Determining Proper A/C Polarity
Every component in an audio system is sensitive to
AC polarity. Ensuring that your electronics are connected to the AC line with
the correct polarity is essential if you want to realize the full potential of
What follows is a simplified explanation of the
phenomenon, and a description of a simple method of determining the proper connection
of the power cord for any piece of equipment in your system.
All of the electrical equipment in your system has been
designed with proper A/C polarity in mind. A specific leg
of the A/C line has been dedicated as the positive (sometimes
referred to as hot) conductor and the other leg as the negative
(sometimes cold) or neutral. Often a third leg for ground,
is included. The problem begins with the A/C wiring in our
homes. If our electrical system is improperly wired we may
not have the positive leg and neutral leg in their correct
orientation. Coupled with design differences among equipment
manufacturers, we have no way of
knowing that correct AC polarity has been achieved by simply
inserting the plug in the wall.
Technically, the transformer in the power supply can induce
a charge (up to 90 volts) on the chassis side of each component.
Interconnects allow currents to flow between all of
the associated components in your system which
is likely to modulate the ground reference of each consecutive
gain stage. Proper polarity alignment is achieved by registering
the chassis potential to ground.
Correct orientation of the A/C plug (polarity) can
be easily determined with a simple Multimeter or Volt Ohm Meter
One accurate enough to do the job (preferably a digital
unit and one with a 10 to 11 Meg-Ohm input resistance) should
not be too
costly (the Meterman 5XP is a good choice an can be had
for less than $40). A local electronics supply, Radio Shack
and even many home centers should have an appropriate model.
A Multimeter can be used for a variety of
tests and is something every audiophile or homeowner
should have in their toolbox.
Before proceeding with the test, I would suggest you check
all of your outlets for correct wiring. An electrical circuit
tester (with three lights that tell you how the outlet is
wired) is available in any home center or hardware store
for a few Dollars.
To find AC polarity with your Multimeter, proceed as follows:
1) Turn off all components.
2) Isolate each component by removing all wiring
including power cord, interconnects, ground leads, antenna
3) On components with a 3 pin power cord, float
the ground with a three-to-two adapter (often called a cheater
plug or ground lift adapter). You can see a picture below.
On many of these adapters the neutral side of the plug is
usually wider than the hot side and reversing can be
difficult. You may need to trim that side to allow reversal.
4) Connect the common probe of the Multimeter (black lead)
to a ground reference point*. I If you have a three-wire
grounded receptacles, use the center pin.
5) Connect the positive probe (red lead) to the
chassis or ground terminal of the unit under test.
6) Plug the component into the wall socket and turn
on the power switch. Note the A/C voltage reading on the
7) Reverse the position of the plug in the wall
socket and repeat step 5.
8) The correct A/C alignment will be the one that
gave the lowest reading.
9) Unplug the component, mark the plug so that you
can properly reconnect it, and proceed to the next component.
If you find that the AC polarity of a component
needs to be reversed, you have two options. One is to leave
the adapter in place and the other is to change the polarity
on the outlet itself. Please do not attempt this if you
are not comfortable working with line voltages and be
absolutely certain the breaker is off and there is no
voltage at the outlet!
Please note that in some rare instances, the higher
reading will produce better sound from the component.
Listening to each and every component in the system can
be an extremely lengthy process. And in some cases the differences
will be so small that mistakes could be made. I would recommend
for most people to simply follow the meter. But if you want
to get picky, listening tests should be employed to determine
which is best.
Significant sonic improvements can be realized by the
proper A/C orientation of all the components in ones system.
The effect can be quite startling in some systems. Improvements
in imaging, low level detail and high frequency clarity
are often noted, with some components benefiting more than
others. In my experience, preamplifiers and CD players (D/A
converters included) are particularly sensitive to proper
polarity, and often benefit greatly. Many tube units as
well, seem to be rather sensitive to this phenomenon. It
is important to do every component in the system,
as improvements are additive. A little bit here and a little
bit there adds up to a lot in the end.
* A good ground reference point may he difficult to identify.
Try using a cold water pipe (do not use a gas
pipe!), if you can locate one. An alternative method
would be to use a copper grounding rod driven into the earth. The center receptacle of a three-wire system may not always
represent a good ground reference. To verify its potential,
connect the common probe to the ground receptacle. The positive
probe then inserted into the hot receptacle should yield
approximately 120 volts, the neutral receptacle should be
less than I volt. If you find greater than a I volt differential,
try an alternate ground. Some Engineers feel that the best
method of grounding employs the use of a dedicated copper
ground stake driven into the earth as near the equipment
as is practical. All component chassis would then be tied
to the stake with a heavy gauge wire, utilizing the star
grounding approach, with either the preamp or amp as the
star junction. Please be sure to follow all local electrical
codes when attempting this type of an installation. This
job may best be left to a qualified electrician.