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Japanese silicon heart
At the heart of the Transporter ticks the so-called 'Miracle DAC' AK4396 by Asahi Kasei Microsystems Semiconductor. It is "a true 192kHz 24-bit 2-channel DSD-capable D/A converter with AKM's advanced multi-bit architecture to achieve a virtually flat noise floor up to 80kHz. The signal-to-noise ratio in the 20kHz band extends to 120dB. In addition to excellent anti-jitter characteristics and a 256-step linear attenuator, the switched capacitor DAC incorporates AKM's unique low-power circuits. This maintains performance while reducing power consumption by 47% compared to the AK4393."


Flemming Rasmussen's Gryphon Mikado uses AKM DACs. With AKM's latest-gen 32-bit 4397 DAC, so does Esoteric in their new D-05 converter. As does Alex Peychev in his Esoteric-based, massively paralleled APL Audio NWO universal machines. In August of 2006, Peychev clarified that while "the Transporter has one physical DAC, it equals two DACs per channel. Each AK4396 (which is the current top-line AKM 'miracle' DAC) has two outputs per channel. One is 0 and the other is at -180-degree, aka differential or 'true balanced'. Since the Transporter uses both outputs of the DAC chips, this equals 2 DACs per channel. Being AKM's flagship part, this DAC has up to 10 times less out-of-band noise compared to anything similar on the market today. It also has the capability to accept a 216KHz sample rate while keeping the same digital filter oversampling rate and the same speed of the modulator."
Richard Kulavik of AKM Semiconductors explained it this way: "This DAC is a large departure from other delta-sigma DACs designed by us and others like BurrBrown, Analog Devices and Cirrus Logic. The AK4396 is an entirely new modulator, pioneered and patented by AKM. It achieves something unique. In the past, many of the old Phillips and BurrBrown parts were R-2R* based products. These older products were looked upon as some of the best. One of the reasons was high frequency noise. In older R-2R parts, HF noise
was not present. In all delta-sigma parts prior to the AK4396, everyone has fought HF noise caused from the delta-sigma modulator with the insertion of large filters and other parts to attempt to solve a problem created by the delta-sigma design. The AK4396 today effectively does not suffer any modulator-induced HF noise and is over 60dB better than the nearest Cirrus and BB devices. All of this HF noise can cause many audible artifacts downstream. That is the 'miracle' we believe is making the difference today. This part gives you the performance and linearity of a delta-sigma device with the noise performance of an R-2R part, something that was never previously available." (In the professional markets, AuzenTech's X-Meridian 7.1 and Sondigo's Inferno sound cards for example each run four AK4396s "for DVD-A/SACD level fidelity for professional audio applications.")
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* From the Wikipedia: "A resistor ladder or R-2R is the most simple and inexpensive way to perform digital-to-analog conversion, using repetitive arrangements of precision resistor networks in a ladder-like configuration. High performance R-2R networks may be printed directly onto a single substrate using a single film, making the resistors share similar electrical characteristics, and may be laser trimmed to provide increased precision."
American applause
Suffice to say this is serious silicon; serious enough to score highly with experienced reviewers even with the stock op-amp output stage. Doug Schneider, publisher of the SoundStage Network, awarded the Transporter Product of the Year 2006 for their SoundStageAV section. He concluded that as a DAC, it performed in the same league as his favored April Music $1,650 audiophile Stello DA220 Mk.II DAC. He could not reliably tell apart the Transporter's wireless streaming capabilities from spinning discs on a CD transport feeding the Korean converter.
By February 2007, Stereophile's Wes Phillips had caught up with the Transporter. Performing equivalent comparisons, he gave playback over his personal $5995 Ayre C-5xe universal player the nod but found its lead narrower than anticipated. Commentary from John Atkinson's test bench confirmed how the Transporter delivered true measured 20-bit resolution at 24-bit word length. "Not only did the Transporter offer superb measured performance in the digital domain, it also did so in the analog domain... despite it receiving data via a WiFi link, and despite its relatively affordable price, Slim Devices' Transporter offers state-of-the-art D/A converter performance." With this review, the Transporter earned Stereophile's prestigious Class A rating.

A year later now, both Alex Peychev and Dan Wright have adopted the Transporter for their respective modifications. This invites heated conjecture. How much better could this machine still be made over the accolades it has already scored? As a product conceived for audiophiles, the Transporter handles attenuation in the digital domain -- presumably over the AKM DAC's native 256-step function -- but does couple that with variable resistor gain settings. Those are selectable via internal jumpers to minimize resolution decimation. If you run the Transporter amp-direct, pick the resistor setting that makes the output just slightly louder than you want (max output is 2.5V). By trimming the small difference digitally via remote, you remain above CD's 16-bit encoding resolution.


The Transporter's internal CPU works with Slim Device's software-based flash memory processor. It loads on demand and decodes compressed files for wireless 24-bit PCM transmission. Hard-drive data are automatically converted from 'computer' to 'audio' files. The Transporter's firmware updates itself automatically if connected to the Internet, just as AVG or McAffee virus protection programs self-update. Because Sean Adams, the visionary leader of Slim Devices, is a big proponent of open-source development, the large community of Slim users can freely share custom features. This flexibility allows the Transporter to go where no audio component has gone before. The cool industrial design of the Transporter's casework and remote is by Fred Bould by the way, the same gent previously responsible for the Slim Devices Squeezebox.
ModWright/Emerald Physic/WyredForSound exhibit at CES 2008
If you're averse to running your PC during audio sessions, a NAS server (short for Network-Attached Storage device) can connect wirelessly or via Ethernet link to your Internet access router to uplink to Slim Device's meta-data library (CD recognition for artist/title/track names) to tag your files. The NAS server then distributes music files wirelessly direct to your Transporter while your PC remains turned off and out of the picture. For our review, Neal Van Berg's Music Vault stands in for this type of device. If you're leaning that way, questions on which NAS device to choose include the following (kindly provided by our resident IT specialists Marja & Henk):
  • which OS runs the NAS (Windows Storage Server, a Linux variant, other)?
  • does it include RAID for increased reliability? Raid 5 is the preference, requiring a minimum of 3 spindles. Four 250GB drives will net out 650GB free storage in a RAID 5 config
  • what is the read/write speed and how noisy is the internal fan?
  • how about fragmentation - since music is sequential, fragmentation can become a problem when disks fill up or if regular deletes/stores occur
  • what backup strategies are employed?
  • what ripping strategies are employed - read until right; bus structure for CD drive (shared bus with discs or 'private')? Does the ripper add tags? From which data base? If not (non-mainstream eclectic music might not be recognized), how can one add tags?

Marja & Henk then suggested the following links to help newbies get a lay of the land:

  • Wendy Boswell, Lifehacker's Weekend Editor, writes on setting up a Squeezebox and the various options you have for where to store your music files (since you don't store them on the Sqeezebox or Transporter)
  • AboutCom's primer on network-attached storage devices
  • Wiki's Beginner's Guide To Servers
  • The Slimserver 6.5.4. download link

For some early user as well as fence sitter feedback, refer to Sidebar 1. If we extrapolate from their responses, we arrive at the following key points:

  • earlier stock Slim Devices products were sonically outclassed by traditional affordable CDPs
  • modified SqueezeBoxes became sonically competitive with affordable CDPs
  • one reviewer found the stock Transporter virtually indistinguishable from a superior standalone DAC of April Music Stello caliber while another preferred his Ayre C-5xe by a lesser margin than anticipated. Stereophile's measurements gave the stock Transporters an extraordinarily clean bill of health
  • first owners of the ModWright Transporter find it to be marginally better than the ModWright Denon 3910 which has been very favorably reviewed as being competitive with $5000 to $10,000 RedBook machines
  • Everyone exposed to the Transporter is thunderstruck by Slim Devices' functionality. They report rediscovering their personal software collections while exploring free new music via Internet or XM radio
Sidebar I: As the very first mod-righted Transporter owner, Ted_b had this to contribute: "I'll start being that I was the first one to receive the Modwright Transporter and did some bug fixes with Dan along the way (Dan is incredible when it comes to the whole beta test/feedback/fix loop). I am a long-time Modwright user, having owned his SLW 9.0SE, his Platinum Sony 999ES and now own his LS 36.5 pre and the Modwright Denon 3910 universal. The Modwright TP is not my first foray into PC-based music nor even my first Transporter... continue

If we extrapolate from this extrapolation, we might conclude well prior to any listening that even if the ModWright Transporter were to be outclassed by truly upscale traditional disc spinners, the flip side of actually listening to all of the 2000 CDs in one's collection via streaming -- versus spinning a bare 100 of them on a regular basis -- should completely rebalance the scales. Needless to say, we expect more from reviewers than secondary evidence. Thus far, we've merely established background...