Cambridge Audio Azur 851C CD Player-DAC-Digital Preamplifier

January 2013

201301 cambridge1What was once called a CD player can hardly be found anymore. Not the least of the reasons why is that many disc players today don’t play only CDs, but also DVDs, BDs, and sometimes SACDs -- hence the product category of universal player. Then there’s the DAC-transport, as Simaudio started calling their players several years ago, which puts the emphasis on connectivity rather than disc-reading capability, even if their transports still read only CDs. Cambridge Audio, of the UK, has kept CD player as part of the name of the Azur 851C ($1999 USD), but they’ve tacked on to that DAC and digital preamplifier -- which do more accurately describe the potential uses for their new, upscale digital source component.


Cambridge Audio’s lower-priced electronics have a somewhat lightweight, flimsy feel that’s more or less what you’d expect for products costing only a few hundred dollars. Those familiar with those models will probably be surprised when they see and feel the Azur 851C -- it’s sizable and heavy, measuring about 17"W x 4.5"H x 14"D and weighing 22 pounds. Much of the mass is due to the thick, brushed-aluminum panels that make up its case -- the 851C’s beefy build meets or even exceeds what most would expect for even a couple of grand, and indicates that it was designed to compete with the very best out there. Even the remote control feels substantial, with a sturdy aluminum front plate and a heavy-duty plastic backside. My review sample came in silver, but it’s also available in black.

On the 851C’s rear panel are: a main power switch; an IEC-compatible power-cord inlet; single-ended and balanced analog outputs; four digital inputs (one USB, one AES/EBU, and two S/PDIF, the last user-selectable as coax RCA or TosLink); three digital outputs (AES/EBU, coax RCA, TosLink); an RS232 connector; a connector for an infrared remote control; and two more connectors labeled Control Bus, which I didn’t use but appear to be part of a proprietary control system that works with other Cambridge Audio components. All the digital inputs support bit depths of up to 24. The TosLink inputs support sampling frequencies from 32 to 96kHz, while the S/PDIF coax, AES/EBU, and USB inputs support frequencies from 32 to 192kHz (provided USB Audio 2.0 is enabled for the USB connector; see below).

Cambridge Audio Azur 851C

The only oddity is that the Azur 851C’s USB input doesn’t support a sampling frequency of 176.4kHz. Its AES/EBU and S/PDIF coax inputs do support 176.4kHz, which I tested by putting a Stello U3 digital converter between my computer and the 851C. During the test period, I and my 24-bit/176.4kHz music files got around this limitation two ways: 1) by using the Stello U3 and connecting via AES/EBU; and 2) by connecting via USB, but having my JRiver Media Center 17 software resample to another frequency that the 851C does support -- my preferred method, and the one I used more often. I could have chosen 96 or even 192kHz, but my preference was 88.2kHz, which is exactly half 176.4kHz, because I believe in whole-integer conversions. Consider the 851C’s lack of 176.4kHz support for USB a slight flaw that can be worked around.

The rightmost portion of the 851C’s front panel contains the usual controls found on any CD player sold over the last 30 years: eject, play, pause, stop, and track skip -- all duplicated on the remote, which adds to them the volume up/down controls, which don’t appear on the front panel. An interesting thing about these controls: they worked not only for disc playback, but also for the music player on my computer when I connected it through the USB port. This made the 851C incredibly convenient and easy to use -- I could control almost everything from the front panel or the remote.

The front panel’s central section has the disc tray, and below that a display that shows playback information (including the output level in dB) as well as the menu system, through which you configure the 851C and activate certain of its functions, most notably: the built-in digital volume control, channel balance, and USB Audio 2.0, the last for up to 24/192 playback through the USB port. Playback at 24/192 works natively with Macs, but Windows-based computers require a driver, which Cambridge Audio supplies. (The 851C’s default setting is USB Audio 1.0, which allows for up to 24/96 playback from Mac- or Windows-based computers without the need for the special driver.) Navigating the menu system to make such changes was a snap.

But despite its being so easy to use, I was at first annoyed at having to enter the menu system to switch the 851C from USB 1.0 to 2.0. After all, most high-resolution-capable DACs I’ve used simply have you install the supplied 24/192 driver for Windows support of USB Audio 2.0 right off the bat and call it a day. I now believe Cambridge Audio’s solution to be a better one, despite the extra steps. There’s always the risk that any third-party driver someday will be incompatible with whatever operating system you’re using, whether because of an upgrade to that OS or something else. If that happens, a digital source that works only with USB Audio 2.0, and relies on that driver to do so, will be rendered useless until a fix is found -- a fix that may not be available. Making the 851C switchable between USB 1.0 and 2.0 avoids this problem.

Cambridge Audio Azur 851C

As far as I can tell, there are two reasons Cambridge calls the Azur 851C not just a preamplifier but a digital preamplifier. One has to do with volume, which, once this is enabled through the menu system, is digitally attenuated via the remote control. Another is that, unlike traditional preamplifiers, the 851C has only digital and no analog inputs -- any switching done will be of digital source components. What’s important to know is that whether or not you engage the digital volume control has no effect on the digital inputs and the ability to switch between them -- those always work. Whether you can make use of the 851C’s volume control (and, in turn, channel-balance functionality) will depend largely on your setup, which I discuss more fully below.

To the left of the display and disc tray are buttons for: Standby/On, for day-to-day powering on; Menu, which activates the above-mentioned menu; Select, which acts like a computer’s Enter key; and Filter, to select among three digital-filter settings and works in conjunction with what Cambridge Audio calls Adaptive Time Filtering, version 2 (ATF2) -- a proprietary upsampling algorithm, developed in conjunction with Anagram Technologies, of Switzerland, that increases the resolution of all incoming digital signals to 24/384. Indicator lights above this button indicate which filter is selected. Digital-to-analog conversion is done by two Analog Devices AD1955 DACs.

The three filter settings are Linear Phase, Minimum Phase, and Steep, each fully described in the owner’s manual. When such a choice of filters is offered, reviewers and audiophiles tend to want to determine which sounds “best.” Based on my experience of the Azur 851C and other digital sources with multiple filters, I’ve learned that different settings can make small but meaningful changes in the sound, particularly in regard to the reproduction of the high frequencies as well as soundstage width and depth -- but which one is “best” most often depends on the recording being played. This is why, after all, companies offer a choice of filters in the first place. I have found no hard-and-fast rules about which filters will sound better. And, as I’ve said, any such changes are small -- no filter I’ve heard has altered the overall tonal balance in any large way.

Other than its lack of support for 24/176.4 play via USB, Cambridge’s Azur 851C is an exceptionally feature-rich, exceedingly well-built digital front end. But would the appearance of its being a top-class design be borne out by its actual sound?


In a word, yes. Whether I played discs in its transport or streamed files of various resolutions from my computer, the Azur 851C sounded utterly neutral, very detailed, extremely transparent, and thoroughly refined. I can’t imagine that anyone who enjoys the unadulterated, uncolored reproduction of recordings would be disappointed by its sound -- or, rather, its lack of sound, as most of what I’ve just listed has to do with the 851C adding no sonic signature of its own. I also think that those who enjoy hearing the fine details of their recordings will revel, as I did, in how well the 851C revealed tiny nuances and could convey the entirety of a recorded space, even with rather poorly engineered recordings.

Case in point: Sade’s Diamond Life, of which I have a few versions on CD and in digital files, some of them LP rips. I’ve written about this album in recent reviews because S. Andrea Sundaram recently wrote an article on the album’s many releases, including a recent Audio Fidelity LP. The recording quality of Diamond Life is pretty dismal overall, with a threadbare, metallic sound that can be heard from every version I have of it. Not surprisingly, the very neutral Azur 851C didn’t transform Diamond Life into an audiophile-grade recording, but it did let me hear, very easily, every subtlety of the various versions, and, I’m pretty sure, every bit of space this recording contains -- which, with some versions, proved to be quite a bit more than I’d ever thought was there. My point is this: Even with a rather poor-sounding recording, I was surprised to hear sound from the 851C that was as layered and dimensional as from the best standalone DACs I’ve heard at or near this price.

Cambridge Audio Azur 851C

To assess soundstage width, depth, and image specificity, I’ve used Ennio Morricone’s mostly choral soundtrack score for The Mission (CD, Virgin 90567-2) for longer than any other recording. The digital files of it that I stream from my computer today are FLACs ripped from the original CD I bought in the 1980s. I played that CD in the 851C’s transport and the files from my computer via the Azur’s USB port, and heard pretty much identical sounds. Any time I thought I heard a difference, I switched back and forth, but still was never sure I heard one -- I’d call that a draw. There was as much width and depth to the soundstage as I’ve heard through comparably priced digital sources.

“Everest,” from Ani DiFranco’s Up Up Up Up Up Up (16/44.1 FLAC, Righteous Babe), is another longtime reference recording that I primarily use for image specificity -- it has some unique recording traits, particularly regarding where DiFranco is placed on the stage. DiFranco’s voice seemed to emanate from just inside the left speaker and a little back from the plane described by the two speakers’ front baffles -- exactly where it should be; and her precise position on the stage in relation to the sound of the double bass played by Jason Mercer, the only other musician on this track, was crystal clear.

The Azur 851C precisely rendered acoustic piano. Glenn Gould’s piano in A State of Wonder: The Complete Goldberg Variations of J.S. Bach, 1955 & 1981 (16/44.1 FLAC, Sony Classical) was reproduced with the kind of incisiveness and attack that his style of piano playing demands. With source components of lower quality, some of the quieter portions of this disc can sound like dead air; through the 851C, the subtlety of Gould’s keystrokes, the humming of his voice, and various other sounds were very easy to hear.

The Azur 851C didn’t sound inherently rich or warm -- tonally, as I mentioned, it was as neutral as anything I’ve heard -- but it certainly sounded rich and warm playing Ola Gjeilo’s piano-based “North Country II,” which is track 14 of our own high-resolution 2L-TWBAS 2012 Sampler (24/88.2 FLAC, 2L/ I heard again the incisiveness and attack I’d heard in the Gould, but the sound of the Gjeilo recording is fuller, richer, and grander. The difference has entirely to do with the inherent nature of this recording, which favors capturing the grandness and majesty of a piano’s sound over the strict accuracy of capturing it coldly and starkly in a controlled space.

Cambridge Audio Azur 851C

A new version of an old recording that I’ve grown to really appreciate is HDtracks’ 24/192 release of Cat Stevens’s Tea for the Tillerman, which was originally released in 1970. There’s a new SACD/CD release as well; I’m not sure how that DSD version compares with the PCM downloads, but the 24/192 version is far and away the best I’ve heard a “digital” Stevens album sound: rich, warm, and textured, qualities you’d normally attribute to a great analog tape or LP source. It’s completely lacking the nasty qualities often attributed to digital sound: sterile, hard, clinical, to name just a few. But it is a digital remastering, and through the Azur 851C, the sound was nothing short of glorious and full. Some might be led to believe that the high resolution of the recording is the main reason it sounds so good, but I attribute it to the quality of the transfer from analog to digital, which is described on HDtracks’ site, and the neutrality and transparency of the 851C, which simply let this spectacular sound shine through. In contrast, when I played the CD of The Very Best of Cat Stevens, released in 2000 by A&M, the sound was thin, bright, hard, and metallic, which is what that disc inherently sounds like, and is typical of the way I’ve heard Stevens sound on digital. As with every other recording I played through it, the Azur 851C remained faithful to what it was fed, never buttering up the sound.


By default, the Azur 851C’s volume function is disabled -- it operates only as a DAC and a CD player. But enabling the volume control through the menu system is a snap (once activated, a Ch. Balance option appears in the menu structure). Once it’s enabled, the volume level can be changed only with the buttons on the remote control, not on the 851C’s front panel.

What’s interesting about the 851C’s digital volume control is that Cambridge Audio claims that their method of digitally attenuating the volume, which involves their proprietary DSP, won’t result in the loss of resolution caused by the truncation of bits of typical digital attenuation. They give no details of how that’s done, but for now I have to take it at face value that it’s true. Whether or not you should activate the volume control will depend on several things, and partly on how you configure your system. As already mentioned, the 851C has only digital inputs; if you need analog inputs, it won’t suit your needs as a preamp, so you might as well leave its volume control disabled. Nor is there any point in activating the 851C’s volume control if, instead of a power amplifier, you hook it up to a receiver or integrated amplifier with no direct power-amp input, as such devices have their own volume controls. (You don’t want multiple volume controls in the signal path.) On the bright side, digital-source switching isn’t affected by the choice to use the volume control -- the 851C always allows switching between digital inputs. But if you have no analog source components but do have a power amp, there are compelling reasons to connect the Azur 851C directly to the amp and at least try its built-in volume control. The main benefit is that you can entirely eliminate the need for a separate preamplifier and interconnects to and from it, which can significantly reduce the cost of your system while increasing the quality of its sound by eliminating an amplification stage.

I plugged the 851C directly into an Eximus S1 power amp via a balanced connection and it worked extremely well, providing sound that was very like what I’ve described above, but just a little more transparent and alive than when I ran it through any of the preamps I had on hand. For the digital-music-loving purist looking for the ultimate in accuracy, this is the best approach.

Still, there’s a chance that the Azur 851C won’t drive your amplifier well, resulting in insufficient volume, a lack of dynamics, distortion, or even a skewed frequency response, if there are impedance problems. I didn’t have that problem, and I suspect that most won’t, but you’ll have to try it with your amp to see if it will work properly, and if the sound is better than with a preamp or AVR in the path.


If, in the Azur 851C, Cambridge Audio intended to create a well-built, feature-rich digital front end that could satisfy the hardcore audiophile, and at a retail price that would be considered sane by audiophile standards, they’ve succeeded . . . and then some. From its build quality to its features to its ease of use, I have abundant high praise for and find little to criticize in the Azur 851C. Overall, it’s a well-thought-out digital source designed by a company that’s been in the digital game a long, long time -- and it shows.

Then there’s the sound. If you value strict neutrality, high transparency, excellent detail, and unflinching, unwavering, unapologetic fidelity to the source, then you’ll find Cambridge Audio’s Azur 851C a wonderful digital source component and, at $1999, an excellent deal.

. . . Doug Schneider

Associated Equipment

  • Speakers -- Vivid Audio Giya G2, PMC twenty.24, KEF R500 and LS50, Audio Solutions Rhapsody 80, GoldenEar Aon 3
  • Amplifiers -- Copland CTA 506, Blue Circle BC204, Eximus S1, Bryston 4B SST2
  • Preamplifiers -- Simaudio Moon 350P, JE Audio VL10.1, Eximus DP1
  • Digital-to-analog converters -- Simaudio Moon Evolution 650D, Eximus DP1, Calyx Audio DAC 24/192
  • Digital converter -- Stello U3
  • Computer -- Sony Vaio laptop running Windows Vista and JRiver Media Center 17
  • Digital interconnects -- AudioQuest Carbon USB and Diamond USB
  • Analog interconnects -- Nordost Valhalla, Nirvana S-L
  • Speaker cables -- Nirvana S-L

Cambridge Audio Azur 851C CD Player-DAC-Digital Preamplifier
Price: $1999 USD.
Warranty: Two years parts and labor.

Cambridge Audio
Gallery Court, Hankey Place
London SE1 4BB
England, UK


North American distributors:
Audio Plus Services (US)
156 Lawrence Paquette Industrial Drive
Champlain, NY 12919
Phone: (800) 663-9352


Plurison (Canada)
313 Marion Street
Le Gardeur, Quebec J5Z 4W8
Phone: (866) 271-5689