It’s the Preamp as you already know.
Both channels is a clue, perhaps a good one.
Some more investigation. Is the hum present at both low level inputs and high level inputs?
Connect only 1 high level source, one input at a time? Is it present at each input?
repeat with low level inputs.
Learn anything?
Have another system, i.e. office, shop, to move the preamp into? Good? If good, then there is some unholy combination of interconnects/speaker wires/crossover component. If ok on the other system, you can in good faith sell it to someone who lives in Lake Woes Be Gone
...........................
My McIntosh SS Preamp C28 had a faint hum on low level inputs only. I bought a box, sent it to McIntosh factory, it came back ’fixed’. Same low level hum, low level inputs only. How the heck can I sell it knowing that?
I took it apart, gave the evil eye to the internal ground connection to the chassis. Unsoldered it, stripped end of wire, removed paint from the area, replaced with bolt and lock washer. Gone.
...............................
Days gone by, FM antennas were like the plague.
Both channels is a clue, perhaps a good one.
Some more investigation. Is the hum present at both low level inputs and high level inputs?
Connect only 1 high level source, one input at a time? Is it present at each input?
repeat with low level inputs.
Learn anything?
Have another system, i.e. office, shop, to move the preamp into? Good? If good, then there is some unholy combination of interconnects/speaker wires/crossover component. If ok on the other system, you can in good faith sell it to someone who lives in Lake Woes Be Gone
...........................
My McIntosh SS Preamp C28 had a faint hum on low level inputs only. I bought a box, sent it to McIntosh factory, it came back ’fixed’. Same low level hum, low level inputs only. How the heck can I sell it knowing that?
I took it apart, gave the evil eye to the internal ground connection to the chassis. Unsoldered it, stripped end of wire, removed paint from the area, replaced with bolt and lock washer. Gone.
...............................
Days gone by, FM antennas were like the plague.