a preamp (or any amplifier for that matter) that
sounds good is not hard to do IF you think about what you want and
don't get too carried away with technology. Here are some of my
guidelines:
* Every component degrades any signal that passes through it so keep
the parts count low.
* The human ear seems to be more sensitive to transient phenomena so
avoid topologies that can aggravate transient problems. You can live
with .5% THD and .1% IMD IF the transient distortions don't rise above
those levels.
* Match the input range of a stage to the expected output range of a
preceeding stage so that you avoid overload of intermediate stages
(this is critical if you are working with feedback stabilized
amplifiers)
* Provide clean, stable, low impedance, well decoupled power to each
stage.
Here is my basic topology for two types of preamps, one with no
feedback loops and one with a feedback loop in one stage:
eq eq
|\ -------- |\ ---------------------- |\
input >---| >--| 75us |--| >--| 318 us and 3180 us |--| >---> output
|/ -------- |/ ---------------------- |/
1st gain 2nd gain buffer
stage stage
eq
|\ -------- +
input >---| >--| 75us |-----|\
|/ -------- | >---------------------------> output
1st gain --|/ |
stage | - |
| --------------------- |
-----| 318us and 3180 us |--
---------------------
Notice that the first stage is never in a feedback loop. This is
because the signal there is at its fastest and most prone to transient
distortion. You just have to make sure that this stage is wide
bandwidth, unconditionally stable, quite, and has very wide dynamic
range. After the signal passes through the first part of the RIAA EQ
(the 75 microsecond deemphasis) the risetimes are much slower so that
most well-designed feedback stabilized amplifiers can deal with the
signal now.
Anyway, that is all I have time for now. I will write more later and
get into actual schematics for individual 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