Musical Fidelity A100

The Musical Fidelity A1 design story is well told now. Tim de Paravicini takes it up. “I try to be inventive, I don’t copy people if I can avoid it”, he told me. “The idea started life as a circuit on a breadboard that I designed to have relatively low feedback and which behaved like a valve circuit”. He specified the basic dimensions and heatsink methods, and the result was what he calls a “waffle toaster form”. It was truly a matter of form following function though, because the A1 looked as it did in order to manage the heat. “It needed to deliver 20W RMS per channel whilst running below 65 degrees centigrade.”

The A1 was a novel design, even for a Class A product. It used self-biasing and complementary output devices in symmetrical, push-pull configuration from the front end to loudspeaker terminals. Its biasing made sure the output could only operate with constant power consumption. The line and phono amp circuitry were discrete op-amp designs. Tim says that inexpensive Taiwanese 2N3055 and 2N2955 transistors were used “to prove a point”.

Clever stuff – it was true affordable esoterica, a high end amplifier from a virtuoso designer in an inspired and zeitgeisty aluminium case. It was so nineteen eighties, in a way that seemed modern, brave and optimistic at the time. The (then rare but highly fashionable) all-black finish complete with powder blue fascia lettering and a half-moon power neon were exquisite details that sealed the deal. 

Living with an A1 was a bittersweet symphony, however. Its reliability was patchy to say the least, although it’s true that it has been perhaps unfairly singled out – many British ‘super integrateds went pop all too easily, back in the day. The problem was that the heat inside the amp slowly cooked the components over time, leaving electrolytic capacitors in a particularly bad way…

This was exacerbated by the fact that bizarrely, in the first production run of the A1, there were no cooling slats in the side panels! Industry rumour has it that the later examples of the A1 had the bias turned down, with the cases getting slightly less toasty due to the amp running more in Class AB mode. There are other stories of A1s coming back to the manufacturer for repair after cooking their electrolytic capacitors, only to return to the customer with new caps and the bias tweaked down a little. In other words, it’s hard to understate just how close to the edge the A1 was as a consumer amplifier proposition. 

Putting all its cooling issues aside, there was one other thing that made the A1 hard to live with – its low output power. Back at that time it was difficult to find a modern pair of loudspeakers that could best exploit the A1’s paltry 20W per side power output. The figure would have been acceptable in 1974, but a decade later it simply was not. Only true A1 aficionados – and there were admittedly quite a few – persevered with it, hooking it up to all manner of weird and wonderful, obscure but highly efficient speakers. Naturally though, the call came for a higher powered version, and Musical Fidelity’s Antony Michaelson duly showed what a good listener he was…

The new A100 arrived in 1985, selling for £399. Effectively an A1 on steroids, “it basically had the same sound but more grunt. I wanted this valve quality, without being syrupy-stupid”, Tim told me. It kept its little brother’s looks but was housed in a slightly taller case that permitted the use of a chunkier power supply and twin cooling fans. This time around by the way, the sides of the case were peppered with cooling holes; unlike the A1 these didn’t arrive in a revised version! The new amplifier produced a claimed 50W RMS per channel into 8 ohms, a big step up from the A1 and giving it true, real-world loudspeaker driving ability. Much the same circuit was used – aside from a larger power transformer with split rails and a 38V DC supply (instead of the A1’s 24V). Musical Fidelity claimed the A100 ran in 99% Class A, which explains the heat it put out. This is arguably more than the A1 ever was, especially the later versions.

Unlike its little A1 brother – which was left to keep itself cool via convection – the A100 had twin slow-running 60mm 12V AC Papst cooling fans. These were thermostatically controlled, but still struggled to keep temperatures down. On a well preserved A100, you’ll find these fans to be near-silent, but hammered examples have noisy fans due to the combination of heat and the sleeve bearings drying up and/or failing. These fans are marginal at best, so need to be in tip-top condition.

Everything else is carried over from the A1, including the amplifier’s poor distortion figures. The good news was that these were almost exclusively benign-sounding even-order harmonics (largely second harmonic), the exact same type that gives valve amplifiers their distinctively warm and fluffy sound. The type of performance figures that the A100 and its little A1 brother had – listing total harmonic distortion as typically around 0.1% – are poor by modern solid-state standards. Yet this is part of the mystique surrounding this highly eccentric amplifier, as it does so much else so well.

The A100 sold for three or so years, during which time the fast-growing Musical Fidelity pushed really hard to repackage the circuit in different formats. The MA50 was arguably the most successful variant, effectively a power amp version of the A100 minus the preamplifier circuitry. It sported a 36V supply, with the outputs of left and right channels paralleled at the loudspeaker sockets. It too had cooling issues, but wasn’t quite as highly strung as the bonkers A1.

The nineteen eighties was a crazy time for hi-fi with some truly left-field products coming out, and this was one of them. A recapped A100 sounds superb, and quite unlike anything around today. All that’s been said about the A100 over the years is basically true. It has a lovely sound, one that’s exotic and surprisingly devoid of flaws – despite being such an eccentric design. Indeed, you can’t buy anything new that sounds anything like it – it’s as close as you can get to a solid-state valve amplifier. Tonally it’s lovely; there’s a warm, silky, saccharine taste to its sound that makes everything you play seem like it’s been subtly sepia tinged. Yet it’s not the sort of coloration that totally takes over the recording; instead all is clean, sweet and agreeable.

It’s true that the A100 cannot muster up a brawny bass response; the power supply is thought to be at least in part responsible here. Feed it some classic eighties Scritti Politti in the shape of Perfect Way and you’re struck by the purity of Green Gartside’s vocals, and the nicer-than-real handling of the drum machine’s hi-hat cymbal patterns. But the thick, fat bassline is texturally pleasant but lacks the grip and definition of a Mission Cyrus 2/PSX of that period. Instead you get a sumptuous and tuneful sound, but one that’s closer to a decent tube amp than a solid-state one.

The midband is where this amplifier excels, and you soon get to realise this is where the action is in most music. Feed it some classic REM for example, such as Fall On Me, and this lively and forward sounding mix is gentrified slightly, and given more room to roam. Indeed, this amplifier has a superb spacial quality at the price, one that placed the vocals dead centre and slightly hung back, with all the accompanying musicians set behind him further still. On a Cyrus 2/PSX of the same vintage, you experience the track as far more aggressive and upfront, yet somehow lacking in musicality. 

Essentially then, the Musical Fidelity A100 offers a unique sound – one that’s butter-smooth, sugary sweet and decently powerful to boot. Yet its stellar midband is what really impresses most people; it has excellent clarity, detail and instrumental separation. Overall, it’s as close to a good valve amplifier that a solid-state amp can get – including the heat at which it runs. If you want a good one, expect to pay around £500 – and then be amazed by how you got such a refined sound so cheaply.

In terms of buying, the Musical Fidelity A1 and its siblings have got a bad reputation – but it’s important to be fair here. They were far more affordable than the quality of their design would suggest; you could say they were expensive products made cheaply, or at least built down to a price. This put genuinely exotic sound within reach of a wider market, but also meant that they were less reliable than most Class AB rivals. To be fair, Musical Fidelity didn’t build these amplifiers to be working perfectly thirty five years on – and no manufacturer does, so we shouldn’t be too critical. That’s why when buying an A100, you need to look carefully at both its overall condition, and any servicing it may have had – and get the best you can afford.

In the case of the A100, that means you need an amp with quiet cooling fans, because it runs hotter than a bandana on a nineteen eighties glam-metal guitarist. These are no longer available and it’s hard to find obvious replacements, so they’re critical. This done, everything else is reasonably fixable. Any amp of this age will need to be recapped, and the more it needs this, the lighter and less punchy its bass will sound. My favourite classic amplifier restoration house, Amplifier Repair Services (www.amprepairservices.co.uk) can do this for under £200, which is excellent value, although they cannot replace noisy cooling fans. This not only makes the amplifier more reliable over the long term, but the sound will be better too as the original product came with cheap capacitors which are easily bettered now.

Other issues include the disintegration of the rotary source selector, which can happen with overuse. Also, dirt in the contact track of the volume control can cause it to get noisy; a squirt of Servisol contact cleaner normally fixes this. As the audio signal in the preamp runs through the tape monitor, if the contacts are dirty on this switch the sound will suffer – ideally it’s best to bypass it. Finally the black paint can scuff off the case; if it’s ever resprayed it needs to be done with VHT-type heat resistant paint. This done, you’ll have something that’s truly special by any standards – true affordable esoterica.

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