Hello Everyone,
Josh from Sonicweld here (I designed the Diverter and build each one personally). There are a few points in this discussion I’d like to address.
First, to Steve: it seems rather cavalier of you to speculate that adding some kind of external supply to the Diverter would add $1k to its cost. You presume to know how I would accomplish such a thing and what my BOM would amount to.
Next, on the subject of a shootout - why impose all of your system restrictions on tpaxadpom? If you’re really confident in your product, allow him test it using whatever system configuration he desires and let the cards fall where they may. It’s one thing to ask, “hey, do you mind if I bring my DAC and cabling so I can compare using familiar equipment?” but quite another to require that many key variables conform to your own arbitrary wishes. If you were performing your own evaluation I would understand and expect that you’d want to use your own equipment, but I can’t see how this would enhance a shootout at someone else’s place or make the results more trustworthy.
For that matter, it seems to me that your very presence at such a shootout would skew the test outcome in the sense that you have an obvious vested interest in having the Off Ramp come out on top (which is fine and expected; I would feel the same way about the Diverter). Clearly, that agenda will be transparent to all the participants, and will thus exert some degree of pressure on them to see things your way. Perhaps I assume that others are too much like me, but I know I could never be fully honest in expressing my feelings about a piece of equipment if I had the designer of said gear looming over me. I would want to take my time with the evaluation, and conduct it in an environment as free of pressure and bias as possible.
Finally, in regards to the power supply and the incredulity of some as to why I continue to use USB power versus some kind of outboard solution - I’ve written at length in other forums on this issue (I think most heavily over at Head-Fi and computeraudiophile), so I encourage anyone who wants to read up on more of my reasoning to search out those threads. But I’d like to make a few additional points here, at the risk of being a bit redundant:
1.) I think there is an unjustified and unsupported level of paranoia about USB power quality. Such pronouncements are usually presented as axiomatic and beyond need of substantiation (“USB power stinks, that's all there is to it.”). Really? How was this collective wisdom achieved? Anyone who questions this oft-parroted canard is seen as daft or ignorant. Granted, I don’t spend much time on forums, but for as many times as I’ve seen this line of reasoning presented as irrefutable proof of the need for outboard or battery supplies, I’ve never once seen any of its adherents present measurements or other data to substantiate the supposed evil of USB power. I wouldn't advocate running an audio device from it directly in unprocessed form, but I have actually measured it on several occasions using a variety of computers, and I don’t think it’s nearly as horrible as most people make it out to be (and I posted some of my results on-line, if anyone wants to hunt for the forum thread). It is certainly addressable through good power supply design practices.
2.) The power supplies in the Diverter have enjoyed continual refinement; the supply that powers the most critical circuitry (namely the output clocking oscillator) achieves, to pick an arbitrary frequency, 133 dB of PSRR at 100kHz with a noise level of less than 1nV per root Hertz. Thus any power supply ripple at that frequency will be reduced by a factor of almost 4.5 million. To put this in perspective, let’s imagine that the USB bus power suffers from 500mV of ripple and noise, which is far higher than I’ve ever measured from any real-world computer. Knocked down by 133dB, this yields .112 *microvolts* even in this extreme, fanciful case. In the Diverter, this 133 dB noise reduction figure accounts for active suppression only, and does not factor in the considerable passive filtering preceding it, nor does it account for the PSRR of the load device itself, so the actual rejection of noise originating from the USB supply will be appreciably higher. My intent in citing such an example is not to engage in some kind of specsmanship, which I think is rather pointless, but to illustrate my view that the power supply is not an appreciable source of error in the Diverter. This isn’t to say that it’s perfect (no such thing) or that I won’t find ways to make it even better, just that I see no compelling reason to offer an external supply other than as a concession to market whims. It wouldn’t surprise me if I sold more Diverters if I offered an outboard supply, but I feel strongly about design integrity, and would never add a “feature” that I didn’t think had true merit simply to satisfy those who feel it should be present.
3.) It has long been my strongly held view that external power supplies have been and continue to be in vogue because they undeservedly give the impression of additional value via the presence of an additional “box.” This imparts warm fuzzies to both manufacturer and end user, but adds little in the way of actual technical benefit, and may worsen things, actually. Most insidiously, an external power supply gives the illusion of “isolation,” one of the golden comfort words for many audiophiles, even if few really understand what this means or why it is desirable. Ask yourself honestly: what exactly do you feel an external supply accomplishes? How does it accomplish it? If a device could be designed to perform at least as well or better without an external supply as with one, would you still want an external supply? If so, why? BTW, if your answer is “because it looks cool” I have no problem with that; I do have a problem with the idea that a power supply is always better simply because it is external to the main device or consists of batteries, a cold fusion reactor, secret alien tech, or whatever else you want to use as a power source.
Here is the reality of isolation: every USB to SPDIF converter I’m aware of which is capable of USB audio class 2.0 performance, mine included, relies on a galvanic connection to the host computer via a USB cable. Even if brute force attempts are made to provide “isolation” such as removing the Vbus and/or ground wiring (an abysmally bad idea in my estimation, but one which I’ve seen marketed as the key feature of some audiophile-oriented USB products), there is still an irreducible noise pathway from host to USB endpoint: the differential data pair. Far from preventing the noise from getting into your device, what this misguided technique accomplishes is to force a much higher level of common-mode noise onto the differential pair than would otherwise be present, where it can wreak all kinds of havoc (or in the case of an ESD event, actual device damage).
A far better design strategy, in my view, is to understand what the noise sources and pathways are and address those issues head-on, rather than throwing a band-aid like an external power supply at the problems. Sure, in the case of a device with a poorly-designed internal power supply, a very good external one may indeed improve its performance, but why not design things properly in the first place? This is a key reason why I designed the Diverter without the option of add-ons or upgrades; I strongly believe that designing things as good as I can make them from the beginning will always be preferable to some sort of after-the-fact bolt-on. Even if the external circuitry is absolutely world-class, there are still the mechanical and electrical weak points of cables and connectors. A very fast, low-noise, internal supply which is able to exploit direct, low-inductance ties to power and ground planes is always a superior solution. It isn’t as sexy because it seems inchoate, hidden away on an invisible circuit board, and is beyond the user’s ability to tweak and fiddle with.
So, if the USB device is never really isolated from the host, and state-of-the art power quality is achievable, what reason is there for me to use an external supply? Steve is at least correct in saying that offering such an option would increase the Diverter’s cost, but I don’t think it would increase its performance or provide additional value, and that’s why I don’t offer it. That said, there are third-party USB supplies on the market which can be used with the Diverter. I don’t think they’re necessary and I don’t recommend them, but I can’t stop anyone from trying them (provided they’re competently designed, the Diverter is well-protected against faults and they’re not going to hurt anything). In fact I have several customers who have tried such supplies with the Diverter, but I’ve never had anyone report that there was any positive benefit, and I’ve had a few tell me they heard no difference whatsoever. YMMV, of course.
Cheers,
Josh
