"Anton Gÿsen" wrote in message
...
David Looser wrote:

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?

Yes, 20VA.

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?

Indeed, and the amplifier designer will have taken that into account when
specifying components. A DAC, on the other hand, takes a more or less
constant load so the designer will not have had to allow for load current
variations in his design, or the use of an unnecessarily large transformer.

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.

Much of it will be due to the rectifier and regulator.

The
"wall wart" PSU gets warm although it is encased in plastic.

It will, it's not a problem.

David.