Checking the AC polarity of your amplifier

1.) Get a simple volt/ohm meter.
2.) Detach interconnects and speaker cables from the amp.
3.) Attach a *bi-polar cheater plug to the three-prong
plug on the amplifier power cord.
4.) Set the VOM to AC volts with an approximate range
of 0-100 VAC.
5.) Remove the trim plate from the wall outlet.
6.) Plug the amplifier power cord (with cheater plug
attached) into the wall socket. Do not turn on the
amplifier.
7.) Using the VOM, measure the voltage between a point on
the amplifier chassis (a bare metal spot like a
chassis screw or some unpainted part of the chassis)
and the galvanized metal mounting frame of the duplex
wall outlet. Note the reading.
8.) Remove the plug from the wall socket, rotate it 180
degrees and re-insert it into the socket. (The plug
blades are now in new slots) Measure the voltage again
as you did in #7.
9.) Whichever plug **position gave you the lowest reading
on th VOM is the way you want to plug in the amp (or
any other device you may wish to measure, into the
wall socket.

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* A bi-polar cheater plug is a cheater plug (three prongs in, two prongs out) which has had the wider (neutral) blade filed down so it will fit the narrow outlet slot when you turn it over 180 degrees in step 8. You can't buy them, you have to make them.

** If you want to ground your amp (using all three prongs) but the best position (as determined above) leaves you with the ground prong out of line with the hole in the wall outlet, get a cheater plug with a green wire coming out of it. File down the wide blade so you can plug the power cord into the wall in the most desireable orientation you determined in step 9, and then wire the little spade connector on the cheater plug to the screw that holds the trim plate onto the wall outlet (you may have to use a longer screw).

I gather from your post the low position in off is correct.
I noticed you said to do the measurements with the power to the
> component
off. I've had some amps that measure low in "off", but measure high when on. Reversing the plug the amp will be high when off, low when on, which is the way I leave it connected. Is this wrong?

Nsgarch - For your ** comment, could you not just switch the house wires into the outlet being used?

There have been instances where I preferred the higher leakage voltage. This also gets quite muddled with parallel transformers, such as Equi=Tech. Sometimes the leakage voltage is shocking (no pun intended).

Robbyg, Stuartbranson, Tbg:

Robbyg: The reason one makes the measurements with the component off, and all input/output connections detached is because what your trying to determine is how all the component's various circuits "grounds" combine and where that total is positioned electrically -- i.e is it closer to the "hot" blade of the power cord or the "neutral" blade of the power cord. Depending which way the blades of your equipment's power cord are oriented relative to the real "Hot" and "Neutral" of the electrical service in your wall, you'll get a bigger potential difference or "leak" in one position or the other. The position with the smallest leak will give you the least hum in your system when the component is finally turned on.

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Stuartbranson: You little devil!! Of course you could, but what about when you start to get oldtimers disease like me, and forget what you did where. Or what if someone buys your house and can't understand why they keep getting shocks from their vacuum cleaner!!

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Tbg: Soooo....you like a little electrical stimulation once in a while, do you?! "Higher leakage voltage" indeed! Listen: Audiophiles are a dying breed, so please be careful, we need you. If you find yourself craving higher and higher leakage voltages, please, email one of us before it's too late, your body fries your computer and you lose all contact with the outside world!

Neil