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
4,651 posts
 

SMPS (one lead in ground of OEM ITC, the other on the sleeve contact of the SMPS):

48V on V

0.13V on LoZ

thoughts?

48V AC on V Might not be real power.

0.13V on LoZ real power .... ???

Thinking on this one.

.

SMPS (red lead center, black on sleeve):

18.5V on B

0L and it beeps on LoZ

18.5Vdc on V correct?

0L and it beeps on LoZ. I may have read the instruction manual wrong. LoZ may only be for AC voltage.

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I can test the outlets where things are plugged in too.

Yes, check them.

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and to elaborate: yes I felt current on the enclosure of the preamp. I also felt current, I believe, on the enclosure of the amp at some point. And when I connected the tone arm ground cable to the amp ground (the amp has a built in phono stage), there was also a spark.

Was the SMPS unplugged from the 120Vac wall outlet or the power cable from the SMPS disconnected from the phono preamp? Preamp was dead?

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I believe current was flowing through the interconnects between phono preamp and amp,

Yes agree. But, my understanding is the SMPS was feeding power to the phono preamp at the time. Correct?

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But since all this I’ve listened to about 3 hours of music using the amp with no issues whatsoever (phono disconnected of course).

Did you verify this question of mine on ?

@obarrett ,

Subwoofer? You keep adding equipment...

 

Does the 120Vac IEC inlet connector on the back of the sub have three prongs? Therein an equipment ground prong? My bet is yes. Correct?

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obarrett OP
20 posts
 

I think I messed up on the DC measurements, i think they were AC. so let me try again:

SMPS (one lead in ground of OEM ITC, the other on the sleeve contact of the SMPS):
0.6 mV DC on V

0.0 mV DC on LoZ

SMPS (red lead center, black on sleeve):
18.15 V DC on V

18 V DC on LoZ
 

 

obarrett OP
20 posts
 

Does the 120Vac IEC inlet connector on the back of the sub have three prongs? Therein an equipment ground prong? My bet is yes. Correct?

Yes I verified your question about subwoofer in earlier comment today. The subwoofer pins are only two even though the power cord has three prongs. So I assume it’s ungrounded. But note the CDP is grounded and the amp is sitting on top of it and connected via coaxial cable.

Was the SMPS unplugged from the 120Vac wall outlet or the power cable from the SMPS disconnected from the phono preamp? Preamp was dead?

I believe it was plugged into but I’m not confident on this. But moreover I was trying to connect the interconnects; at some point they were connected, then they were disconnected. So when I felt current on the enclosure of the amp I do not know what was connected to what.

Yes agree. But, my understanding is the SMPS was feeding power to the phono preamp at the time. Correct?

yes with 90% confidence.

obarrett OP
20 posts
 

I tested the outlets where things were plugged in. The hot/neutral is reversed. So the hot is the longer left slot, the neutral is the shorter slot on the right. The ground appears to be functioning.

jea48
4,651 posts
 

@obarrett Said:

I think I messed up on the DC measurements, i think they were AC. so let me try again:

SMPS (one lead in ground of OEM ITC, the other on the sleeve contact of the SMPS):
0.6 mV DC on V

0.0 mV DC on LoZ

SMPS (red lead center, black on sleeve):
18.15 V DC on V

18 V DC on LoZ

SMPS (one lead in ground of the OEM IEC connector of the power cord , the other on the sleeve contact of the SMPS):
0.6 mV DC on V

0.0 mV DC on LoZ

Multi-meter should have been set to AC voltage not DC. I am looking for AC mains voltage on the SMPS output power cord connector. The measurements would be good if only AC measurements.

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SMPS (red lead center, black on sleeve):
18.15 V DC on V

18 V DC on LoZ

This is correct. Voltage looks good.

That doesn’t mean there is not a problem with the preamp. I believe there is. The Blue power light maybe saying there is.

Again, I would NOT connect the input or output of the preamp to any equipment.

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