CAMBRIDGE AUDIO CXA81 Integrated Amplifier Reviewed

The original CX range from Cambridge Audio will I’m sure be recognised as landmark products of the company. They gave the traditional stack of hi-fi 21st-century styling and upgrades commensurate with the digital era, bridging the gap between your grandad’s hi-fi system and the modern devices carried in the pockets of the younger generation.

By the time they graced the scene building a DAC into an integrated amp wasn’t a new concept, but the CX series were well equipped to cater for almost any taste and system; unless you wanted a recording output for your tape deck, in which case you were out of luck. 2019 Saw the introduction of revised ‘V2’ components in the CX range. The CXN received incremental updates to the Stream Magic platform, and the CXC got nothing other than a colour change to bring it in line with the rest of the range. But the two CX amplifiers were reworked electronically from the ground up, concealing big upgrades behind their broadly similar fascias. Cambridge sent over a CXA81 for review so let us dive straight in.

I preface the following paragraphs with one of my many unpopular opinions. That is the opinion that, in general, DACs have no place inside an integrated amp. Amplifiers are analogue in nature, and the principle of an amplifier hasn’t changed since the switch from tube to transistor. There have been advancements, sure; microprocessor control, advanced volume controls and the inclusion of balanced designs in consumer audio to name but three. Modern components will however connect to a 50-year-old integrated amplifier without issue, and a maintained example of such an amplifier will work as well in a modern system as it ever did.

Digital technology however is ever-changing. 30 years ago when manufacturers realised they needed to come up with more gimmicks and better sound to sell more CD players) and hence the 16/44.1 CD resolution was deemed old hat, manufacturers began to include oversampling DACs, digital filters and later ‘high-definition’ digital audio formats including HDCD and SACD. Manufacturers like Marantz had huge stocks of CD players and quickly found themselves without outdated products that nobody wanted, so they resorted to analogue tweaks and a price cut to shift them. It so happened that some of those ended up performing better than their newer counterparts, but I digress.

These days streaming has taken over from the silver disc, but digital audio is still advancing at an unprecedented rate. We have numerous codecs, formats, digital sources, streaming services and digital rights management licensing. While the efficacy of formats like MQA are beyond the scope of this article (I don’t think favourably of it, for those who care), our DACs require constant updates to ensure we can consume the latest content regardless of the source or format. Some of those updates can be delivered in software and some require hardware-level upgrades. In the case of the former, it’s up to the manufacturer to decide which products get which features, and which fall by the wayside.

The DAC section in an integrated amp thankfully has little involvement in the handling of streaming audio, but they do still need to be capable of decoding the audio you feed them. But unlike an external DAC, when the DAC in your integrated amp becomes obsolete you can’t simply replace it without replacing the amplifier itself. You can run an external DAC into the analogue input of your integrated amp to give you support for new codecs and formats, but that leaves a wasted DAC you can’t use and you may as well have used an external DAC from the get-go. Besides, far too many integrated amps have only one or two analogue inputs, Technics and NAD being two culprits that spring to mind. While it’s true that not everyone wants a stack of hi-fi boxes cluttering up their living space, an external DAC needn’t be large. The DAC board in a modern integrated amp rarely needn’t be larger than a pack of cards, and a switch-mode power supply man enough to power it can be a fraction of that size.

With all that said, I do see the motivation behind Cambridge’s inclusion of the DAC in the CXA81, even if I think the company’s flagship Edge integrated amp would have benefited from a more comprehensive analogue front end. Cambridge are no stranger to building great analogue-only integrated amps; their 851A is a prime example of a perfect integrated amplifier implementation. Unlike some amps, however, the DAC inside the CX series amplifiers is no afterthought and is a very good unit indeed. For a product intended to bridge the gap between traditional hi-fi and a lifestyle system, it is a welcome inclusion.

The packaging is unchanged; no need to fix what isn’t broken. Sparse documentation is supplied, along with a CX series remote, control bus cable and a Bluetooth antenna. The latter is a welcome upgrade; owners of the CXA80 required the optional BT100 Bluetooth dongle to add Bluetooth streaming functionality to the amp, at a cost of £70; more than a dedicated outboard Bluetooth streamer. Both the CXA81 and the smaller CXA61 integrate Bluetooth and support aptX HD into the bargain.

The remote is identical to that supplied across the CX range. It is almost indistinguishable from the original, though lacks the rubberised texture on the rear of the handset. This rubberised material would break down over time, forming a horrible sticky sludgy mess, and this smoother matte finish plastic is better off for the lack of it. The remote is nicely balanced in the hand, with all of the important buttons in the right places. These include central sculpted volume and navigation controls with tactile switches that gently click when pressed. The remote has individual input buttons and controls all functions of the CXN and CXC too, as well as older Cambridge streamers and any CD player that uses the RC5 control protocol.

Turning to the amplifier itself, we see the familiar CX series styling. A central foot spans almost the full width of the amplifier, set back to disappear into its own shadow and give the appearance of a floating case. The wrap-around lid acoustically damps the chassis and the face of the front panel is a slab of aluminium albeit with plastic framing visible at the sides. They could leave off the enormous advertorial sticker above the display, reminiscent of the dealer advertisements you find in the windows of new cars. The CX range makes enough of a statement by itself and there’s no need to spoil the otherwise uncluttered fascia.

My only gripe with the build quality concerns the plastic cover adhered to the top grille vents. Presumably this is there as a barrier against the heat coming through the vented panel. But even when driving a heavy load the panel doesn’t reach a temperature above ‘relatively warm’, and the plastic covers tend to peal off over time. Beneath is a neat metal vent, which has a much nicer finish, so the plastic seems superfluous.

Running the amp through a heavy test, producing roughly 30W into a fixed 8 ohm load until the temperature stabilises gives a temperature reading just shy of 60 degrees Celsius measured in the centre of the grille. In use the amp will never be required to maintain such an output for any period of time. We can conclude then that its thermal design is perfectly up to the job, which will help to guarantee the amplifier’s long-term reliability.

On a black control strip set against the ‘lunar grey’ fascia are situated neat groups of input selection buttons for the four analogue and four digital inputs. Buttons A1 and D4 toggle between balanced / unbalanced analogue and USB / Bluetooth inputs respectively. The design has changed slightly; the buttons now have a flat profile rather than the domed profile of the older models. The same is true for the volume knob which is now flat with a beveled edge and no-longer concave in its centre.

A single central button switches between speakers A, B or A+B. Holding the speaker selection button with the amp in standby mode enters a setup menu. Here certain options can be toggled using the four analogue buttons including auto power down (A1), clipping detection (A3) and the USB Audio Class (A4). You can also perform a factory reset by pressing D1, D3, USB, and D2 in a u-shaped sequence.

LEDs indicate sources, speaker selection, power and protection status. The front panel is otherwise sparsely furnished besides the large volume knob, standby button and 3.5 mm headphone jack. There are no tone or balance controls, nor a 3.5 mm front-panel input on the CXA81. The volume knob is analogue so there is no volume display, though there is a small position indicator on the knob itself.

The buttons all have a pleasingly tactile action when pressed, augmented by the clunks and clicks of various electro-mechanical relays. Strange though it may seem, these mechanical noises make the CXA81 deeply satisfying to operate. Changing the input produces 4 clicks, two of which are from the large speaker muting relays and two from the smaller signal relays. Massive power relays give further pleasing ‘clunks’ when bringing the amp into and out of standby. It’s a small touch and one that is unintentional on the part of any designer, but the mechanical noises a product makes give it a certain character of its own.

Around back are four analogue inputs, one of which on both balanced (XLR) and unbalanced RCA connectors. Overall output gain is lower for the balanced inputs at approximately 30.8dB as opposed to 40dB, though both are sensible for a line-level integrated amplifier. The CXA61 lacks the balanced input and adds a 3.5 mm auxiliary input on its front panel, but its analogue connectivity is otherwise the same.

There’s an analogue subwoofer output and a preamp output, though sadly a line-level recorder output is still noted only by its absence. When fed a single-ended line-level input signal, the unbalanced preamplifier output has a maximum gain just shy of 10dB and the headphone output 18.6dB.

Speaker outputs are on substantial binding posts and accept stripped wire or banana plugs. The two pairs of terminals allow for the pointless exercise of bi-wiring, or more usefully two pairs of speakers to be used independently or simultaneously. When combined, the two speaker pairs are wired in parallel so the overall impedance seen by the amplifier is effectively halved. If both sets of speakers have a nominal impedance of 8Ω, the amplifier would ‘see’ an impedance of 4Ω with both pairs of speakers connected and playing. This is perfectly acceptable. However one should avoid combining 4Ω and 8Ω speaker pairs, or running two pairs of speakers with a nominal 4Ω impedance as doing so would present the amplifier with a nominal 2Ω load, and possibly less under dynamic conditions. A 2Ω load is a challenge for any amplifier, and can result in instability or damage, or falsely trigger the amplifier’s short-circuit protection. Cambridge don’t give a 2Ω power output rating and I’m unsure whether or for how long the amplifier would drive a 2Ω load.

There are ports for integration including an infrared input, Cambridge’s unmodulated control bus and even RS-232C (unusually on a female DB9 connector), for which the control protocol is published on Cambridge’s website. You get 12V triggering in and out too. The control bus connectors link up other compatible Cambridge equipment; most products from the Azur, CX, Edge, and Stream Magic range made from 2003 onwards. Not only was my 651T tuner able to wake the CXA81 with its alarm function, but the control bus also allows the CXA81 to be controlled by a CXN network player via the Stream Magic app.

Control bus support in the Stream Magic or CA connect apps has always been rudimentary and is yet to implement CD player control for a connected CXC, full control over amplifier input selection and power toggling for individual components. These simple upgrades would make it a hugely useful function to allow full system control from a mobile device, but as it stands now the control over the system volume is still welcome.

On the digital side, two optical inputs are joined by a single coaxial input and a USB B input with associated ground lift switch. I’d be glad to see audio equipment begin the switch to USB C, which is becoming a universal connector.

The CXA81 also gets a completely new DAC chipset – the ES9016K2M from Less Technologies. The CXA61 gets the lesser ES9010K2M, but both are a huge upgrade over the previous Wolfson WM8740, supporting 24-bit, 384kHz PCM audio, DSD up to DSD256 and DoP256, though only via USB. Its optical connections are sensibly limited to 24-bit, 96kHz and the coaxial input to 24/192 PCM. The bluetooth 4.2 implementation supports aptX HD (24-bit, 48kHz lossless) and A2DP/AVRCP codecs. It would be interesting to swap DAC boards between a CXA61 and CXA81 to hear what, if any, sonic difference would be present between the two but I imagine the difference is fairly marginal.

On the analogue front, symmetrically arranged power amplifiers are rated to deliver 80 watts per channel RMS into an 8Ω load, and 120W into 4Ω at 0.01% total harmonic distortion. Output impedance measures just 0.112Ω from 20-1000Hz, and at the top of the audio band (20kHz) measures only 0.13Ω. These figures mean that the amplifier should produce a linear response that is relatively load-invariant, which is to say the amplifier will behave similarly with any loudspeaker.

Measured from a single-ended input to the speaker output, the amp is actually flat to within 0.1dB across the audio band (20Hz – 20kHz), and down only 3dB at 100kHz. Channel separation is excellent, at its worst measuring 65dB at 20kHz. Output power at reasonable levels of distortion (<1% THD) exceeds Cambridge’s spec by more than 10% into an 8Ω load, and 7% into a 4Ω load, comfortably producing 90W and 129W respectively. Mains voltage was 235V in all tests. On the subject of power, I noted Cambridge’s maximum power rating for the CXA81 as a staggering 750w; nearly 5 times the rated power output with both channels driven. I asked for clarification on this, and was told that the reason for the seemingly high power consumption figures is due to the fact that the components are rated with an input voltage tolerance of 10%, nominally 230V. With a 253V mains input voltage, the amplifier could in theory produce a continuous 150W into a 4Ω load, and more power still in short bursts under dynamic conditions. Cambridge’s maximum power consumption figures are therefore exactly as suggested; an absolute maximum, worst-case scenario that would realistically never be encountered in real-world use. In a world where we’re all conscious of the energy we use and our impact on the planet, it might be wise for Cambridge and other manufacturers to publish some real-world power consumption figures (including idle draw) as well as theoretical maximum ratings. The CXA81 is what I like to call a semi-dual-mono design. A large toroidal transformer has separate taps for each channel. Each channel has a pair of 6800UF 63V power supply reservoir capacitors and independent rectification, and are physically positioned symmetrically within the amplifier. Thus there is less noise, less crosstalk between channels and less risk that noise from the high-gain, high-power amplification circuitry will negatively impact on the sensitive gain stages in the preamplifier. The amplifier’s layout also gives uniform weight distribution throughout the chassis which helps to minimise any negative impacts of vibration through the supporting surface. It probably won’t make a sonic difference, but the smallest things all add up. This is evidenced in the fact that the CXA81 produces almost non-existent levels of idle noise. If there is one positive I can draw from my total blindness, it is my heightened auditory senses. I can hear beyond 20kHz easily; a trait that is often a gift, though can cause quite a shock when walking past a house with a 13kHz, 19kHz or 21kHz animal deterrent alarm. There are a few of those evil contraptions along a walking route in my local area that give me the fright of my life whenever I pass. Similarly audible idle hiss from amplification drives me insane. Some components of my reference system are facing imminent replacement for this very reason as though they are fine performers, I can’t leave the system idling. To spend any length of time in my system, and amplifier must be quiet when playing and at idle and I’m often trying to chase down the slightest noise in my system. With the CXA81 connected to a pair of Fyne Audio F700 loudspeakers, and my ear almost touching the tweeter, I struggled to detect the almost imperceptible hiss produced by the CXA80 with an analogue input selected and no music playing. There was also no appreciable hum from the amp itself either, suggesting a toroidal transformer of excellent quality and adequate DC filtering in the power supply. A few manufacturers could learn from this - I’m looking at you, Yamaha. I noted in my CXA80 review an interference when using the headphone jack. I’m pleased to say that this too seems to have been rectified, as the headphone output as every bit as quiet as the speaker outputs are. It has a usefully low 33Ω output impedance too, and plenty of power to drive inefficient headphones to high levels. Bravo, Cambridge. Other notable upgrades include the use of JRC op-amps in the line stages. Previous CX amps used the tried-and-tested, cheap and cheerful NE5532 which are still a fine performer. Crack open an 851A and you’ll fine NE5532s throughout. There are a few in the CXA81 complemented by Texas Instruments TL072s. I struggled to identify the JRC op-amps but they appeared to be NJM8801s, which are a very high quality op-amp designed specifically for stereo preamplification, active crossovers and line stages. Cambridge also spec high-quality Japanese capacitors, particularly in the signal path. Not only will these have a positive sonic effect but they’ll be more reliable in the long run than the generic Chinese-manufactured bargain-basement components which tend to dry up in a decade or so. A good electrolytic capacitor running comfortably within its voltage and temperature specification can last 40 years or more, contrary to what some manufacturers (Naim) would like their users to believe. Cambridge has never been one to foist overpriced regular service plans on its users, but it would be fair to say some of its products haven’t always been at the cutting edge of reliability. The first time my 840A amplifier volume control failed, producing its considerable full output into my nearfield monitors just a few feet away is an experience I won’t forget in a hurry. This issue was caused by a cheap mechanical rotary encoder that is not a fault limited to Cambridge products but one shared by most modern manufacturers and products with digitally governed volume controls. I have repaired many of those amplifiers and others like it in the years since. These days Cambridge components are well engineered and a lot less ‘British’ in nature than their neighbouring manufacturers, much like how British car brands instantly became more reliable after corporation buyouts. I would have confidence in the long-term reliability of the CXA81. The CX amplifiers incorporate a comprehensive five-way protection system that kicks in immediately if something does go wrong. CAP5 (Cambridge Audio Protection 5) is fully microprocessor-controlled and protects the amplifier from overcurrent, over temperature, short circuited speaker outputs, DC on the speaker outputs, and clipping. The status of CAP5 is indicated by the protection LED. If a fault Is detected during the amplifier’s startup procedure or during operation, the amp shuts down immediately to spare itself or other equipment from damage. The exception to the rule is the detection of clipping. This is when the amplifier cannot produce sufficient power to drive the speaker to the desired volume level, normally caused when playing dynamic music with a lot of bass content at high volume levels into inefficient speakers. Clipping can be seen on an oscilloscope as a flattening of the peaks in the audio waveform, and contrary to popular belief is the main cause of blown speakers - not excessive power. If the CX amplifiers detect clipping in their output, they will automatically lower the volume until clipping is no-longer detected. These amplifiers have plenty of power on tap and it is unlikely that you will experience clipping in an average room with all but the most difficult loudspeakers, but it’s nice to know that if you do turn it up too much the amplifier will keep you from destroying your equipment, if not your hearing. I never knowingly caused the amp to clip during the review period, and it wasn’t for lack of trying.

And try I did. I noted in my original CXA80 review that it, and its partnering components, appeared to have been voiced toward musical excitement and satisfaction rather than outright neutrality. I’m happy to say this character isn’t changed; if anything the CXA81 is more exciting, irrepressible and eager to ball both fists and jump head first into the fray than its predecessor. I tested the CXA81 using my own CXN V2 connected to the balanced analogue inputs, and my CXC CD transport connected via optical. My iPhone was connected via Bluetooth and my MacBook Pro was used both via Bluetooth and USB using a commonly-available USB B to USB C cable.

The iPhone connected via Bluetooth and worked perfectly first-time, though getting the Mac to play nicely with the CXA81 was a greater challenge. It often refused to connect at all, and took an age to discover the CXA81 despite the two being a metre apart. When it did connect however the stability of the connection and the sound were flawless with no glitching or dropouts. The Mac (a 2019 16 inch MacBook Pro) only supported 44.1kHz streaming audio via Bluetooth and given the seamlessness of the experience with the iPhone I a-tribute these issues to the MacOS Bluetooth stack. The Mac connected straight away via USB and was able to transmit at the full resolution of 24-bit, 192k PCM and DSD256 running in USB Audio Class 2 mode.

I also connected my Technics SL-1200G turntable via the Musical Fidelity M6x Vinyl phono stage, using its single-ended analogue output into the second analogue input of the CXA81. The speakers were Fyne Audio F700s, Tannoy Precision 6.2s and my DIY implementation of the Markaudio CHN-50 full-range driver in a small bookshelf design. Headphones were a mixture of Meze 99 Classics, Audio-Technica M50X, the recently reviewed Sivga Robin and Sendy Aiva. Cables were the perfectly adequate type that carry electrons from A to B at a reasonable price; Cambridge AUD500 RCAs, XLR cables from Studiospares and Sommer speaker cable with banana plugs. There was no power conditioning as it is unnecessary unless there is a wiring fault or interference that a well-designed power supply can’t handle, and the power cables were the generic IEC cables supplied with the components.

The CXA81 has been at the centre of my system for a month and has played every genre of music going; from classic rock to country and heavy metal to alternative throwbacks, from Beethoven to Bread, from Ella to Ed Sheeran and everything in between.

It manages to impart its characteristic excitement without every straying far from a faithful reproduction of the source. Subjectively at least I wouldn’t describe the CXA80 as absolutely neutral though it is not voiced with a particular signature. Rather its character is in its power delivery. Where other amps drive the speakers, the CXA81 drives them with real intent. This is an amplifier that can produce thunderous undertones from small loudspeakers, yet maintain enough delicacy at the top end to accurately portray the beautiful harmonics of a slide guitar.

Let it off the leash, however, and you’re in for a treat. This is an amp that should be played loud, and play it loud I did. It never once failed to put a smile on my face even through the darkest day. All of that energy doesn’t come at the expense of emotion. If anything emotion is enhanced. ‘Hello’ from Evanescence’s ‘Fallen’ album sores to new heights, Amy’s voice hanging majestically in front of the listener. It’s moving and exciting all at once, yet so palpable you feel you could reach out and touch it, whatever ‘it’ is.

The CXA81 is a real breath of fresh air in a market dominated by boring black boxes with average build and same-old specs. Sonically It’s bold, exciting and tremendous fun. It’s beautifully built, well finished and packed to the hilt with enough features to put it front and centre in any system. Reviewer cliches don’t do it justice; this would be a bargain at twice the price.