The nineteen seventies saw Japanese companies experimenting with different types of output devices in a bid to bring better sonics and greater power – for example, Sony and Yamaha launched super sounding but unreliable V-FET amplifiers at the beginning of that decade. But the real action started when Hitachi perfected the mass production of the MOSFET (Metal Oxide Silicon Field Effect Transistor) in 1978. Conventional transistors worked by permitting a small flow of current to control a larger one, but MOSFETs switched by voltage control – which required far less energy, and in turn produced less heat. The result was that the same amount of silicon could yield far higher power outputs than conventional bipolar trannies; simple circuits could make lots of watts. Other benefits included lower noise and less distortion, too.
Hitachi – known as Lo-D in some markets – launched its ‘power MOSFET’ amplifiers with double-page spreads in British hi-fi magazines, proclaiming the technology as special. The HMA-9500 was the flagship power amp, putting out a gargantuan 120W RMS per channel; the smaller HMA-7500 delivered 80W and the HMA-6500 was good for 50W. The matching preamplifiers were nice things to have, but not as interesting as their partnering power amps. Then came the integrateds – of which the HA-5700 was the most affordable. The HA-7700 was the flagship, but due to its price proximity to popular British designs such as the aforementioned A&R A60, was totally overlooked by the British press.
“The Integrated Amplifier which adopted Power MOSFET”, is how Hitachi touted the HA-5700 in Japan. It was essentially a stripped-down, cost-cut HCA-9500/HMA-9500 – and that was no bad thing. Selling for Y70,000 in its native market under Hitachi’s Lo-D brand name, in the UK it was sold as a Hitachi and cost around £195. That was a lot of money for an integrated amplifier back then, and put it firmly in the upper mid-fi segment. Pushing out a claimed 2x50W RMS per channel into 8 ohms, it had superb measured performance for its day. Total Harmonic Distortion was quoted at 0.02% (20Hz-20kHz), frequency response was 10Hz-100kHz (+0.5, -4.5dB) via line and 20Hz-20kHz (±0.3dB) into phono. The latter had switchable sensitivity, with 0.25mV or 2.5mV. Signal to noise ratio of the amplifier was 100dB, claimed. This was breathtaking for 1979.
The shiny brushed aluminium front fascia panel is full of features; bass and treble knobs gave ±8dB at 100Hz and 10kHz respectively; there’s also a defeat switch, a mono button, loudness and subsonic filter (15Hz, 6dB/octave). Full twin-deck tape monitoring is offered, plus MM/MC phono, tuner and aux inputs. Switching for two sets of speakers is provided, and there’s a switchable, dual range LED power meter for added showroom appeal. The large 435x110x383mm case is heavily vented, because the HA-5700 runs surprisingly hot – being heavily Class A-biased. Quoted power consumption is a solid 140W.
Total weight is 10.8kg, in no small thanks to a dual power transformer power supply, each with 1,000mF of capacitance. Inside there’s a wealth of Hitachi’s own components to be found – a reminder of the company’s industrial might at this point in time. The preamp section has two main ICs, one for the tone control circuitry and another for the phono equalisation. The direct coupled power amplifier sports 2SK133 and 2SJ48 power MOSFETs complete with a large heatsink bar that runs from one side of the chassis to the other. Robust protection circuitry is also fitted.
The HA-5700 gives high quality sound with serious levels of grunt, and is remarkably consistent across all inputs, into many different loads and also at anything from low volumes to almost full rated output. That’s a great feat for an amplifier of this era, and a rare one too. Sonically, Hitachi MOSFET amplifiers were criticised for being a little analytical sounding, and I think that’s fair – but only to an extent. Actually, fed with a good source, properly warmed up and with the tone defeat on, it proves an enjoyable listen. It has a very interesting sound; it’s very ‘hi-fi’ inasmuch as the treble is quite sweet but slightly opaque; the midband is a little stark and unromantic but it is never, ever, harsh (thanks to its low distortion) and the bass is dry and taut and decently tuneful – although you’d never call it gushing with emotion!
The end result is a very tidy sounding amplifier, one that isn’t as transparent as the best Class A designs, but which is smooth and unerringly powerful. The sheer weight of bass is a little lighter than you’d expect from an amplifier that’s built like a brick outhouse, but it has great reserves of power and never compresses things as the volume control goes northward. Actually, this is its great trick – some amps start sounding better than the Hitachi then begin to lose the plot as the going gets tougher and the music gets louder or more complex, whether this remains utterly unflustered and unflappable all the time. Its this consistency and even-handedness than begins to make you warm to it, even if it’s not the most romantic sounding design in many ways. In this respect, there’s shades of the Audiolab 8000A and also the Myst, which trainspotters will know also ran Hitachi MOSFET power output devices.
Hitachi’s MOSFET amplifiers aren’t for everyone – valve fans for example may run screaming in the other direction – yet they still have an undoubted ability. It you want the hi-fi equivalent of a JCB, this is it. Brilliantly for the secondhand buyer, they’re still cheap and relatively plentiful – and the HA-5700 is the most. Pay up to £150 and you’ll have a great workhorse, and you’ll cast a wry smile when your hi-fi friends make snide comments behind your back. Quality shines through…