TESTED: Benchmark DAC1 Pre Digital-to-Analog Converter and Preamp

Equipment report
Categories:
Digital-to-analog converters
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Products:
Benchmark Media Systems DAC1 Pre
TESTED: Benchmark DAC1 Pre Digital-to-Analog Converter and Preamp

I first encountered the Benchmark DAC1 digital-to-analog converter two years ago at an audio show. The exhibit was in an area of the show that did not allow playback via speakers. But Benchmark had some high-quality headphones on hand, and they were offering people the opportunity to hear for themselves the extent to which their DAC1 was free of digital artifacts. Headphones are very revealing of such things, and the sound I heard on that occasion was a revelation. It was, indeed, completely devoid of anything like the digital nastiness that had been almost ubiquitous in audio since the introduction of CD digital.

Now at this time, twenty-five years into the CD era, I had had on hand other digital devices that I found quite satisfying, notably dCS’s upsampling system. But the dCS system cost as much as my newest car. And it also seemed to be somewhat sensitive to the transport used with it. Here from Benchmark was artifact-free digital that was accessible in price and apparently worked perfectly with ordinary transports—the show demo involved a non-audiophile transport. As you can imagine, I bought a Benchmark DAC1 soon after. And I have been using it on a regular basis ever since. (Our own Paul Seydor has also been using the Benchmark DAC1 in his system for the last year or so with complete satisfaction, as he volunteered that I could say.)

Further exposure has only confirmed my original impression. The Benchmark version of digital lives up to the promise of the CD digital process, without any of the artifacts—the nastiness, buzziness, edginess, whatever your pet peeve—of earlier, jitter-prone, non-linear versions of Red Book digital. And to my ears, the Benchmark system also lives up to the company’s claim of suppression of the effects of input jitter. It finally succeeds in the realization of what had always been the theory, but rarely the practice, of digital: Only the input bits should matter. I shall discuss in a moment how this works. But on the practical level, it has the important consequence that one can use an inexpensive transport without penalty, as long as it is “bit perfect.” (This “bit perfect” property, producing the correct bits on output, is not uncommon: It is the norm among the standard brands such as Pioneer, Technics, and the like, even at a low price level.) Not only are the Benchmark DAC1 and the presently reviewed DAC1 Pre, which includes preamp functions, very reasonable in price themselves; they do not require or even benefit from any substantial investment in a transport. They are simply unaffected by anything but the bits they receive. At well under $2000 for both DAC /preamp and transport, the DAC1 Pre, like the DAC1 before it, offers sound that is truly in the top ranks of digital sources. Really!

Just to clarify which device is which: The DAC1 is a DAC with a volume-controlled output and a headphone amplifier with volume control. The volume-controlled stereo output could be put directly into the input of your amplifier. No separate preamp stage was needed. The new DAC1 Pre adds to these functions two items. First of all, it allows an analog input. So you could use it, for example, as the linestage part of a phono playback system, if you used a separate phonostage. (There is no balance control, however, something that is useful for records in my experience. There is also no remote control, not that I care.). Second, it allows a USB (24-bit, up to 96kHz) input, so you can use it for the conversion part of a computer-based playback system.

The essential operating mechanism of both Benchmarks as DACs is as follows (stand by for a moderate amount of techno-babble). The jitter independence is accomplished by doing a sample-rate conversion of the output, which is clocked on a crystal-oscillator internal to the Benchmark and not correlated in timing to the timing of the input signal. The input data is processed algorithmically to the output sample rate. Thus, in effect, the sample-rate conversion calculations are necessarily treating the input as just bits. And while the clock of the converted sample could have been somehow synchronized to the input signal’s clock rate, as happens in some “upsamplers,” this is, in fact, not done. The converted sample-rate clock’s timing is set independently. So the final digital signal being converted to analog is, in fact, determined from the input bits but is not otherwise related to the input at all. Here, bits really are just bits, and jitter on the input is simply ignored. This can be checked explicitly, by introducing jitter on the input and observing the effects if any on the output. Even at very high levels of such introduced input jitter, the output jitter artifacts are far below the level of audibility—on the order of 140dB down from full level. 

This is a really vital matter for people like me, who like to use DSP processors, since the bit output of such devices is always as it should be, but jitter problems may have developed from, if nothing else, transmission of digital through multiple cable connections. Input jitter immunity is also vital for computer playback, since USB transmission is, it seems, rather jitter-prone. The Benchmark’s conversion method simply makes these non-issues.

The electronics industry has always been full of claims of technical perfection, and one has, in view of history, to ask oneself: Is this input jitter-independence real in audible terms? Benchmark in a polite sort of way seems to challenge anyone to demonstrate that the transport matters audibly, as long as it is bit-perfect. And I must say that this is not a challenge I would bet that I could meet, after some trials. And anyone who thinks he can ought, I think, to try it blind. But before you go to the trouble you might also want to have a look at Benchmark’s test wherein it introduces jitter artificially into the input signal and check what it does to the output. “Audibly nothing” is a good way to describe what change occurs in the output signal—unless you really think that things 140dB down from signal are significantly audible.

Benchmark is not a “we promise it works but pay no attention to the man behind the curtain” company. It almost bombard you with technical data, even in the owner’s manual. Its design work, like the sound of its devices, is ultra-transparent. (This means a lot to me. Call me a skeptic, but I am quite tired of companies that promise amazing results but offer no test data to support their claims).

Still, it is the listening that counts, and I have been listening to the Benchmark conversion method (in the DAC1, which I bought) for more than a year. To say that it wears well would be to understate the case. It has become for me simply the way I listen to CD when I want to hear exactly what is on it. And it seems to do the job so nearly correctly that if I am disturbed by what I am hearing, I look elsewhere for the cause without hesitation. The conversion link in the chain has become anything but the weak one. The Benchmark conversion scheme was developed for pro-monitoring, as a device to enable professional audio people to check the results of their digital work, and in particular to evaluate A-to-D devices, without any deviations from the truth as far as conversion back to analog is concerned. It does its job superbly and accomplishes its intended monitoring function completely. (The Benchmark is in wide use in the pro world. Odds are that a great many of your favorite recent recordings were made with it as a monitoring device.)

As I pointed out in my review of the admirable Marantz SA-7S1 SACD/CD player, with its switchable digital filtering schemes, there are, within essentially flawless conversion, some small variations. And I suppose it is of interest to describe where in this spectrum of conversion possibilities the Benchmark lies. In those terms, it is a little on the “softer” side. Indeed, initially, when I came from another converter to which I had become accustomed, the Benchmark seemed slightly devoid of attack, on piano music for example. But further experience convinced me that actually what I was hearing with the Benchmark was not absence of attack that should be there but absence of distortion that should not. In short, “softer” came to seem to me just freer of digital errors.

Traditionally, at this point in a review, I ought to start talking about the spatial presentation of the device being reviewed. About this, there is really not much to say. If there is depth, you hear depth. If there is width, you hear width. Low jitter does have an effect on spatial perception, just because spatial perception is related to unmasked micro-detail. The ear/brain uses low-level cues from recorded room reflections and so on to create a sense of space. Of course, this process is rather hit or miss in stereo. If you want to hear real space you need to listen in surround sound, well recorded, what little there is of that. But to the extent that space works in a given stereo recording, it will work here. One hears all the way to the bottom of the resolution possible with whichever type of digital source you are using. There are effectively no jitter artifacts, and the unit is extremely quiet in terms of analog noise, as well. It is really giving you all the signal-to-noise ratio that the digital medium allows. There is also total channel separation and exact channel match. Hence there is total space, to the extent that space is recorded.

One might want to give a passing thought here to the fact that in any way that one could imagine space being encoded—interchannel phase matching, interchannel amplitude matching/channel balance, interchannel frequency-response matching, channel separation, signal-to-noise ratio, etc.—a device like the Benchmark DAC1 or DAC1 Pre completely trumps anything one can even remotely imagine from vinyl or indeed from analog tape. On top of that, using the DAC1 with volume control or the DAC1 Pre, the quietness, the signal-to-noise ratio, goes straight into your amplifier. The DAC1 Pre into a solid-state amplifier of good quality produces a system that is dead quiet, the noise remaining being theoretical, indeed. The music emerges from a totally black background. This is a sound simply not available from analog. Moreover, the direct connection without an intervening additional preamplification stage gives an amazing sense of directness, of nothing between oneself and the source. It is as if electronics had simply vanished, except for the power amplifier, as if the original recording were being piped straight into the amp.

I suppose that the picture emerges that I like these Benchmark devices. I definitely do. But my reaction goes somewhat beyond that. It seems to me that at this stage, the whole process of accurately reproducing the content of a CD or other digital sources (except SACD) is beginning to sound very much like a solved problem. No problem in audio is perhaps ever totally solved. Each generation’s improvements in some department reveals needs for improvement elsewhere, just as improved speakers made the graininess of early solid-state more obvious and the better bass of CD made the need for subwoofers more obvious, and so on. Perhaps in the future, some new revelatory clarification elsewhere in the chain will show a need for better D-to-A conversion. But right now, it seems to me that one can simply stop here and look at the problems elsewhere: the difficulties of speakers and rooms, the way recordings are made, the need for surround sound and so on.

The DAC1 Pre includes an analog input. I think it is fair to say that the Benchmark people to some extent included this as a convenience and a way to encourage people to connect their device directly to their power amplifier. (The owner’s manual mentions using it to play the sound off a VCR and things like that, no mention of phonostages being attached—I do not think these are vinyl people, and why would they be?)

But superb digital conversion, of course, involves superb analog electronics. The output of a DAC is ultimately an analog signal. And, however Benchmark may have thought of it, the analog input stage here works superbly. People who are looking for a “linestage” to make subtle modifications of the sound of their systems may want to look elsewhere, but if you just want clean, pure, low-distortion, flat-response transmission of a voltage input with some gain and volume control added, this will do the job. I know it is almost an article of faith that compact circuitry involving op-amps cannot sound as really good as large, discrete circuits, but the Benchmark’s performance gave this the lie. Its analog stage really does offer, to my ears, top-drawer performance: totally clean, transparent, neutral, and dead quiet. (There is a DC blocking cap on the analog input. In the unlikely event that you need flat-to-DC, be advised.)

The DAC1 Pre is up against a marketing difficulty. It is a little box, something you can hold in one hand, and people who are used to preamps being large or who labor under the strange illusion that a preamp transmits power in a substantive way and needs a big power supply like a power amp are perhaps going to have trouble relating to it. This really is a misconception: A preamp does not “drive” an amplifier in the sense that an amplifier drives speakers, putting lots of energy into them. A preamp sends a voltage to an amplifier with small current and hence small power. It is more like a message to the amplifier about what to do than a matter of “driving” it. In particular, the high-current op-amps in the DAC1 Pre have more than enough moxie to get the amplifier to do what it should, even when used with long cables.

I would suggest listening without knowing what you are listening to. Try replacing some behemoth old-style linestage preamp with the DAC1 Pre and listen impartially. All those almost subconscious preconceptions about how such a little box cannot have big dynamics and so on will simply vanish in the face of the evidence, if you do not know that the little box is what is playing.

To my mind and ears, the Benchmark DAC1 Pre marks something of a new era in audio. I would not want to see the big and expensive tries for absolute audio perfection to cease; humanity should never stop trying to explore the boundaries of the possible, and someday, improved recordings and improved speakers—vast improvements remain possible in both places—may reveal subtle errors that need correction. But extremely subtle they would have to be in the analog domain, and even more so in digital conversion. In the world as it is now and as it is likely to be in the foreseeable future, it seems to me that this small, inconspicuous, and not very expensive device does its job so well that one should turn one’s attention elsewhere in the audio chain to look for further improvements. The Benchmark DAC1 Pre is not only an excellent device for the money; it is excellent compared to anything that I have encountered at any price. To my mind, it is the beginning of a new era in audio, in which the regeneration of the recorded signal has become a solved problem.