The Gyratec 22 is a true tube stereo compressor based on the Vari-Mu VCA principle.
G22 is an elaborated and dualified version of our venerable G10 vari-mu compressor. It can be set to dual-mono, but still keeps a backwards-compatibility "G10 mode" where one set of knobs controls real stereo, like you'd want most of the time in mastering.
The audio part of the circuit is a faithful reproduction of the G10 that has been our flagship for more than 15 years - if it works, don't fix it. The only minor change is a re-bias of the output stage, which allows some 4-5dB more headroom while preserving the original stage's soft transition into overload.
Some changes has been made to the sidechain functions, including a wider threshold range (to allow S compression in weak-S M/S-mode) and even faster fastest attack time (because we can, it's a vari-mu you know...)
A simple sidechain high-pass filter was added (located on the bypass switch) which cuts off compressor keying below ca. 80Hz at a slope of 6dB/oct. This mainly to keep pumping artifacts under control when working fast in bass-heavy material.
Input and output transformers can be switched between standard two-channel L/R mode and the M/S mode where both matrixing and dematrixing done is internally: M/S mode allows you to independently control dynamics (and levels) in mono and side parts of program material and still have the result on the output as standard stereo information.
Linking/dynamic interaction between channels in dual-mode can be set continuously from none to full by the Vari-link control knob - enabling you to dial in a difference in channel processing, and then varying difference amount in a simple mode. When initially getting to learn the unit, I myself was amazed how intuitive this control worked.
The G22 is as standard available as 230V or 115V mains voltages - Please specify when ordering
This compressor is based on two closely-matched differential pair 7ES8/PCC189 remote-cutoff triodes, differentially feeding two
6922/ECC88 cathode follower output stages. No feedback is used in the signal path, and the topology is pure class-A all the waythrough. Lundahl audio transformers with internal electrostatic shielding are used for both in- and output interfacing, giving a true floating input impedance of about 10KOhm, and an outputimpedance of less than 1KOhm.
This unit was originally intended for use with our analogue tape recorders, which means that the optimum operating levels arearound that of +4dBu - and at this point you still have some 10dBup 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 factory 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 commonpractice (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 around +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 sidechains 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 - and thus on the stage gain. Thequiescent current in the input stage is monitored by the frontpanel meter, which then reads stage gain.
We use two types of tubes in the G22: The vari-mu set are7ES8/PCC189 remote cutoff dual triodes, and the output driver setare 6922/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 theunit.
Although semiconductors and op amps are used in this unit, they'reconfined to power supply and sidechain functions. At no time willyour audio pass through anything but transformers