HiFi Advice 04/2013

Ayre AX-5 twenty integrated amplifier

HiFi+ 02/2016 - Alan Sircom

If you have been writing about audio for a long time, there’s a delicate trade-off, between spinning a tale out of every product, and starting your next review with “this is the 374th amplifier I have ever tested.” However, in the case of the Ayre AX-5 twenty amplifier, this dichotomy is resolved because there is a genuine tale to be told in its development, and its performance is good enough that you don’t need to be scrabbling round for filler.

The big story here is the VGT (variable gain transconductance) approach used in the preamplifier stage, and first seen in the company’s KX-R preamplifier. To understand precisely why this is such a big story, you need to step outside the received audio wisdom for a moment and think in first principles. If you do this, the way a line level signal passes from source to power amplifier actually becomes a little screwy: attenuating a signal to taste before passing the signal to a gain circuit to boost it to amplifier-friendly loudness is – at best – the tail wagging the dog. As the amplifier has a fixed level of noise, the maximum signal-to-noise ratio is only achieved at full volume. The other analogue option is to use a passive preamplifier. This has the advantage of not boosting the gain (so the signal-to-noise ratio of the input signal remains the same), but often causes as many issues as it resolves in terms of cable length having an influence over sound quality. Also, the volume level of the system is ultimately governed by the output voltage and impedance of the source component, which is taking matters too far in the other direction.

Basically, Ayre’s VGT circuit uses a pair of double-pole silver-contact rotary switches, connected to an array of precision, hand-selected resistors. This is not a stepped attenuator, however: these resistors alter the transconductance of two pairs of complementary JFETs in the power amp’s input gain stage. In essence, the volume control is influencing the power amplifier, leaving any signals passing through the preamplifier entirely unattenuated, meaning no changes whatsoever to the signal-to-noise ratio during the line-level stages (where comparatively small changes make large differences). This makes the signal path extremely simple, but dictates the kind of switchgear used in that signal path (very low resistance and linear switching is needed), with FET switches instead of relays in the input selection because that’s the best sounding line up Ayre has found for the circuit. Most amps are not designed to these lengths, and the end result sounds good, but doesn’t come cheap from a bill-of-materials standing. By its inherent characteristics, VGT cannot work in anything other than a zero-feedback environment and, as is the case with all Ayre amps, it’s run as a balanced circuit – there are two single-ended inputs, but think of them in the same way you might think of salad at a fast-food joint.

At the other end of the circuit, Ayre goes right back to the beginnings of solid-state technology, using a form of gateable bridge network of bipolar transistors. Ayre’s Charles Hansen is something of a student of amplifier design and utilised Richard Baker’s ‘diamond circuit’, so called because the original notes written by Baker in the 1950s show the circuit drawn in a diamond shaped configuration, even before there were the components to use in that circuit. The diamond buffer is not uncommon as the output buffer stage is several high-performance IC op-amps, and even a few discrete preamplifier designs, but is extremely rare in a power amplifier output stage. The reason this circuit is rarely found in power amplifiers is that the driver stage must operate at the identical bias current as the output stage itself.

So far, so original AX-5: this sounded great, but in environments with ambient temperatures as high as 35°C or more, the AX-5 occasionally tripped the amp’s thermal protection circuitry (living in the UK where 35°C is the stuff of holidays abroad and oven temperatures, I have to take that as read). The chance to celebrate Ayre’s 20th year led to the ‘twenty’ modifications, which revised the output stage with a ‘double diamond’ circuit to run cooler. This also allowed for additional AyreLock regulation to better control output voltage. This is available as an upgrade to existing Ayre AX-5 owners.

Ayre is the kind of product that attracts engineers, real and wannabe. Products like the AX-5 are extremely well designed and built, they perform their allotted task beyond expectation, and without extraneous goodies, and they are often more than a little counterintuitive to us ‘civilians’: in the entry-level AX-7e integrated amp, for example, normal legends like ‘CD’ or even a spinning disc are replaced by stars and moons and meteors. Here, it’s the set-up procedure: you have to allocate an input a name to activate it and – because we aren’t of engineer mind – this means some Tekken-style button mashing on the front panel until you begin to get the hang of things. The amplifier is also said to be best after 100 hours of running in (mine arrived with many more hours on the clock) but also needs several hours of ‘settle time’ on standby to bring it back from the cold. Once it’s plugged in and left in standby, it can be battle-ready in about as long as a live Carlos Santana guitar solo to sound great.

What the AX-5 twenty delivers is absolutely stunning amounts of detail retrieval, always staying the right side of ‘forward’, but with a fine sense of musical order and a good deal of enjoyment thrown in for good measure. It’s the resolution that hits you first, though – you get a sense of being almost injected into the music, an upclose directness and energy that could make you smell the rosin on a violin bow. It’s a vivid, visceral, and lively presentation. The secret here is to spend as long as possible listening to the AX-5 twenty with as wide a range of music as possible, then go back to your previous amplifier… and wonder how you failed to spot the blankets your old amp threw over the loudspeakers.

At which point the AX-5 twenty is quickly pressed back into service, and you begin to delve deeper into what it does so well, and the next element that presents itself to the listener is the sheer musical enjoyment it delivers. It’s strange, but normally amplifiers this vivid and detailed suffer musical fools badly; anything less than beautifully recorded material sounds like a musical experiment gone horribly wrong. The Ayre amplifier is one of those rare exceptions that serves up insight and entertainment in equal measure: I listened to ‘Dimples’ by The Spencer Davis Group, Somebody Help Me: The Best of 1964-1968 [Raven], which is a great piece of British Invasion Blues straight out of the John Lee Hooker playbook, but is a harsh, brash, screechy early 1960s recording cut loud. The Ayre – like any good audiophile amplifier – doesn’t mask these qualities, but it also doesn’t destroy the music by emphasizing the flaws. A lot of this comes down to that fluid naturalness normally associated with valve amps, but this time without with the associated softness in the bass or a laid-back treble, and with a lot of power in reserve.

But all this could easily be attributed to any one of maybe a dozen or so very decent amplifiers. The Ayre AX-5 twenty uses unique technology and claims it makes a difference. Where does this difference appear? Put simply, late at night, early in the morning, or any other time you need to listen to music at less than ‘lusty’ levels. This is when an amplifier really shows its hand – some seem to underplay bass, or lose some upper-mid clarity at quiet levels, as if the loudspeaker is dominating the presentation. Here, the Ayre’s character stayed uncannily intact even at whisper quiet levels. Even the fun aspect of musical replay, which usually demands a fair bit of volume to realise, came across at low levels.

That Ayre makes a well-engineered amplifier in the AX-5 twenty is something of a given; the brand has the reputation for good design and well-made products. That it sounds this good under such a wide range of conditions shows just how good Ayre is at making amps. If there is a sweet spot in audio amplifiers where quality, performance, and price converge, then the AX-5 twenty must be sitting right in the middle. Strongly recommended!

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