Adjusting the 115V Transformer Primary Polarity for Minimum Noise.

This change involves coming near and possibly touching (with a meter) the 115V wall voltage.
Only trained qualified technicians should do this.

Don't try this unless you are qualified to solder inside 115V equipment.

Tools you'll need:

TWO 3 prong to two prong wall adapters (cheater plugs).
Medium duty metal cutters.
Permanent Marker.
AC voltmeter 0 to 100V/ 200V. DC voltmeter 0 to 10V/ 20V. Ohm meter, >1 megaohm scale.
A switched wall outlet (all ready installed and working in the wall).
A buddy to be in the room to laugh, I mean help you, if you get in trouble.
A working fire extinguisher in sight and reach.

Tools you may need:

Soldering iron, solder wick, soldering heatsink, electrical tape, small cable ties, nonacidic RTV, Outlet tester (usually < $10 at a hardware store.)

Test Procedure:

1)    Mark the side of the adapter with the wide plug as "FOR TEST ONLY." Mark the narrow side as "HOT".
2)    Turn the switched wall outlet off. I prefer to check the outlet with an outlet tester. If you don't have one, at least verify that the switch works with a desk lamp if you are not sure that the switch works.

3)    With the wall socket adapter (cheater plug) unplugged from everything, modify/cut the cheater plug's polarization tab so that the 115V Cold tab (wide one) is the same size and shape as the smaller hot tab. Clean off any and all metal filings. I mean really clean them off.

4)    Unplug the UUT (Unit Under Test -- the piece of electrical equipment you want to "polarize") from everything. If it has a volume control, set the control at minimum.

5)    With an alligator clip, not your fingers, attach the metal chassis of the UUT to one side of an AC voltmeter. Set the voltmeter to the 100V or 200V AC range. Remember what I said about being careful and qualified. If this even makes you nervous, buy a technician friend of yours a Dr Pepper and after he does the work, a beer and a pizza.

6)    With another alligator clip, not your fingers, attach the remaining AC voltmeter lead to the metal chassis of a reference piece of electrical equipment that is three pronged and that is plugged into the wall. As a second choice, check your outlet with an outlet checker (I've seen miswires) and use a banana plug to attach the voltmeter to the ground hole. If you don't know which one is ground, buy a technician friend of yours a Dr Pepper and after he does the work, a beer and a pizza.

        The UUT should be switched on at this point, the UUT's wall outlet MUST be off.

7)    Check the three prong adapter for metal dust again, put the modified cheater plug on the UUT and plug the UUT in to the switched wall outlet with the side marked "FOR TEST ONLY" into the wide slot.

8)    Double check that the meter is on AC volts. You may see up to 1-2 V at this point.

9)    Stand clear of your UUT and flip the wall switch on. If the UUT is tubed, let it warm up. DON'T TOUCH the UUT. Read the voltmeter and write the voltage down next to the words "STOCK". If you see anything close to 115V, shut the switch off, the equipment probably is seriously defective.

        If you saw 115V, you'll be darn glad you weren't touching it when you flipped the switch.

10)    Turn the wall switch off.

10)    Unplug the cheater and plug it in upside down.

11)    Stand clear of your UUT and flip the wall switch on. If the UUT is tubed, let it warm up. DON'T TOUCH the UUT. Read the voltmeter and write the voltage down next to the words "FLIPPED". If you see anything close to 115V, shut the switch off, the equipment probably is seriously defective.

12)    Turn the wall switch off.

13)    Remove the modified cheater adapter and lock it up someplace safe.

On my Foreplay Preamp I got off easy, STOCK was 9.4V RMS and FLIPPED was 33V RMS. On my Dynaco MK IIIs, the reverse was true and I had to solder in them.
14)    If the "FLIPPED" voltage was lower than the "STOCK" voltage by more than 10% the following modification may help your system sound better. . .

The Modification that Experts with No Warranties can do

Unplug the UUT (Unit Under Test -- the piece of electrical equipment you want to "polarize") from everything. Or should we call it the UUM (Unit Under Modification). Wait a couple minutes for all the capacitors to bleed down.

Using the red lead, ohm from the UUT wide plug and narrow plug (at the same time) to UUT chassis.
Chassis must be probed using the black lead.
RECORD this reading.

Take the cover off (there goes the warranty) and check the all capacitor voltages to make sure they are less than 9 V DC. Remember, your voltmeter was on AC before, you need to use DC now. Take a good look at the internal wire dress. You'll need to return it to this condition after you are done.

Find the primary of the transformer. Unplug/Unscrew/Unsolder the primary leads and flip them. USE THE SOLDERING HEATSINK CLIP on the wires to keep from melting the wire insulation. This flip must occur at the transformer, not before the EMI filter, not before any lightning protection! If you flip the wires before the EMI/ lightning filter, you may generate a shock hazard.

        Check your solder joints.
        Check for solder balls.
        Check for stray wires.
        Check for wire clippings.
        Check for nicked wires.

Clean your solder joints.

Check the wire dress to make sure it is just as safe and pinch free as it was before you opened the box. Use cable ties and/or acid free RTV to tie the wires down if you have to.

Using the red lead, ohm from the UUT wide plug and narrow plug (at the same time) to UUT chassis.
Chassis must be probed using the black lead.
RECORD this reading.

The reading should not have changed by more than 5%. If it went down, you may have made a mistake. If it went up, your unit may have been dirty.

Close the box up.

Check out
1)    Make sure the switched wall outlet is OFF and the UUT is not plugged into anything.
2)    Attach an AC voltmeter set to 100V/ 200V AC between the UUT chassis and the ground reference like you did before.
3)    Plug the UUT into the wall socket using the unmodified 3 prong to 2 prong adapter.
4)    The wall switch must be off and the power switch on the UUT on.
4)    Make sure you are not touching the UUT. If a lead falls off, turn the wall switch OFF before you touch anything.
5)    Turn the switched outlet on. If the voltage reads with in 10% of the lower voltage you recorded before, you did good. If it reads higher, figure out what you did wrong and fix it. If it reads lower, is the meter on AC? Did you clean a lot of gunk out of the inside of the UUT?
6)    Turn the switched outlet OFF.
7)    Is the power off? If so, remove the cheater plug and use your upgraded equipment.
8)    If this solved a problem or improved the sound, you owe me a cold Dr Pepper. Note: The filament snubber does more good. But correct line polarity is a cheap modification.

How does it work?
One end of the 115V power transformer winding has more effective capacitance to the secondary and chassis than the other primary end. By placing the primary side with the least effective capacitance to the 115V HOT, the noise injection is minimized. The 115V cold is almost always quieter than the 115V HOT even after the 115V 60 Hz component is removed. The 115V cold is attached to ground in your service entrance. The 115V HOT has all the noise made on the entire utility grid running through it at some point.
Please notice that I said effective capacitance, not measured capacitance. Because of how the transformer is wound and used, it is possible for the effective capacitance to be different than the measured capacitance.

What's up with the black lead to chassis bit during the ohm testing? Because some equipment has internal lightning protection in the EMI filter, changing the color of the lead that attaches to chassis can change the bias of the lightning protection and give a different reading.
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First version TBD.

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