USB DAC - A Digital Voyager?

The times I've been asked "when are you doing a USB Voyager"?

Well, for an analogue veteran this computer audio takes some learning, but I managed to learn enough to make this device below...



It's obviously a prototype and it took me 12 hours to put it together.

The last bit was interfacing the Windows volume control to those two tact switches you can see on the right hand side of the stripboard. These operate this...



They don't automatically bring the control up on screen, but we all found it interesting to watch it move up and down as you press the buttons, so you may wish to open your volume control to see it move...

And yes, this prototype is shown connected to a pair of AKG K701's...so does it drive them well? You bet! Powered from the USB bus at 5 Volts, with the USB DAC chip taking nearly 60mA, there's only 40mA of juice left from the 100mA available, so it's not a head banger, but it's plenty loud enough for our eclectic tastes here. The volume control is down the width of the slider knob to be comfortable with the K701's playing Hell Freezes Over by the Eagles in FLAC. Playing Kate Bush's 50 Words For Snow in WAV (the 96/24 download), it needed an extra notch, but it's still not up full. It's easy to tell Kate's voice from her son's choir boy voice, demonstrating it's good tonality.

Switching to a pair of Grado SR80's the volume doesn't change all that much, and the results aren't that far off those obtained with the K701.

It's never going to be a Solo headphone amp in miniature, but you'll hear most of our hallmarks of sound quality and 3 dimensionality sound-staging. It's just the thing for those traveling with a (fully charged) laptop etc.

It is also useful to obtain an analogue line-output, with the volume control being used to set the required level.

But that's not all! I couldn't squeeze it on this little piece of strip-board but the finished product will also feature a S/PDIF coaxial output!

This is not a boastful specification product - it does 48/16, but my bet is you won't find an analogue output quite like this on a more highly digitally specified product.

Pictured with it is a case we quite like. It shouldn't be much of a struggle to reduce the PCB size to fit.

UPDATE: Just trying it with the HD250II, simply because they're so revealing and unforgiving. At 300 Ohms impedance you wouldn't expect much volume but whipped up full on the volume up tact button, it's loud enough for me. It will no doubt be too loud for Miguel who listens at low levels but the good news is he can easily turn it down with the other tact button. Playing Jon and Vangelis Short Stories album, "The Road" is almost the same as I would expect off the vinyl cut, and comparatively speaking, the same sort of level as I'd listen on speakers. However, a low power device such as a USB powered headphone amp is best used with lower impedance and reasonably sensitive headphones. Not forgetting it's other use as a line-out from USB... and S/PDIF!


Edited by Graham Slee - 05 Jun 2012 at 2:36am

In 12 hours Graham, you have designed and built a USB DAC with hi-fi headphone amp and USB/SPDIF convertor. That is impressive on more than one level.  

Many USB-powered external hard disk boxes have a second USB plug connected in parallel with the first, but drawing power only (no data). Perhaps this could be an option?

Is there anyway of subverting the usb hub specifications which allow for 500 ma ( 100 each for four devices ) ?