Alien DAC + Chu Moi = Headphone bliss in a box

Regular listeners will know that I'm always searching for high quality headphone audio. In the past I've built a CMoy amplifier and an Alien DAC USB audio device.

Yeah it's a bit rough but it fits nicely under my computer monitor.

It was time to put them together in one box and dispense with the excess wires.

I started with some 0.5mm sheet aluminium:

Marked out to make a box 50mm x 100mm x 100mm. It was cut with tin snips and simply bent over the edge of a bench by hand. The sides were joined using angle aluminium stock drilled 4mm and tapped.

For now I'm powering the amp on 12V supplied by an external AA battery pack with 8 cells. Can't wait for GreenPlug to arrive..

I thought I was doing the right thing choosing metric screws but even in a metric country the range is severely limited and I've had to saw off the rather long machine screws I got.

This is not a bad way to make a small project box. Even 0.5mm aluminium feels pretty rigid with the help of the angle stock.

Sounds great with my HD560s by the way.

Rough guide to surface mount soldering

I share an interest in good quality headphone audio with many including Alastair who purchased the board and parts for the Alien DAC. Not being too confident with the soldering iron he made a deal, he bought two sets, one for him and one for me, if I'd help him construct his one.

Surface mount components are either tiny themselves, like the resistors and capacitors, or if large, they have pins that are very close together and hard to avoid having the solder bridge between them. The move to computer manufacturing with surface mount components is unfortunate for us home constructors. Some parts are only available in surface mount packaging and I fear for the future of this fine past time.

I got both boards going and thought I'd share my tips on construction, which you can see from the image are not too good, but serviceable.

For the chips with many pins, hold down the chip with the point of angle ended needle nosed pliers (the weight of the tool will hold it in place - hands shake too much), tack solder one corner pin and one on the opposite corner, then remove the pliers. Just flow solder across all the pins on each side, then go back with fine solder wick and suck back all the excess solder.

For resistors and capacitors again use the point of angle ended needle nosed pliers to hold them in place while soldering one end.

I think I'll put my new audio output device in a nice box along side a powered amplifier as covered in the past. Thanks Alastiar for the bag of bits!

Tracks for evaluating Hi Fi

Headphones and the amplifiers to drive them have become a bit of an obsession around here. For me, Alastair started it here for me. 

Clearly my hearing is not as good as it was when I was in my teens but there is a visceral pleasure in high quality audio even now.

Not all music shows it up and here is a little list of tracks I use to evaluate a new amplifier or headphone. It doesn't mean that these are particularly Hi Fi tracks, just that I know them and they reveal the differences for me. YMMV.

• Jean Michelle Jarre, Equinox Part 4
• Ry Cooder, Bop Till You Drop, I think it's going to work out fine.
• Eagles, Hotel California, Hotel California - not really Hi Fi but so familiar that I can pick difference easily and hear the bad edit in the middle
• Keith Jarrett, The Koln Concert, Part 1 (well any part really)
• Dire Straits, Love Over Gold, Love over gold
• Music for the Funeral of Queen Mary, John Eliot Gardiner; Monteverdi Choir, March 1
• Steely Dan, Remastered: The best of steely dan then and now, Hey Nineteen
• Talking Heads, Stop Making Sense, Psycho Killer
• Eric Clapton, Unplugged, Tears in Heaven

Hmm, maybe this list reveals something about me rather than Hi Fi evaluation. Anyhow, it's my little list for what it's worth.

Chu Moy Headphone amp PCB design

I've built a number of Chu Moy design headphone amplifiers over recent months and recommend them so highly to friends I end up giving them away. Previously written up here.

Ugly construction is fine for one or two off, but it was time to try manufacturing a printed circuit board.

When I last made a printed circuit board, it was done photographically, by exposing a chemical resist to ultra violet light. Having just dismantled my dark room, it was time to try a different technique.

I used some blue "press-n-peel" transfer film. The design was done manually in OmniGraffle, printed on the film with a little HP laser printer, ironed on to the board on a wool setting, etched and drilled all in a couple of hours.

This technique works pretty well, I've had a little trouble with the ironing phase, the transfer moves a bit when I iron it on. On one occasion I had to rub off the bad transfer and iron on again. The instructions say to set the iron to polyester, but our iron doesn't have it so I set it to wool.

The actual circuit for this board uses two OPA134 amp chips (rather than the dual chip) and a TLE2426 rail splitter. I don't include any volume control as the device driving it, generally a computer or digital player has one.

I present here revision 2 of a PCB design. It works but could be more compact and has two links. PDF here, OmniGraffle source here. Note that the writing will be mirrored on the copper side when you make it. (I haven't figured out how to mirror text in OmniGraffle..) 

You are free to use these for any purpose. (Let me know if you improve it).

Be careful that your printer is close enough to 100%, I suggest test printing and lining up the 8 pin IC which is the only critical spacing.

ITunes feature creep getting out of control

iTunes started out as a fantastic tool for organising, searching, browsing and playing digital media files. The ability to browse by genre, album, date added and so on, was a revelation to me - and it was really fast too.

But now, iTunes has changed so much the name doesn't even suit it any more. 

Here's my list of features that have ended up in what used to be iTunes:

• Update firmware in telephones
• Purchase electronic books
• Synchronise calendars
• Monitor RSS feeds
• Share music on the local network
• Burn CDs
• Enforce parental controls on content
• Backup phones and one model of iPod
• Movie rentals soon too?

Does this sound like feature creep to anyone else?

When Apple created iSync and the whole Sync Services concept, it sounded like we would get a single place for doing that hard task of synchronising our computers with our portable devices.

Of course it's more extreme on Windows where an install of iTunes also installs QuickTime, I think they should extend this software beach head and also install Safari 3 (weird how it's still a beta even though Leopard has shipped).

It's easy to be a critic, so here's what I'd suggest:

• Split up the iTunes functionality, give us back that simple media player with fantastic slicing and dicing features
• Create a "device manager" that is responsible for talking to devices, including media players, Apple TVs, phones, cameras, tablets, and doing the syncing that needs to be done.
• Put the iTunes store on a web site and just make it part of the general excellent Apple online store experience, sure you can link from tracks but don't make me shop inside that little box.

iTunes must be well overdue for a re-write, I still see the old watch cursor from classic days so my guess is that it's still a carbon app - that must be a nightmare code base to work on!

There's no doubt that the iTunes team has been the first to show us new user interface features that have ended up in the OS: smart folders, live search, and now coverflow. That must be a hot team, but I think it's time to split up and focus.

Ultra high quality headphone amplifier

I read Alastair's post about high quality headphones with great interest. 

After finding the excellent Headwize site, I rushed down to Jaycar this morning for bits, and built the cmoy headphone amplifier (in an Altoids tin, with space to spare, as shown above right).

What really got me was the data sheet for the OPA2134 operational amplifier from Burr-Brown which says, in part, "The distortion produced by OPA134 series op amps is below the measurement limit of all known commercially available equipment."

Further: "THD+Noise is below 0.0004% throughout the audio frequency range, 20Hz to 20kHhz".

My experience.. 

• This is easy to build. I did a hack job, as you can see above, and it worked perfectly first time.
• I'm driving Sennheiser HD 212Pros.
• Ripped some CDs at AAC 256kbps as sample content.
• iPod shuffle has noticeable hiss
• iPod 30Gb has less noise
• Switching the headphones between the iPod direct and via the amplifier makes the iPod sound relatively dull.

It's hard to explain, but this little amplifier gives a real sparkle to the sound. It's not artificial or boosted in any way, but things like cymbals sound quite different - better. Sometimes there is too much bass for my liking.

Other notes:

• Jaycar don't advertise the OPA2134, I went to buy the NE5534AN which is in their catalog and they gave me what I really wanted as a substitute - excellent! (AU$3.95)
• This chip is broadband, when I touch the input it picks up all sorts of hum, I expect that it will be susceptible to RF from things like mobile phones and will need to be in a well shielded box (Altoids tin for example) with filtering to avoid picking up hash.
• I used "ugly construction" which works well for RF projects so it's probably pretty stable as it's all ground plane.
• Didn't bother with gain control as I figure whatever is driving it has it's own volume control. Mine has a bit too much gain for my listening levels.

So, one more thing to carry on the train.. thanks Alastair.

Update

I've spent a very entertaining evening re-importing some of my old favourite CDs at 256Kbs/AAC and of course listening to tracks in different headphones. There is a story around about how your brain works harder listening to music which has been compressed for space (no, not level - that's another topic). Basically masked parts of the audio are removed to reduce the data rate, but in fact you miss those parts of the signal and have to imagine them yourself.

In my youth I was very interested in "hi fi" and well remember the arms race that would follow the upgrade of one component in the system: a new moving coil cartridge would show up the noisy amplifier, upgrading that would show up the speakers, and so on.

Recent years have seen my music move totally on to computers and mostly in to headphones. Loud speakers are always a compromise existing as they do in a room that resonates to some extent. Little computer speakers have advanced tremendously in recent years and work damn well at low level. Headphones can reveal detail and texture in an audio track that will be missed on even the most high end speaker system.

With the falling cost of storage it's now time to re-import my CD collection at a higher bit rate - or perhaps I should just bite the bullet and go loss-less at last.

Update 2

Hmm, not sure if the higher bit rate AAC is worth it for me. I created this test which chops back and forth between 128Kbps and 256Kbps every ten seconds and I can't tell the difference. Of course I'm getting old and probably not listening in the best equipment.