Variable Mutual Conductance Compressor

Testing

Turn trimmer RV1 from both sidechain boards to the most clockwise position and measure the voltages

Voltages

Voltages for the rotary sidechain version here!

* Measure the voltage and then turn the trimmer RV1 on sidechain board counter clockwise until the voltage is approximately 0.1V greater than the original value. If the voltage originally measures 3.9V then turn the trimmer RV1 on sidechain board counter clockwise until it is 4.0V. Do this measurement and adjustment for both channels!

0dB led should be always lit when the power is on. Rest of the leds should only light up when compressing except there might be light glow on 1dB led when at idle.

The latest revision of the led board has a trimmer to adjust the 1dB led. Adjust the trimmer until there is only light glow on the 1dB when not compressing.

Tube Balance

For checking the tube balance audio interface and software like ARTA or Room Eq Wizard are needed. Or use your DAW if you have a signal generator plugin.

Channel 1

Switch link on.

Turn threshold to max on both channels

Turn attack and release on both channels to fast position.

Turn ratio on both channels to max.

Feed channel 2 input with 50Hz signal. Do NOT feed any signal to channel 1 input!

Turn channel 2 threshold down until 8dB led lights up on both channels.

Measure output voltage from channel 1. Adjust balance trimmer RV1 on main board until lowest output voltage is found. Output level should -40 dBu or even much less if the tubes are in good balance.

Channel 2

Switch link on.

Turn threshold to max on both channels

Turn attack and release on both channels to fast position.

Turn ratio on both channels to max.

Feed channel 1 input with 50Hz signal. Do NOT feed any signal to channel 2 input!

Turn channel 1 threshold down until 8dB led lights up on both channels.

Measure output voltage from channel 2. Adjust balance trimmer RV2 on main board until lowest output voltage is found. Output level should be -40 dBu or even much less if the tubes are in good balance.

Another method of testin tube balance

20 kHz - 1s on 1s off wav file

Turn attack and release to fast position. Turn ratio to max. Play the audio file and and adjust the volume and threshold so that 3 dB led lights up and listen for audible "thumps". Adjust balance trimmer for minimal "thump".