[sdiy] diy autotansformer?

[JH.]

> > I think I should try to reduce the mains voltage for these - build a box
> > with 230V
> > input and 220V output. As no isolation is needed, an autotransformer
(one
> > winding
> > with a tap at the right place) would be fine. Actually, there are even
> > variable
> > toroidal transformers that work like this.
>
> Nooooooooooooooo!!!!!!!!!!!!!!!!!!!!!!!!!!!
>
> Gasp! Glurgl... urp! No!
>
> Just don't do it! Forget it! I understand why it may sound like a good
idea,
> but it isn't. Trust me!
>
> Here are a few issues just from the top of my head:
>
> * Security - you *don't* know the polarity between the zero and phase.

First of all, thanks for actually _having_ objections. Better to check
everything twice
than making a bad mistake.

But I don't understand this objection. We always have to leads that can
possibly be hot
(even though one of them is neutral, you can never be sure, so inside an
instrument with
cable to plug into mains, *both* wires must be (and are) insulated anyway.
The protection
Ground (if there is any), is always used seperately here in Germany.


>   I have friends who suffered personal dammage from autotransformers.
Let's
>   just say that it is *NOT* a good thing to have 230VAC arm-to-arm.

Well, autotransformers must always be used in combination with a normal
(insulating)
transformer. That would be the configuration when I leave the internal
(isolating) transformer
untouched and just add en external autotransformer.


> *IF* you are to wound your own mains transformers, here are my
recommendation:
[...]
> I really wonder if it is worth the time and money.

I don't plan to wind my own. I just used this example to show what I'd
consider a good solution
*if* winding my own were easy. As it is not, I tried to deduct a cheap
alternative method from there.


> If you didn't get it, I think single-wound transformers should be extint.
Do
> yourself a favour and learn yourself to view it as a historic artifact
that you
> *may* encounter but should be moved over to the museum and be showed off
as an
> example of how wrong things was done in the old days.

Just to clarify again - I am *not* speaking about replacing the internal
transformer. The
autotransformer is *extra*. Insulation / protection must be done (as before)
by the
synths internal transformer.

JH.