Full expert review and laboratory test of the Cambridge Audio CXA80 I Integrated Amplifier/DAC by Australian Hi-Fi Magazine.

The following review consists of a full subjective evaluation of the Cambridge Audio CXA80 I Integrated Amplifier/DAC written by Peter Croft, as published in Australian Hi-Fi Magazine, November/December 2015. At the end of the review is a link to a complete set of independent laboratory tests conducted on the CXA80 by Newport Test Labs and a report about those tests written by Steve Holding. The link also downloads the original magazine pages, in pdf format.

I think Cambridge has done itself—and audiophiles the world over—a disservice by presenting the CXA60 and CXA80 to the market in the way that it has, by giving them similar model numbers and allowing them to share product brochures, user manuals and web pages. The problem—at least as I see it—is that this approach will have many people thinking that the CXA80 is simply a higher-powered (80-watts per channel) version of the CXA60 (60-watts per channel). Nothing could be further from the truth. They’re almost completely different amplifiers. The CXA80 is dual mono; the CXA60 isn’t. The CXA80 has USB; the CXA60 doesn’t. The CXA80 has balanced inputs; the CXA60 doesn’t. So keep all that in mind when you’re reading this review, which applies to the CXA80 only!

The Equipment

The very first thing you notice about the CXA80 is that it has no support feet. Or, rather, it does have the usual two rubber support feet at the rear, but someone clever at Cambridge Audio has devised a way to eliminate the front feet, which it’s done by extending the front panel downwards, but then cutting it in, and then hiding a long central support foot behind the front panel. You might imagine this would make the CXA80 easy to ‘rock’ but unless you push very hard downwards on one of the front corners, you’ll not manage to induce any instability.

The downwards-extended front panel also hides the massive bolt that fixes the huge toroidal transformer to the CXA80’s chassis. That it has a toroidal transformer at all is one of the CXA80’s claims to fame: many other similarly-priced amplifiers use EI transformers, which are inferior in many respects (but not necessarily all… circuit designers do have some very high-performance EI transformers available to them, but only if their build budget is up to it). Cambridge Audio is being slightly ingenuous when it says that it was ‘one of the first manufacturers to use toroidal transformers’ because to me this implies that it did so simply because they were superior devices. It omits one of the major reasons it started using toroids (back in the 70s), which was because it wanted to stand out from the crowd by being the only manufacturer offering slimline, low-profile chassis, and a toroid is the only way to achieve this other than using an output power supply. That said, the toroidal transformer inside the CXA80 is so big it wouldn’t work in a slimline design (being 65mm high and 100mm in diameter).

However, there is only the one toroidal transformer and the left and right channels share the four 8,800uF smoothing/storage capacitors, yet Cambridge Audio’s literature says the CXA80 is a ‘dual mono’ amplifier, which didn’t accord with my understanding of a true ‘dual mono’ design, which entails the amplifier in question having two completely different power supplies: that is, with no shared components at all. The requested clarification from local Australian distributor Synergy Audio advised that the amplifier can be classified as ‘dual mono’ because the CXA80 ‘has separate transformer taps for left and right channels, twin rectifiers and separate PSUs’, so it looks like we disagree about what defines a ‘dual mono’ stereo amplifier design.

The DAC inside the CXA80 is Cirrus Logic’s WM8740, which is a very high-performance stereo DAC that’s much-loved by audiophiles for its superb sound. It supports data input word lengths from 16- to 24-bits, sampling rates up to 192kHz and is a single-chip implementation of a serial interface port, digital interpolation filter, multi-bit sigma delta modulator and stereo DAC. It is, however, very slightly technically inferior to Cirrus Logic’s own (newer) CS4398 24-bit/192 kHz device, which has an oversampled multi-bit Delta-Sigma modulator that incorporates a mismatch-shaping technology that eliminates distortion due to capacitor mismatch.

One thing I did not particularly like on the CXA80 was that it is fitted with a small 3.5mm headphone socket, despite there being room for a full-sized 6.35mm one. I prefer the larger version because it’s mechanically and electrically superior and means that when using good-quality headphones there’s no need to use a headphone adaptor. But if you don’t use headphones at all, or only occasionally, I guess the 3.5mm socket won’t be an issue for you, and at least Cambridge Audio has actually provided a headphone socket… many amplifiers don’t have one.

One feature of the CXA80 that I’ve never seen before concerns the operation of its clipping detector. Clipping is what happens when an amplifier tries to deliver more than its rated power—80-watts in the case of the CXA80. It’s called clipping because instead of the tops and bottoms of the musical waveforms being nicely rounded, the amplifier literally ‘clips’ off the tops and bottoms. You can see this clipping effect in oscillograms 1 and 2. Oscillogram 1 shows a clean 100Hz sine wave, without clipping. Oscillogram 2 shows the same 100Hz sine wave, this time with the peaks clipped. For small amounts of clipping, most people hear the bass seeming to ‘firm up’ and become ‘harder-sounding’. When clipping increases, distortion becomes audible. You can easily see the difference in distortion levels between an unclipped 100Hz sine wave (Figure 1) and a clipped 100Hz sine wave (Figure 2).

Obviously, the higher-powered your amplifier is, the less likely it is to clip. However, if your amplifier is rated with an output of less than 200-watts per channel, it’s likely that it will occasionally be clipping, even if you play at relatively low volume levels. Many amplifier manufacturers accept that this will happen and, knowing that it won’t actually damage the amplifier, do nothing about it. Others put clipping indicators on the front panel which flash if the amplifier is clipping, to alert you to the fact that you should turn the volume down. Still others (NAD for example) fit circuits that, if clipping occurs, cut in to ‘round off’ the edges of the waveform, to minimise the audible effects. Such circuits are generally known as ‘soft clipping’ circuits.

In the CXA80, Cambridge Audio has taken a revolutionary—though, when you look at it in hindsight, blindingly obvious—approach to the problem. If, when the amplifier is playing, it detects that its own output stage is clipping, the CXA80’s anti-clipping circuit just turns the volume control anticlockwise a few notches, dropping the output level. I think this is an absolutely brilliant solution. It’s completely automatic, and, unlike almost all soft-clipping circuits, it doesn’t affect the sound quality of the amplifier in any way whatsoever. I initially thought this circuit might be the brainchild of amplifier design whiz Douglas Self, who designed the unique displacer circuit (which Cambridge calls XD) that Cambridge uses in its 851W power amplifier (as reviewed in Australian Hi-Fi Magazine Volume 46 No 4) to reduce distortion by removing audible crossover notch distortion, but it turns out it was the work of Cambridge’s own in-house design team. As with most anti-clipping circuits, you can switch the CXA80’s off if you want, but it’s so non-invasive I can’t see why you would want to do this.

According to David Moore, one of the designers who worked on the anti-clipping circuit, the same circuit is in all Cambridge amplifiers that offer ‘CAP5’ protection, but in the CXA80 (and the CXA60) the circuit’s sensitivity has been adjusted so that infrequent slight clipping won’t nudge down the volume: it’s only nudged when heavier clipping occurs. According to Moore, the process works like this: ‘The clipping circuit converts the clipping signal to a logic level and passes the clipping signal to the MCU (the processor that controls the CXA) which then instructs the volume control motor to go anticlockwise. The clipping circuit itself does a bit more than just pass the clipping signal over to the MCU. If only one channel is clipping then non-continuous clipping durations less than 1mS are not passed to the MCU. For both channels clipping then non-continuous clipping durations less than 0.35mS are not passed to the MCU. The MCU then does some processing on this signal to decide when to nudge the volume motor. We adjusted the parameters in software based on real music testing on real speakers, as we wanted to make sure this function was optimised for real use. Note that clipping protection is not for protection of the amplifier but for the speakers. The amplifier can happily clip and operate fine but it has been said that clipping could potentially damage the speaker tweeters.’

The CXA80 is certainly not short of inputs, with six analogue inputs (including one balanced input), two optical digital inputs (via standard Toslink connections), a coaxial digital input, and two USB inputs. One of the two USB inputs (the one with the Type B fitting) is intended for use with Cambridge Audio’s BT100 Bluetooth dongle (sold separately for $140). Plug the BT100 into the CXA80 and you will be able to stream Bluetooth and aptX Bluetooth directly to the CXA80 from your mobile phone (or any other BT-equipped device.) Out-of-the-box, the CXA80’s USB input is set for USB 1.0, which will make it instantly ‘plug ‘n play’ with any device, but will limit you to playing 24-bit/96kHz files. However, you can switch the CXA80 to USB 2.0 mode (see the Set-Up Menu, on page 5 of the Owners’ Manual), which will then allow you to play up to 24-bit/192kHz files, and will also allow you to use ASIO (Audio Stream Input/Output) which bypasses Windows’ own (rather ordinary) mixer. However, if you switch it to USB 2.0 you will have to load a USB 2.0 audio driver onto your computer. This is available as a free download from Cambridge Audio’s website or here: www.tinyurl.com/CXA80-USB2

The front panel design of the CXA80 has, to my mind, been very tastefully executed. I particularly liked the black finish of my review unit, and the way Cambridge had included a small silvery highlight around the outside of the volume control. I think Cambridge has perhaps taken the idea of being ‘tasteful’ a bit too far with the Cambridge logo, which is etched black on the black front panel. I wouldn’t have minded that to be silvered too… if only to show my good taste in choosing a Cambridge component in the event I purchased one. Cambridge has even put effort into the cooling holes on the top of the amplifier, which have been formed into an attractive herring-bone array, rather than the more usual boring rectangular slotting.

Looking at the front panel, you’d be forgiven for thinking the only analogue control was the large rotary (motorised) volume control. All other controls appear to be pushbuttons. If you were thinking this, you’re in for a surprise. Just to the left of the volume control, what look to be three buttons (which control channel balance, bass and treble) are actually spring-loaded rotary knobs that are normally recessed inside the front panel. Press and release any of these and the knob will spring free from the front panel, after which you can rotate it to the left or right as desired, then press it back so it’s flush with the front panel. Each of these controls has a central detent point so there’s no mistaking the ‘no effect’ calibration. And if you’re not convinced about the efficacy or non-intrusiveness of bass, treble and balance controls, you can switch all three out of the signal path by pressing the ‘Direct’ button located alongside the ‘Speaker’ button… which has, since I’m mentioning it, positions for Speakers A, Speakers B, and Speakers A+B.

Although the Cambridge has a ‘Mute’ function, which instantly mutes the output of the amplifier so you can answer a phone or a front door, it doesn’t operate the way I’d like… though at least it’s consistent no matter whether you use the remote or the front panel, which is more than can be said for most mute functions. When you engage the mute function, either from the front panel or the remote, a soft blue light on the front panel will flash to indicate the muting circuit is engaged. The only way the circuit can be de-muted is by once again pressing the mute button on the front panel or the remote. This means that it’s possible to turn the volume of the amplifier to maximum while the amplifier is muted, using either the front-panel control or the remote’s ‘Up’ volume button. If you do this, then un-mute the amplifier, the resulting maximum volume level could harm your speakers. What should happen is that if the amplifier is muted, and either the volume control is rotated clockwise, or the ‘Up’ button on the remote pressed, the mute circuit should instantly de-mute, restoring sound to the speakers. Maybe on a MkII version…? The mute circuit also remains active whenever you switch from one input to another, which also is probably not best practise. Better if muting was disengaged when switching inputs.

Since I’m on grievances, here’s another one: plugging headphones into the front-panel headphone socket instantly mutes the speakers, so you’re hearing sound only through your headphones. When you pull the headphones out, the speakers are re-enabled. This meant I couldn’t indulge in one of my favourite listening modes, which is to wear headphones whilst also listening to the speakers. I particularly like doing this in my den, because I get the bass from the speakers, but the ‘direct inject’ of midrange and high-frequencies directly into my ear canals. I would have preferred it if plugging in headphones did not disable the speakers, and there was instead an additional ‘Speakers Off’ position for the Speaker switch.

If you’re not an inveterate reader of Owners’ Manuals, two things about the Cambridge Audio CXA80 might puzzle you… which is that there are six analogue inputs, yet only four analogue source selector buttons (A1 to A4), and five digital inputs, yet only four digital source selector buttons (D1 to D4). This is because the A1 button has two modes (A1 unbalanced and A1 balanced); the A4 button has two modes (A4 rear panel or front panel input) and the D4 button has two modes (USB and Bluetooth). In all three cases one mode is indicated by the usually-light blue symbol alongside the button shining bright blue, or instead shining red. I wondered why Cambridge Audio had used this rather strange system for input selection, rather than just providing two extra buttons, and the only reasons I could think of were either cost-effectiveness or cosmetic appearance (or both).

If you’re not an inveterate reader of Owners’ Manuals, you may not also realise that you can alter the time it takes before the CXA80’s auto-power-down circuit cuts in to switch the amplifier to standby: you can choose between 10, 30 or 60 minutes or you can turn it off entirely, so the amplifier will stay on until turned off manually. You may also not realise that in its default mode, the CXA80 comes with its unique anti-clipping circuit switched off, so if you want the anti-clipping on (which I would personally recommend) you’ll have to do this before you start using the amplifier. (Again, I would prefer that Cambridge delivered the CXA80 to customers with the circuit switched on, so that owners would have to ‘opt-out’ of using the anti-clipping, rather than ‘opt-in’ to using it.)

I could not conclude this section of the review without mentioning the remote control, because it’s a real beauty… in every sense of that word! First, it’s beautiful itself, with a metallic top surface, a soft, curved, ‘velvet’ finish rear surface, and beautifully-labelled soft-touch pushbuttons. Second, all the controls on it work beautifully, requiring just the ‘right’ amount of pressure to work, and not one skerrick more. Third, it operates not only the CXA80, but other of Cambridge Audio’s components, so you’ll need only the one remote. The remote also gives direct access to the two USB inputs, and to the front panel output, but even using the remote you still have to toggle the A1 input between balanced and unbalanced. The remote also provides an additional function—one not available from the front panel—of being able to dim and switch off all the LEDs on the front panel (except that on the power switch).

In Use and Listening Sessions

Using the CXA80 involved a very weird experience. After listening to it in my main system (during which time I conducted the listening sessions that were the basis of this review), I received a second amplifier for review, so I moved the CXA80 over to the system in my ‘den’ only to find that when I plugged it in, it no longer worked. ‘Oops, this will mean an embarrassing call to the editor,’ I thought to myself. But before I made the call, I decided to put the CXA80 back in my main system in the hope that it would start working, and save me that phone call. Surprise…it now worked! Heaving a sigh of relief, I carried it back to my den, only to find it didn’t work in that system, exactly as before. This then involved much scratching of the head. What the hell was going on?

I knew the den system was working properly, so it wasn’t the wiring or the speakers, so I started thinking about the differences between the two set-ups (other than the fact I was using different components in each… duh!). Suddenly, the light dawned. My main system uses pretty thick speaker cables that have bare-wire ends and thus have to be tightened under the speaker terminals. The speaker cables in my den system, on the other hand, are terminated in banana plugs. When I’d loosened-off the screw terminals to remove the amp from my main system, I’d left those terminals loose, and simply inserted the banana plugs into the CXA80’s (also banana-capable) speaker posts. ‘What if…?’ I thought… Yep, you guessed it… even though the banana plugs were making good contact with the exterior metal of the speaker terminals, there must be some other termination inside the amplifier that disconnects if the speaker terminals aren’t screwed up tight, irrespective of whether you are using cables or plugs. So when I screwed in the speaker terminals tight (onto nothing!), the amplifier suddenly sprang into life. This functionality was a first for me, and certainly what I’d consider a trap for young… and even old… players.

I liked that all the connectors on the rear panel are of very high quality (all are gold-plated) and that in usual Cambridge Audio fashion, every connector has a two labels, one you can read right-side up when you’re looking at the back of the amplifier from behind it, and one label you can read when you’re bent over the amplifier from the front, and therefore reading ‘upside down’. I thought the lettering itself could have been a bit bigger, but perhaps that’s just the result of my medically-proven poor eyesight!

Although, not having any other Cambridge components available, I had to use either the remote control or the front panel control to adjust volume, there is a third way to control volume. If you own a Cambridge CXN Network Music Player (a really nice unit, by the way, that allows you to play virtually any digital file up to 24-bit/192kHz, from almost any source: internet radio, Spotify, Airplay, NAS drive, UPnP server, and aptX Bluetooth) you can use the control bus connection on the back of the CXA80 to link it to the CXN, which will then allow you to use Cambridge’s ‘Connect’ app to control the volume of the CXA80.

Naturally I was really keen to try out the anti-clipping circuitry, but I ran into a problem: the CXA80 amplifier is so powerful that when it was driving my speakers, which are only moderately efficient (87dBSPL/w/m), I couldn’t get the amplifier to clip! All I succeeded in doing was over-driving the speakers, causing the voice-coils to pole. Based on this, I’d say that it’s only those who use fairly inefficient speakers (less than 87dBSPL) and play at very high volume levels that are going to benefit from the anti-clipping circuit. I decided to add some serious external resistance to the speakers, in order that I could induce clipping at lower volume levels and, when I did this I still found I had to be clipping the amplifier hard enough for the clipping to be clearly audible before the CXA80’s volume control wound itself down. So, if you know what clipping sounds like, you’d probably turn down the volume yourself, before the circuit could do it for you. However, if you don’t know what clipping sounds like… then turn the circuit on and let the CXA80 do the work for you!

Once I’d satisfied myself that the anti-clipping circuit worked—and worked well—I removed the external resistors and settled-in for some serious listening. Although I intimated it in the previous paragraph, let me make it plain that the CXA80 is an audibly powerful amplifier. Given that I could crank the volume up high enough for the bass drivers to start poling, it wasn’t only my speakers that were in danger, but also my hearing… we’re talking loud, VERY LOUD! Indeed so loud that there would be few situations in which I think you’d really need more power than the CXA80 has available. However the idea of having this type of power on tap isn’t so that you listen to continuously high volume levels, it’s so that when you’re listening to music at ordinary levels and a musical transient comes along, the amplifier is effortlessly able to reproduce it at the correct level, without clipping. After several months with the CXA80, playing at a wide range of volume levels, I was left in no doubt that the CXA80 will be able to do this with ease… and the result is that you’ll hear tremendous dynamics when listening to your music, certainly from compact disc, but even more so from high-res files with their improved dynamic range.

However, I was most impressed by the bass capabilities of the CXA80 when playing a CD without much dynamic range at all, that being ‘Crazy Rack’ which is the latest album from four-piece Palms. Whether it was reproducing the high-energy bass/drums intro to One Cold Night, or the slowly-realised low frequency energy on Dreamcatcher, the CXA80’s bass delivered in spades: total power, total control, total bass realism. Bass doesn’t get better than this. If you’ve been put off listening to Palms because you’ve heard them described as a ‘trash’ band, I’d suggest listening yourself, because I’d disagree with this description. ‘Fun rock n’ roll’ would be closer, IMHO. You can always listen for free on Soundcloud before you commit to buying something in higher fidelity. There’s certainly lots to love on Crazy Rack… not to mention lots to love about the bass from the CXA80.

More great bass on Philadelphia Grand Jury’s latest ‘Summer of Doom’, but on this rather-better-recorded album (and now back with the original line-up of Berkfinger, MC Bad Genius and Dan W. Sweat), I could admire the midrange delivery of the CXA80 as well as the excellent channel separation… dual-mono or no. The separation was exhibited not only by the beautiful stereo imaging, but also by the separation of the instruments. Listen to the left/right channel trickery at 1.14 in Crashing and Burning Pt II, and in the introduction to Bit of a Bummer and you’ll hear what I mean. The midrange ability of the CXA80 is highlighted on Better Send Someone, depressing though the lyric is. (And a warning: don’t play Pull Some Strings… it’s just too silly!)

Sound quality as good as this was just begging for some hi-res material, so it was time to play the 24/96 version of Albert Lee’s album ‘Tearing it Up’ which has Lee on guitar, of course, plus Randle Curry on pedal steel, J.T. Thomas on piano, Jim Cox on organ, Bob Glaub on electric bass and Don Heffington on drums. It’s a bit overly country/rock but the sound is fabulous, and the playing masterful from all members of the band, but particularly from Lee, who’s backed Eric Clapton and was with the Rhythm Kings for years, and is often called ‘the guitar virtuoso’s virtuoso.’ As I suspected, the sound with the Cambridge CXA80 was to die for: the pedal steel capture is incredible, and the drum sound totally immediate. I know it’s a cliché, but it really was as if the band were playing in my living room.

Conclusion

I was really excited by this amplifier. It had all the features I want in an amp and all the performance I demand: high power output combined with the ability to drive low-impedance loads, plus the CXA80 was beautifully clean-sounding and able to deliver the intricacies of a musical performance while still sounding musical, rather than clinical. And did I mention the superb build quality and the sophisticated industrial design? But I became even more excited when I discovered that the recommended retail price was around half what I’d expected it to be. In my view, Cambridge Audio’s CXA80 is a bargain. Snap one up while you can! # Peter Croft


Readers interested in a full technical appraisal of the performance of the Cambridge Audio CXA80 Integrated Amplifier should read the LABORATORY REPORT HERE. Readers should note that the results mentioned in the report, tabulated in performance charts and/or displayed using graphs and/or photographs should be construed as applying only to the specific sample tested.