Replacement transformer
 

Anton Gÿsen wrote:

Adrian C wrote:

Use a PC switchmode power supply? or just disconnect the whole thing and
run from the original audio outputs of the CD player.

/me looks, ducks and runs for cover ...

Nice try ;)

Seriously, the replacement "enthusiast" power supply market for digital
addons is getting a bit OTT. I've got an Audio Alchemy dac-in-the-box
(use it for PC audio from S/PDIF) and lots of folks are brewing
alternative power supplies for that. Same goes for the
Slimdevices/Logitech Squeezebox.

Glad I'm in the right ballpark and my idea is not ridiculous. I love the
DAC but they really scrimped on the cheapo Chinese PSU.

Inside the DAC there will be a 'regulator chip'. Or possibly it's inside the
PSU itself.

It will make **** all difference other than deal with your entirely misplaced
preconceptions. Some of the best quality electronics comes out of China now. I
know. I've been there and seen the factories and worked with them.

Graham

Replacement transformer
 

"Adrian C"


Use a PC switchmode power supply?


** It's a 12 volt AC output adaptor !!!!!!

Do learn to read things before you SNIP and ignore them !!!




....... Phil

Replacement transformer
 

Anton Gÿsen wrote:

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.

Toroids are great when mounted INSIDE equipment since the stray radiated
magnetic field is low helping to lead to low induced hum levels. Better than
toroids are R-core designs and the very best are O-core designs. In the long
past C-core designs were also well considered but are humungously expensive to
make and I haven't seen one in decades.

For an EXTERNAL power supply located say a metre or two from the DAC it's
doesn't make a tinker's cuss of difference.


Graham

Replacement transformer
 

David Looser wrote:

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

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.

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.

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

Well said that man. Give him a cigar.

Graham

Replacement transformer
 

Anton Gÿsen wrote:

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?

No, the magnetising current (and field) stays largely constant regardless of load.
Basic Physics.

You are fretting over nothing.

If you don't like this DAC buy another one - don't fiddle with it.

Graham

Replacement transformer
 

Serge Auckland wrote:

If you want to add an on-off switch,
then why not make a small mains extension, and put a torpedo switch near the
socket

I think 'torpedo' switches are now illegal but you can get switched power
blocks.

Graham

Replacement transformer
 

"David Looser"

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.

** True only for small transformers - say under 80VA.

Above that, regulation steadily improves to around 4% at rated VA.


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.


** Ignoring core magnetising losses, transformer efficiency IMPROVES when
the load VA is made less than the rated VA.

Percent efficiency = 100 minus the ACTUAL percentage regulation - so a
transformer rated at 75VA and 15 % regulation will have 3.6 % regulation at
20 VA.

The above transformer is 85% efficient at full load and 96.4 % at the
reduced load.

BTW

A 75 VA toroidal will dissipate about 1 watt due to magnetising losses.


...... Phil

Replacement transformer
 

Phil Allison wrote:

"Anton Gÿsen"

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.

** You cannot legally build your own AC "plug pack" - such items require
specially design transformers and must be made and ** agency approved **
to meet the Class 2 safety standard.

So I was wondering whether I could build a new transformer for it based
around a toroidal core transformer,

** Worst possible choice.

Would something like this do?

http://preview.tinyurl.com/6q5ceu (eBay item # 270286161572)?

** No - a standard toroidal like that cannot possibly meet Class 2 safety
requirements.

Onlt specially made toroids can meet Class 2 and the leakage field goes UP as a
result.


What else would I need, other than a circuit board, a rocker switch and
some kind of housing? Or should I just give up on the idea and stop
wasting my time?

** Yep.

..... Phil

Succinct and true.

Graham

Replacement transformer
 

Phil Allison wrote:

"Anton Gÿsen"

Yes but it consumes electricity when it is doing nothing useful
whatsoever. That, in my mind, is extremely poor design. Why couldn't
they have integrated it into the DAC itself so the power switch on the
DAC actually cuts all power to it? It's not rocket science. This poor
design is ****ing the planet up.

** Oh dear - we have yet another rabid, Green Nazi ****wit.

That tiny AC adaptor is warming up the WHOLE planet !!!

Right now over here it could do with some warming !

Already 60% of the British public think 'global warming' is ****witted. At
the end of this winter expect that to be more like 90%.

Get out the guillotines for the 'greens'. And for the politicians like Al
Bore who fell for (or wanted to make money out of) it. He has a 'carbon
credits' company. Nice way to line your pockets at everyone else's expense.

Graham

Replacement transformer
 

Anton Gÿsen wrote:

David Looser wrote:
"Anton Gÿsen" wrote in message
The
"wall wart" PSU gets warm although it is encased in plastic.

It will, it's not a problem.

It's inefficient!

Oh GROW UP !

Graham