Audio Blast: B.M.C. PureDAC and PureUSB1 Active USB Cable

Help From the PureUSB1 Cable

The first system I assembled with the PureDAC was as follows:
Mac Mini using iTunes using a Clarity Cable Organic USB connection to the PureDAC, Clarity Organic ICs from the PureDAC to the Pass Labs X600.5 Monoblock Amps, and a double bi-wire speaker cable set of Clarity Organic Speaker Cables to the Vapor Audio Nimbus White speakers recently reviewed. These big block amps had vast headroom and a seemingly endless soundstage. With the PureDAC, however, they were not warm and full. This was a combination that impressed with dynamic capacity rather than tonal accuracy.

Big sound pieces shone brilliantly with this rig, and I relished James Horner’s score for The Perfect Storm, as well as selections from Oleta Adams’ Circle of One, which evoked memories of hearing her powerful voice in concert. In this fashion the commanding power of the PureDAC with the X600.5 monos was unassailable. By exchanging the interconnects and power cords for the Silent Source “The Music Reference” series I was able to smooth and darken the mood such that I could play at a slightly higher listening level with less treble “spikes” assaulting my ears.

If confronted with a system having too much mid-high to high-end energy much of it can be ameliorated by swapping the USB cable. I had on hand the BMC PureUSB1 Cable that had just arrived for review, and this active USB device fairly torqued the Pass amps into better tonal position. They picked up an unnerving amount of low-end heft and mid-bass presence as heard through the Nimbus White; all this from a $300 USB device! It reinforced my caution that one run through with a component can never reveal its extent of capacities.

I have not been terribly impressed with cables having passive electronics inserted into them in the past. After assessing several of them early on in my reviewing career I changed my initial assessment and have since declared them as a group to be not as efficacious as straight wire, their principle shortcoming being occlusion of microdynamics in an attempt to increase macrodynamics.

The PureUSB1 is a hybrid product, a combination of USB correction device and cable conjoined. It differs from cables with passive electronics by incorporating an active, i.e. powered, device. BMC describes the PureUSB1 thus, “…an active electronic circuit restores and reshapes the digital USB signal just before entering the DAC. Beside this it filters the noise on the USB power supply. This solution provides a better USB signal and ultimately sounds better.” Thus, it is more akin to a hybrid cable than those incorporating passive networks.

The effect of adding the PureUSB1 was not dissimilar to the use of passively networked cables. There was a noticeable diminishment in absolute definition; however, spatial-soundstage characteristics were improved, as well as overall heft, or weight, of the system. Immediacy was enhanced, making the PureDAC sound more intense and assertive. In this instance my ruling is that the PureUSB1 is worth considering for those who want to improve macrodynamics and impact over seeking out every last bit of detail. Note that definition can be found in many places in a system, from the source to the speaker cables, so a minute loss of this in the active USB cable is not fatal to establishing a premium sound. I would encourage those especially with smaller systems or bookshelf speakers to try the PureUSB1.

How About Adding A Passive Preamp?

[Such a device is more accurately described as a passive linestage, or passive attenuator. – Ed.]

I like trying unexpected combinations of gear, as they often reveal surprising results. Would an audiophile typically reach for a preamp when the DAC contains a volume control? More than a smattering of enthusiasts with volume controlled DACs find that adding a preamp is preferable, despite the slight loss of definition, to not using one. The reasons typically boil down to a more massive soundstage and a greater sense of palpability and improved macrodynamics.

I would not have guessed, however, that the Teo Audio Liquid Preamp, currently under review, would revolutionize the sound of the Pass X600.5! Following the Chicago Axpona show Taras Kowalczyszyn of Teo Audio impressed upon me the necessity of hearing his preamp in my system, so I obliged. Prior to this time I had concluded the Pass amps were largely incapable of butter-melting warmth (figuratively, not literally), even after working extensively with the Music First Baby Reference transformer-based passive preamp. But the Teo Liquid Preamp brought out of them tones I had never heard before with Pass amplifiers. The richness level far outshone that of the XA160.5 Class A Monos when they were in my possession, and I felt they were tonally sweet at the time. The insertion of the passive preamp along with the digital volume control of the PureDAC was unquestionably a boost to performance.

Replaying Horner’s Perfect Storm I could feel the swell of the ocean with the pulsating of the strings, a majestic, terrible mood growing – and myself grinning from ear to ear! Oleta Adams’ “Circle of One” captured the power in her resplendent Alto voice, reminiscent of that night my wife and I heard her live. It certainly is not a proper conclusion to make a swift judgment and say the PureDAC eliminates the need for a preamp. The X600.5 vastly benefitted from the Teo, and I encourage Pass Labs owners to turn an eye toward Teo Audio.

I have saved the best and most surprising information about this combination for last, because it didn’t start out all that great. What really made this combination of gear shine was the interplay between the Teo’s passive preamp volume control and the digital output level control of the PureDAC. According to high-mucky-muck audiophile theory the proper way to use a combination of volume controls – truly, the best is to avoid two of them, we all know – is to run one wide open and attenuate with the other. I tried both permutations of that, and was not happy. The result was a diminished clarity and still too much high-end energy with insipid low end.

Just because someone tells you how to run volume controls, do you ever try otherwise? I’m sure glad I do, because despite it not being accepted audiophile protocol, lowering part-way the output of the voltage-controlled level of the BMC brought an embarrassing wealth of richness to the system, perhaps similar to the light switch in a room being replaced with a dimmer switch, allowing for a nearly infinite progression of mood lighting. I assume this is due to the Current Injection function of the PureDAC, which influences the volume as a function of the voltage. In this way the PureDAC seems to have a very pure, direct variable tonal and definitional influence upon the attending preamp, and hence the system, based on where the volume control is set.

I rolled back and forth individually both the BMC’s and Liquid Preamp’s volume controls until I settled on the PureDAC at about 45 (of a top end of 66) on the digital meter, and the Liquid Preamp dialed back four notches from wide open. With the Liquid Preamp full open I had a background electronic hum no matter the speakers used, most noticeable through the higher efficiency Daedalus Ulysses. But when I scaled it back and brought up the PureDAC’s volume it was nearly unheard. Since the Liquid Preamp has no remote function, I left it at that setting and controlled the listening level via the PureDAC’s preamp function. One might suggest that doing so would vary the previously mentioned tonality and definition, but moving the level up and down only 4-5 digits from my preferred baseline volume did not have an undesirable effect. If I wanted to change the range for different speakers, I simply revisited the setting of the Liquid Preamp and adjusted the range of the PureDAC’s volume accordingly.

Here was a means of absolutely contouring the system! In keeping with my Law of Efficacy, which readers of my articles over time have become familiar, this was not a subtle change. I do not accept subtle changes, but demand sweeping improvements, or else I consider them unworthy of my time and dispense with them regardless of cost and pedigree. In this instance I could bring the precise amount of weight, dynamic energy, tonal richness, clarity, etc. to the X600.5 monos, and more importantly, to the inimitable Nimbus White speakers. This rig rocked, hard and beautifully, with tracks from classics like America’s “Tin Man” and “Horse With No Name” to Seal’s “Love TKO” and Pablo Cruise’s “I Go To Rio.” I often listen for the “realness factor” of the opening of the latter piece; a rotary phone rings at an intermediate distance, and way back in the soundstage a muffled voice suggests someone get the phone. Up until a year ago, even though I was putting together very fine rigs I had never heard the voice in the distance. Now, I could nearly make out the phrase, though the wording is wretchedly indistinct. At this point with the systems I build I can hear the inflection in the voice rising, indicating a question.