In article , Don Pearce
wrote:
On Tue, 03 Aug 2010 16:29:26 +0100, Jim Lesurf
wrote:

Hi,

Just to let people know that I've added some more info to

http://www.audiomisc.co.uk/HFN/Headp...C/HeadDAC.html

This now gives some values for the distortion under various conditions.
(Finally got around to doing reliable measurements on this!)

Also a little more info on the battery PSU connection.

The battery part was interesting. Could this DAC be the makings of a
decent amplitude modulator?

I have wondered if - over a limited range - you could adjust the volume by
changing the PSU voltage. However I have no idea if it would be OK to
*quickly* vary the rail voltage. And so far as I can tell thus far you are
limited to the range from around 2 - 5.5 V and only get about 5-6dB change
in level. I assume there is some internal smoothing since ripple isn't
evident when I use the (fairly small) wall-wart PSU.


On 03 Aug in uk.rec.audio, Don Pearce wrote:


A question occurs. Is the output of the DAC bipolar? If not the net half
scale DC could be compromising the transformers a bit. Maybe a big cap
in series?

No sign of any 'half rail' dc offset on the output of the DAC. Just checked
it quickly with a DVM to confirm. Around 0.2 mV dc. This is with nothing
except a (high impedance) DVM connected and using the battery supply I
made. (Currently providing about 4.95Vdc.)

The AU-D3 is designed to be used as a normal DAC in HiFi and AV systems,
but meant for people in the 'installation' trade so a sensible price, etc.
I don't think 'audiophiles' were on their sales radar or they might have
added a zero. :-) TBH if there were 2.5Vdc on the output I doubt the
transformers would be working anything like as well as they are! I also
doubt people would be happy to use it in installations.

And when used with no o/p load the transformer saturation is symmetric at
LF. Which I'd not expect if there were significant dc feeding into the
transformer.

So far as I can tell thus far, it is a decent little DAC. Bargain for 35
quid. Maybe a reviewer sometime will tell us if it is better than a 1000
pound DAC. 8-]

Slainte,

Jim

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