Cambridge Audio may no longer operate in the collegiate city that gave the brand its name, but the product design and engineering is still very much British. Now based in Bermondsey in the heart of London, Cambridge Audio’s sizeable R&D team beaver away on products for the brand.
The latest creations from Cambridge include the Minx wireless devices (that compete with the likes of Sonos) and the ever-evolving Azur range; of which the 851W is one of two standalone power amplifiers, and the 851D the only dedicated DAC. Cambridge Audio also makes the DacMagic line of DACs, but not in the Azur range. The mix of 851D and 851W is a good one, because the 851D also functions as a digital preamplifier, with volume controlled output. It can support up to six digital inputs, including BNC, AES/EBU, asynchronous USB, and Bluetooth. So, for the contemporary listener who hasn’t got the vinyl or open-reel bug, it’s as much preamplifier as he or she will need. As with many Cambridge Audio Azur components, the 851D is replete with features; such things are clearly still selling points despite the ‘less is more’ zeitgeist that dominates the high-end.
Each input can be named, and you can choose a filter setting for each input from three options; linear, minimum phase, and steep. These are all easy to differentiate, and you can even change filters on the fly from the remote handset. You can also bypass preamp mode and use the 851D as a conventional DAC, and connect up PCs of most stripes in USB cclass 1 or 2; the former does not require a driver to be installed, but does limit the maximum sample rate to 96kHz. Everything that goes into this DAC is upsampled to 24-bit/384kHz and jitter is kept at bay by Anagram Technologies adaptive time filtering.
The 851W power amp has twice as many connections as the average stereo amp, and has the biggest bolt I’ve seen on any component for some time. This is underneath and clamps the toroidal transformer to the chassis; attention is drawn to it because a piece of packing is moulded in its likeness as a means of support. This is one of two transformers – one for the output stage and another for the rest of the circuit. As with all Azur series amps, the 851W employs Cambridge’s proprietary Class XD system, which is not as the name might suggest anything to do with Class D. Instead, it’s a mix of Class A and Class AB that switches dynamically between the two systems. The 851W is the most powerful example yet, delivering 200 watts into eight Ohms, a figure that nearly doubles into four Ohms.
Alternatively, it can be bridged to operate as a monoblock and produce 500 watts. Like the 851D, it has XLR and RCA phono connections plus a bus and trigger connection for auto power up; it powers down on its own if it doesn’t see a signal. There are two sets of speaker terminals per side for easy bi-wiring, and the chassis is covered in attractive perforations to let the heat out, the quantity of which is about what you’d expect from a conventional 200 watter. It uses the chunky C20 IEC mains inlet, mains inlet, which I don’t think I’ve seen used in a UK-made product before. I asked why this inlet was chosen and told that in bridged mono mode with low impedance speakers, power consumption can run to almost 2.5kW, and any output in excess of a kilowatt runs close to the 10A limit of conventional C18 inlets.
Listening commenced with a Naim NDS connected to the BNC input on the 851D, which in turn was hooked up to an ATC P1 power amplifier and PMC fact.8 loudspeakers. This revealed the DAC/pre to be capable of a detailed presentation with good image width. It’s a little more relaxed than I expected, which means that timing is a on the ‘mellow’ side. Moving over to the more likely scenario of a Macbook and connecting via USB delivered a similar result: good detail on percussion, plenty of texture, but limited muscularity. Gain did seem to have to be very high with this power amp as well, so I moved over to its natural 851W partner, which allowed a level setting some 10dB lower according to the display. I also experimented with the filter settings and discovered that with the USB source, the linear setting gave the greatest image depth and stronger tonal rendering, which made saxophone sound good and complex mixes remain coherent.
The minimum phase filter makes for a faster, more engaging result, but one that is ultimately fatiguing and tonally lean. Clearly this is dependent on system, source quality, and ultimately personal taste, so it’s nice to have the choice.
I routinely use RCA phono terminated connections, because most of my equipment is single-ended and as a result, most of my decent cables are thus inclined. But, as this pairing offers ‘balanced’ operation through its XLR hook-up, I gave them a try with some fairly run of the mill Van Damme cables. This delivered an increase in bass extension that was uncanny; a major upgrade in fact, despite the downgrade in actual cable and the fact that only the 851D has a balanced output. It made me wonder about my RCA interconnects, the same cables that provide bludgeoning bass from other amplifiers! Regardless, this shot in the arm did wonders for these amps. There was a clear increase in quality from USB over S/PDIF sources, even though the two sources involved (Macbook and NDS, respectively) should have given S/PDIF the upper hand. It comes back to needing to inject enough energy into the 851D to overcome its natural restraint; something that may have been put in to stop lesser quality signals from sounding too bad. Bluetooth or low bitrate MP3, for example, can sound pretty nasty when reproduced on an overly transparent system, so a degree of smoothing will help level the field.
This doesn’t stop these two from delivering fine results fortunately; pick the right filter setting for the source and you get open, extended, and full-width soundstaging, with real gravitas in the low end, and sparkle and life in the mid and top. This will never be the fastest combo in the world, but it makes up for it with lots of detail, strong voice projection, and nicely textured instruments, especially percussive ones.
Contrasted with a ‘less is more’ Octave 2 DAC from Metrum Acoustics, the 851D sounds a little pedestrian, lacking in absolute transparency and falling short where pace is concerned. But if you want features, the Octave with its three inputs and lack of controls isn’t on the charts. The only similarly priced amp I could muster to compare with the 851W was an Atoll IN200 integrated (£1,495), with a bypass option that turns it into a power amp. The integrated delivered a more coherent and solid result, sounding more like real music. The 851W produced greater image scale and has a more lively balance that will suit some speakers well, both offered the same degree of low end grip. However, the Atoll forced a move back to RCA connections, which as I described earlier, puts the Cambridge at a distinct disadvantage.
There is no avoiding the sheer flexibility and feature count of these Cambridge components. Few DACs come close to the 851D’s range of features; especially Bluetooth, which could be a significant factor in its success in the market place today. The 851W is a very substantial and capable amplifier, more so if you connect with balanced cables, which I feel is almost mandatory for the 851W. We would normally suggest this might pose problems, but the 851D and 851W work so well together the problem is solved, and it’s clear those boffins in Bermondsey know a lot about audio engineering!
DAC: Dual Analog Devices AD1955 24-bit DACs
Upsampling: to 24-bit 384kHz, Linear Phase, Minimum phase or Steep modes.
Digital Inputs: S/PDIF, Toslink optical, BNC, AES/EBU, BT100 A2DP plus aptX Bluetooth
USB Audio Input: USB Type B Audio profile 1.0 or 2.0
Analogue audio output: Balanced XLR and unbalanced RCA analogue audio outputs, 6.35mm headphone jack
Dimensions (H x W x D): 115 x 430 x 360mm
Power output – stereo: 200W/ch 8Ω, 350W/ch 4Ω
Power output – bridged mono: 500W 8Ω; 800W 4Ω
THD: < 0.001% 1 kHz; < 0.005% 20 Hz – 20 kHz
Frequency response: 5Hz – 80kHz
S/N ratio (ref 1W / 8 Ohm): >90dB (unweighted)
Sensitivity – stereo or mono: 1.5V rms
Sensitivity – bridged mono: 0.775V rms
Input impedances: Balanced 38 kΩ; Unbalanced 68 kΩ
Power Amp damping factor: > 110 at 1 kHz
Dimensions (H x W x D): 148 x 430 x 365mm
Weight: 19.1kg (42.2lbs)
Price: 851D: £1,000; 851W: £1,500
Manufacturer: Cambridge Audio
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