Philips GA 202 Electronic Turntable. Price: L64 Complete with plinth and GP411 Cartridge. Manufactured by Philips Electrical Ltd., Century House. Shaftesbury Avenue. London, WC2.

I have always stood slightly in awe when contemplating Philips research and engineering. The first example of a well designed and engineered 'wireless set' which I can remember was a Philips 3-valve mains receiver in the late 1920's. At that time most British manufacturers were producing battery operated receivers using a wooden breadboard and ebonite front panel, although a few had metal chassis, but from an engineering point of view they were an assembly of components rather than an integral system.

The Philips set, using bakelite moulded end plates and an integrated mechanical design, was at that time a marvel of wireless engineering, most of the components being specifically designed for their own particular function. But it must be admitted that it was the very devil to service, all design effort being concentrated on mechanical and electrical stability coupled with case of production.

Throughout the 1930's and since the last war, this design philosophy has always been paramount at Eindhoven: it is very rare indeed that one can criticise design or production methods of Philips products.

The GA202 electronic turntable is no exception. It is a beautiful instrument in which every part appears to have been designed specifically for its function. The prime mover is a small DC motor driving the turntable through two separate belt systems, the speed being electronically controlled. The turntable proper and pickup arm are carried on a sub-chassis, resiliently sprung from the plinth. The plinth consists of a teak shell with matt anodised aluminium front and top panels. The moulded. smoke-grey, clear plastic cover is hinged at the rear and has a spring loaded strut to hold the lid open during record changing. The base of most turntable plinths is usually an anachronism, a piece of hardboard cut approximately to size. The GA202 is an exception to this rule: the base is black moulded polypropylene with four integral rubber feet and, on the inside, there arc three projections which support the motorboard.

SPECIFICATION AND TEST RESULTS PHILIPS GA202 TURNTABLE

I. Speeds (rpm) 331, 45, 78 Accurate 2. Speed Adjustment ±2%, on —

Stroboscope 4. Motor Type DC servo - s. Wow and Flutter (7/e at 33-)rpm)

Turntable Diameter (in.)

7. Turntable Weight (lb) 8. Turntable Material 10. Pickup Arm 11. Auto Operation

Maker's I Test

Specification Result each speed driven 0.13 0.03 9. Rumble (dB) —eo

Yes

Auto-stop photo-cell

Iti 2 —70

The motor and intermediate drive pulley are contained in a small moulded box resiliently sprung from the main chassis. At first sight this prime mover is ridiculously small, being but 11 inch in diameter by 11 inches long but, as the manufacturers rightly point out, with an accurately designed servo system only sufficient mechanical power to keep the turntable revolving at the correct speed is necessary providing that the mechanical and electrical constants meet their specification. Carrying this philosophy to its proper conclusion indicates that the mass of the turntable is of secondary importance and, indeed, the 114 inch diameter turntable is extremely light by established transcription turntable criteria; it weighs 2i lb. Be that as it may, wow and flutter are the lowest we have attempted to measure and were less than 0.03%. These include residual wow and flutter of the test record and are peak unweighted values. Values approximately 50% lower than these were obtained when using the DIN network. In view of these extremely low measured values, the figures are literally meaningless! Motor rumble is of an equally low order, being better than —70 dB. Again, this is approaching the limit of the test record. Certainly, under listening conditions, rumble and wow and flutter were conspicuous by their absence.

As mentioned before, the turntable and pickup are mounted on a sub-chassis independently sprung on a three point suspension, damping sponges being fitted inside the suspension springs. The drive to the turntable is via a belt from the lay shaft, thus there is no direct mechanical connection between the turntable and the plinth or the prime mover. Finally, the sub-chassis (which also carries the pickup lifting and lowering mechanism) is counterbalanced, maintaining the turntable in a horizontal plane.

The main bearing is approximately th inch in diameter and inches long, the spindle being ground and lapped hardened steel. There is no discernible 'slop' and it would appear that the assembly has been lapped in situ. The motor is driven from a 9 Volt supply via a small power transistor. Unlike most electronically controlled systems, which sense the speed of the turntable in terms of frequency, the Philips system makes use of the fact that the back EMF generated from the motor is directly proportional to its speed. The magnitude of the back EMF is compared against a standard voltage and the error (if any) applied to the drive transistor, thus correcting the variation in speed. Provision is made for operating the turntable at 78, 45, and 33f rpm, and three pre-set controls are available on the top panel for precise adjustment should this become necessary. The circuit is insensitive to mains voltage variations: with voltage selector at 240 V, the speed was within ±0.15% between 220V and 255V input, and over a period of 4 hours the difference in turntable speed could not be measured. The mean speed was independent of the playing weight to the limit of 4 grams (maximum available on the pickup arm) and was also unaffected by record modulation depth.

The automatic stop mechanism is unique. A photo-electric switch is connected via a multi. vibrator interlock to the electronic drive system. When the pickup head approaches the centre, the illumination of the photo-cell is gradually interrupted by means of a flag carried on the inside of the pickup arm main bearing, the actual operation of the light switch being governed by the rate of change of light on the photo-electric cell. (The absolute magnitude of light is controlled by a V-shaped mask on the flag intercepting the light beam.) When this rate of change exceeds a certain value, the bistable multivibrator is triggered, which cuts off the motor supply voltage. The motor is restarted by the stop-start switch in the bottom right-hand corner of the main turntable. The advantages of this system of switching arc that it works without any mechanical force being applied to the pickup arm, it is noiseless and should require no maintenance.

A total of 7 transistors, 7 rectifiers and one zcner diode are used in the motor control circuit, the power transformer being astatically wound and contained in a magnetic shield. The pickup lift and lower mechanism is remotely controlled through a Bowden cable via a rocker switch adjacent to the stop-start switch. It is hydraulically damped and the speed of raising and lowering is independent of the operator.

The pickup arm is lightweight aluminium alloy tube, about a quarter of an inch in diameter, carrying a skeleton head shell at the front and a mass counterbalance which is resiliently mounted to the rear of the pedestal. It is suspended on gimbals: the friction is such that a force of less than 10 milligrammes is required to move the pickup in any direction. The offset angle and overhang appear to be optimum and a simple offset bias (or antiskating force) is fitted consisting of a tension spring controlled by a sliding arm. A knob on this arm is carried through a slot on the motorboard which is calibrated "0- 4". and is adjusted to correspond with the playing weight of the particular cartridge in use. This offset force is actually equal to 300 milligrammes when set to "4", and the force is directly proportional to the indication of the pointer.

The shell accepts any cartridge with standard 1 inch fitting centres and is supplied fitted with the Philips type GP411 cartridge as standard. This will be the subject of review next month together with the more expensive GP412. A 6 ft. length of twin core mains lead is fitted. whilst the pickup output is taken from a twin shielded lead approximately 4 ft. long and terminated in a DIN 5-pin plug.

In common with all Philips equipment, the operating instructions, service manual and leaflets are lucid, informative and exact. The packing is likewise excellent and as usual the equipment worked according to specification first time.

To summarise: I cannot say more than that I would have been proud to have designed this piece of equipment. Priced at £64 complete with cartridge, plinth and lid, it is excellent value for money. The decor is simple and aesthetic and above all it performs in an exemplary manner. STANLEY KELLY.