[sdiy] transformers and power supplies, etc... for newbie

[harrybissell]

Hi Tim

While experimenting I would DISCONNECT the transformer from the synth
so if you fvck up you will not destroy the circuit.

Some transformers have dual primary taps.  There are two ways...

1) Dual Primary windings - these would have four taps, either wired in
parallel for 120V and series for 240V

2) Tapped Primary - there would be three taps. You use the "outside" taps for
240V
and the center and one outside tap for 120V

If you think you have #2... measure the resistance from the unused tap to each
side of the primary.  If the ohmic readings are EQUAL ... that is a center tap
and can be used for 120V operation.

If that tap is NOT connected to the primary (high ohms) you can't use it.

Usually the fuse rating for 120V is 2x the 240V rating... so a .2A fuse at 240V
would be replaced by a .4A fuse for 120V

If you are not sure DON'T DO IT !     Its straightforward but a mistake at the
mains can
be fatal to instrument and technician alike !!!   :^(

H^) harry  (note the rare 'frowny face' above :^)

Tim J wrote:

> Ok, so I need to learn a bit about transformers and power supplies.  Anyone
> know of any good online resources?
>
> I recently bought acquired an old korg micropreset synth.  Its in perfect
> shape (even came with a hard shell case).  Unfortunately its 220v and I'm in
> the US.  The fuse was also missing when I got it.  To get her running I
> guess I need a step up transformer.  Do most transformers have taps for 110
> and 220 volts?  There seem to be at least one unused tap on this
> transformer.
> Also, can anyone test me how to test this transformer to find out if its set
> up for us or european voltage?
>
> Lastly,  since nobody in my neck of the woods has a .2V fuse would using a
> .25v fuse cause much of a problem?  I realize using a higher rated fuse
> defeats the purpose of using a fuse but should this small difference cause
> much of a problem?
>
> Thanks,
> Tim