Phono Preamp Noise - At Wits End

Try this; unplug the SACD player when you're listening to vinyl. See what happens.
I have three phono pre's and they are also all dead silent, although had to do some work on one of them.

If it turns out the SACD player being on is the cause of the issue (it's a hum so I assume 60 Hz from a transformer), then you can just unplug when playing vinyl, or shield the transformer with mu-metal.

 

Do you still have hum if you disconnect the turntable and short the inputs? Sacrifice a generic interconnect - short the signal to the shield on each channel close to the preamp and try it out.

 

So, you’re suggesting to short the signal inputs to the shields on the preamp? I could try that. I have plenty of cheapo RCA cables lying around.

 

Yes. That would tell you whether the hum is being generated by/at the preamp or before.