TJ Hertz wrote:
Richard Crowley wrote:
"TJ Hertz" wrote ...
I've got a Japanese-bought AKAI S1000 sampler that says
"100v AC" on the back. I live in the UK, where the power
supply is 240V or thereabouts. Can I use a 110V transformer,
or does it need to be strictly 100V?
I wouldn't risk 110V. So get a 10-12V transformer and hook it up
to "buck" part of the 110V to reduce it to ~100V.
Can you explain this in more detail? Thanks.
Usual warnings about this is mains and can easily kill.
Usual warnings about getting it wrong can cause a fire and
burn the house down. Usual warnings about not doing it
unless you are a professional. Usual warnings about, at the
very least, getting this wrong could destroy the equipment
you are actually worrying about. Usual warnings about, if
you have to ask what a "buck" or "boost" circuit is, you
quite possibly don't have the knowledge and experience to be
attempting this for the first time - especially on anything
that you value.
In theory:
You get a mains to 10 or 12 volt transformer and connect its
primary across the mains - thus producing 10 or 12 volts ac
from the secondary. You get a mains to 110 volt transformer
and connect its primary across the mains - thus producing
110 volts ac on its secondary. So the primaries are in
parallel across the supply.
Then you connect the secondaries in series, thus:
You then take a wire from the 110 volts secondary terminal
and connect it to one terminal of the 10/12 volts secondary.
Measure the voltage between the remaining unused secondary
terminals (one unused on each transformer secondary). If the
voltage is 100 volts - then those are the terminals that you
take power off for the load. If the voltage is too high
(higher than either secondary on its own), move the link
wire to ther other terminal on the 10/12 volt secondary and
repeat. Bingo, it should have dropped and you should have
100 volts now.
Basically, one secondary winding is made to be out of phase
with the other and thus cancels out some of the voltage
produced by it.
One variant of the technique is to connect the secondary of
the second transformer in series with the primary of the
first. There are other variants.
However, it all gets a little more complicated than that in
practice. Picking the right transformers is the key -
particularly as small transformers typically have terrible
regulation and their output voltages can vary widely with
load. Thus, while the output voltage may look fine off load
- it can change substantially when load is applied.
For many bits of equipment, too low a supply voltage can be
as bad as too high.
Personally, if I was concerned that the voltage was out of
specification for the equipment, I would use a variac and
set the voltage precisely, whilst on load. You can get
little variacs cheaply enough - try ebay, for example, that
is where I have got several of mine. Once set, fix the
adjusting knob in place - if it gets accidently moved you
would be in the doo doo. You can buy them bare or in an
enclosure with fitted mains lead and output socket - the
latter may be what you are looking for..
--
HTH
Sue
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