Hands up those who have seen a Bryan amplifier before, let alone heard one. Me neither – until I unpacked the Mark III Model 500/700 pairing seen here. The first 500 arrived when higher-power transistors were beginning to be used in quality audio, yet while the technology became universal, British brand Bryan sank without trace.

The Cheshire company's first range of stereo transistor amplifiers was launched in 1963 – a respectably prompt start for such a small manufacturer. One advance brought by higher-power transistors was that they made it possible to eliminate the component that was the most difficult to design when it came to valve amplifiers: the output transformer. This transformer is needed because valves are high impedance devices. They work at high voltages yet pass on small amounts of current.

All exposed ready for chassis-mounting, the Model 700 power amp includes a hefty frame AC transformer and a pair of OC35 germanium transistors, on heatsinks, per side

Conventional loudspeakers work the other way around in that they require large currents at low voltages. This conflict is solved by an output transformer, which matches the two characteristics in much the same way a car's gearbox matches the engine's power to the speed and torque required at the vehicle's wheels.

Fragile State
Valve amps have worked like this since the 1920s, but for quality applications the cardinal issue was (and remains) that of designing an output transformer that is sufficiently phase linear across the audio band to allow enough negative feedback to be applied to reduce the amplifier's distortion figure to an acceptable level. Transistors, on the other hand, already work at high currents and low voltages and can therefore drive a loudspeaker load directly. In the circuits used by Bryan (and everyone else during this period) it was necessary to place a large capacitor between the transistors and the loudspeaker to block the DC content still present in the signal, but this introduces far fewer difficulties than even the very best transformers.

Bryan's Model 900 integrated was reviewed in HFN Oct '66, the Mono 303 amplifier a few year's earlier in HFN Nov '63

However, the situation was not yet ideal, for the transistors available in the early '60s were fabricated not from silicon but from germanium. This meant they were fragile, heat sensitive and noisy. Care was therefore required to obtain the best performance from them, although the major semiconductor manufacturers (Philips in Europe, RCA in the US) produced copious application notes to get designers up to speed with the new techniques. Bryan did not have to design its amps from scratch; the key circuit blocks were already developed and in place.

Life Of Bryan
The company's 1964 range consisted of the Model 400 integrated amp and Model 500 and 600 pre/power pairing. Both offered similar performance, but while the 400 was free-standing the 500 and 600 were made for cabinet mounting. One piece of valve practice Bryan retained was to have the preamp take its power from the power amp via a thick umbilical cable. Improvements came in 1965 when the 500 became the Mark II 500. The key change was that the MM cartridge input now met the widely accepted 2.5mV into 50kohm standard rather than 5mV into 6kohm. At the same time, the Model 600 became the 700, retaining a 13W-per-channel maximum output but with a new layout that reduced the amp's external dimensions.

The Model 500 control amp is built onto etched-copper circuit boards and features a deal of point-to-point wiring – all by hand, of course

The Model 500 was tweaked again for 1966 to become the Mark III. The action of the bass, treble and balance controls was improved, as were the tape recorder connections. Outwardly the control knobs gained polished aluminium inserts and the size of the power amp was again reduced. An FM tuner/preamp was also offered, but the big news was the introduction of the Model 3000 – an integrated combining both halves of the 500/700 in one chassis.

Top of the Model 700 showing reservoir caps and fuse protection. The underside [bottom] includes ACY17 and OC45 germanium transistors and full-sized passives. SMDs were years away...

Bryan was keen to promote the reliability of its amps and these models were shipped with a five-year guarantee – virtually unheard of at the time. This came at a price though, as a Model 3000 cost £56 when a Leak Stereo 30 was just £49.

Not So Modern
The Mark III 500/700 has a charm to it, but by 1966 amps like Sony's TA-1120 [HFN Sep '13] were appearing which defined a new generation of 'user experience'. Suddenly, the idea of mounting metal boxes linked together by heaving cabling into holes cut into furniture did not appear so modern – transistor circuitry or not.

Another aspect of the design which harks back to an earlier era is the optimisation of its output stage for 15ohm loudspeakers. The fact that no output transformers are used means little can be done about this, but in practice the design works well enough with standard 8ohm types. The Mark III 500's Perspex front panel is well stocked with controls, but the rumble filter and treble-cut filter at 4, 6 or 9kHz should no longer be needed with modern equipment. The function switch, which reverses the two channels and gives three versions of mono reproduction, is best left simply set to 'stereo'. Another quirk of the design is that the power switch is combined with the balance control and not with the volume, as one might expect.

Bryan's mid-1960's amplifiers were joined by a partnering FM tuner/preamplifier, complete with volume/on/off knob and selector for the BBC's Light and Home services

Live 'N' Dangerous
Of the various inputs available, PU2 should match any modern MM cartridge. The auxiliary group (radio, tape, aux) all suit components like CD players, though the sensitivity is a little on the high side. Bryan does provide a four-position preset volume switch on the rear panel which should help, but in practice I found that both treble and bass sounded curtailed at the lower settings. Things fill out when the higher gains are chosen, but it sounded a bit too brash on the top setting. Second from top turned out to be a workable compromise. The PU1 input was designed for ceramic cartridges and is unequalised. This would be a good place to connect an external phono stage, as long as its output level is not too high. Both units were designed for mounting in a cabinet and the Model 700 power amplifier bristles with live connections which pose an obvious hazard if the unit is used uncased. The 500 control amp, meanwhile, runs from a low voltage but still presents a potential danger because the AC mains switch wiring runs through it. So paying careful attention to the earthing arrangements is vital.

Tim Listens
Bryan's promotional literature declares that the 700 provides 'flawless bass' and 'superb transient reproduction', both claims due to the elimination of the output transformer. The response is also said to be substantially flat from 40Hz to 20kHz with 'no hum', so it should sound pretty good. And indeed it does – this amplifier has a surprisingly modern sound for something based on germanium technology. I don't think I ever managed to squeeze a full 13W of sound out of it without obvious distortion making its presence felt, but in the usable range below this, where it can still see off any valve amplifier based on ECL86s, ECL82s and the like, there was sufficient level for 'proper' listening.

Rear of the Model 500 has RCA inputs for MM and ceramic pick-ups, 'Radio', 'Tape' and 'Aux' plus a tape loop and preamp output. The octal socket feeds AC mains to the partnering Model 700 and PSU rails back to the 500 via an umbilical with L/R input leads tied alongside.

Tonally the Bryan combo sounded balanced. I'd imagine that the designers wisely cut off the very low bass to prevent the expensive output transistors working too hard reproducing record warps, but what remains is pleasingly dry. Equally, some more modern designs can produce more treble sparkle, yet it is the avoidance of a prominent midrange that makes this a satisfying amplifier to listen to.

Being critical, the bass isn't quite 'flawless' as it has a discernible muddle in its lowest register that can cause it to bloom and give it a 'one note' quality. I was also aware of a haze present over the rest of the sound that manifested itself as a blurring of each element. This was certainly subtle, but it prevented pin-sharp focus being achieved. In these two observations I am admittedly judging the Bryan amp against the best in class performance of newer and more expensive equipment, in order to illustrate where its limitations lie. In the context of designs that were on the market at the time, it remains an impressive performer indeed.

King Crimson
Mark Knopfler's 'Madame Geneva's' from Kill To Get Crimson [Mercury 1724908] sounded suitably warm and intimate through the Bryan pairing, as befits a close-miked acoustic recording. Solid vocal centre presence made it easy to relax into the sound, which was marred only by an occasional trace of roughness around some of the guitar notes. With material like this it would be hard to ask for more from an amp. After all, there's something appealing about hearing simple recordings through well designed circuitry that isn't too complicated.

By contrast, Handel's 'Arrival Of The Queen Of Sheba' [DG/Archiv 447 279-2] was rendered in a less satisfying manner. The performance was surprisingly bright and lively, but the lack of full bass extension meant that overall the sound was on the strident side. Clarity across the orchestra was retained to an impressive degree, yet I couldn't escape from the idea that the soundstaging lacked both width and depth compared to when the piece is heard through some more capable amplifiers. It is only possible to judge the Bryan 500/700 pairing to this standard because it gets the basics so close to right – I've heard much newer amplifiers which are far less enjoyable. For this alone the duo earned my admiration. One can only speculate how far Bryan would have got with the lineage had the company lasted a few decades longer.

Bryan amps, distributed by Tellux Ltd, Romford, featured in the 1963-65 Hi-Fi Yearbooks (Model 400, 500 and 600 power amp are seen here)

Buying Secondhand
Both units were solidly built and finished to a good standard. Our example was fitted with many small capacitors from Philips and these have proved to be famously durable. As such, they are best left alone.

Problems usually centre around the transistors – noise, lack of gain or silence from one channel or the other normally resolve to a transistor problem. Replacing the OC45 transistors used in the preamp with AC107s will result in improved noise performance – if you can find them. The OC35 output transistors can be replaced with slightly sturdier AD149s if these are faulty.

Hi-Fi News Verdict
A glimpse of the future wrapped in the cabinetwork of the old, I imagine the Bryan Mark III Model 500/700 would have changed the minds of many who thought transistors could never adequately replace valves. This duo is not easy to setup and use safely with no case for the Model 700, but the all-enclosed Model 3000 would make a fine choice for anyone keen to hear the sound of germanium transistors.

Bryan Mark III Model 500/700 Pre/Power Amp Lab Report

Over a half century out of its five-year guarantee period, our sample of Bryan's Mark III Model 500/700 combo was still going strong. Specifications from the era are limited and the 2x13W power output needs to be viewed with some caution as this was rated into 15ohm, not the 8ohm standard of today. However, the 2x6W/8ohm achieved here is largely in line with what might be expected, and the 2x10W/4ohm rather better still. Unusually, output under dynamic conditions was less than its continuous power [see Graph 1], ranging between 2-4W from 8 to 4ohm even with a high 5% limit on the acceptable distortion. Harmonic distortion was also rather higher than the 0.25%/10W quoted by Bryan Amplifiers Ltd back in the day, this figure also referenced to an easier 15ohm load. Into 8ohm, midrange distortion increased from 0.9%/100mW to 1.9%/1W and 2.1W/5W. Distortion also increased significantly at low frequencies to 8.5%/20Hz and high frequencies to 4.4%/20kHz (all re. 0dBW).

Otherwise, the Model 500/700 combination matched or exceeded its other specs, including its 40Hz-20kHz/±1dB frequency response, with bass/treble controls set to 12 o'clock. In practice the roll-off was pronounced above 20kHz, falling to –3dB/25kHz and –40dB/100kHz, while sub-bass extended to 14Hz (–6dB), albeit with a max +1dB 'boost' from 40Hz-200Hz [see Graph 2, below]. The 'Rumble' filter [dashed trace] kicks in a little earlier at 23Hz (–6dB) while the HF 'Scratch' filters almost exactly meet their 4kHz/6kHz/9kHz (–6dB) roll-offs. Finally, the combined 500/700 amps' gain is +31dB (Aux input) and although the A-wtd S/N ratio is a little below par at 75dB (re. 0dBW), allowances should always be made for vintage pieces. PM

Continuous output vs. distortion into 8ohm (grey trace) and dynamic power output vs. distortion into 8ohm (black trace) and 4ohm (red trace)

Freq. response (black); rumble filter (dashed), 4kHz filter (blue); 6kHz (green) and 9kHz filter (red)

• Power output (<2% THD, 8/4ohm) 6.1W / 10.5W
• Dynamic power (<2% THD, 8/4ohm) 2.3W / 3.8W
• Output impedance (20Hz-20kHz) 0.25-0.95ohm
• Freq. resp. (20Hz-20kHz/100kHz, 0dBW) –1.4dB to –1.5dB/–39.7dB
• Input sensitivity (for 0dBW/6W) 77mV / 235mV
• A-wtd S/N ratio (re. 0dBW/6W) 74.9dB / 82.7dB
• Distortion (20Hz-20kHz, 1W/8ohm) 2.4-8.5%
• Power consumption (Idle/rated output) 8W / 40W
• Dimensions (WHD; Model 500/700) 279x108x175/257x156x168mm 

Review: Tim Jarman

Source: www.hifinews.com