Associated Equipment:
Digital Front End
Amplification
Loudspeakers
Cabling
AC Conditioners
Accessories
 
Bel Canto VBS1 Virtual Battery Supply
and DAC3-VB
The Truth and nothing but...

 

 December 2009



 


One ordinarily doesn't begin writing a review before the product being reviewed is in hand. But in this case that course is justified. Let me explain. In recent months I've reviewed two audiophile power cords by the same manufacturer, and what LessLoss is after in their power cord designs, I believe Bel Canto is after in its Virtual Battery Supply (VBS1): the reduction of noise and noise products. Those reviews reiterated the idea that perceived improvements in the sound as a result of changing power cords stem not from changes in readily measurable standard parameters like frequency response, harmonic distortion and so forth, but from the removal of noise. Gross noise from all the electromagnetic garbage riding piggy back on commercial AC power. And subtle noise, the noise of electrons and photons making their probabilistic journeys in and out of reality, getting from here to there. Most of this noise is inaudible in itself yet is audible in its masking and distorting effects on the music, in detail, in timbre, in sense of presence. The empirical evidence is quite clear: as power source noise is reduced, music sounds more real.

And the sure-fire method of reducing power source noise to a bare minimum, a method superior even to purchasing the world's most expensive power cord, is to not use commercial AC power at all. Presenting, voilą: the battery. And that's what the Bel Canto VBS1 is about, delivering power like a battery while running off the mains. “[I]n the low frequencies,” the Bel Canto white paper states, “the VBS1 provides an even lower noise floor than a lead-acid battery.” How does it work? Does the power cord supplying the VBS1 make a difference? What does the VBS1 “do” to the sound? Perhaps most interesting of all: What precisely does inaudible noise do to the audio signal?

But getting back to power cords, what do you get for the hundreds, even thousands of dollars you can lay out for high-end power cords? Well, in my limited experience, what you may well get is astonishment that a mere length of wire can make a clearly audible difference. Plus some handy, provocative opinions such as, My new power cord made more difference than my new preamplifier, a statement designed to separate the believers from the nonbelievers. The issue of 'clean power' cannot be over-emphasized: it's fundamental, it's the foundation of the whole show. The music may go 'round and 'round, but it starts right here with the quality of the electricity. In a real sense what an amplifier actually does, particularly an analog switching amplifier, is employ the input audio signal to modulate the power source; other things being equal, the purer that source, the more linear the amplifier. By limiting high frequency noise, power cords can take us down a path toward superior sound. How much further down that path does the Bel Canto VBS1 take us?

For the necessary modifications, I entrusted my DAC3 to UPS for delivery to Bel Canto in Minneapolis. (The Bel Canto shipping boxes are very well designed; thick foam cut out to exactly fit the standard e.One shape. Even UPS would be hard pressed to cause any damage.) The upgrade procedure will involve replacing the original power supply board and adapting the chassis to accept the cable that connects to the Virtual Battery Supply. (It is noteworthy that the umbilical delivering power from the VBS1 is constructed using low noise, low resistance, shielded microphone cable with an attractive woven black outer cover. Using a quality, shielded cable here is a nice touch, eliminating yet another possible source of noise contamination.) There will also be a new BNC connector, as well as an RCA, for unbalanced S/PDIF input. The revision level of the DAC firmware will be updated from 1.04 to 2.12. This revision does several things, only one of which is conceivably audible. It enables use of a different remote control. (There are durability issues with the original remote, which is unfortunate, because it is small, simple to use, and its shape corresponds with the lozenge motif of the e.One series faceplate.) The new firmware will also change the analog output from inverting to non-inverting. Now, there are some among us who will insist that this item, absolute phase, is audible. I don't deny the possibility that some people can actually hear it, but I am not one of them. And I find it noteworthy that some high-end audio gear is inverting and some is non-inverting, implying that even the engineers who design the stuff don't regard absolute phase as critical. Finally, the crystal in output clock of the asynchronous sample rate converter, ASRC, will be changed to enable inputs up to 192KHz at 24 bits. This will increase the range of input frequencies but will have no effect on quantization noise.

The core of this business of power cords and power sources, indeed the core issue of my recent reviews, is the benefit of removing noise from the mains before it reaches the audio circuitry, random, non-correlated electromagnetic energy at frequencies far beyond the upper limit of audibility. Here is what Bel Canto Design owner and chief engineer John Stronczer wrote to me concerning noise:

“This is all about noise modulation – similar to the effects of jitter. Noise modulation masks signal and adds an unnatural quality to the sound – the ear has to sift through the noise – we have found that very low levels of noise and jitter are easily audible in a transient audio signal. The ear is much better at picking up on this information than a test instrument is – in order to SEE the signal in a noisy environment we need to average the test signal over a long time period – 20-30 seconds – while the ear can pick this up immediately – so it is not possible to use a transient test signal to measure everything that the ear/brain is capable perceiving. Really quite a commentary on the power of human perception.”

Talk about concision. As a thought experiment, consider that the typical complex audio sine wave – whether you're playing CD, DVD-A, SACD, tape, vinyl, or HD digital files – is the only form of information that can drive a woofer, a midrange or a tweeter and produce music. Now, enlarge a portion of a slope on any one of those sine waves till you begin to see a loss of smoothness, till you can see noise signals riding on the legitimate, musical sine wave. It doesn't look right, does it? And if the picture I've drawn is correct, it won't sound right either, certainly not once you've heard the same sine waves minus the noise modulation. How do these spurious signals get there? How do frequencies at the far reaches of the spectrum effect frequencies at the low (audible) end?

Of course there are, in the case of a DAC, two areas that are effected by noise modulation, digital and analog. In the case of the latter, intermodulation distortion, IMD, is probably an important factor. After all, even if the voltage samples coming from the digital filter accurately correlate to the original analog wave form, a poorly designed or executed analog stage will produce inferior sound quality. Bel Canto is keenly aware of this and put a lot of design effort into this stage. And as with any analog stage, the cleaner the power, the more accurate the amplifier, the more realistic the music.

Inter-modulation distortion is a standard test measurement of audio performance. REF1000 amplifiers, for example, are rated at 0.0007% IMD (CCIF) at one watt into 4 ohms, using 14:15KHz tones. IMD occurs due to circuit nonlinearity and sounds especially harsh and unpleasant because it is not harmonically related to the audio signal. “These [products] are found by subtracting the two tones...then subtracting the second tone from twice the first tone, and then turning around and subtracting the first tone from twice the second, and so on.” (rane.com/note145.html) In the specified test used for the REF1000, sidebands of 1KHz, 13KHz, 16KHz, etc. will be generated, none of which are harmonically related to the original frequencies of 14KHz and 15KHz. (At one watt output, overall IMD for the REF1000 will be in the range of seven millionths of a watt. Can we actually hear the effects of such minuscule distortion? Apparently.) The same thing happens with those spurious high frequencies I'm calling noise, they inter-modulate one another and generate products that can fall within hearing range. These products are very low level, they are random, they are unrelated to the music, they are virtually impossible to measure with certainty and accuracy (partly due to the noise floor of the test equipment), but their effects are audible. How do I know? Because their reduction in the DAC3VB produces an audible change.

Just as IMD in the analog realm can result from the products of high frequency noise, so noise modulation can also produce problems in the digital realm. This manifests as phase distortion. I am on less intuitive ground here, but I know that noise can cause phase modulation of the clocks in a DAC, it can make them less stable and less accurate. The complexity of the conversion process in a modern DAC, and the fact that it works as well as it does, is little short of amazing. And certainly, no component of the DAC topology is more critical than clock accuracy. This type of distortion is audible and is similar to jitter, the long-time bane of digital processing. Jitter, like much that I'm talking about, doesn't necessarily declare itself to untrained ears like mine, but it's removal certainly does.

 

                            

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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