Sidechain R1 can be 0.6W. I think I originally used 2W resistor there because I have a bunch of 1 ohm 2W resistors. I’ll need to add the missing components to the mouser cart.
Scott is in the process of modding his compressor to the mastering version. I gave him some advice how to measure the threshold to make sure the threshold hi-low switch works as I intended. Now that I think about it, if hammond 107V is used instead of 107N the 5.6k resistor value might need to be different.
Edit: I think if 107N is used the resistor on the hi-lo threshold switch should be 4.7k and if 107V is used it should be 5.6k.
Here is the email I sent to Scott how to measure if the threshold is working correctly.
I’ll try to describe how to measure the threshold.
Turn gain to max, ratio to max, release and attack to fast. Make sure the threshold hi-lo range switch is NOT switched on. Turn threshold to min position/rotary position 1. Use your DAW to feed 1 kHz signal to the compressor. At first make the signal so low that there is no compression. Then increase signal until you start seeing the 1 dB compression LED lighting up. Write down the compressor output level where the compression starts happening.
Now turn the threshold switch to position 2. Now the 1 dB compression LED should turn off. Increase the signal from you DAW until you start seeing the 1 dB LED lighting up again. Write down the compressor output level where compression starts at position 2. Do the same to all the steps up to position 11. (Step 12 is always off)
After you have measured position 11 turn the switch on so it connects the 5.6k resistor to the circuit and turn the rotary back to position 1. Now there should be no compression going on. Increase the signal until you start seeing the 1 dB led lighting up and write down the compressor output level. Do the same again to all the steps now that the 5.6k is in the circuit.
Does this make sense?
The amount needed to increase the signal should stay fairly constant in dB between the steps and where the error might happen is when going from position 11 to position 1 with the switch flipped on.
On the front panel it might best to mark the position 12 for threshold OFF instead of MAX.
Edit 2:
The way the threshold and mastering modification is supposed to work is.
Threshold steps
Step 1 compression starts approximately at -10 dBu output
Step 2 compression starts approximately at -9 dBu output
Step 3 compression starts approximately at -8 dBu output
Step 4 compression starts approximately at -7 dBu output
Step 5 compression starts approximately at -6 dBu output
Step 6 compression starts approximately at -5 dBu output
Step 7 compression starts approximately at -4 dBu output
Step 8 compression starts approximately at -3 dBu output
Step 9 compression starts approximately at -2 dBu output
Step 10 compression starts approximately at -1 dBu output
Step 11 compression starts approximately at 0 dBu output
Step 12 compression starts never
Then you flip the threshold range switch
Step 1 compression starts approximately at +1 dBu output
Step 2 compression starts approximately at +2 dBu output
Step 3 compression starts approximately at +3 dBu output
Step 4 compression starts approximately at +4 dBu output
Step 5 compression starts approximately at +5 dBu output
Step 6 compression starts approximately at +6 dBu output
Step 7 compression starts approximately at +7 dBu output
Step 8 compression starts approximately at +8 dBu output
Step 9 compression starts approximately at +9 dBu output
Step 10 compression starts approximately at +10 dBu output
Step 11 compression starts approximately at +11 dBu output
Step 12 compression starts never
These are when Hammond 107V is used on the sidechain boards. With 107N the output levels where compression starts will shift few dB up.
Edit: 3
Scott has confirmed the mastering modification works as planned.