Gyraf Audio Gyratec G20 (Used)

Gyratec G20 is an all-tube mono compressor, based on the classic variable-mu principle. Controlling the volume by a changing current in differential tube pairs is a much faster way than the electro-optical principle. Speed was the main reason for using it in the first limiters such as Fairchild 670 or Universal Audio 176, but the sound characteristics of this circuit are the main reasons for their popularity.

Gyratec 20 controls:

The input control allows you to control the input level and thus the "drive" of the preamplifier.

The Threshold knob sets the threshold of compression. Rotated counterclockwise, a lower threshold can be established, which leads to more compression. Fully clockwise the compression is disabled.

Ratio control allows adjustment of compression, depending on the input level. Fully clockwise, the compression is disabled.

Attack and release times can be adjusted with the corresponding controls.

The output knob controls the level of the output signal directly.

The signal can be bypassed via relay. The inputs and outputs are transformer-balanced and ungrounded. The input impedance is > 10 kΩ, output is <1  kΩ. Based on a very short, balanced signal path from input to output, carefully selected PCC189 (7ES8) dual-triodes are used for the amplifier stages, whereas low-noise triodes E88CC (6DJ8) can be found as cathode-pursuers at the output stage. Both types are very easily available. The semiconductors and op-amps which are built in the G20 serve only the power supply and the side-chain function. At no time does the audio signal passes anything else but transformers, tubes and passive components. So we're talking - just as we do with all other Gyraf devices - about REAL tube sound.