Did I just cook my preamp?

@obarrett 

I'm not sure preforming the same test for checking the wall outlet the TT plugs into for reversed Hot / neutral wiring connection to the duplex receptacle outlet and to check for the presence of an EGC will work in this situation. Don't see a receptacle Hot equipment very often.

I've looked at different scenarios for how the equipment ground could be Hot to a known EGC ground and the test with the mm would be flawed.

The most common instance is when an equipment ground is not present at the outlet box. Therein a two-wire branch circuit wiring. A homeowner replaces a two-wire duplex receptacle with a three-wire grounding type duplex receptacle. He wants a ground, so he installs a jumper wire from the neutral terminal on the receptacle and connects it to the safety equipment ground terminal. Called a Bootleg ground. Very Dangerous! It doesn't matter if a plug-in circuit tester is used, or a digital multi-meter is used it will show the presence of a ground. 

One danger with a Bootleg ground is if the Hot and neutral conductors are reversed on the duplex receptacle. That's not good... The ground contact of the outlet will be HOT!

Is that what you have? Maybe, maybe not. You measured two different voltages in an earlier post. On V 121Vac and 68.9Vac on the LoZ setting. For that to happen with a bootleg ground there would have to be a poor and or corroded connection. The high megohm internal circuit of the mm V setting won't add any load to across the high megohm Voltmeter Like the LoZ setting will. Could that be the case. Maybe. But the only true way would be to pull the outlet out of the box aways for a look.

I cannot advise you to do so.

First, you are not the owner of the building.

Second, the breaker feeding the outlet would have to be turn off. And verified 100% it is dead.

Third, and very important reason you said the building is old. Hard telling what type insulation covering was used on the branch circuit wiring. If really old wiring it could rubber and cloth insulation. That stuff gets old the rubber gets really hard and brittle. It doesn't like to be disturbed.

It's time to call building Maintenace. A hot safety ground is definitely electrically dangerous. A reversed hot and neutral on an outlet is also electrically dangerous.

@obarrett 

I believe I have a way to check the duplex receptacle outlet the TT is plugged into. 

I'll post it later.

For now, hopefully for the last test, the solution would be to use another EGC grounded outlet. Like the subwoofer receptacle. I don't want you to use the CDP receptacle though, for the test. The CDP, I believe, because it uses the EGC is grounding all the non EGC equipment. It was providing the return path for hot to EGC faulted circuit.

The properly EGC grounded TT, (Which I don't think is right), will do the same.

(FWIW I doubt the CDP signal ground is directly connect to the EGC grounded CDP chassis. Just a guess the signal ground is in series with around a 10ohm resistor. This helps prevent ground loops, hum.

As for the TT EGC connected to the tone arm, I would contact the VPI support on that. That makes no sense to me.

Post back the results.

.

I've looked at different scenarios for how the equipment ground could be Hot to a known EGC ground and the test with the mm would be flawed.

The most common instance is when an equipment ground is not present at the outlet box. Therein a two-wire branch circuit wiring. A homeowner replaces a two-wire duplex receptacle with a three-wire grounding type duplex receptacle. He wants a ground, so he installs a jumper wire from the neutral terminal on the receptacle and connects it to the safety equipment ground terminal. Called a Bootleg ground. Very Dangerous! It doesn't matter if a plug-in circuit tester is used, or a digital multi-meter is used it will show the presence of a ground. 

One danger with a Bootleg ground is if the Hot and neutral conductors are reversed on the duplex receptacle. That's not good... The ground contact of the outlet will be HOT!

Bootleg ground and reverse polarity, isn't that exactly what I said?

I made the following measurements, both on V and LoZ. All the measurements were identical on both settings. I made the measurements two times: once with the 2-to-6 outlet converters on, and once with them off (accessing the bare outlets). The 2-to-6 converters made no difference in the measurements. So I make no distinction between V/LoZ or converter on or off in the below.

Let R denote the (shorter) female slot, L denote the (longer) female slot, G denote the ECG which sits below in the middle.

Outlet 1 (amp, preamp, CDP):

RL: 120Vac

LG: 120Vac

RG: 0.09Vac

Outlet 2 (TT, subwoofer):

RL: 120Vac

LG: 0.36Vac

RG: 120Vac

Now I took a 3-prong power cord, first from the CDP, next from the TT, and plugged into Outlet 1. I used two different cords to ensure one of the cords isn’t the problem. I plugged one MM lead into the ground of the other end of the power cord, and the other lead into the ECG of Outlet 2, and registered 120Vac on V and LoZ.

There is a third outlet where no equipment is attached. It’s on the same wall as Outlet 2. It’s measurements are the same as Outlet 2 and it also has 120Vac between its ground and the ground of Outlet 1.

I am not really following from the recent messages if there are additional tests I should run. It seems like next I should call a professional electrician.

From reading about reverse-polarity bootleg ground, it seems too lethal to be the source of the issue. I should consult with a professional either way though.

Thanks again for all your help.

I concur, a professional electrician is definitely your next step.

It’s a detail, but since your landlord is required to pay for the electrician’s bill, you might want to give them a heads up if you haven't already.