"Michele Ancis" wrote in message =
...
Hi,
=20
a friend has bought from US a guitar amplifier, 100W. It has a =
switching
power supply (yes, I know it's strange).The amp is to be used in =
Italy,
where the voltage is 220, 50Hz: supposedly, the supply needs some
adjustment. The vendor refuses to give information on how to do that.
Besides the idea of just putting a stepdown transformer and to feed =
the amp
with 110V, 50Hz (wich shouldn't be bad at all, being a switching it =
first
rectifies the voltage), I was wondering if there would be the =
possibility
just to change some components and have the supply work with these new
ratings...but I have no experience with those devices...the only thing =
I
can think of is the voltage on the diode bridge...or across the =
"chopping"
transistor...
=20
Any suggestions are welcome
=20
M
--=20
email:

Michele,
Many switching supplies use a doubler for 110 operation in the line =
rectifier circuit. There is usually one wire to disconnect which turns =
the rectifier into a non doubling full wave bridge. If you can power it =
up on 110 and measure the DC feeding the switching transformer primary, =
and it measures about 300 volts, than you have a doubler and it can be =
rewired easily for 220 operation.

David