I’m a fan of far-eastern hi-fi, especially the output from China of late. They produce some killer kit at bargain basement prices using fairly generalised chipsets of varying specification. They usually measure well and sound great, and given the lack of affordable hi-fi from major brands they are the only way for buyers on a budget to get a foot on the ladder. And if you’re limited on space, or don’t want a rack of separates, these tiny desktop boxes might be just the ticket.
Aiyima recently sent over the A07 MAX – a 300W (into 4Ω) stereo amplifier capable of bridging to form a 600W (into 2Ω) monoblock with its partnering 48V, 12A power supply. It is based on a Texas Instruments TPA3255 class D amplifier chipset, claiming a signal to noise ratio better than 110dB and 0.007% THD, though no reference figures are given for either measurement.
The design is smart with a single-piece aluminium extrusion forming most of the casework, with machined aluminium front and rear panels slotted neatly into the respective sides of the extrusion, clamping the PCB in place. Most of the interesting stuff happens on the back with a single RCA input pair, 3.5 mm audio output, a 5.5 mm power jack and staggered speaker terminals. The terminals are well spaced given the limited space and will take a 4 mm banana plug or stripped wire. You can use spade connectors providing they’re small ones, though they should be sleeves or you risk them touching and tripping the protection if you’re lucky. In mono mode, the two + terminals are used for the output and the left-channel input jack. The 3.5 mm output feeds a buffered signal to a subwoofer, additional amplifier or active speaker system. This output is not controlled by the front volume control.
Long hexagonal standoffs bolt the front panel in from behind keeping visible fixings out of sight. Not that Aiyima doesn’t encourage you to take it apart. Their product information lists a number of compatible op-amps, including OPA2604AP, OPA2134, MUSEO1/02/03, LME49720NA, LM4562 and AD827AQ. The amp comes fitted as standard with NE5532s but the op-amps are socketed so you’re free to engage in ‘rolling’ if that’s your thing. Switching the op-amps out can tailor the sound to your taste to a degree, though it has to be said that getting the best from any op-amp requires further circuit optimisation so chip rolling is one of those audiophile endeavours probably best avoided unless you have a lot of time on your hands, or some electronics knowledge to change out supporting components accordingly. socketed op-amps do make replacement simple though if something upstream or downstream of the amplifier fries one in a fit of instability.
Those op-amps are part of an input buffer, with respective output to feed downstream power amplifiers and an RCA audio input, both with a 1V nominal input sensitivity rating. The single front-mounted volume control, and the switch on the bottom to switch between stereo or bridged mode are the only controls you get. This amp is designed to be used with a preamplifier or a DAC, the output level of which would likely be variable. To that end I’d have liked to have seen the volume control left off altogether. Perhaps substitute it for a simple rotary gain switch to select between a few levels of fixed gain. The volume control doubles as the power switch so you’re forced to use it, regardless of anything downstream.
Elsewhere inside we have a fairly typical implementation of the TPA3255. The power supply reservoir capacitors were only 50V rated in the initial production, so running the amp with a 48V power supply was sailing very close to the wind. They have now been uprated to 63V caps as in the below image taken of the sample I received. If I were going to use the older amp extensively, particularly with a 48V power supply, I would swap them for 63V rated components.
Likewise, the volume potentiometer is a cheap thing. It’s one of those sealed plastic-encased units ubiquitous in Chinese amps and amplifier boards. Channel balance suffers as a result, though it has to be said my example was far better in this regard than the unit tested at ASR.
If your’e interested in comprehensive measurements, Amir at Audio Science Review tested the A07 both the stock 36V, 6A power supply, and a 48V 5A power supply. The A07 max is available with the 36V power supply or a 48V 12A power supply unit as standard. This is the version Aiyima sent for this review.
With the 36V power supply you get about 75W per channel into a 4Ω load at below 1% THD. The output nearly doubles with the 48V power supply, assuming the power supply can deliver the current it claims. Amir’s bridge mode tests indicate that the 36V power supply, at least, is not capable of the full 6A current rating as it produced significantly more power with a 48V 5A unit in a current limited power test.
I have no way to accurately assess the maximum current capability of the 48V power supply I was sent, though in reality this is all immaterial. It is unlikely that any speakers you might pair with this amp will demand particularly high power or current, and 75W with a bit of headroom can make a lot of noise in an average domestic room. These amplifiers aren’t selling for thousands, nor are they claiming to be the next best thing in audio. You could spend a lot more money – a thousand times the cost of the Aiyima – and do a lot worse.
When I look at these amps I consider stability, reliability, protection for upstream and downstream equipment, and sound quality to be the primary concerns. These are not high-end power amplifiers, nor are they built with military spec components. They sound exactly as the measurements suggest – very flat and even-handed, with surprising dynamics and plenty of power. Current delivery isn’t a strong suit, but using a switching power supply means the limited reservoir doesn’t hamper dynamic performance to any significant degree.
The Aiyima amps do suffer variance in frequency response with load, unlike the best class D implementations by Hypex, Purifi and IcePower. However in practical terms this isn’t a dealbreaker. The kind of speakers you are likely to pair with this amplifier will be skewed in response to a far greater degree than the amplifier is. They’re also likely to be fairly easy to drive, as most budget models are, so will be an easy load for the amplifier. That’s not to say you can’t run £20,000 speakers with an amp like this; you certainly can and you’ll likely be pleased with the result. But with the components being chosen for economy and the on-chip protection of title use if the chip itself goes up in smoke, it’s a decision you might end up regretting.
I paired the A07 MAX with Michael Fidler’s S30 preamp, spartan 5 phono stage, a Sony CDP-XE370 CD player and a pair of restored AR18BX loudspeakers that I must get around to detailing here. The result was excellent – a genuinely wonderful sound that belied the price. I could have cut further corners – the preamp, for example, is itself several times the price of the A07, but it was all I had to hand. Aiyima themselves sell a couple of preamps and tube buffers, and DACs with variable outputs that would be an ideal match.
Aiyima’s A07 Max is a fantastic budget (around £100) amp if you want to assemble a tiny system with plenty of power. The flexibility to use it as a stereo amplifier or to pair them up as monoblocks in stereo, bi-amped or even tri-amped configurations is a tremendous advantage for the money. A stack of 4 or 6 of these little boxes with suitable speakers and a decent front end to drive them would bely its size.
If you’d like one for yourself and would like to support my work, purchase your A07 MAX through Amazon using This Link. Amazon pays a small commission on each sale at no cost to you, and it helps keep independent sites like Audio Appraisal alive.
