![[SoundStage!]](../sslogo3.gif) D-I-Why & HowBack-Issue Article |
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January 2008 DIY Paradise USB Monica Digital-to-Analog Converter
As is often the case, however, the DIY world was well ahead of the mainstream curve and do-it-yourselfers have been enjoying the benefits of PC audio -- on the cheap -- for quite some time. Now, before anyone sends me e-mail questioning my sanity, let’s be clear that we are emphatically not talking about audio reproduction based on the typical computer sound card, mangled MP3 files, or an iPod dock. What we’re dealing with here is honest-to-goodness high-end sound for ridiculously low cost. If you have a computer (and you must because you’re reading this) and a USB port, you’re already two-thirds of the way there. For the past two years, my reference digital source has consisted of a low-end laptop computer, a Hagerman Technology HagUSB (which converts USB signals to S/PDIF) and an Audio Note Kits DAC 2.1. This combination has proved to be very satisfying -- much better, in fact, than my Roksan Kandy player mated with the DAC 2.1. You can't play music from your computer unless you upload (or download) it first. To rip bit-perfect music files to hard drive I use the renowned Exact Audio Copy (EAC). This easy-to-use wonder does a fantastic job of pulling every last bit off Red Book CDs and is the standard by which all other rippers are judged. On my system, playback is handled by the equally well-known Foobar2000 (FB2K). It isn't the most user-friendly software, but I can't argue with the growing consensus that it is the best-sounding player available. And now for the best part: Both programs are absolutely free. Operating systems can be an issue. Windows XP routes audio through a nasty bit of work called the K-Mixer, which is effective at dramatically reducing sound quality. Not to worry, though, because a free utility, Asio4All, bypasses the K-Mixer and keeps the signal clean. Ubuntu, the easiest-to-use Linux variant, does a nice job with music files and (to my ears) has the edge over XP/Asio4All. A huge downside to Ubuntu is that it can’t run EAC. The new Windows Vista was reportedly designed with high-quality audio in mind, and the K-Mixer is no longer part of the operating system. I’ve been using Vista for a few months now and though I don’t like the sound of the new Windows Media Player, the audio subsystem is definitely superior to XP's. Vista and Foobar2000 are a great match. Of course, we’re not here to discuss computer audio per se, but the DIY Paradise USB Monica DAC. Monica (named for Italian actress Monica Belluci of The Matrix fame) is a tried-and-true digital-to-analog converter that has garnered ardent fans and acclaim over the past few years. DIY Paradise proprietor C. W. Yeo doesn’t rest on his laurels, though, and his original Monica has been tweaked, modified and massaged through four generations. The latest variants, Monica 3 ($375) and USB Monica ($145 USD), add a new gain stage, designed by Rudolf Broertjes, which addresses the rather low output level of the previous-generation Monicas. All versions of Monica have used the non-oversampling Philips TDA1545A DAC chip, which its maker describes as a "stereo continuous calibration DAC." Yeo’s loyalty to this little piece of silicon led to some sleepless nights as he worked to overcome a daunting technical challenge. You see, all existing USB receiver chips output the I2S digital format. That’s fine for some DAC chips, but if he was going to stick with his beloved TDA1545A, Yeo had to find a way to convert the I2S signal to the EIAJ format, required by the Philips part, without mangling parts of the signal. In Yeo's words, "I could have opted for the easy way out and just ask the USB receiver to output S/PDIF then use a S/PDIF receiver (like CS8414) to convert to EIAJ format. But my friend, this solution SUCKS big time. Sounds HORRIBLE!" How he got it all to work is between the man and his soldering iron, but the end result is what Yeo proudly proclaims is the first USB DAC using an EIAJ-based DAC chip. Take that, audio mainstream!
The USB Monica is a very friendly product for the novice DIYer. Because the circuit uses a number of surface-mount components, Yeo and his partners do all the stuffing and soldering in their workshop. What arrives at your door is a completely assembled, tested and calibrated DAC board needing only a power supply and a USB cable to become fully functional. The output stage is even trimmed to perfection, ensuring that both channels are at the exact same level. This is bespoke audio at a workaday price. The USB Monica continues the DIY Paradise tradition of employing high-quality parts. Capacitors are by Panasonic and Black Gate, and the sturdy circuit board has gold-plated contact points. The design has been massaged so thoroughly that the only tweaking option is the choice of a single or dual power supply. As delivered, the USB Monica is configured to use a single power supply for both the DAC and output stage. However, by clipping the lead on a single diode, the power rail of each section becomes isolated, allowing the use of a dedicated supply for each. I used two discrete power-supply kits from Dantimax: an 18-volt unit complete with transformer for the output stage (part 78l8PSUl) and a 12-volt supply using a spare transformer for the DAC (78l2PSU2).
The DAC's USB input connector comes pre-attached at one end of the circuit board, with the pads for outputs at the opposite end. The through holes on the pads are small, and anything larger than a 24-gauge wire probably won’t fit. Keep in mind that it’s a good idea to twist the output wires to keep unwanted interference at bay. I used 24-gauge silver hookup wire and a pair of silver-plated RCA sockets on the outputs, which worked very well indeed. Wiring up the USB Monica is an exercise in simplicity. The hot and neutral leads from the power supply are soldered to the board, and the left and right outputs are wired to their respective RCA jack. Connect the Monica to your PC with a USB cable and you’re up and running. Adding the second power supply means connecting two more wires. If only all kits were this easy!
A great aspect of USB Monica’s design is its tiny size -- as wide as a business card and maybe half again as long. Even with a couple of power supplies, this DAC will fit into a shoebox-sized enclosure. Placing the transformers away from each other, and from the sensitive DAC circuitry should be a piece of cake for most builders. I put the review sample in a spare chassis from an old preamp project. Yeo’s ready-to-play finished USB Monica ($300) comes in a lacquered box made of tropical hardwood, and includes an upgrade of four Black Gate non-polar capacitors (the lauded "Super E-Cap" configuration) on the outputs, versus the kit version’s single Black Gate per output. Skeptics might be wondering if something so easy to assemble can offer a major sonic payoff. I won’t keep you in suspense: Monica is Undoubtedly Sonically Brilliant. Yes, yes, I can hear you groaning, but I had to work it in somewhere. During the three months Monica replaced my Audio Note Kits DAC 2.l/HagUSB combo I never felt like I was missing a whole lot. Because both DACs employ "zero oversampling" and dispense with digital filters, it is not surprising that both also share an analog-like sonic character. There is a pleasant musical wholeness to the USB Monica that is the antithesis of the hard, sterile sound some vinylphiles associate with digital reproduction. Bass is tight, controlled and deep, with punchy notes coming through with their verve fully intact. Percussion is snappy, tight and just plain delicious. On poorer recordings, cymbals and other residents of the upper treble can be a little fatiguing at times, which perhaps indicates that USB Monica neither adds to nor detracts from the script. In fact, this DAC occupies neutral territory better than any UN peacekeeper, and she’s as transparent as a cold winter sky. Detail retrieval is excellent and not at all analytical. USB Monica’s musical abilities aren’t quite on par with the much more expensive Audio Note DAC, but certainly comparable to those of DACs or CD players costing many multiples of the asking price. Having the Audio Note DAC on hand actually allowed an interesting experiment, pitting the USB Monica and laptop against the Audio Note using NAD C521i and Roksan Kandy CD players as transports. In all cases, USB Monica and the laptop smoked the opposition. There is definitely something to be said for doing away with the CD transport mechanism. When both the USB Monica and Audio Note DAC kit were fed by the computer, the difference between the two came down to the USB Monica being excellent and the Audio Note exceptional, which it should be at around ten times the price. Bear in mind USB Monica’s low price of $145 (figure around $250 with two power supplies and RCAs), and her performance is almost miraculous. USB Monica is a stellar bargain. ...Colin Smith
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