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Sounds like a ground loop. Assuming all the components are connected to the same AC, I would start by disconnecting the TT from the pro-ject phono box 2. If there is still hum, try grounding the pro-ject phono box chassis to the amp chassis to see if it goes away. If so, good. If there is no hum, reconnect the TT and see if the hum returns. If it does, try another ground from the TT chassis to the phono box.
Thank you.
I tried this. All 3 devices are hooked to the same ac. When I disconnected the Tt RCA from the phono box, the hum got louder. So I tried ground between phone box and several locations on the amp chassis and the hum never went away. When I re connect the Tt RCA the humm gets about reduced in half. I tried this with multiple sets of RCA cables to try and eliminate that variable, and it that had no effect. Does this mean my phono box is shot? Maybe struck by lightning?
2 more things to try.
1. Insert shorting plugs into the phono box and see if there's hum.
2. Try grounding link from TT chassis to phono box or preamp.
I am not familiar with shorting plugs?
They are RCA plugs with the signal and ground pins shorted together. You can approximate this by gettting the cheapest RCA interconnect you can find, cutting it in half and twisting together the shield (ground) and signal wires on each side. Result: two shorting plugs.
The reason to use this is that some phono inputs will hum like crazy with no input load.