[sdiy] How to predict a transformer's current capability?

[John L Marshall]

It used to be 220 volts nominal on the Continent and 240 volts nominal on
the Island. I would think that transformers designed for European use would
handle the 240 volts.


----- Original Message -----
From: jh. <jhaible at t-online.de>
To: SynthDIYmailinglist <synth-diy at dropmix.xs4all.nl>
Sent: Monday, December 24, 2001 1:33 PM
Subject: Re: [sdiy] How to predict a transformer's current capability?


> > If you want the ultimate transformer, get a donut, a toroidal
transformer.
> > Toroids do the best job of keeping the magnetic field where it belongs.
> The
> > core is powered iron for lowest eddy current. They seldom hum.
>
> Yes, toroidals - I don't use anything else anymore.
>
> BTW, if your country's mains supply voltage has been raised in recent
> years (as it was raised from 220V to 230V in Germany), don't expect
> too much from salvaging transformers from old gear. They are very likely
> to produce excessive hum on today's higher voltage. The core is built
> for a certain maximum magnetic field, and nobody would have used
> more iron (bigger core) than necessary when the voltage was lower.
> (Well, some have, but that's the exception.)
>
> You probably won't blow anything with an "outdated" transformer,
> but you're producing a much higher stray field which can induce hum
> into your circuits or even produce mechanical hum in the transformer.
>
> I have replaced a lot of transformers in analogue synthesizers (230V,
> and mostly with a toroidal transformer), and cured a few hum problems.
> In a way, recycling transformers from old broken gear is the exact
> contrary ...
>
> JH.
>
>