2. amps-preamps
  3. 193768-203308

Did I just cook my preamp?

I have a Simaudio Moon 110LP phone preamp amplifying a Dynavector 20X2L cartridge on a VPI Classic. It feeds in to an Outlaw Audio RR2160 amp which drives Magnepan LRS speakers.
 

I recently moved and two months in I realized my speaker placement wasn’t quite right, so today I reorganized my listening room. This involved unplugging some power cables but I kept most of the interconnects in place. I did have to disconnect the phone stage from the amplifier.

 

After getting things back into place, I listened to some music using coaxial input before reconnecting the interconnects of the phono stage. When I tried to, I actually got some electric current that burned my hand slightly. This came from the back of the amplifier. I made sure everything was unplugged and tried again - this time a spark and smoke from the interconnect making contact to the back of the amplifier.

 

I’m so confused why this would happen, but eventually I did get everything connected. Now the output from the phono stage is just a bump every 1 second. It doesn’t amplify the signal from the TT.

 

My amplifier has a built in phono stage and using this I was able to verify that the turntable is still producing a signal. The built in phono stage sounds terrible, however, as thin and flat as paper. It is music, however.

 

When I connect the phono stage to the power, the blue light on the front illuminates for a moment and then goes dark.

 

Incredibly, when I was unplugging the phono preamp, I actually got some current from simply touching the exterior of the box. Something is seriously wrong and dangerous with my setup, and this box was grounded to the turntable with a ground cable, which was connected to the outlet with a three prong cable with ground.

 

Has anyone experienced anything like this before? I will email Simaudio and see if they’ll repair it. I’m also taking recommendations for replacements. I liked the 110LP and maybe will just replace with the 110LPV2.

obarrett
jea48
4,668 posts
 

@obarrett Said:

There is continuity from the ground prong of the TT to the tone arm ground lug. No continuity from either of the other two prongs of the TT.

OK

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I attached one three prong power cord to the outlet where the amp/preamp/CDP are connected and then the other to the outlet where the TT is plugged in. I turned mm to V/LoZ, attached one lead to the ground of one, the other to the ground of the other. 120Vac.

IF true that indicates the wall outlet the TT is plugged into has a Hot equipment ground contact at the receptacle. (At this point there is not an internal Hot fault in the TT)

Before I go any farther... Test the receptacle as you have the others for the correct AC hot and neutral connections polarity on the receptacle outlet and from the Hot to the equipment ground contact. EDIT. Use both the V and LoZ mm settings.

Is the Electrical panel for your outlets in your apartment? If not do you have access to where it is located?

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Post removed 
obarrett OP
26 posts
 

I haven’t yet had the chance to do the tests you suggested in your last post @jea48

I just want to mention that @jea48 ’s advice, contrary to the statements of @erik_squires and @devinplombier , has been essential to understanding what’s going on. I’m inexperienced so I make many mistakes and my messages have been confusing at times, but I don’t see the need to come in to this thread and criticize @jea48 for providing the only instructions that have advanced my understanding of what is a dangerous situation.

regardding LoZ on my MM: without this I’d be thinking that the SMPS has 48Vac on the sleeve which is what the reading was on V and which is factually false.

jea48
4,668 posts
 

@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.

 

 

 

jea48
4,668 posts
 

@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.

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