Rogers Cadet Mk II stereo control unit and amplifier
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Taken from The Gramophone magazine, August 1962

At the London Audio Fair, back in April, one of the nicer demonstrations was given by Messrs. Rogers who had in their room three complete sets of equipment of ascending price and rang the changes on them for the benefit of their visitors. Now whether or not that will prove to be a good thing from their point of view I do not know, but it is a fact that after a demonstration of the cheapest group many people thought that they would have difficulty in proving the need for anything better! Well, of course, in truth the more costly affair showed considerable improvement for those with golden ears; but nevertheless since then the talk has been of the comparative excellence of this low cost set-up which to many people has obviously remained an outstanding feature of their visit to the show.

The principal actors in this very successful presentation were the "Deram" cartridge, Goodman's Axiom 10 loudspeakers in Design Furniture GD10 cabinets and the subject of this report, the new Rogers "Cadet" stereo amplifier and control unit. Now I am very much in favour of anything like this which reduces the cost of high quality listening: and there are several reasons why the combination is both successful and economical. Mr. Rogers deserves praise for realising these possibilities and will I hope, reap the reward of his skill. At the same time it should be remembered that this very acceptable sound for £X is not equal to the results produced by the £3X and £4X equipments in spite of a few somewhat naive voices to be heard saying just this.

The designer of a high quality stereo amplifier which is to enter a low cost market is at once worried, not by the complexity of his circuitry but by the nagging problem of what can be left out. In theory, I suppose the man who can omit the most without it becoming too obvious is the winner of this particular race; but if our designer has a conscience and also a good name to maintain, then he can only omit those things which his skill renders unnecessary. To help him he has the parallel skill displayed by fellow designers of pickups and loudspeakers. And it is with the pickup designers that the first big economies begin.

A rising standard of performance in the new generation of ceramic pickups helps the amplifier designer in two ways; for by restricting his new baby to a ceramic or crystal high-protein diet he can omit a stage of amplification (the voltage produced by a ceramic is ten times that of a magnetic); and more important still he can omit the components normally required to equalise for the (RIAA) recording characteristic, because a well engineered ceramic will do it automatically if the amplifier load is properly chosen. The reason for this is that crystals and ceramics produce an output which is proportional to the amplitude of the recording: i.e. a large wriggle of the groove produces a large output. (By comparison, the output of a magnetic pickup is proportional to the speed at which the wriggle takes place.) Now it so happens that recording characteristics are chosen which are almost the exact opposite of the ceramic's behaviour. Treble is recorded more strongly to counter hiss, and bass is reduced to permit closer grooves and long playing time. Thus a practical recorded groove is not very far from constant in amplitude for all frequencies and the skill of the pickup designer, who has as his allies a collection of resonances, several compliances and a few spots of damping, can soon take up the slack and produce a flat response.

At the other end of the chain it is reasonable to assume that no one is going to use a pair of expensive, very wide range, loudspeakers and so the elaboration of a low pass filter is unjustified and the roll-off in the extreme treble is left to the customer when choosing his speaker systems. Bass and treble controls are necessary though, for low cost loudspeakers can often benefit from a little help in this way. Similarly, output power can be restricted for inexpensive speakers are not necessarily inefficient. A contrary factor arises in the need for a rumble filter to allow the use of the cheaper gramophone motors without distress to amplifier, speaker or listener: but our designer can't expect to have it all his own way.

The picture of what is required is now plain and I am sure it will come as no surprise to the reader to learn that the new "Cadet" fills the frame almost exactly. The power amplifiers use two ECL86 valves each, the pentodes as push- pull output and the triodes as amplifier and phase splitter, with negative feedback overall. Output and mains transformers are housed under a metal cover finished in hammer silver enamel. The familiar Rogers maroon chassis is used, but the valves and small components are in fact mounted on a sub-chassis and the successful type of construction previously used in the HG88 amplifier, involving the extensive use of tiny stand-off insulators is continued. A selenium bridge rectifier with resistor/capacitor smoothing supplies high tension. No one would question the integrity of the components or wiring even before they know the price!

The control unit has a brushed brass and matt black panel with good ivory knobs and clear markings. The three push buttons select input from radio, disc or tape: adjacent is a 5 pin socket, continental type, for tape input/output connections. The large knob is volume and by its side is an on/off switch. Above are a rather brilliant amber pilot lamp and two slide switches providing mono/stereo selection facilities. The other three controls are balance, bass and treble. At the rear are sockets for all inputs (the tape ones have adjustable input potentiometers to avoid overload with some recorders) and a rumble filter switch. Each half of the pre- amplifier uses a single ECC83 double triode valve.

The measurements made on this model fit the specification very closely and are so nearly identical between channels that I shall only quote for one.

Frequency response: Radio input, tone controls flat volume max. ± 1 dB 30 c/s to 30 kc/s.
Power/Frequency response: 6 watts between 140 c/s and 8 kc/s; 5 watts at 40 c/s and 16 kc/s; 4 watts at 30 c/s and 21 kc/s.
Range of bass control at 40 c/s: ±14 dB - of treble control at 10 kc/s -16 dB +9 dB - Of balance control -3 dB +5.5 dB. Rumble filter operates on all inputs and has an insertion loss of 2 dB. -2 dB at 60 c/s, -4 dB at 50, -8 dB at 40, -12 dB at 30 Input required was 68 millivolts for 6 watts output into 15 ohms load. Stability was adequate for all normal loads. Negative feedback was 14 dB. Cross- talk at full gain was -43 dB. Hum and noise at full gain 50 dB below 6 watts, at minimum gain 76 dB below 6 watts.

What the "Cadet" sounds like has been discussed at the beginning of this report and so it only remains to conclude by saying that to produce equipment which performs so well, looks so nice and costs so little is a rare and welcome achievement