David Looser wrote:
"Anton Gÿsen" wrote in message
...
David Looser wrote:
"Anton Gÿsen" wrote in message
...
Hi all,

I am wishing to build a replacement transformer for my Cambridge Audio
DacMagic DAC (the new one that's just come out). I am unhappy with the
original PSU because it is inefficient and doesn't have a physical
on/off switch so it's constantly drawing a current unless you unplug it,
and I like to save evergy where I can.

So I was wondering whether I could build a new transformer for it based
around a toroidal core transformer, in the hope that it will reduce
power consumption and, if I'm lucky, make the DAC sound better.

Would something like this do?

http://preview.tinyurl.com/6q5ceu (eBay item # 270286161572)?
That is a 75VA transformer, far too large for what you want.
Will the DAC not just draw what current it needs? Is there danger of
damaging my DAC with that transformer?

Transformers are designed to produce the nominal output voltage at full
current draw, when under-loaded the output voltage is higher, typically
10-15% higher. This may not damage your DAC, but it will increase the heat
dissipation within the DAC and increase the stress on the internal
components. In addition an over large transformer is, well, over large;
bigger, heavier and more expensive than you need. Oh, and it will be less
efficient than one of the correct size.

OK so a lower rated transformer would be more appropriate?
So... when my amplifier for example (which has a toroidal core
transformer) is operating at low volume and therefore drawing a low
current it is stressing the components in the way that you describe?

And what makes you think it would be any more efficient that what you
already have?
Wikipedia reckons they're more efficient than the standard type of cheap
transformers (the name of which escapes me). They seem to be the
audiophile transformer of choice.

They are *slightly* more efficient (if correctly rated). But most of the
total inefficiency is due to the rectifier/regulator part of the PSU, which
is inside the DAC. Toroidal transformers also have a lower external magnetic
field, but if the transformer is external to the DAC that isn't important.

The DAC does get rather warm but I thought that was the DAC ICs. The
"wall wart" PSU gets warm although it is encased in plastic.

Changing the transformer will make negligible difference to the efficiency
of your DAC, and no difference whatsoever to the sound.

Thanks David, your information is useful.