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
Post removed 
Post removed 
erik_squires
16,900 posts
 

This conversation is going a little nuts. Testing with multiple devices for this is nonsense, except maybe as a learning exercise for new techs.

You should let a tech do all of this instead but if you must, wear insulated shoes and avoid any other points of contact after the device is plugged into the wall. Touch the device ONLY with your meter. Same for the EGC. If you are holding the EGC when you touch an active AC voltage you can be electrocuted. Set up your test area so that you can reach everything, and the EGC is readily accessible for your probe before you plug anything in. If you are squirming and contorting to connect your meter you are likely to make mistakes. Use alligator leads so you can leave the ground attached without moving it.

First make sure you have a good outlet. Use a tester like this one to make sure your ground AND neutral are good. It will also measure your N-E which is important in this case. Yes, an experienced tech can do this all with a good meter but this removes a lot of guesswork.

Plug in one piece of gear at a time, connecting nothing but the power cord. Measure voltage to the EGC using LoZ. Do this from the chassis to EGC and the outer ring of the RCA connectors to the EGC. You should measure practically zero.

If you find a high voltage use a cheater plug and measure the CURRENT from the same points to the EGC. Again, current should be nearly zero, but small leakages around 10 mA are OK. This will tell you the magnitude of the short. I suspect you have a relatively high voltage with medium current (2A or so).

Please note that using a cheater plug is dangerous as it may elevate the chassis voltage. Take extra care after attaching it.

If none of these yield answers, check the voltage on the INSIDE of the RCA. Take care as it may be high especially with tube gear. It’s worth sacrificing a cheap RCA cable to do this easilly. Cut an end off and expose the inner wire for your probe.

If you suspect a tube pre/amp, you may have DC on the inner wire.  That's bad too, but also will need you to select DC on your meter.

devinplombier
856 posts
 

This thread has become surreal.

Post removed 
More to discover