Did I just cook my preamp?

@obarrett Said:

Incredibly, when I was unplugging the phono preamp, I actually got some current from simply touching the exterior of the box.

To receive the electrical shock your body had to have a point of entry and a point of exist. Can you recall what two metal objects you were contacting at the same time? One was the metal case of the 24Vdc fed phono preamp. I assume the plug in power supply (output 24Vdc) for the the phono preamp is plastic. Is the wall duplex outlet cover plate plastic?

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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.

That doesn't sound right. The phono preamp should be grounded to the tone arm, not to the wall AC mains safety equipment ground...

Using a multimeter, this could easily be verified. 

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After getting things back into place, I listened to some music using coaxial input before reconnecting the interconnects of the phono stage.

 @obarrett 

??? please explain ??? coaxial input? Source?

To get a spark as well as an electrical shock there had to be a difference of potential, voltage, of a least around 40V to 50V measured between the two points you received the electrical shock. I assume all the equipment is plugged into a single duplex outlet fed from a single circuit breaker in the electrical panel.

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Simaudio Moon 110LP phono preamp. Factory plug in power supply is two blade, no safety ground pin. I assume the power supply is the original.

Outlaw Audio RR2160 amp has only a two prong power inlet connector. No safety ground prong. Unit has the Double D symbol logo on the unit indicating the 120Vac power wiring is double insulated. Chances of a hot bared conductor to chassis fault? Slim to to none.

VPI Classic. Has a 3 prong inlet connector. Safety equipment ground is used.

I wouldn’t think the tone arm would be connected to the AC mains safety equipment ground.

Do you have a multimeter you can use to check for continuity/resistance, as well for voltages? If not buy a descent one. You can pick a descent one for around $50.00.

If you have one or buy one, post back.

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How the preamp became so suddenly hazardous is beyond me.

This is exactly why I tell people not to ever remove a ground pin. What happens is, as an example, the amp shorts the chassis to a high voltage, anywhere from imperfect to solidly shorted. That voltage is now on the chassis AND on the signal ground, to some degree. In other words the outer ring of the RCA cable. That current and voltage is now flowing from amp, through IC to other equipment, causing (potentially) a fire on the IC if the current is high enough and damage to other connected equipment.

The problem is complicated by the relatively high resistance of the interconnect ground. They both heat up and prevent the ground pin from forcing a breaker fault, as they should.

What should have happened, normally with a ground pin, is that the amp should have shorted the chassis/ground voltage via the thick ground pin to your outlet, and if the short is strong enough force a breaker or fuse to pop letting you know something happened without an electrocution or fire.

While you are at it, I do recommend you get one of those cheapy ($12) outlet testers to make sure your outlet is also in good shape.

@obarrett - I'd have the AMP checked out, inside and out before you do anything. I looked at a picture of the Outlaw RR2160 receiver, and the IEC plug on the back does not have a ground prong.  If that is correct on yours, then 3 pronged power cord isn't going to do anything. Something maybe wrong on the inside of the Outlaw.  Loose wire, someone may have made a modification (to add a ground prong???), who knows what.  It is even possible that the amp's chassis is now hot (power wise).  The fact that you got a spark when connecting the TT/Cartridge's ground wire to the ground on the Outlaw is saying there is some significant voltage on the chassis.

Thanks for this advice. I agree with what you wrote. I bought the amplifier used and it came with a power cord without a ground. I’m going to immediately replace that power cord with a proper three prong power cord. I think that the preamp developed a short and current was definitely flowing through the interconnects into the amplifier. What a mess.

How the preamp became so suddenly hazardous is beyond me. I can’t rule out the possibility that I connected it to the power when the other end of the TT interconnects wasn’t connected. It’s hard to remember assembly details like that one years later when you’re just moving some equipment around. Nevertheless, that should NEVER cause the dangerous situation that ensued. When I connected a ground wire from the TT to the amplifier after it had been roasted by the preamp, it SPARKED. Very upsetting.

I don’t ignore the possibility that the ungrounded amplifier could be the source of the current, but the amplifier continues to function normally and doesn’t become charged unless connected to the preamp.

Hey OP,

I just ran upstairs to answer you. I’m not usually an alarmist but it sounds like you have a potentially dangerous situation here.

It seems like 2 things have occurred:

1. Equipment has had a malfunction shorting the power supply to the chassis
2. The equipment’s chassis ground is not functioning either by the deliberate removal of the ground pin or a bad outlet.

I strongly encourage you to take this seriously and resolve this. Potential side effects are electrocution or fire.

What may have happened is that the power supply has become shorted to the chassis, hence the burn you received while attaching interconnects. That should _never_ happen. This happens when a short has developed and the normal path to ground (the ground AC pin) is not working correctly. In addition to potentially lethal shocks a fire can also happen as the current is flowing through your interconnects, which are absolutely not designed to do this.

If you have previously removed a ground pin or used a cheater plug, immediately remove the cheater plug and/or get a properly functioning power cord with the ground pin working on both ends.

Otherwise, find a qualified technician to examine your equipment and/or an electrician to inspect your outlets. You may also want to use a cheap AC outlet tester like this one.

Be extremely cautious and use the breakers to disconnect power at the slightest hint of a shock. Also, of course, keep liquids and wet hands away from your equipment and wear insulated shoes while touching it while plugged in.

This an excerpt from the user guide. May have something to do with it.

Or not.

IMPORTANT: A turntable with a functional cartridge MUST be connected to the MOON 110LP prior to connecting the AC power cord, otherwise you may damage your amplifier and/or loudspeakers.