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

Leveraging Advantages

It’s noteworthy when a component utilizes a technological advancement, but when it is paired with a nouveau application which leverages the former it’s a big win for the audiophile. Such is the case with the PureDAC, as it has a powerful tool, DIGM, or Discrete Intelligent Gain Management. It is but one of the systems in operation inside the PureDAC which contribute to its excellence.

The beauty of design is fully realized when functionality is streamlined while yielding superior performance. I am in awe of the system of systems contained in living creatures, the beautiful integration of operational functions! I remember once seeing an X-ray image of a 1/32” Tarnished Plant Bug; at one glance it was obvious that this Lilliputian creature was vastly more complex than anything humans have ever created! On a much more humble scale, since my teen years I have obtained joy from putting together a network of boxes and wires to create an ineffable musical experience. For me reviewing is an extension of that fascination. Thus, when I behold a component which gives me a distinctly audible advantage in building an audio system, and which accomplishes this more elegantly and inexpensively than conventional methods, the designer wins my admiration.

So, then, what’s so great about this DIGM anyway? Carlos calls it, “…a new approach for replacing a lossy volume control.” At the heart of it lies a DAPC (Digital Analogue Power Converter) that affects the volume of the headphone section and the main DAC’s output. From the Owner’s Manual, “… the headphone amps’ voltage is generated from a special type of I/V converter, which is an integral part of the DAC. Eliminating an entire amplification stage results in a shorter and cleaner signal path… the PureDAC applies BMC’s proprietary CI (Current Injection) circuitry for a virtually lossless current to voltage conversion… the CI stage provides very low distortion and very high stability without the use of a negative feedback loop.” When you can obtain the same goal with loads less circuitry the result is musical intimacy that touches the soul in a deeper fashion.

To that end BMC has done away with the preamp, that is, the typical preamp, and replaced it with a function. In other words, a slew of circuitry normally thought necessary for contouring and controlling the signal has been replaced by an operation performed by the DAC. Rather than using a fixed I/V the PureDAC makes it variable, so that the volume can be set without additional circuitry. A huge benefit to headphone users is that the PureDAC is optimized for a wide range of headphones.

Carlos explains it: “The Current Injection absorbs a source signal current (e.g. DAC output) and cleverly routes the original current in a way that the output voltage is made from the original current and is therefore virtually lossless. Any OPAMP or standard feedback amplifier replaces the original signal by a ‘copy’. We consider it natural to keep the number of copies as small as possible for preserving musical quality.”

How unique is this solution? BMC calls it a “Load Effect Free” circuit claimed to be even more linear than a class A stage! Because it delivers the signal current and voltage from two separate sources phase independent it can drive complex loads with ease. Did you catch that? Cleaner than a class A linestage and able to drive a load with a wicked impedance with ease! Audiophiles have been searching for the Holy Grail of sound for decades, and some would consider this a good candidate. Class D amplification was supposed to give it all to us, prodigious power and rich tonality, but by and large it has failed, though later generation Class D is making strides (and charging the customer plenty!). But here is a leveraged technology bringing three virtues of the High End together; extreme cleanness, ultra-short signal path, and the ability to drive inefficient speakers easily.

There is much more to the technological prowess of the PureDAC’s design, but this is enough to paint the portrait of a component that has the power to revolutionize how DACs and preamps are designed. I believe the hybrid DAC/Preamp has the power to shift the playing field in terms of the types of components audiophiles will consider when building a rig. For years the SET/HE (single ended triode amp/high efficiency speaker) crowd has been smug in their assuredness that no solid state products can touch the pristine character of their low powered tube amps, because said amps are simpler. Well, that was then, this is now, and innovations like DIGM and CI are game changers. Now, the purity that has been crowed about by SET enthusiasts is available to non-tube fans blessed not only with copious amounts of power but every bit as clean sound. The efficacy of the PureDAC is such that one can take any number of fine solid state amps, pair them with the PureDAC, and have an excellent chance of coming out ahead of a traditional DAC/Preamp/Amp combo, even when that combo involves a low-power schema.

This is the benefit realized while using only the PureDAC. Consider the leveraging upon leveraging which can be obtained potentially by the use of the upcoming BMC PureAmp, which will incorporate the Current Injection technology. The BMC Link between the PureDAC and PureAmp will allow the amp’s DIGM to be controlled by the PureDAC such that the amp gain and DAC output are always in optimum relation. Carlos says simply, “It is just a better way of operation for no extra cost.” I will be exploring that claim and reporting on it in due time as the PureAmp arrives.