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
obarrett OP
20 posts
 

I will test now following your instructions and report back. The subwoofer plug into the wall has three prongs but when it plugs into the subwoofer it has only two. So it’s not grounded either. I will be around for the next few hours and will send messages as I proceed through your instructions. Thanks so much.

jea48
4,655 posts
 

EDIT:

Be careful, the outer sleeve contact of the SMPS power cord connector may be Hot voltage ground.

Should read:

Be careful, the outer sleeve contact of the SMPS power cord connector may be a Hot voltage to ground.

EDIT:

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).

Should read:

Next, depending on how much time has elapsed the MM may have turned itself off.  Reset .  Turn the selector switch to off, then turn to "V".

 

obarrett OP
20 posts
 

The CDP appears to be grounded with three pins and the power cord has three prongs. The amp is placed on top of the cdp so they are touching.

jea48
4,655 posts
 

The CDP appears to be grounded with three pins and the power cord has three prongs. The amp is placed on top of the cdp so they are touching.

OK ...

@obarrett

Hopefully you can understand my long above post. Looks like I should have proof read it a couple of times after posting it. I spotted a few double words here and there.

I corrected a couple of poorly worded sentences in my post above. Read through the Long post... I will check your thread occasionally tonight for any posted questions you may have.

I watched your video a couple of times again today. I can’t explain why the SMPS could pass an AC mains voltage to the phono preamp, You wouldn’t think it could... But, you said in the video you received an electrical shock touching the metal enclosure of the preamp. The power supply DC B-, and circuit signal ground, is connected to the preamp metal enclosure, directly or indirectly. If not the enclosure would act as an antenna.

 

obarrett OP
20 posts
 

I did your test from your long post.

wall:

hot neutral 121.7V

hot ground: 122.0V

Neutral ground: 0.285V

 

OEM ITC:

Two females: 121.3V

female ground: 121.7V

 

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?

 

SMPS (red lead center, black on sleeve):

18.5V on B

0L and it beeps on LoZ

 

Note: this wasn’t using the outlet where everything is currently plugged in. I used a spare outlet. I can test the outlets where things are plugged in too.

 

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. I believe current was flowing through the interconnects between phono preamp and amp, but i don’t know the source. But since all this I’ve listened to about 3 hours of music using the amp with no issues whatsoever (phono disconnected of course).

More to discover