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
4,690 posts
 

The OP should first locate the problem. Was it the phono preamp power supply that caused the problem?

Or was it x or y or z that caused the problem that damaged the phono preamp?

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FYI, in older homes with old two wire branch circuit wiring, a plug-in circuit tester works good for finding reversed AC polarity. They will tell you if there is an OPEN GROUND. What they don’t tell you if the tester says OK is the EGC (Equipment Grounding Conductor) really an EGC that runs back to the electrical panel or is it a Boot Leg EGC created by installing a jumper from the neutral terminal on a duplex receptacle to the EGC terminal screw on the outlet. It will also not tell you if the neutral conductor and EGC conductor are reversed on the outlet.

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jea48
4,690 posts
 

EDIT:

works good for finding reversed AC polarity.

works good for finding reversed Hot/neutral AC polarity.

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obarrett OP
28 posts
 

Thank you all for your responses. It’s a big help to me as I’m not an expert on electromagnetism.

 

@jeffbij although the amp is not grounded, it functions fine with no voltage/charge unless connected to the phono preamp. When connected to phono preamp it predictably becomes dangerous.

 

@erik_squires as it turns out as others have pointed out, no ground pin was removed and the amp is by design ungrounded. I agree it’s dangerous. Could you elaborate on what an outlet tester would tell me?

 

@jea48 RR2160 amp has built in DAC and has two coax inputs. One to CD player one to bluesound node. Since this episode I’ve been listening to music off the node without problems. Thank you for pointing out the RR2160 doesn’t have a ground pin. At least one of us is paying attention, I guess. The preamp and amp are plugged into the same single duplex outlet; the TT is plugged into a different single duplex outlet but was OFF when this happened. Could you describe what information I could use a multimeter to obtain? I will get one if it will help diagnose.

yes you’re right the preamp was grounded to the tone arm.

yes the outlet cover is plastic and the plug in power supply for the photo preamp is plastic.

you asked what two metal objects I was connecting. I was connecting the interconnects from preamp OUTPUT to the analog INPUT of the TT. those inputs are near the speaker wire plugs for the right speaker. When I touched the interconnect from the preamp to the amp analog input the second time, there was a large SPARK and even some SMOKE. It created a small crater on the housing of the interconnect. Obviously extremely hazardous. 
 

@lynn_olson @jea48 do I need a multimeter, socket tester, or both?

 

I had an idea which may be totally wrong but I noticed the blue light in the 110LP flickering the last couple months, and it’s connected to the circuit inside the preamp by a wire. Maybe something went wrong with that wire and it shorted to the exterior of the preamp box. It would be easy enough to check by disconnecting that wire, but first I need to get the appropriate equipment. I was going to just get a no contact voltmeter, but it seems maybe I should instead get a multimeter? Let me know what you would advise.

 

thank you. 

jeffbij
146 posts
 

@obarrett You said:

you asked what two metal objects I was connecting. I was connecting the interconnects from preamp OUTPUT to the analog INPUT of the TT. those inputs are near the speaker wire plugs for the right speaker.

Do you mean that you connected the interconnect cables running FROM the turntable and plugged them into the INPUT connections on the Moon 110LP, and the ground cable from the turntable to the ground stud on the Moon 110LP as well? And then plugged interconnects from the OUTPUT connections on the Moon 110LP to one of the AUDIO IN connections on the Outlaw receiver, correct?

... just trying to get it straight in my head...

- Jeff

 

 

 

erik_squires
16,645 posts
 

 as it turns out as others have pointed out, no ground pin was removed and the amp is by design ungrounded. I agree it’s dangerous. Could you elaborate on what an outlet tester would tell me?

A basic one would tell you if you if the wiring to the outlet was correct and reasonably functional.  For instance, the ground wire may be missing or broken, in which case a ground pin on your gear would be useless.

Now that I think about it, get a more advanced one so you can see the N-E (neutral to earth) voltage.  This will help you see also that the neutral wire is near ground (should be 2V or less). 

 

 

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