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
 

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).

obarrett OP
20 posts
 

I just tried an additional test.

I plugged in the preamp to the wall using its SMPS.the blue light went on, off, on, off four times getting fainter then went off.

I plugged the black lead into the ground of the OEM IEC power cable. I put the MM on V. Red lead on any one of the four RCA inputs/outputs of phono stage. Same reading as in the SMPS: 48V, but when I switch to LoZ, drops to 0.128V.

 

i then unplugged the phono, connected it to TT via RCA Input on phono, plugged in again. Measured 49V with red lead on the shield of the interconnect plugged into the R input of the phono, which dropped to 0.14V on LoZ 

jea48
4,651 posts
 

i then unplugged the phono, connected it to TT via RCA Input on phono, plugged in again. Measured 49V with red lead on the shield of the interconnect plugged into the R input of the phono, which dropped to 0.14V on LoZ

I would NOT connect the input or output jacks of phono preamp to anything .

.

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.

.

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

Yes, check them.

.

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?

.

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?

.

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?

.

More to discover