Gyraf Audio Gyratec 10 Vari-Mu Compressor
Gyraf Audio Gyratec 10 Vari-Mu stereo tube compressor.
Preliminary user manual, 12. June 2003.
The Gyratec 10 is a true tube stereo compressor based on the Vari-
Mu VCA principle. This method - controlling the gain by the means
of varying the DC working point of a tube differential pair, and
hence the Mu, is much faster than the electro-optical method used
in our G3, but also less subtle sonically. The Vari-Mu principle
is known from e.g. the classic Universal Audio UA176, the RCA
BA6A, or the legendary Fairchild 670.
In use:
First of all, when turning on the compressor, allow the unit to
heat up for ten to fifteen minutes - to get the tubes stabilised
in their working temperature. The sound and operating levels will
change somewhat within this period.
The controls on the Gyratec 10 are as follows:
The inputs are floating transformer balanced, 10K Ohm "bridging"
type, meaning that we don’t load the output of the previous stage
too much. The input connectors are standard XLR jacks, pin 2 hot.
The "bypass" function switch (4) bypasses the unit completely for
reference. The bypass is “hard”, meaning that the input is simply
shorted to output through a gold-plated relay. The light in the
GR-meter will dim a bit when set to bypassed, in order to let you
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