This article is from the rec.audio.* FAQ, by with numerous contributions by Bob Neidorff others.
Some equipment is available with an international power supply,
which can be rewired by any serviceman to either power line
voltage. If you expect to be moving abroad, look for this kind
of equipment. Often, the same model is available both as US
only and as International. Some equipment will be rewirable and
won't say it. Adcom amps are known to be rewirable.
If you rewire equipment from one voltage to another, be sure to
also change the fuse(s). The correct value is often printed on
the case or chassis of the equipment. If an amplifier, for
example, is rewired from 115V to 230V, the fuse current rating
needs to be reduced by 50%.
If you know that your gear is limited to one power line voltage,
you can order a new power transformer for that receiver, CD
player, amplifier, or tuner which will be wound differently.
Contact the manufacturer's local service center. This can be
very expensive. A new transformer for a 40 watt receiver would
wholesale for under $25 but cost $75 from a service center.
Another alternative is to buy a power transformer that will
convert 115V to 230V and vice versa. This is only practical
for smaller gear. Larger power amps require prohibitively
massive and expensive transformers. Also, the addition of a
transformer may hurt the sound quality.
Here are some common transformer models and 1992 list prices.
Power ratings are total line current multiplied by line voltage
(2A at 115V is 230 watts). Larger transformers cost more. Some
of the costlier transformers are constructed with plugs and
jacks for immediate use. Those marked * have wire leads and
need safe connections to be used.
Before spending money, check into other things about audio in
the new country. Broadcast frequencies are slightly different
in some countries than in others, so a receiver or tuner bought
in one country may not be able to receive some or all of the
stations in another country. The US separates the AM broadcast
band frequencies by 10kHz while the UK uses 9kHz. Similarly,
the US separates FM stations by 200kHz, where the UK has
stations on a 50kHz spacing pattern. It MAY be very simple to
modify a receiver from US to UK spacings, but may not. Last,
but not least, some equipment will NOT work well on 50Hz power.
Also, FM Radio preemphasis is different in North America and
Europe. One uses 50us while the other uses 75us. To change
receiver deemphasis may require a modification by a technician
with special factory information.
Also, power line frequency is 50Hz in some countries and 60Hz
in others. Some equipment will overheat if it was engineered
for 60Hz operation and run on 50Hz power lines. Some equipment
uses the power line frequency as a reference for motor speed,
such as turntables and tape decks. Check the label first.
Step Down (230V in, 115V Out) MagneTek/Triad N1X* 50 Watts $11.83 Stancor P-8620* 50 Watts $14.16 MagneTek/Triad N3M 85 Watts $29.95 Stancor P-8630 85 Watts $43.65 MagneTek/Triad N6U* 200 Watts $25.72 Stancor P-8632 200 Watts $51.80 MagneTek/Triad N5M 250 Watts $42.60
Step Up (115V In, 230V Out) Stancor P-8637 85 Watts $43.10 MagneTek/Triad N150MG 150 Watts $49.46 MagneTek/Triad N250MG 250 Watts $54.69 Stancor P-8639 300 Watts $55.51