A. & G. Reiswig
March 10th 04, 03:45 AM
McGuire, that is.
I recently went through the process of modifying my Symetrix SX-202 as per
Monte's description at
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=Gpop71.KD4%40world.std.com&rnum=1
I thought it might be helpful to post my impressions here.
Previously, the preamp was usable in stock form, but not really great. It
seemed to lack "sparkle" or transparency in the highs, and lacked detail.
Monte was kind enough to help me in detail when I ran into problems with the
modifications; it seems that early Rev. G boards such as mine have very
different part numbers from the ones he had worked with, and different still
from the numbers on the only schematics to be had at
http://www.symetrixaudio.com/tech_support/schematics/202_1A0.pdf . So it
was not a quick, step by step process that Monte outlined, but rather relies
on the reader to understand enough theory to extrapolate from his
instructions to their own board and components. I don't have that kind of
theory...so Monte got a lot of emails from me, and never lost his sense of
humor.
Anyway, the only thing in his suggested modifications that I have *not* done
as yet is to replace the potentiometers with a switched resistor net. That
will be done when my switches get here. One thing that ended up being
required on my board was to omit the summed output altogether: there is no
longer even an opamp hooked up to it. This was required if I was to bypass
the output coupling caps.
Another poster (Paul Stamler) had suggested that I bypass the phantom
blocking caps with some film caps, and I was able to fit some Panasonic
polypropylene .15uF caps on the non-component side of the board. Thanks for
that suggestion, Paul.
For a test, I plugged in microphones to an FMR RNP and the Symetrix.
Microphones are Gefell M294s. I placed the microphones as close to one
another as possible on a vertical line, and aimed them at my guitar. I got
the preamps to equivalent gain (possibly something I will *not* be able to
do as precisely after the pots are replaced). Then I recorded. I then
calibrated the resulting tracks for levels, and was able to switch back and
forth between the two.
It is very difficult for me to distinguish between the two tracks. The RNP
has a slightly more "forward" sound to it, as though it wants to come
forward in the mix a bit. But this difference is very subtle. Both seem to
have very low noise, and the "air" and detail that I was missing in the
Symetrix is there now. This is a completely subjective test, as I don't
have a way to measure the distortion, response, etc. But I thought it might
be helpful. Whether *you* could hear the difference as greater or lesser
than I do is an interesting one. I have the .wav files, and if someone
wants to post them to a web site or something, I can make them available.
Again, many thanks to Monte for all his help and suggestions. This was not
a project for the faint of heart, but the results seem to be worth the
effort. Including the $125 used price I paid for the unit, I have a total
of about $160 in it including parts right now. Not bad for a preamp that
sounds this good.
George Reiswig
Song of the River Music
I recently went through the process of modifying my Symetrix SX-202 as per
Monte's description at
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=Gpop71.KD4%40world.std.com&rnum=1
I thought it might be helpful to post my impressions here.
Previously, the preamp was usable in stock form, but not really great. It
seemed to lack "sparkle" or transparency in the highs, and lacked detail.
Monte was kind enough to help me in detail when I ran into problems with the
modifications; it seems that early Rev. G boards such as mine have very
different part numbers from the ones he had worked with, and different still
from the numbers on the only schematics to be had at
http://www.symetrixaudio.com/tech_support/schematics/202_1A0.pdf . So it
was not a quick, step by step process that Monte outlined, but rather relies
on the reader to understand enough theory to extrapolate from his
instructions to their own board and components. I don't have that kind of
theory...so Monte got a lot of emails from me, and never lost his sense of
humor.
Anyway, the only thing in his suggested modifications that I have *not* done
as yet is to replace the potentiometers with a switched resistor net. That
will be done when my switches get here. One thing that ended up being
required on my board was to omit the summed output altogether: there is no
longer even an opamp hooked up to it. This was required if I was to bypass
the output coupling caps.
Another poster (Paul Stamler) had suggested that I bypass the phantom
blocking caps with some film caps, and I was able to fit some Panasonic
polypropylene .15uF caps on the non-component side of the board. Thanks for
that suggestion, Paul.
For a test, I plugged in microphones to an FMR RNP and the Symetrix.
Microphones are Gefell M294s. I placed the microphones as close to one
another as possible on a vertical line, and aimed them at my guitar. I got
the preamps to equivalent gain (possibly something I will *not* be able to
do as precisely after the pots are replaced). Then I recorded. I then
calibrated the resulting tracks for levels, and was able to switch back and
forth between the two.
It is very difficult for me to distinguish between the two tracks. The RNP
has a slightly more "forward" sound to it, as though it wants to come
forward in the mix a bit. But this difference is very subtle. Both seem to
have very low noise, and the "air" and detail that I was missing in the
Symetrix is there now. This is a completely subjective test, as I don't
have a way to measure the distortion, response, etc. But I thought it might
be helpful. Whether *you* could hear the difference as greater or lesser
than I do is an interesting one. I have the .wav files, and if someone
wants to post them to a web site or something, I can make them available.
Again, many thanks to Monte for all his help and suggestions. This was not
a project for the faint of heart, but the results seem to be worth the
effort. Including the $125 used price I paid for the unit, I have a total
of about $160 in it including parts right now. Not bad for a preamp that
sounds this good.
George Reiswig
Song of the River Music