Son of HeadDAC
This month Jim Lesurf takes his home-brew headphone DAC a stage further in search of better sound, this time with the help of a compact kit amp that can be yours for less than ten pounds...
RIGHT: The HeadDAC-2 built using the PMK136 kit from Velleman and an AU-D3 DAC from CYP. Both can be bought from CP Electronics at http://cpc. farnell.com. Part numbers are HK00815 and AV18219 respectively
ABOVE: Close up of the Velleman-branded kit

A couple of years ago I devised a very simple circuit that people could use to build a headphone amplifier/DAC. I named it the HeadDAC. The aim was to come up with a unit so easy to put together that someone with no previous experience of practical electronics would feel able to make one if they fancied. I 'unveiled' the design in the December 2010 issue of Hi-Fi News along with a link to details of the circuit in case any reader wanted to give it a try

www.audiomisc.co.uk/ HFN/ HeadphoneDAC/ HeadDAC.html

Since then I've been thinking of a 'Mark 2 improved' version. It would still be easy and fairly cheap to make, but would sound a little better and this time be more conventional in design. Enter 'Son of HeadDAC'...

SNEAKY TRICK

The original HeadDAC did not require components to be put onto circuit boards. Neither did it use any active components, apart from the pre-built DAC unit. This was achieved by employing a couple of small-signal transformers rather than transistor or chip amplifier stages. The drawback was that technical performance was limited by the small transformers chosen.

When it came to improving the sound of the original design, my first step was to see if I could source better transformers. However, I failed to find any that were significantly better but which did not add greatly to the cost. So I decided to adopt another approach. You can find the full details of the new design at

http://www.audiomisc.co.uk/ HFN/HeadDAC2/ HeadDAC2.html.

To arrive at the finished design I used a sneaky trick. This was to base the circuit on an existing 'mini kit' - the Velleman PMK136 Super Stereo Ear Kit - which can be found online for less than ten quid. The Velleman comes with its own printed circuit board, all the components needed and instructions. The locations of components are marked on the board. Follow the instructions and you are able to assemble the Ear Kit as if you are 'painting by numbers' - even if you don't understand how the circuit works. For my purposes I simplified the circuit and used just some of the components supplied. If you're looking for 'high-end' performance then I have to admit that the new design - which I call with stunning originality the 'HeadDAC2' - certainly works well but probably won't win any

prizes. That said, as with the earlier design, I've been using it very happily with various brands of headphones. Once built, it may even prompt the budding DIY-er to experiment with improving its performance. For example, I used the standard cooking-grade components that came as part of the cheap Velleman kit. But it may well be that swapping these for audiophile or high quality components, or investigating some simple tweaks, would deliver even better results. In that sense it isn't meant to be a finished product or project, just a useful starting point for anyone who'd like to learn more about how audio equipment works, or see if they themselves can make something that reproduces sound. One of the real pleasures of engineering is being able to make things that perform a task you want done.

SAFE PLACE TO START

A headphone amp can be powered by batteries, or even via a USB connection so, as a starting point and a practical way to gain experience, it's also much safer to build and use than something like a valve power amplifier. The only real risk is that you may find you enjoy engineering and being able to explain to friends and family how things work. Oh, and that you made what they are listening to!