I was looking at photos from an old preamplifier and I was surprised that they didn't use shielded wires for the signal path.
They do use a metal chassis as a ground point, but the grey input/output wires don't look like being shielded, also the wires that go to the switches and pots are just twisted together.
I've done that and ended up with antennas that picked up noise.
They do use a metal chassis as a ground point, but the grey input/output wires don't look like being shielded, also the wires that go to the switches and pots are just twisted together.
I've done that and ended up with antennas that picked up noise.
The grey wires look shielded to me. Notice how all the wiring is twisted and/or close coupled. Inside a screened enclosure it's usually fine
That's an Audio Research SP3a preamp. The thick gray cables are indeed shielded,
with the shields connected at one end only.
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I can confirm that separating the crossovers supply got rid of any ground loops. I made no other mod, just used the big transformer only for the amps. 
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