"jakdedert" wrote in message ...
"David" wrote in message
.com...

"Michele Ancis" wrote in message
...
Hi,

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...

Any suggestions are welcome

M
--
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

I once was touring Europe with a piece of outboard audio gear, which I was
operating with a transformer. The transformer died....

On a hunch, I opened the case, and sure enough there was an unmarked switch
in the (analog) p.s. section. I disconnected the p.s. from the rest of the
circuit, flipped the switch and tested with a multimeter. All voltages (+/-
15v) seemed within tolerances, so I buttoned it back up, whacked off the
Edison connector, installed a Euro spec' plug and operated it that way
reliably for several months until I got back to the States. In fact, the
plug's still on there. I just adapted it back to Edison when I got home.

On another occasion, I wanted a certain piece of gear which I couldn't
purchase in time for the tour. I purchased the European version in Holland
when I got to the continent, then sold it (for a profit) several months
later in Germany. (This was in the 80's, before the EU) For some reason,
the used value, there, was greater than the new price in Holland. I guess I
could have gotten into trouble--not exactly legal--but....

If the OP's friend is actually 'moving' to Italy, perhaps he can adapt his
amp to the local standards utilizing parts from its European counterpart.
If he's merely touring the country with a band, he should know that it's
commonly requested for promoters to supply step-down transformers for this
purpose. The Tour Manager needs to include this requirement in the
equipment contract rider. Most sound reinforcement/live production
companies in Europe carry them in their inventory. It's done all the time,
he just has to ask. Possibly, he can even spec' the exact model of his
amp--the European version--and leave his at home.

A transformer big enough to operate a 100 watt amp is going to be cumbersome
if he has to carry it back and forth.

jak

Yes I understand ya problem sometimes we try certain things to
satify our curiocity. I think a way round is to use 2 similar
electrilytic capacitors connected back to back to serve as a potential
divider. I have seen this in old transformerless battry chargers and
my Oldman used to say its better than the ones with tranformers. the
rule is that the caps get bigger in capacitance and may be size as the
power goes up. Let me hear from you if you have any problem
All the BEST. Catch u on the net again with the job done.