Cambridge Audio A5 Repair & Review

my hi-fi journey began over 15 years ago, standing in my local Richer Sounds. In front of me on the store shelf was a Silver Cambridge Audio A5, a product of the brand at the time sold exclusively through Richer Sounds, under the ownership of parent company Audio Partnership. A lot has changed since the day I left with the A5 and 2 pairs of ‘Atlantic’ interconnects in hand. ‘Budget’ products have gotten a lot more expensive for one. Had the prices back then been what they are today, I likely wouldn’t have entered the game until years later – if at all.

My A5, a gift from my wonderful and long-suffering parents, cost £109.99, and it was a mid-level model in the series. These days the cheapest Cambridge amp will set you back over £200 –  not nearly the value for money that the A5 was. The A5 was a descendant of the A1, by then in its third generation with a couple of ‘special edition’ models along the way. Other notable models in the same lineage were the A2, A3i, A300, A4, A5I, A500, and at the top of the range the C500 (control amp) and P500 (power amp). When the Azur range took the high-end reins the A-series became the AM series and gained ‘Topaz’ branding, and more recently was given a facelift and rebranded to become the current AX line of ‘budget’ separates. Buy an AXA25 today, and it’s not too dissimilar to the later revisions of the A1 of 25 years ago.

My first new hi-fi amp was actually a Sony TA-FE370, one of Sony’s last hi-fi component amplifiers with a simple electronic design with excellent performance, but a volume control that ultimately proved unreliable. It had a tendency to engage the motorised knob of its own accord and turn itself to max, in appreciation of my – at times questionable – music taste, perhaps.

The Cambridge was undeniably better built, with discrete output transistors instead of the Sanyo STK-based hybrid amplifier of the Sony, and solid metal casing. One reviewer once claimed these early Cambridge amps had “something of the biscuit tin about them”, which I don’t find to be the case. The fact is the esteemed press couldn’t accept that a three-figure amp of a high-street retailer’s own brand would often wipe the floor with the audiophile favourite of the day.

Back then the press were pushing Arcam, smaller Naim Naits, the early Rega Brio, the underpowered and hopelessly unreliable Cyrus or, for the budget-conscious, a NAD. All significantly more costly than the Cambridge and only ever able to match the performance, if that. Cambridge made boatloads of these amps and they were an easy sell, evident by the sheer number of them that are still around to this day. If you want one, you don’t have to look far.

I knew nothing of this at the time. All I wanted was an amp that aided my never-ending quest for music discovery, and could, at times, play loud as is the wish of any Teenager. That’s what the Cambridge did for several years until it came time to upgrade, though not because of any sonic dissatisfaction. I had a pair of Wharfedale speakers from the late ’70s, Laser 80s if memory serves. I remember fondly discovering Meat Loaf, and playing midnight at the lost and found wide open. The memory still brings the feeling of the pounding rhythm to my chest, and knife-sharp vocals cutting through my imagination. Great times.

The A5 was a well-featured amp at the time. It was essentially the same as the more upmarket A500, lacking the infrared remote volume control and the extra 5 watts of output power per channel. You got 6 inputs, one of which could have the optional PM01 phono card fitted. There was 1 tape loop with true tape monitoring, a preamplifier output, bi-wireable speaker outputs and subtle tone controls with bypass. No headphone socket sadly, which was the only feature I longed for on my original.

The amp is 60W per channel and is rated into a 6-16Ω load. A 4Ω load will bring the power supply to its knees, and the cooling is insufficient for heavy loads. Cambridge are keen to boast their use of Toroidal transformers in almost every amp they’ve ever made, bar the standard editions of the A1, the AM1 and the AXA25. This amp is no exception, but it’s quite small given the output and the roughly 8800uF of power supply reservoir capacity per channel, comprised of two banks of four 2200uF capacitors for lower ripple and equivalent series resistance (ESR).

The two pairs of speaker terminals are wired in parallel to allow for the pointless exercise in bi-wiring, which is really just another audio industry con to help line the pockets of profiteering cable companies, dealers and hi-fi industry gurus who will believe anything they’re fed regardless of whether it has any basis in scientific fact. They could theoretically be used to run two pairs of speakers, providing that the speakers were of a nominal 8Ω impedance or higher and a very easy load to drive. Typically the cause of failure in these amps is the user running two pairs of 4Ω speakers simultaneously, or running a single, difficult 4Ω load at high volume.

That was the case here. I purchased this example for the grand total of 5 great British pounds, plus a nominal amount to cover shipping. It has been used with a quartette of Bose speakers, nominally rated at 4Ω, with the seller stating “It was fascinating hearing footsteps move across our room (from one speaker to the other) in a drama, or hear instruments in different places in the room on an orchestral piece.”. No wonder it stopped working.

There’s not much going on inside. In the middle is the amplifier and power supply board. It contains the bank of reservoir capacitors, and symmetrical power supply rails for the amplifier and preamplifier, the latter regulated. The SAP15 output transistors, 2 per channel, are centrally mounted to the two independent heatsinks with simple driving circuitry. The transistors are biased at 13mV so the amp doesn’t run especially hot and idle power draw is not excessive. It’s a simple and well executed push-pull class A/B amplifier implementation.

To the right is the large signal routing board. Most of this board is empty of components, though there are connection headers for the optional phono board. Neither my original nor this amp have that board, and they can fetch more than the amp itself. Given that there are thousands, if not tens of thousands of these amps still in use, I’m considering designing a phono module that will be pin-compatible with the original, which was used in all of the A-series amps and some of the earlier Azur models too. Cambridge got a lot of mileage out of that design. I might also build a Bluetooth module to fit the amp. We’ll see.

The preamp is a simple design using NE5532 operational amplifiers with minimal supporting circuitry, decent signal capacitors and close-tolerance resistors. It’s a clean, quiet design, and in my opinion a lot better than the preamp you find in the current AXA35 and the proceeding Topaz AM10. A variant may still be found in the current AXA25 which forgoes the digital interface of the more upmarket unit in favour of a similar interface to the A5, but I haven’t had the lid off of one of those so I can’t say for sure. There’s plenty of opportunity for a bit of op-amp rolling. One could, for example, pop in a pair of OPA2134s for a supposed performance gain, though whether it would be worthwhile remains to be seen.

Certainly Cambridge might do well to rehash this old design in current products. Paired with the LM3886 amplifier stage in the AXA35, a beefed-up power supply and something like an MAS6116 or or an MAX5486 digital volume control, they’d have a formidable budget amp that would, I’m sure, keep a few competitors up at night.

Back to our issue. Thankfully Cambridge had the good sense to install a pair of T4AL fuses across the secondary side of the power transformer, as well as a primary T2AL fuse on the mains input. The mains input fuse was fine and the transformer working perfectly, but both 1.4A secondary fuses had blown. This happens when something in the output stage draws too much current, which will occur if the load on the amplifier exceeds what the power supply can deliver. Two pairs of 4Ω nominal speakers in parallel gives you a 2Ω load. Orchestras are challenging musical pieces for an amplifier to reproduce, and playing them loud enough to be somewhat lifelike more challenging still especially into two pairs of relatively inefficient speakers. So the fuses did what they were designed to do, and blew to stop the transformer burning out from overload.

I checked the output transistors for short between each pin and combinations of pins, and they had survived. The SAP15 is a relatively durable thing, though the internal emitter resistors tend to fail long before the transistor itself. Because of this they were subsequently discontinued by Sanken Electric, and replaced by the STT03N and STT03P which lack the inbuilt emitter resistors. If you’re repairing one of these units where the transistors have failed, the SAP15s can be substituted for STT03s, with an additional 0.22Ω resistor of at least 3W mounted externally. Replace the bias trim pot at the same time, and the cap across it which will likely be destroyed by a failing SAP15.

If treated well the SAP15 is fairly reliable. It usually takes a failed component downstream or an excessive load to destroy one, which hadn’t happened here. It’s worth noting that Cambridge’s spec biases the output transistors to 13MV, or around 60mA of idle current whereas the official spec calls for 40mA.

I’m not sure it makes much difference in reality. If anything, the amp will run a bit warmer and may have slightly less measurable distortion. But as you may have gathered by now these are not party amplifiers. There was no thermal paste to interface the output transistors to the heatsink, so I took care of that. The small signal transistors also tested OK. The solder joints on the two preamp regulators were cracked as were a number of others on the amplifier board, so they were re-soldered. The components all tested fine.

I replaced the fuses, swapped out the bank of reservoir capacitors as most were leaking, powered up the amp and voila, a working amplifier. Well, not quite.

The analogue switching was rather crackly. The tape monitor switch caused channels to drop, and the volume knob loud static through the speakers. So I disassembled the front panel and treated the switches to Servisol Super 10 switch cleaner. The pushbuttons can be cleaned from the front, the input switch has a convenient hole in the top, and the potentiometers all have small holes in either side through which cleaner can penetrate. There were broken solder joints on at least one leg of every pot, so I fixed those. While I was there, I noticed the power LED had come free from the aluminium fascia. It’s held in with a blob of hot glue, so I reinstalled it in the same way.

There was a strange static noise on the output. I traced it down to a failing NE5532 which was replaced, along with a couple of the small electrolytic caps in the power supply that were starting to leak electrolyte onto the board.

Now the amp is working, and it was time for me to become reacquainted with a sound I’ve not heard in over a decade. Or was it? It seems that what I have here is an original A5, whereas my original was the (largely undocumented) V2 revision. The later version had a slightly different Cambridge logo in line with the Azur range of the time, and the finish on the case was different. The speaker terminals were better, and could take a 4 mm banana plug if you removed the plastic end cap.

I’m led to believe, however, that the biggest difference was in the output stage – which apparently used LM3886 amplifier chips, in place of the discrete output board shown here. I never had reason to take the cover off of my A5 so I can’t confirm for certain that this is the case, but it seems likely. The amp I have here has no power on delay and no speaker protection what-so-ever. If something goes wrong in the output stage, you’d better hope those fuses blow! It’s highly likely that a DC fault occurring in the amplifier will put an end to the loudspeakers very efficiently indeed.

My original A5 had a 4-second power on delay and was better behaved in startup and shutdown, typical of an LM3886. It was also specified to run a 4Ω load and it always handled my exuberant application of the volume control without complaint. It appears there was also an A5I integrated amp at some point, though I’ve found no information about it so I’ve no idea where it fits in the A5 timeline. 

The original A5 is a very clean sounding amp, and it sounds a lot more powerful than it is. Though on the small side, the power supply has reasonable current delivery and the amp will meet its 60W specification and then some into an appropriate load. This original doesn’t sound noticeably different to my version 2, but keep in mind that was more than 15 years ago. If anything this is lacking a little in ‘oomf’ (a technical term) and given the fragility of the output stage I doubt I’d try reliving my teenaged escapades with a pile of classic rock CDs and the volume control wide open. That didn’t stop me pushing it a few times though, and it’s quite capable of cranking out the tunes into the right speakers; just know its limits.

Tone controls are subtle; bass or treble adjustment of ±6dB (four times intensity) at 100Hz and 10kHz respectively. Channel separation is >72dB at 1kHz – not state of the art, but better than the separation of the human ear. Total harmonic distortion reference 1W of output power is 0.02%, and the A-Weighted signal to noise ratio reference rated power is 92dB.

Frequency response, -3dB is 10Hz to 60kHz. The 500mV preamp output has its own unity gain buffer and will happily drive most power amplifiers, though naturally the matching P500 was sighted as an optimal pairing for those who want to bi-amplify more difficult loudspeakers. The preamp is its best-kept secret. Partner the A5 with a pair of speakers capable of running in a bi-amped setup, and run it with a cheap class D amp to run the bass in a horizontally bi-amped configuration, and you can safely play as loud as you like.

This original edition of the A5 is a nice looking and relatively frill-free amp that provides decent sound. It’s from a time when it looked like eh iPod would kill hi-fi altogether, yet the mass-market appeal of Richer Sounds and the budget-friendly Cambridge Audio was still as attractive to consumers as it is today. No big brand makes such great-value hi-fi any more, and I doubt they ever will again.

A great amp for the budding electronics enthusiast wanting to dive in at the deep end and fix something, as there are plenty of broken ones about. The A5 is probably all the amp many would ever need. Pair it with efficient speakers and consider its fragility when you turn up the volume, and it rewards with a pleasing sound, decent connectivity and it looks more expensive than it is. Guide price on the used market about £50 working (£75 if mint), £15 broken (£25 if mint) depending on condition. I think I’ll try to find a version 2 for comparison and to continue my trip down memory lane.