Outboard DAC solutions

Scouring DIY audio forums proved beneficial as I found plenty of attractively priced DAC kits based upon some of the most revered DAC chips available. The availability of USB to I2S and S/PDIF converter boards opens the doors to team commercial outboard DAC solutions as well as complete DIY kit builds to provide a high-end sound experience. DIY solutions are still confined to 16-bit 44.1KHz-48KHz resolution via USB due to hardware/software limitations in the DIY small scale market. It is expected that 2009 will see the availability of 24-bit USB to I2S and S/PDIF chips while Vista should provide native output support for these formats. For now, 16-bit resolution and two-channel playback is adequate for most audio seeing as practically all of our music is recorded with CDs in mind.

Two kits stood out from the pack and present complete solutions that are available in either a modular approach or a single PCB with all components in place to convert data from the digital realm to an audiophile grade audio output. The first is the Doede Douma USB to I2S converter. Doede's solution uses the Texas Instruments 2707 USB to I2S and audio out chip. The venerable TDA1543 is the centrepiece of this kit, favoring a purist mindset as it does not use any kind of oversampling of the digital signal. Audio output from the TDA1543 is configured to use a minimalist passive I/V approach with a final output of 0.6V, which may be a little low for power amplifiers that require higher input voltage to reach full output power. PCM2707 audio output is also available if required, although most people put its subjective abilities behind the TDA1543. Pricing options start at the €49 for the basic kit, while dropping an additional €29 will allow you to experiment with a low jitter master clock based upon a 12MHz VCXO from Tentlabs.

The best two features on this particular kit (aside from cost) are the asynchronous clocking that frees us of the sonic confines imposed by CPU and system loads at the USB end of things. Secondly, Doede does not rely on the USB bus to power any of the circuitry on the PCB. This leaves us with the chance to explore various low noise linear PSUs and batteries with relative ease. Either way, the sonic performance should be in excess of designs that rely solely on internal PC power. Also worthy of a mention here is that the I2S output allows us to try out various DAC kits in the future. For example, we could use the Doede kit solely to provide the USB to I2S conversion and proceed to add a separate I2S input DAC kit as an alternative to the TDA1543. This element of flexibility is especially important to me as I already have the outboard tube stage that I used to provide the audio zest from the Pioneer player. Most modern DAC chips available today feature balanced voltage or current outputs. In my case, a balanced voltage output DAC chip allows me to transplant the tube based audio output stage and enjoy its sonic merits at my leisure.

Doede's kit is available either pre-stuffed and ready to go, or with all of the thru-hole parts loose, leaving you to stuff the PCB and do the soldering. As the PCM2707 is an SMT device, it comes pre-mounted and pre-soldered regardless of the kit option you choose. I decided to purchase the kit without the thru-hole components soldered in, as I felt confident enough to tackle this element of construction myself. I must note that there are no part-by-part instructions supplied with the kit. However, basic instructions and pictures on the DDAC homepage are clear enough to provide a good point of reference should you wish to confirm device orientation or placement in some situations.

If you've never built or soldered a kit before you're best advised to go for the pre-built option at additional cost. Either way, you'll have to provide a suitable case to house the kit. Do make sure to buy a case large enough to house additional PCBs for discrete regulated power supplies or additional DAC boards should you get the bug to upgrade things later. Audio output from Doede's module is configurable via the TDA1543 or from the output of the PCM2707 chip itself. In either configuration, the audio performance is quite good, although the TDA1543 is clearly the better performer in most situations (there will be more subjective stuff later).

The Test System, Cont'd Twisted Pear Audio Opus
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  • phusg - Monday, December 15, 2008 - link

    > It'll please you all to know I have no plans to write another audio article.

    Doesn't please me at all Raja! As I said I'm very grateful for you opening my eyes to the possibilities of DRC. Shame you (or your editor?) don't fancy taking all the criticism and making a kick-arse follow-up article.

    All the best,
  • Rajinder Gill - Monday, December 15, 2008 - link

    I do have some work at hand that I've held back from posting mainly because it opens up another huge can of worms. The testing involved is arduous and takes up copious hours. I am in a position to make spectral measurements, although I need to confirm a few things before I'd even come close to disclosing all of the results. Initial tests show a marked difference between the 2 DAC's used in the article at equivalent levels of gain (between 1-3db at certain freq points). There's a pattern to some of it. Although, I can attribute much of this to noise generated by the amplifier due to the increased gain required by the TDA1543 (ac related hum). I have a few things I can do to cross-correlate those results though, so it's not a complete dead end.

    Blind testing has shown that human can discern down to .75db of gain. I'm not sure on the consistency of all of that as some of the blind testing involved in the research did show an element of placebo in places. Once I’ve eliminated some of the variables and more importantly tested an internal soundcard output in comparison, I might be in a position to post something worthy of reading.

    I'll probably blind test a few of the solutions I have at hand before I add anything else here though. It's very difficult to keep all camps happy, and to keep it interesting enough for me to want to commit more time to it all...lol

  • DorkMan - Sunday, December 14, 2008 - link

    Raja, sorry if I had the Sarcasm dialed up to "11" when I made my previous post. It takes a lot of work to create an article like yours, and you did a great job. My beef was not with the quality of your work but with some of the "religion" that seems to surround this hobby. Whether it's tubes, coaxial speaker wire, or whizzer cone transducers, there seems to exist a group of people with a religious zeal for these things and for whom specs and double-blind tests are irrelevant. Whatever.

    But I commend you for your article. It was well-written, and I have no issue with your conclusions. I, too, calibrate my video-editing workstation position for response flatness.

    If you're not too turned off by all the sniping, why not do a series on audio myths? Double-blind testing of tubes and solid-state, and speaker wires?

    Anyway, hope you have a great Christmas season.
  • audionewbieyao - Wednesday, December 10, 2008 - link

    If you're a true PC audiophile, I'll say do you best to stay away from gaming sound cards, 'cause they're just not made for audiophiles.

    I suggest try out Asus Xonar, Auzentech, Onkyo, and if possible, the new Xonar Essence STX would be the best.
  • thietavu - Tuesday, December 9, 2008 - link

    I have myself tried to solve this "problem" for years: to create a good quality audio system around my computer. Since all my CDs and even a few of my vinyls are now digitized into almost 100 GB of data on the hard disk, the challenge was to get some good sound out.

    I kind of made a mistake by buying "too high-end" (or too good anyway) headphones (Grado SR-325) and a headphone amplifier (Musical Fidelity X-Can v3). After trying two high quality studio sound cards (M-Audio AP2496 and later AP192), I realized that the sound just wasn't what it should have been. There was always a slight "harshness" in what I heard, making the system sound a bit unpleasantly cold and mechanical.

    After a long consideration I then bought Musical Fidelity's X-DAC v3 D/A converter, plugging it to AP192's SP/DIF digital output. That made the change. The slight but disturbing harshness disappeared and some originally cold-sounding albums (like Poco's Inamorata) suddenly became both listenable and even enjoyable. And excellent recordings now sound excellent.

    Where did the difference come from? Judging by normal measurements, there should be no audible difference at all, since M-Audio card's analog output is of high quality. To me, it appears like the "magic" happens in digital->analog conversion somehow. In cheaper devices like most sound cards, that conversion seems to be somehow "rough", a bit like using a digital camera with too few real megapixels available (imagine a 10 Mpix camera with bad optics etc, and the result becoming maybe equal to a real resolution of only 3 Mpix or so).

    I admit that the differences aren't that big, and only very good quality headphones or loudspeakers etc. can reveal them. But after it is revealed, music simply sounds more like "music" in one system compared with another. After that, it's unpleasant to go back to more "mechanical" sound. But as said, everything is relative. I can enjoy an old, noisy C-cassette in an old car stereo as well, as long as the music is good! That's what it is all about: creating feelings. :)
  • DorkMan - Monday, December 8, 2008 - link

    Sorry guys, I know many of you are really into this nitpicky level of Audio Purity. I've been into audio since the late 1960's, when I, too, was fanatical about specsmanship. Now I see the error of my ways.

    Bipolar loudspeakers have been around since, say, the 1950's. They're a decent solution as long as you can deal with room resonances, as this article does.

    But a whizzer cone speaker? When did we fall off the truck? Please tell me that the whizzer is driven by a separate coil subsystem. If not, you'll get decoupling resonances as various frequencies and these effects can change as the transducer ages.

    I went to the manufacturer website. Not embarrassed about selling speaker "ribbon" cable for $1,000? Tells me something about the company--long of PR and a bit short on electrical engineering.

    Okay, on to the amps. Tubes! The retro look! I have familiarity with tube amplifier designs and think it's great if you want odd harmonics near clipping, a bulky box that actually glows and a chance to heat a cold room at the same time. Hey, it's okay; odd harmonics sound nice--but they're not an accurate reproduction of the input signal.

    Finally, I'm all for balancing out a room--as long as the listener sits in the same spot. In a living room, every guest is going to get a different response curve, with some probably getting socked by boost when there should have been cut for that location.

    Finally, trust your microphone. If it says the room is flat, you're done. By putting in a slight bass boost, you're making the music sound good to "your" tastes, but be honest--the room then isn't flat. Might as well use tubes as amps.
  • ackcheng - Monday, December 8, 2008 - link

    Not sure if this is mentioned before, other than Audiolense, there are a few other programs we can consider for room correction

    They are DRC which is free http://drc-fir.sourceforge.net/
    and Acourate http://www.acourate.com/">http://www.acourate.com/

    I myself use Acourate and found it a very good tool for DRC!

    But I do not think the so called DRC in Windows Vista a real DRC software!
  • RagingDragon - Saturday, December 6, 2008 - link

    Certainly not what I expected at AT, but I enjoyed the article, and I'm OK with AT expanding it's range of covered topics (i.e. audio, digital photography, and home theatre).

    The DRC software is certainly interesting, though not really relevant to my setup (headphones). Based on manufacturer specs the TDA1543 isn't very impressive; however, the Wolfson WM8741 looks much more promising. The article's conclusions suggest the WM8741 has a wider dynamic range, flatter frequency response, and is more accurate/precise. Which is exactly what I would expect from the DAC spec sheets. I'd like to see these external DAC's compared to some high quality PC sound cards - like the Asus Xonar series, or even the M-audio revolution/stereophile cards (though if I recall correctly the DAC's in these and equivent cards from Terratec are inferior to the Xonar DAC's).

    I was looking at prebuilt external DAC's a couple months ago, and was extremely disappointed in what I found. Despite high prices most of them used cheap DAC chips which would have a hard time beating integrated audio, let alone a discreet sound card with high quality DAC's. The author's Twisted Pear Opus kit has a better DAC (WM8741) than *any* of the prebuilt external DAC's I looked at, and units equalling the Doede Douma kit (TDA1543) were ludicrously expensive.

    I'm not conviced that external DAC's and amps sound better than high quality PCI cards - and even if they do, I still don't want the extra clutter.

    Since I'm living in an appartment I use headphones rather than speakers to avoid annoying the neighbours, so the upcoming Asus Xonar Essence seems perfectly suited to my needs: stereo only (I'm using stereo headphones so surround sound is irrelevant), an extremely high quality DAC (Burr-Brown 1792A), built in head phone amplifier, swappable opamps, and "professional audio capacitors" (probably snake oil, but they won't make the sound worse).
  • prd00 - Friday, December 5, 2008 - link

    I'd pick Onkyo USB sound card up anytime compared to those stupid creative cards. I've tried all sound cards, but right now, I've ended with onkyo.
  • htgts350monaro - Wednesday, December 3, 2008 - link

    Thank you Rajinder for this, and what looks like will be, a great series of articles.

    Please be aware that despite all those who profess this to be an inappropriate article for this site that I, and I think many others, feel they are incorrect.

    Being an amateur audiophile and computer enthusiast myself this is a great mix of both my interests. I have been wondering for a while whether it would be possible to combine these interests and simplify my current combination of source components for my home theater system which I also use for critical 2 channel listening. (not ideal I know but limited space and budget regretfully denies a separate 2 channel system for me unfortunately)

    It looks like you may be on the path to solving my problem - please keep going with this. One thing I have gained from this article at least is a new interest in DRC software...

    For all thos who say that all audiophile claims are 'snake oil' I ask this - have you actually gone into a high end hifi store and LISTENED to any of the products available and done your own comparisons? Have you ever compared different DAC's/OP-AMP's in the same circuit and system with components of a high enough quality/resolution to expose those differences YOURSELF? I have and the differences can be VERY obvious, to the point that double blind listening is not needed - you would not need to double blind test two LCD's if one had half the contrast range of the other - you would be able to detect it quite easily and this can be true of audio components no matter how many tests say that the components measure the same frequency response/ dynamic range/ s/n ratio etc.

    But please go out and try it for yourself BEFORE you claim it is all bogus. (and no - not being able to hear a difference between components on your $300 minisystem or $50 PC speakers does not count!)

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