Halo P3 Phono Hum

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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It sounds to me like you may not have finished grounding your TA/TT to the preamp.

First of all, your cartridge ground(s), blue and green, should not connect to any EARTH ground, neither must the cartridge body be grounded (even if it was metal.)

So, the black ground wire comes out of the tonearm wand and screws to the tonearm base which is electrically connected to the TT ground lug, is that correct? If so, you then need to run a small insulated wire from the TT ground lug to the ground screw on the back of the preamp (near the phono inputs.)

Use the AQ cables, and don't lift/cheat the ground on the preamp. You might want to lift the ground on the amp, though it's probably not necessary since it's connected to the pre with XLRs which are hum cancelling anyway.
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