Gyraf Audio Gyratec III

The Gyraf Audio Gyratec III is a true tube stereo compressor based on the opto VCA principle.  This method - controlling the gain by the means of a light dependent resistor - is not as fast as the vari-mu method, but much more subtle sonically.  This principle is known from eg. the classic Universal audio LA2, LA3 and LA4 compressors..

We have recently updated the front panel on the G3 - that’s why it dosen’t look like the image in the Resolution review above.  The inside has had minor updates, but roughly speaking it’s kept the same as the old one.

The controls on the Gyratec III are as follows:

The input level pot is positioned right after the input transformers, thus allowing you to control the input level, the “drive” for the compressor.

The Threshold pot controls at what level the compression will set in.  Turning counter-clockwize will select a lower start point, resulting in more compression. When turned fully clockwize, the compression is deactivated.

The Ratio pot controls the amount of compression in relation to changes in the input level, that is, for the part of the signal that exceeds the threshold value that is set. Setting Ratio fully counter-clockwize will deactivate compression.

The Attack pot controls the time the compressor takes to react to a rising input level.

The Release pot controls the amount of time it takes from the input signal falling below threshold, to the gain reduction being returned to unity.

The Output level pot controls the signal level to the output driver stage and the output.

The Bypass switch bypasses the unit completely.  The hard way. - A relay simply takes out the active electronics and shorts the input to the output connectors.

The Gyratec III is floating, transformer balanced in and out. Input impedance > 10K Ohm, output impedance < 1K Ohm.

It is based on SRPP gain stages with no feedback, using selected 5814 dual triodes for both input and output stages.  These tubes are still fairly easily available today.

Although semiconductors and opamps are used in this unit, they’re confined to powersupply and sidechain functions.  At no time will your audio pass through anything but transformers, tubes and passives.