@obarrett
Curiosity killed the cat.
Assuming the subwoofer uses the EGC, (Equipment Grounding Conductor) from the 120V wall outlet,
and assuming the sub amplifier’s circuit ground is connected to the chassis, (high probability),
and therefore the return signal ground in the RCA interconnect cable is connected to the signal ground of the RR2160 amp,
And therefore the circuit signal ground of the RR2160 amp is, (high probability), connected to the chassis, either directly or indirectly, the RR2160 amp is grounded to the 120Vac wall outlet EGC.
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Therefore, the first thing I want you to check is the output voltage of the plug-in SMPS Wall Wart) for the phono preamp.
Here is a photo, I believe, is the same as yours.
plug-in SMPS. 18Vdc output.
The test:
You might want do the test on a kitchen counter top or a table.
mm meter.
Install the two test leads. Black lead in COM jack. Red lead in VΩ jack.
This test will, should, tell if the SMPS power supply has some kind of an internal fault that somehow is passing a high AC mains line voltage to the output of the power supply.
For the test you might want to use a factory OEM three wire grounding type power cord. The center offset ground IEC EGC ground contact will be used to hold the black lead probe tightly in the EGC ground contact. That will free up a hand...
Set the mm to V (volts). V is to the right side of OFF. mm will default to AC volts.
First check the wall receptacle outlet, you will be using, for the correct Hot / neutral AC polarity. At the same time you will be checking checking for an EGC ground.
Insert a test lead probe into each of the two straight slots contacts. You should measure 120Vac nominal.
FYI (If the duplex outlet is a 20A the neutral will have a "T" slot. If a 15A duplex receptacle the neutral contact will be the longer slot of the two parallel slots. Therein the Hot is the shorter of the two.
Next insert a test lead probe in the small slot Hot contact of the receptacle. Insert the other test probe in the ground hole. You may have to move the tip of the probe to one side or the other to make contact to the ground contact. You should measure, read, 120Vac nominal. The same voltage as you measured from Hot to neutral. This shows two things. The hot /neutral wiring AC polarity is correct and an EGC ground is present.
(FYI the reading could be slightly higher due to a loaded VD (Voltage Drop) on the hot and neutral circuit.)
One last test. Measure for voltage from the receptacle neutral contact to the ground contact. (Using a wall duplex receptacle I measured 1.4mV ac.
(Note. On a regular grounding type receptacle the center trim screw that holds on the outlet cover plate is also connected to the EGC ground. You can also use the screw head for the ground connection. Insert probe tip tightly against the straight recessed slot for the screwdriver to make a good electrical contact.)
FYI, use the same method above to check the two wall duplex receptacles that feed your audio system equipment, for the correct hot/neutral polarity and and the EGC is present.
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Finally, testing the plug-in SMPS.
Plug the OEM power cord into the wall 120Vac receptacle outlet. (Outlet has been checked, OK.)
Set the mm to V (volts). mm will default to AC volts.
OEM IEC power cord. Insert one test lead probe in one of the outside female contacts. Insert the other probe in the other outside female contact. You should read around 120Vac, nominal.
Insert one test lead lead probe in the center offset ground contact. Insert the other test probe in one of the outside female contacts.... From Ground to Hot contact you will measure 120Vac nominal.
Leave the test lead probe inserted in the ground contact of the IEC power cord.
Plug in the SMPS into the same duplex outlet as the OEM power cord.
Be careful, the outer sleeve contact of the SMPS power cord connector may be Hot voltage ground.
Next, depending on how much time has elapsed the MM may have to be shut off. Then turn mm selector switch back to "V" (Volts).
Next touch the other test lead probe to the outer sleeve contact of the SMPS output cord power connector. Does the mm meter display a AC voltage? How high of a voltage?
If you measure a high voltage you need to check it’s a real power voltage and not a false phantom voltage.
Remove test lead probe from the SMPS output cord connector. Turn mm selector switch to LoZ setting. (Last setting on right side of off.) Never change the selector switch with lead probes connected to a possible live voltage.)
Check for the high voltage again on the connector sleeve contact.
Also measure for a voltage to the center female contact of the power connector.
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If you did not read, measure, high voltage, or any voltage... Question... Is the SMPS 120Vac plug in blades the same width or is one wider than the other? Therein polarized. If both blades are the same reverse the SMPS 180 degrees in the receptacle and preform the test for high voltage again.
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If still there is no voltage readings, you should then check the output DC voltage of the SMPS to make sure it is working properly.
Remove test lead probe from the ground contact of OEM IEC power cord.
Test;
Set MM selector switch to "V" (volts)
Press the SEL button once to switch to DC volts. mm should display V DC.
Voltage test. 18Vdc female connector. Without touching the metal probes with your fingers... Touch, contact, the RED lead probe to the center female contact, of the power connector and touch the BLACK lead probe to the outer metal sleeve of the connector, both at the same time. You should read + 18Vdc nominal. If you do not read +18Vdc make sure you a making a good contact to the connector.
You can Also use the LoZ setting as well. Rotate the selector switch to LoZ. Press SEL button. mm should display V DC. Red lead probe to center contact. Black lead probe to outer sleeve contact on power connector.
FYI the outer sleeve electrical contact is B- negative of the DC power supply. It also should be circuit ground of the power supply and Phono preamp when connected to the preamp.
If it does not read +18Vdc? or the meter reading is + - + - + - + repeatedly 18V? Or maybe the mm is reading a higher voltage??? Note what you are seeing.
Post back the results of the testing.
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