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.
Hey Jim, the reason why I didn’t have an issue before is that I wasn’t using outlet 2 before. Everything that needed a ground was in outlet 1. Only after I moved things around could I access outlet 2. thanks again to you. Thanks also to you Devin. If I actually have a reverse polarity bootleg ground I will be so angry. You guys saved me more than money. |
Reverse polarity OR bootleg ground alone won't manifest until something else goes wrong. It's the combination of the two that is potentially lethal, because any grounded (3-prong cord) piece of equipment you plug into such an outlet sees its chassis, cover (and anyone who touches it) energized. Please do post your electrician's findings. Curious now! |
@obarrett said:
FYI, outlet 2 has an earthed ground. Well, the mm measurement says so. A plug in circuit tester would say so. A Bolted Hot to the EGC ground fault might tell a different story. Using outlet 1 you didn’t/don’t have a ground. The ground contact on the outlet is HOT 120Vac with reference to an earthed ground. All the metal enclosures of the audio equipment were HOT 120Vac referenced to ground. Even audio equipment that didn’t use an earthed EGC. The TT power cord is a 3 wire cord. When plugged into outlet 1 it fed the branch circuit HOT 120Vac to the TT IEC inlet connector EGC prong. That in turn fed HOT 120Vac to metal parts of the TT and to the tone arm ground, *(by the way the tone arm was HOT with reference to an earthed ground), to >> the phono preamp enclosure, which made all the RCA jacks outer ground shells HOT 120Vac that contaminated all the other metal enclosures through the interconnect cables signal ground conductor. Why you never got an electrical shock or had problems with your audio system equipment? There was not an earthed ground introduced into the equation. So, for the same reason a bird perched on a high voltage power Line doesn’t get shocked. Now the Squirrel is a different story. He will jump onto High voltage power Line and run down the Line without a care in the world. It’s his dismount from the high voltage power Line to the top of the metal earth grounded pole transformer is his fatal problem. If only he had jumped instead of stepped.
FYI, I am pretty sure the heat radiator shown in the video is earthed grounded. Had you been able to touch it with one hand, (in the summer months), and touched any of the HOT 120Vac metal enclosures of the audio equipment with the other hand there is a chance you would have been electrocuted. Therein dead. DO NOT use outlet 1, until it is wired correctly by an electrician. . I suggest you try another test. Plug an OEM power cord into outlet 1. Insert one of the test lead probes into the IEC female ground contact. Turn mm to V and touch the other test lead probe to a bared (unpainted) metal place on the heat radiator. You can also use the LoZ setting on the mm as well. Post back the measurement. . |
@jea48 , I tried to follow this thread but it became too complex for me to understand what was happening, so I apologize if this question was asked and answered and I missed it. Bootleg grounds: now I understand what they are and the reason someone might wire an outlet with a jumper from neutral to ground in order to put a (3 hole) grounding receptacle on a (2 hole) ungrounded circuit to make it pass the test with a real basic EZ CHECK circuit tester. Since my house was built in early 1960s and has (2 hole) ungrounded outlets in the back of the house and (3 hole) grounding outlets in the front, although the grounding outlets all pass the EZ CHECK circuit tester, it still seems like my house might be a candidate for those grounding outlets to be bootlegs. I went to google to look for a simple answer of what to look for with an AC VM to identify bootlegged and normal outlets and got drastically conflicting results from AI. Again, I apologize if you previously covered this, but is there a way to verify with an AC VM whether a 3 hole outlet has been bootlegged or not? I compared an outlet on a circuit that I installed myself that I KNOW is NOT bootlegged, and ground to neutral reads 0.105; then on a 3 hole outlet that was there when I bought the house and it reads 0.25. (My meter does not have an LoZ setting.) Do those readings mean anything, or is the only way to know for sure to remove the older grounding outlets and visually inspect them for jumpers from neutral to ground? I am getting the impression that there are more expensive meters that will verify whether or not a bootleg ground was used? Thank you, and again, my apologies if I am asking a redundant question on this thread.
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Here is a photo of a two wire old rubber cloth covered conductors Bootleg grounded outlet . The wiring is really old. pre-Thermoplastic, PVC, insulated wire. PVC Thermoplastic insulation is really old too. THHN/THWN replaced it, going from memory, in the early 1970s. Here is good video on Bootleg ground wired outlets. (FYI, a bootleg ground is a NEC code violation. Alwas has been) Reverse Polarity Bootleg Ground Testing Amprobe INSP-3 Wiring Inspector Circuit Tester Price over $400.00 How many wall outlets are there in the old part of the house? The only 100% sure way to check the outlet is look for the jumper wire. Remove the wall outlet cover plate. Good chance using a high power LED small diameter flashlight with the lighting in the room subdued you should be able to see the jumper on ground terminal side of the duplex receptacle outlet without pulling the outlet out of the wall box. (Turn off the circuit breaker at the panel if you are going to do any poking around. Another sure way is plug in a high current load into the outlet like a hair dryer or portable vacuum cleaner. Anything that draws enough current on the branch circuit wiring to cause a voltage drop on the wiring. First measure for AC voltage from neutral contact, (longer straight slot of the two.) Notate the small voltage reading. Next plug in and switch on the load. Check the voltage again from the neutral contact to the ground contact on the outlet. If the outlet is bootleg ground wired the reading will be the as the first measurement. If the measured voltage is a few to several volts lower, it is not a bootleg ground. . |
