First of all, if you want to lift the ground, you don't need a cheater plug because the P3 has a ground lifter switch on the back. Second of all, DON'T lift the preamp ground, it's the ONE component that should be grounded!
Next, are you using Hero XLRs between your TT and your preamp (I didn't think so). So what cables are you using? (If they have arrows on them, make sure they are pointed to the preamp) And what kind of cartridge? It better be a moving magnet.
Are your phono cables connected to Aux/Phono inputs and is the Aux/Select toggle switch pointed to those inputs? Good. BTW, you'll almost always get hum through "Phono" if the inputs or ICs aren't connected to anything.
If all the above is in order, check the cartridge clips. Make sure they're all connected and to the proper pins -- especially important w/ MM carts because they have a common ground.
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Next, are you using Hero XLRs between your TT and your preamp (I didn't think so). So what cables are you using? (If they have arrows on them, make sure they are pointed to the preamp) And what kind of cartridge? It better be a moving magnet.
Are your phono cables connected to Aux/Phono inputs and is the Aux/Select toggle switch pointed to those inputs? Good. BTW, you'll almost always get hum through "Phono" if the inputs or ICs aren't connected to anything.
If all the above is in order, check the cartridge clips. Make sure they're all connected and to the proper pins -- especially important w/ MM carts because they have a common ground.
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