Technical:
This compressor is based on two closely-matched differential pair
7ES8 /PCC189 remote-cutoff triodes, differentially feeding two
6DJ8 /ECC88 cathode follower output stages. No feedback is used in
the signal path, and the topology is pure class-A all the way
through the unit. Lundahl audio transformers with internal elec-
trostatic shielding are used for both in- and output interfacing,
giving a true floating input impedance of about 10KOhm, and an
output impedance of less than 1KOhm.
This unit was originally intended for use with our analogue tape
recorders, which means that the optimum operating levels are
around that of +4dBu – and at this point you still have some 10dB
up to the point where the unit starts to get tired, which happens
around 15Vpp AC output – and then some before it starts sounding
bad. This means, however, that you should consider checking your
levels if you’re running a modern-day DAW, which often comes fac-
tory set to extremely-high levels like +24 or +28 for 0dBfsd.
Those kinds of levels are aimed at keeping a good safety-margin
before running into digital-clip, but at the same time it’s common
practice (for a good reason) to try getting as close to clip as
possible. A good level for use with the G10 (and for most analogue
gear in general) is somewhere 10dBu for 0dBfsd (full scale
digital)
Our audio path consists of ONLY transformers, tubes, and passive
components, and is true-differential (balanced) all the way from
input to output.
The sidechain and power supply circuits are solid-state based
though. The sidechain senses the incoming signal, rectifies and
times the voltages, and controls the DC voltage applied to the
differential input stage in order to set the quiescent current of
the stage, reflecting on the
µ
- and thus on the stage gain. The
quiescent current in the input stage is monitored by the front
panel meter, which then reads stage gain.
We use two types of tubes in the G10: The vari-mu set are
7ES8/PCC189 remote cutoff dual triodes, and the output driver set
are 6DJ8/ECC88 medium-mu dual triodes. Both types are still fairly
available today, so don’t worry too much about availability for
the future. These tubes should last for at least a couple of years
- and often a lot longer than that. If and when changing tubes,
contact Gyraf Audio for instructions on proper adjustment of the
unit.
Although semiconductors and op amps are used in this unit, they're
confined to power supply and sidechain functions. At no time will
your audio pass through anything but transformers, tubes and
passives. So - as with the rest of our product range - we're
talking REAL tube audio here..
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