Cambridge Audio AXA35 Integrated Amplifier Reviewed

Covering the history of Cambridge Audio and the evolution of its budget offerings would serve only to prematurely wear the keys of my already battered keyboard. If you’re interested, I wrote on the subject at length in my AX series summary. If you’re not, the review herein is strictly dedicated to the AXA35 amplifier and will also detail the AXA25. On paper the two amplifiers are very similar with only a 10W jump in output power and specification improvements setting them apart, but in practice they are two very different amplifiers. The AXA25 is a very indirect successor to the A1 and to an extent my A5, whereas the AXA35 is cut from the same cloth as the proceeding Topaz AM10 and the Topaz receivers.

One of the key differentiators is the user interface. The AXA25 has old-fashioned analogue knobs for bass, treble, volume and balance. I presume that it is a fully analogue component design, though I don’t have one here so I can’t lift the lid to say for sure. The AXA35 has a digital interface as evidenced by the push-button input selection and digitally-controlled volume, complete with volume level display and tone and balance controls hidden behind a simple menu system. Assuming I’m right about the AXA25’s implementation of good old-fashioned potentiometers, the better AXA35 should be a significant jump in performance without the channel mismatch and noise issues associated with cheaper analogue pots.

Regardless of their user interfaces these are strictly analogue amplifiers with four inputs on the back and a convenient 3.5 mm input on the front. The AXA35 also has a front-panel headphone jack and a moving magnet phono stage onboard, and I was also very happy to note the presence of a line-level recording output on both amplifiers for those of us with tape decks and external headphone amps. Line-level outputs are often omitted in modern amplifiers but whether the omission of this simple feature is an exercise in cost-cutting or a positive step forward is a matter of opinion. Suffice it to say that I fall firmly into the former camp, and I’m glad to see recording outputs on these amps even though they’re not accompanied by the monitoring facility found on budget Cambridge amps of years gone by.

There is a nod to the digital age on both amps with a USB power jack, supplying five volts at a maximum current of 500mA to USB devices such as miniature streamers or bluetooth receivers. This cost would be better spent elsewhere in my opinion, but it’s there.

There are connections for a single pair of speakers and a grounded IEC power inlet. Both amps feature an eco-friendly standby mode which consumes only 0.5W of power, and an automatic power-down function that can be disabled by holding the power button for a few seconds. A flashing standby light indicates status of the APD – five flashes for disabled, ten flashes for enabled.

The rest of this review focuses on the AXA35 exclusively as I don’t have an aXA25 for comparison. The AXA35 has plenty of useful facilities for a budget amplifier in the contexts of an aptly specified hi-fi system. When compared against a 2004 era Cambridge A5, years of inflation and cost prioritisation mean the omission of a preamplifier output and the second pair of speaker outputs for bi-wiring, not that bi-wiring offers any real-world advantage. There’s no true tape monitor in the newer amps either, nor an option to bypass the tone controls. You do get a remote though, which the A5 didn’t have.

Otherwise the amps are functionally similar, broadly speaking. One reviewer referenced past Cambridge amps as having “something of the biscuit tin about them” with “casework that wasn’t what you’d call well-damped”. Neither comment I feel is justified based on my experience with multiple iterations of the A1, the A5, early CD players and the first models in the Azur range.

It’s true to say that the new casework is better, but examples of poorly damped biscuit-tin casework are more prevalent in boutique British equipment at several times the price of any Cambridge. Poorly built casework and preschool electronics design aside, some of that gear is ugly enough to offend a blind man’s sense of aestheticism.

Not so the AXA35. Its casework better resembles the newer CX range than its predecessors, with a backset front foot and casework designed to naturally dampen resonance. The front is aluminium and finished in Cambridge’s latest ‘Lunar Grey’ finish, a kind of dark silver that I’m told goes equally well with traditional black boxes. Stacking the amp atop the matching CD player makes for a discrete, relatively compact and smart system that gives the appearance of something a great deal more expensive than it is.

Across the front are headphone and input sockets, an IR receiver for the included remote control, buttons for power, source and menu and a volume control. The central display shows the current source and the volume attenuation in decibels. It also shows values for bass, treble and balance when those settings are toggled using the menu button and volume control.

The remote is functional but a bit naff. It comprises a cheap plastic handset with spongy rubber buttons and obvious indents where additional buttons would go on other models. It transmits NEC IR codes for which there is a full control protocol on the Cambridge website, so you can easily program a better universal remote or custom install system. Besides a mute function there are no controls on the remote that aren’t found on the amp itself. If you don’t have the remote, or don’t wish to use it, the mute function can be engaged by turning the volume dial past the minimum setting, and disengaged by turning the volume dial.

Around back from left to right are inputs A1 through A3, a moving magnet phono input with ground and the A4 analogue input which is associated with the line-level recording output. The single pair of speaker outputs facilitate stripped wires or banana plugs,. There’s the aforementioned USB power port, a voltage selector and an IEC inlet for the included mains power cable.

Just like the partnering CD player, the AXA35 feels solid when you lift it. There’s no flex in its casework which is perfectly fitted and neatly presented with the side screws in deep recesses to obscure them from view. The top of the amp is vented with a grid of tiny holes to let the heat escape, though it doesn’t get above mildly warm in operation.

Pressing the power button brings the amp out of standby and, after a few seconds, the speakers are connected with the clunk of a substantial relay. I was surprised to learn that, just like the AM10, the AXA35 doesn’t remember the previous volume setting when the power is cycled. It does remember the settings for balance, bass and treble, so this is a daft omission on Cambridge’s part.

Speaking of the tone controls. They are of the shelving type and cut and boost at 100Hz and 10kHz respectively. They’re not subtle as a result, but as this amp is likely to be paired with smaller bookshelf speakers or less capable floorstanders they will be more useful than controls that adjust the 20Hz and 20kHz frequency extremes.

It should be noted though that abusing the tone controls to get more bass out of a low-powered system is not always a good idea. It’s nothing to do with some snobbish view that “it’s not how hi-fi should be heard” blah blah, but because with a 35W amp excessive use of the tone controls at high volume will cause the amp to clip sooner. Clipping, a flattening of the peaks in the audio waveform, is more often than not the cause of blown speakers, not excessive power. Thus you’re more likely to damage your speakers with this amp if you turn the bass to max and crank up the volume than you will if you leave the tone controls flat.

The AXA35 has plenty of power to fill a mid-sized room providing you’re using efficient speakers. Most budget amps of the ‘70s and ‘80s were this way, and they survived many a party. The A1, the amplifier that revived the Cambridge brand after the Audio Partnership takeover, was only 25 watts per channel and it can make a lot of noise with the right speakers.

Inside, an oversized toroidal transformer feeds split power supplies based around beefy rectifiers and a pair of 2200UF reservoir capacitors per channel. There’s no shielding around the transformer, so keep the amp away from other sensitive components like turntables, tape machines and phono stages, lest a 50Hz hum be electromagnetically induced on their output. The AXC35 CD player was unaffected by having the amp stacked on top of it.

The AXA35 like the AM10 predecessor is essentially a commercial ‘Gainclone’ implementation. The LM3886 output devices can theoretically deliver 68W per channel into a 4Ω load and 38W per channel into an 8Ω load with a symmetrical power supply delivering +/-28V. Cambridge’s specification of 35W into an 8Ω load is therefore a sensible one. The AXA35 will actually deliver the 38W into 8Ω before clipping.

Cambridge do not give a spec into a 4Ω load, which is unsurprising given that the power supply isn’t built to drive difficult or low impedance loads. Larger reservoir caps, for example, would have given the AXA35 a significant bump in headroom and a bit more grunt. It’s not uncommon to see 4700UF caps as a minimum on the PSU rails of a DIY-built Gainclone. You could up the voltage too – the LM3886 can handle peak input voltages of +/-94V, and comfortably up to +/-40V with ample cooling, which the AXA35 certainly provides.

You can drive a 4Ω load with the AXA35, and you’ll get just shy of 60W per channel before clipping starts to occur. Expect about 50W into a 4Ω load at more reasonable distortion levels. I didn’t test this extensively as blowing up the review sample is generally frowned upon, accidentally or otherwise.

The LM3886 does, however, have inbuilt protection against over and under-voltage, power supply and output short circuits, thermal runaway and instantaneous temperature peaks. They are durable and reliable chips and offer excellent performance comparable to a discrete output stage. Regardless of the amplifier you use you should always consider its limitations in partnering equipment and the environment. I’ve fixed a few AM10s over the years with blown output chips all as a result of driving too heavy a load at too high a volume. If your system is obviously distorting or if you’re running the amp at or near its maximum volume, upgrade to a model with more power.

The preamp appears similar if not identical to the AM10. It is responsible for most of the noise in the amp’s output – 79.8dB signal to noise ratio (A-wtd, ref 0dBW). It’s a bit of a shame Cambridge didn’t spec up the preamp a bit to better match the performance of the output stage. Nevertheless it is well designed with NE5532s unsurprisingly making up the basis of its audio circuitry and input selection and volume control handled by digital logic.

Assuming the preamplifier in the AXA35 is similar to the AM10 (it certainly sounds that way), its headphone output is driven by the preamp, not by the output of the amplifier via dropping resistors. As a result the headphone output on these is excellent. It does have an audible background hiss which is a shame, but it has plenty of power to drive moderately difficult loads to uncomfortable levels.

Traditionally, headphone outputs in cheaper amplifiers are nothing more than a socket connected directly to the speaker outputs with a couple of big resistors to drop the output power considerably. The problem with this approach is that the load presented to the amplifier is different to that which it was designed to drive, and thus the frequency response can be effected. Driving headphones from the preamp is a much better solution and a headphone output of this quality is a nice inclusion.

The frequency response is relatively flat. There’s a gentle roll-off below 100Hz and above 10kHz, but it’s only 0.2dB down at 20Hz and 20kHz, the limits of the audio band. In reality this won’t be audible, so any characteristic sound will be due to its limitations in power, component-level tuning and preamplifier noise more than anything else.

The noise from the preamp is the only drawback as in other respects the AXA35 is a very clean design. Its idle hiss is noticeable from a distance with sensitive speakers though thankfully it doesn’t increase as the volume rises and is not obtrusive when listening. It might mask some low-level detail but given the speakers these are likely to be paired with it’s not a concern. The tonal character is generally quite forward with a slight hump in the upper midrange that projects vocals and acoustic instruments to the forefront of a stereo image of reasonable dimension. The stereo image extends well in depth but is restricted in width and height. It’s not an amp that can make the speakers disappear, but it does paint a reasonable stereo picture with good separation between instruments and layers, and a decent amount of detail throughout the spectrum.

Its biggest strength is in top end detail. Its biggest weakness is, unsurprisingly, low-end performance. The AXA35 won’t produce ground-shaking quantities of bass. It simply doesn’t have the power supply headroom to do so. It’s not something you’d notice unless the amp was side-by-side with one that did do bass well and it doesn’t detract from the performance. I suppose the best way I can describe it is that the AXA35 is a little more light-footed than some. Low bass notes run out of steam at high volume levels and it doesn’t have enough power to portray the impact of the air leaving a kick drum, or the resonance of the lowest strings of a grand piano.

It’s hard to sum this one up. The AXA35 is a smart-looking, well-featured amplifier. It’s nicely made and finished with plenty of versatility for most users. It has a lot of competition at this price, and with a £299 asking price it is more a mid-fi contender than a budget bargain.

I can’t help but feel it could have been better engineered in places too. A bigger power supply would vastly improve the performance of the amplifier, and a better preamp would give the amplifier a chance to show what it is really capable of. Neither are difficult to design, and neither should add significant component cost to the product. If you’re competent in electronics and DIY-minded though, the older AM10 and the AXA35 are perfect candidates to form the basis of a DIY Gainclone.

With that said, I can’t fault the AXA35 for what it is. I think the AXC35 CD player is the crowning jewel of the system, and if you want an amp to match the AXA35 is the logical choice. Choose your speakers wisely and you have a system that will sound very nice indeed, and look the business too.