For future ref, to avoid labourous pouring of silicon etc, just lift the transformer onto a car/kitchen sponge or an old pillow, this will immediately isolate cabinet humming....
then, you can move onto the silicon part or rubber blocks etc.
Is the soundboard (or speaker) anyway close to the transformer getting induced hum into the wiring?
Other than that, you might need to get techy with a Cro, and 'look' at the audio signal throughout the audio amp to see if the hum is within the sound board, or coming out of somewhere else?
I'd still like to see the power rails on the soundboard with a Cro, i reckon you could slam an extra 10,000uf to 50,000uf on the soundboard filter cap and note any difference.
Another thing to note, most of the older power supplies (not sure about modern ones) only use 1/2 wave rectifiers (2 diodes) on most of the Power Rails which means the A.C ripple voltage is a
lot more noticeable (hum-wise) than if you used a full rectifier (4 diodes) in the supplies.....don't know why they always did that.
saving money on diodes ?
It might also be some grounding humloop issues, at those high currents the varying lengths of ground wiring might also be the problem.
You might need to ensure that ALL ground wiring coming out the the main supply distribution are all EQUAL lengths to each card they go to....this means having some slack in the closer boards ground wiring to match the longer lengths to get to other cards.
This will help reduce stray currents that will riddle your rails with hum.
another manufacturuer oversight ???
Marty Machine.
