[sdiy] Oberheim OB-Mx PSU question

Tue Nov 19 00:25:56 CET 2002

Most transformers are designed for 50/60Hz operation...

however the 50Hz use will drive the transformer further into
magnetic saturation...

if the transformer was marginal at power output at 60Hz... 50Hz
will push it over the edge.

They hum loudly when run in the non-linear region of the core...

and even 60Hz Oberheims hum like hell. My Matrix 1000 does...

H^) harry

>--- Tony Allgood 
>wrote:
>> Hi Seb and all,
>> 
>> OK, that plate near the actual inlet socket aperture
>> is removable
>> without too much force. I actually can't remember
>> how its actually
>> removed, but it took me only seconds to work out how
>> to do it with the
>> unit in front of me. [Now if it were very hard to
>> get off I would have
>> remembered this all in detail :-) ]
>I figured it out and it was easy as you say, but too
>complex for my English to describe :^o
>> There is a little switch underneath that simply
>> selects between either
>> 110 or 230V. The new voltage setting will appear in
>> the window once the
>> plate goes back. And its not paper but a white piece
>> of printed plastic
>> and part of the switch itself.
>It's a piece of plastic that just needs to be removed
>and inserted 180 degrees flipped. The OB is up and
>running now. BUT...
>> Also change the fuse inside to half the original US
>> fitted value... I
>> think you'll need a 250mA from memory.
>The inscription on the lid says "use only with 250
>volt fuse", and that's what's in there, so I thought I
>shouldn't change anything. The local computer shop
>told me they'd never seen anything like this, and
>advised leaving the fuse where it is.
>However, while the instrument runs, it hums like a
>refrigerator. The 50 Hz sound comes from the PSU's
>corner, is not audible in the signal path, and is
>completely static (that is, no phase cancellations or
>frequency changes were observed during several
>minutes).
>Conclusion?
>Thanks again, any help appreciated.
>Sebastian Kuehnl
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