Power to please
A well-equipped former awardwinning amplifier is upgraded to a new generation, and proves capable of even more power, and more hi-fi joy.
Our last visiting amplifier from Cambridge Audio left a permanent impression: the company’s ‘Edge’ pre- and power combination, which was created to mark the company’s half-century by releasing its highest level of product in decades. The power amplifier in particular proved a slam-dunk favourite, so effusively and effortlessly did music simply gush forth from its speaker outputs.
So we welcomed the CXA81, the integrated amplifier from the second of Cambridge’s four ranges of separates, above the recent entry-level AX range, below the 851 series, and looking very much the classic yet modern hi-fi separates amplifier. At this price it’s all about balancing the right features with the best possible amplification, and since Cambridge has been succeeding in that regard for so long (and remains, unlike so many early hi-fi houses, a UK-based company), we had grounds for initial optimism.
The two amplifiers in the current CX Series 2 range are an evolution of the original CX models released back in 2014, when this amplifier’s predecessor, the CXA80, won itself a Sound+Image Award in its price category as Amplifier of the Year. So on the whole we were perfectly happy to hear that for the new model, Cambridge hasn’t messed with the fundamental circuit design of the amplifier, but has rather focused on “the desire to progress... doing everything we can to make it ‘more’... more refined, more precise, more engrossing… more musical.”
So while the fundamentals remain the same, Cambridge’s engineers have gone right through the circuit tweaking at the component level, notably upgrading most of the op-amps in the signal path, and the capacitors in both the pre and power sections of the amp. Notably they have not switched to some new-fangled Class-D amplifier. Here you get 80W of
solid Class-AB power into eight-ohm speakers, rising to 120W into four-ohm speakers. And if you’ve recently been reading, say, soundbar reviews and are thinking that a figure of 80W pales beside the 400W you heard quoted for some three-speaker soundbar, please wash your mind out. Soundbar power ratings are measured with an allowed distortion level of 1%, sometimes 10%, which strikes us as borderline evil (who wants 10% of their sound to be distortion?) yet is actually a European measuring standard for AV equipment.
True hi-fi manufacturers thankfully wouldn’t dream of allowing such terrible noise as part of their specification, and Cambridge’s power rating is specified at a distortion level 10,000 times lower! — under 0.002% when measuring at 1kHz with the amp running at 80% of its rated power, or below 0.02% across the full audio spectrum of 20Hz-20kHz. At such measurement standards your precious soundbars might score a dozen watts at best, which is why they use the weaker criteria.
We should note that the CXA81 also goes notably beyond that 20Hz-20kHz audio bandwidth. If you’re a fan of high-res audio and want an amplifier which actually reproduces the higher frequencies involved (a great many hi-fi amps don’t), you can revel in this amp’s delivery from 5Hz to 60kHz (plus or minus a mere single dB).
Talking of power, the CXA81 offers two sets of speaker outputs at the rear, so you can connect a second pair of speakers to be heard elsewhere in a large room, or in another room entirely. The ‘Speaker A/B’ button on the front panel selects whether you want to listen to only speakers A, only speakers B, or speakers A and B together. Normally we preach some caution with such abilities, because doubling up on speakers effectively halves the impedance seen by the amplifier, which can thereby get into trouble. But Cambridge positively encourages it. Nor does its power output into each pair halve, since as noted the CXA81’s 80W per channel into eight-ohm speakers will rise to 120W into paralleled pairs presenting four ohms, so you still get 60W of well-specified power for each.
The manual doesn’t even caution again pairing up lower impedance speakers. We’d certainly think twice about it, but Cambridge’s confidence may be because the amp is unusually well protected by no fewer than five different systems, most of which will shut the amp down temporarily before damage is done.
So were you to bang away too high for too long into low impedance speakers, you might invoke the over-temperature detection system that monitors the heat generated by the output transistors. Give it 15 minutes chill-out and you should be good to resume the party.
If you are simply pushing them a voltage or current above the ideal working parameters of those output transistors, then the amp will protect them but keep playing, though distortion levels may rise.
Or, since this distortion may not be kind to your speakers, especially if clipping occurs, you can choose in the set-up menu to invoke intelligent clipping detection, where volume is reduced automatically if the amplifier starts to clip or overdrive its output. There is also DC detection to turn the amp off automatically if there’s an excessive high DC voltage, though this would most likely be caused by some internal fault requiring attention.
And finally a short-circuit test takes place at start-up, checking the loudspeaker terminals each time in case a stray wire or fault has shorted them, in which case the amp just won’t come out of standby mode.
For each of these issues you’ll get a series of stars on the front panel so you can tell what’s going on. So this combination of checks seems supersafe, like having a giant condom wrapped around your amplifier; it should stay out of trouble no matter how frenetically you choose to bang with it.
We often gaze in confusion at the decisions made by manufacturers when deciding what inputs to include on an integrated amplifier, but for our money Cambridge nails the choices almost perfectly here.
For analogue sources you get a healthy five inputs — four of them normal unbalanced using RCA phono sockets, one balanced on XLR connections for any special source that offers them. The obvious omission here is the lack of a phono input for a turntable; the CXA81 has no built-in phono stage, though Cambridge can offer the
Solo or Duo standalone phono stages, either of which would perfectly match the design of the main amplifier.
Digitally all is covered, if in less profusion, with two optical and one coaxial digital inputs, a USB-B socket into which you can connect your computer, and also Bluetooth available. The Bluetooth spec offers both aptX and aptX HD, so Android phones supporting those codecs can stream at only slightly lossy CD quality and even above. It appears to lack the AAC codec, so Apple devices are less well served, with only the base-level SBC codec available to them.
Behind all these digital inputs is an entirely new digital board designed for the CX Series 2 amplifiers, incorporating the highly regarded ESS Sabre ES9016 DAC. The optical inputs will accept signals up to 24-bit/96kHz, the coaxial input up to 24-bit/192kHz, and according to the manual the USB-B computer input will accept up to 32-bit/384kHz, along with DSD up to DSD256. However, when we connected our music-orientated Mac Mini to the CXA81, this proved not to be the case. It offered still higher, with a selection available of 32-bit/764kHz! (We have quite the collection of test files but not yet one of those, so we can’t actually confirm it would play at this sampling rate. But it was offered, which is impressive enough.)
There’s no networking here, no Wi-Fi or Ethernet, nor any USB-A slot to which you could attach a stick or drive of files. This last omission is likely a byproduct of the first, since file playback really needs an app for control, which the CXA81 doesn’t have, because you need networking for an app to work. But there can be an app, if you invest in the matching CXN network player, which is also the obvious addition if you need more digital inputs, since it is loaded with them, as well as full networking including AirPlay 2 and Chromecast streaming. The CXN does have an app which can, via a cable between their control bus sockets, also control the CXA81 amp. A stonking combination of traditional and modern would that pairing deliver.
As usual with a much anticipated hi-fi delivery, we didn’t read the manual and just plugged everything up so we could start playing, or at least running in the CXA81, sending through random computer music for 24 hours before we sat down to listen. One early delight was noting that Cambridge is one of those rare companies that labels each input twice on the back panel — once normally and once upsidedown, so you can read them more easily when peering over from the top.
We missed until later, therefore, the set-up menu (we’ll make the excuse that the amp came to us without its manual). Indeed you’ll be unlikely ever to bump into the set-up menu if you don’t read the manual, because there’s no button for it — to reach it, you have to put the CXA81 into standby mode, then press and hold the Speaker A/B button until the A/B lights on the front display flash alternately and the sources A1-A4 light up. This then allows a few options to be selected, including the aforementioned soft clipping option, and the choice of USB mode (Class 1 for stupid early Windows computers without a driver, which it limits to 24-bit/96kHz output; Class 2 for everything else). We did immediately disable the Auto Power Down function, which will turn off the CXA81 after 20 minutes. Many will prefer this power saving mode, which is on by default, and may even be a legal requirement in these green days. Being badly raised, however, we like our amplifiers permanently on and ready to play.
The remote control was initially confusingly busy, but that’s because it’s a full system remote, so most of the buttons don’t operate the amplifier at all. The volume controls are reasonably well differentiated, but surrounded by a circle of transport controls, along with preset buttons and another set of transport controls below, and four with dots and squiggles above, none of which do anything if the amp is your sole focus. So focus just on those volume keys, the input buttons (one
of which is relevant only to the lower CXA61 model), plus power and mute at the top, along with a useful display brightness button shuttling through two brightness levels, or completely off. Once mentally decluttered in this way, we found the remote effective for even incremental nudges of volume level, while still being quick to drop the level when held continuously. The physical volume knob rotates mechanically as you do so, which is always more fun than a boring old numerical readout.
That onscreen display is similarly busy, showing all the available inputs in white and highlighting the selected one in amber. But if this disturbs, just use that dimming function; even when set to off, the display temporarily illuminates whenever you make a change.
Besides, your mind will soon be calmed by the sheer pleasure of listening. Our very first impression of the CXA81’s sound was of its tightness and speed, the taut whack of foot pedal on a central kick drum delivered with full power but lacking either image smear in the spatial domain or overhang in the time domain. The soundstage around it seemed entirely empty up to the position of the next instrument in the mix, the music delivered not as a wall of sound but rather pinpointed individual musicians playing their part while between them were spaces of silence, a highly impressive feat of soundstaging bred of excellence in signal separation and sonic recombination.
Indeed this is an amplifier that reveals the art of the mix. Played at volume without distortion, the immediacy of Neil Young’s Heart of Gold shone brilliantly, the snare slaps to the left, the rich guitar right, and harmonica centre, even before the pedal steel and vocal arrive. Ever noticed the female back-up singer on this song? You will when listening with the clarity of this amplifier; you might even guess that it’s Linda Ronstadt doing the little rise back there on the last line. (James Taylor is also in there too, but the harmonies are so tight it’s harder still to isolate him.)
During one midnight listening session we had the CXA81 up at its extremes and gave it the 24/96 remaster of Four Sticks, which confirmed the trick of listening to Led Zeppelin at high level — you keep nudging it up until the drums sound absolutely real, and it’s then that the mixes truly fall into place. For this you really do have to play very very loud, as Bonham was no slouch even with four sticks in hand, and most ordinary amps simply won’t allow you to get there and remain distortion-free. The Cambridge was able to cook this slice of production delightfully through on all sides, and Plant’s vocal, so often recessed when played at lower levels, was released in its true acoustic, while surrounded by an extraordinary army of sound layers.
Even with lesser-quality files, the Cambridge was able to kick quite the arse, which is a tribute to the DAC implementation. Our digital copy of Santana’s She’s Not There is a rip from a dubious Japanese compilation CD obtained from a back street record store in Tokyo, yet the Cambridge delivered it with such impeccable soundstaging that a thrillingly complex mix was opened up, from the gentle roll of the percussive marimba/bass opening, through the rich Hammond B3 organ tones and on to Carlos entering at the end of the first verse in the left channel and ruling the mix thereafter, leaping to the centre when things go hair-shakingly wild in the middle. The Cambridge grabbed the complex rhythms firmly while keeping the ensemble locked together, as it should be.
We also used the Cambridge for TV audio, and of course any high quality amplifier with a good pair of stereo speakers will put your average soundbar to shame. Take the Nilsson track Spaceman which features at the beginning and end of Netflix’s entertaining ‘Space Force’ series: through the Cambridge it sounded rich and involving, an almost vinyl-like presentation. When we replayed this later through two different leading-brand soundbars under test during the Cambridge’s visit it was a sad weedy pretend version of the song.
Tivoli Audio’s gold SACD of Nat King Cole (played through an analogue input) gave this amp a time capsule to unearth, and it presented impeccably the almost subliminally smooth entry of Shearing’s string arrangement on Let There Be Love, while Cole’s durrie-scratched vocal sits off to the left, perhaps to give Shearing’s piano the space to achieve its percussive effect on the right. This is a stereo delight. Again we lifted the level high and the Cambridge showed no sign of approaching stress, just opening and enlarging the soundstage so the percussion rolls achieved greater realism and space.
Caveats to our joy? Not many, and all incidental to the music. The front headphone socket is a minijack, to which we say ‘ugh’; it may natively fit more headphones without the need for an adapter, but we have far more minijack-to-jack adapters in the house (more than 20 at a quick glance in our sockets box) than we do jack-to-minijack adapters (one, a bit dodgy). So we tried some mobileorientated headphones, but not the lovely expensive ones we’d preferred to have used.
We’d also have liked an ability to switch the variable preamp output sockets to a fixed level, so they’d be more like a ‘record out’ pair. Fewer folks may wish to record these days than of old, but probably at least as many as will use the preamp output to upgrade to separate power amps.
We thank Cambridge for the musical joy we experienced during this amplifier’s visit to our listening room; the CXA81 delivered the timing, separation and power of true hi-fi and had all our reference speakers singing whether small and insensitive or large and generous. Also of high merit is the sensible set of inputs that could make this amplifier more useful to many users than the current trend towards sparse inputs and snazzy displays. And if you want streaming beyond Bluetooth then consider adding the CXN. But the CXA81 will deliver a beating heart to any system, whether Cambridge or mix’n’matched. It’s at the top of its class, and beyond.