Richard Allan Class A amplifiers

The Richard Allan versions of Jim Sugden’s amplifiers made their first public appearance at the Audio Fair, held at the Hotel Russell in London, 18th - 21st April, 1968.

Richard Allan were well established as a manufacturer of excellent loudspeakers. They were located in Cleckheaton, Yorkshire, and were near to Sugden. They had got into discussions with Jim Sugden and arranged to market his Class A designs under their name. This was useful for both parties. Jim Sugden was developing exciting designs that audio fans were interested in buying, and Richard Allan had extensive experience with manufacturing for the UK Hi Fi market. The result was a dramatic change from the Si 402 so far as the customer was concerned. The price for the Richard Allan A21, announced in April 1968, was just 52 Pounds (49 Pounds if you didn’t need the wooden sleeve for the amp.). This was about half the predicted price for the Si 402. The A21 was also an neatly styled integrated stereo amp, complete with control unit, RIAA disc input, etc. Hence it was a far more attactive proposition for the domestic audio market than the Si 402.

In their issue cover-dated April 1968, Hi Fi News ran a “Show Preview” for the Fair which included:

“Richard Allan: Celebrating their 21st Birthday this April, Richard Allan offer one of the Show’s most interesting departures by entering the amplifier field with two Class-A transistor systems. Designer behind this project is James Sugden, known to readers through his various articles on the subject.”

The two systems were the the A21, an integrated amp, and the more powerful C41/A41 pre/power combination.

Specifications for the A21.

Max o/p Power into 6 Ohms	10 Watts
THD at 7·5 Watts	0·25%
THD at 1 Watt	less than 0·03%
Frequency and Power Response +/- 1dB	20Hz - 20kHz +/-
Output to Tape Recorder	200 mV
Input sensitivity: Radio / Tape / Aux inputs	200mV 250 kOhms
Disc 1: Magnetic Cartridge input (RIAA)	3·5mV into 70 kOhms
Disc 2: Ceramic Cartridge (Flat)	50mV into 1MOhm+470pF
Overload capability	20 dB on Disc
Noise (30 phon weighting) 200mV inputs	-80dB
Noise (30 phon weighting) Disc 1	-70dB
Noise (30 phon weighting) Disc 2	-65dB
Rumble Filter (built into RIAA)	12dB per Oct below 45Hz
Bass Control	+/- 16dB at 40Hz
Treble Control	+/- 12dB at 10kHz
HF Filter	12dB per Oct above 7kHz
Power Consumption	60 Watts
Size	394 x 127 x 229 mm
Weight	11·3 Kg

The instruction manual for the Richard Allan A21 followed the standard practice for the period and included circuit diagrams, along with a parts list and instructions for adjusting the amplifiers.

Click here if you wish to see a more detailed circuit diagram and parts list, etc.

The above shows the circuit diagram for the Richard Allan A21. Click on the above image if you wish to see a larger, more detailed version of the circuit diagram, along with a list of component values, etc.

It is worth noting that although the Si 402 was rated in terms of 15 Ohm loads, the Richard Allan A21 was rated in terms of a 6 Ohm load. The nominal quiescent current chosen for the amplifier was around 0·92 Amps, and the voltage rail was at 32V. This implies that the maximum output power available in Class A operation varied with load (i.e. loudspeaker) resistance as shown in the plot below. (Although higher powers into low load impedances would have been possible in principle by moving out of Class A operation.)

The A41 power amplifier was able to deliver higher powers as a result of being given more generous heatsinking, higher rail voltages, etc. The A41 looked almost identical to the Sugden A51 that was destined to appear in later years. However – as with the A21 – the specifications for the Richard Allan version differed slightly from the later Sugden-branded amplifiers.

Specifications of the A41.

Maximum output power into 15 Ohms	20 W rms
THD at 15 W	less than 0·1%
THD at 1 W	less than 0·01%
Frequency response +/- 0·5dB	20Hz - 20kHz
Power response at 20 W	-1dB at 20Hz
Input sensitivity	500 mV into 200k
Noise rel 15W output (10k source)	-90dB
Rise Time	5 microsec
Output Impedance	0·25 Ohm
Load Stability	Unconditional
Power Consumption	100 W
Size	843 x 216 x 254 mm
Weight	10 Kg

The issue of Hi Fi News cover-dated June 1968 carried an article reporting on the Fair. This included the following:

“Richard Allan. The A21 and A41 Class-A transistor amplifiers caused a considerable - and perhaps predictable – flurry of technical interest; in fact this comprised one of the few genuine new developments of the Festival. Sound produced were certainly extremely clean and easy...”

There were also enthusiastic reports in The Gramophone magazine and Audio Record Review. But for some unknown reason Wireless World made no mention of the amplifiers in its report on that year’s show.

As claimed in their adverts, the Richard Allan versions of the A21 and A41 were probably the first domestic audio Class A transistor power amps to go on sale. If so, although the first commerical design was developed by Jim Sugden, it was initially sold under the Richard Allan brand-name. However it wasn’t long before other Class A amps appeared. The Richard Allan A21, and A41/C41 were soon joined by equivalent designs which carried J. E. Sugden’s name.