Briarsfield Hi-Fi - Technics A900 Mk II

The A900 sat on a pedestal, right at the top of Technics' 'normal' audio range with some audiophile features which would normally cost well above £1,000. Launched in 1996, the original retail price was just shy of £800, for your money you got the SU-C800U Mk II pre amplifier and the SE-A900S Mk II power amplifier, both combined into an integrated amplifier combo which sat above Technics' range of integrated amps and which posed as a fully fledged pre-power combo.

Our Technics A900

I bought one of these 'ex-demonstration' in 2000, developed almost a 'love hate' opinion of it over time. Actually, it was my first foray into the realm of higher end audio, for that alone I feel that I should cut it some slack.

One thing I should mention here, Technics have always gone in more for technology and quirky features than a brand like Pioneer would - for example, Technics started filling everything to the brim with ICs back in the days when a more 'serious' brand such as Pioneer wouldn't have touched those components with a long stick because they weren't judged to be anywhere near good enough for high quality audio. This isn't a slight against Technics, I've owned a lot of Technics gear over the years and remember much of it fondly, I'm just trying to give some context to the rest of this article.

The sound was a revelation at the time, it definitely had power but the actual tonal quality was quite soft, a definite contrast to the bright, flat, almost 'heavy' characteristic sound that I had always noticed in Technics gear before.

The whole thing was quite heavy and weighed in at around 15kg, the vast majority of this being the weight of the power amplifier.

This was slimline and very lightweight, as it took power from the power amplifier via a small umbilical cord and hence didn't have the weight of its own supply. Much was made at the time of the pre and power not actually being truly separate, but was this really a handicap or a shrewd cost saving idea?

Power supplies are probably the most costly part of audio gear. They're heavy, in the case of power amplifiers they require some large components, for sensitive low level circuitry they need to be designed for good regulation and very low levels of noise. Technics' famed AVBO (Advanced Virtual Battery Operation) circuit uses a dedicated circuit to smooth the output from a second transformer in the amplifier case and send the smoothed voltage to the low level circuits inside the pre amp. By keeping the power supplies all in one place and away from the signal circuits it's not only cheaper but also helps eliminate any noise problems at the signal end. So quality and build are sometimes a two edged sword, in this case a small cost saving works well for the design.

Signal lines were quite pure, running through the CD input there was little more than a relay, a couple of capacitors and an op-amp. There was a tone defeat switch but this only switched out the filter components themselves, not the actual amplifier section.

As with most higher end audio gear the tone controls were based at the far ends of the audio spectrum (50Hz and 20kHz). This actually works very well, you could add a lot of weight to the low end of the bass without making the sound overly murky; to me, the region below 100Hz is the 'sweet spot' for bass, this is where many loudspeakers begin to run out of puff and need it most.

Everything else was pretty unremarkable. All switching except for CD was done via Toshiba branded IC switches, there was a reasonably good phono stage, a tone defeat switch and a remote control.

The A900S power amplifier was the most interesting part of the combo. Quoted power was somewhere around 85 watts into 8 ohms, 120 watts into 4 ohms; I did feel that this was a bit optimistic at times, the soundstage would begin to harden before the meters were peaking past the 10 watt mark, although it would drive them all the way across without audible distortion if you pushed it hard enough.

Inside was a reasonably sized single power supply feeding both channels via a pair of 10,000µF capacitors of Technics' own design. Down the middle was a large heatsink, attached to that a pair of MOSFET IC power modules. There were two sets of loudspeaker sockets, both being relay switched via the front panel.

The most striking thing about the amplifier were those huge retro style VU meters, these were heavily damped and would gently dance around in a fluid motion...watching these at night with the lamps switched on was mesmerising.

After a while I noticed the amp developing an annoying problem, depending on the volume the left channel would drive the power meters a bar further than the right channel. Barely audible but it would eventually drive me crazy. This turned out to be the volume control and set the upgrade bug going.

The A900 was never going to be a contender for a high end amplifier even if it was rebuilt - the design limitations rooted it firmly at the top of the mass market 'mid-fi' audio market and it would have been difficult to improve these by much margin. It had power, not a great deal by high end standards but with the room and speakers I used it in it had enough, the actual tonal quality and transparency were enough to make me think it deserved upgrading somewhat.

The first step on the upgrade route was the volume control. This is something which bothers me with a lot of modern equipment, the volume controls are too sensitive. Grab a really highly powered piece of high end vintage gear and the volume control is still very gentle, you can use the full range of the control. With most modern equipment by the time it reaches 9 o clock the sound is already pushing the meters halfway on their scales. For some unknown reason, the original control behaved more like a linear type, even though it was labelled as a log part - I changed it for a higher quality logarithmic one better suited to audio.

The volume control is remote controlled so this limits the amount of upgrades available. Ideally I would have fitted a stepped attenuator but this would have meant losing the remote control; I never even used the remote but keeping everything original as far as possible was important. The original seemed fairly good quality but was unbranded and the mismatched channels problem speaks for itself. In the end I fitted an Alps Blue Velvet, for the price they're a very good upgrade and luckily they're also sold as a motorized version for remote control.

The difference in size shows the quality difference between the Alps and original part, however there's enough space in there albeit with some cutting, the original PCB won't fit the new part but that's okay - it can be hard wired and I was going to ditch the original connector sockets in favour of direct soldered connections anyway (direct soldered connections are always better for low level audio).

The volume shaft needed to be modified, most higher end equipment uses 6mm round shafts with the control knobs fixed on with grub screws; however, the knobs here are fitted to D shafts and I wanted to keep things as original as possible. A flat to accept the knob is carefully ground into the shaft, it takes care to make sure everything is kept square while this is done and not to remove too much material.

Originally, as with most mainstream equipment, these were built with low grade tin/nickel input sockets. These sockets are ok on normal cheap plugs but once you start using higher grade cables with better plugs you encounter problems where they don't always fit well and also the sockets break very easily under the weight of better plugs and cables.

You can buy sockets already mounted on a chassis to solder straight into your PCB. These are fine - however, just to be difficult Technics use a slightly different socket pitch which is difficult to match.

The sockets were custom made - chassis phono sockets fitted to a 1.2mm aluminium chassis, the holes for them punched for neatness and then wet sanded to remove any burrs which could cut through the insulation and cause ground loops.

Because of the design of the case, it was difficult getting everything lined up and fitted together, I ended up locating them with dabs of solder and then fixing everything together after test fitting.

The custom made input sockets, during assembly (L) and after fitting (centre and R). Connecting wires are angled to fit original holes in PCB. Thick blue interconnects are new pre-out jumpers between pre-amp and amp. Click images for larger version..

Op-amps are small ICs which replaced transistors in almost all audio gear after about 1980. These look just like a generic IC, the selling point of these was that they could make a complete audio circuit with just a power supply and a handful of small components.

The Technics pre amp used two op-amps, one for the phono stage and one for the tone circuits. These amps have a surprising influence on the quality of audio you hear, just as the quality of your amplifier or speakers does. We're not talking a 'night and day' difference but definitely a change in character and tonality if you listen.

Large companies have to work to tight price points. Using a marginally better part which costs $0.20 more ends up a great deal if you build 100,000 units with that component, the company bean counters would need to offset this extra cost against perhaps thousands of other factors to keep to their profit margin.

Hence your very expensive £800 amplifier will often contain some very cheap, outdated parts.
The amp used in the tone circuits of the pre-amp was a 4580DD, a warmed over version of the old 4558 which was ubiquitous in audio equipment from around 1980 - the DD means that it's a slightly more expensive lower noise version than you'd get in a base model £120 amplifier. The phono stage used a AN6558 because the noise and slew specs of the lower chips just weren't good enough for the sensitive phono input - this is a decent components but there are still better alternatives.

After a lot of listening I replaced the tone amp with an NE5532, not the most expensive but seemed to work well. The phono stage got a more expensive low noise OPA2604, the improvement in sound quality this makes over the original 6558 was impressive, on a par with some dedicated phono stages.