Whilst very little has been heard of home recorders during the past year or so, the possibility of being able to make one’s own records is such an attractive one that some interest was bound to survive the first wave of popularity. Experimenters who may have found some difficulty hitherto in obtaining the necessary apparatus will doubtlessly be interested to learn that development in this field has so far progressed that home recording equipment, or a complete home recording radiogramophone, is now obtainable from the Linguaphone Institute.
A demonstration of this apparatus was given recently to The Wireless World, and it would appear that most of the defects that beset some of the early recorders have been successfully rectified, and that exceedingly good records can be made with relatively simple and inexpensive apparatus. Furthermore, the Linguaphone equipment is so designed that it can be embodied in the construction of a radio-gramophone, and the principal parts are used in the orthodox manner when not required for record making.
The recording equipment consists very largely of standard parts, the whole being assembled on a Garrard Radio-Gram unit, the plate of which measures 16 x 14in., or the same overall size as the existing Type A Garrard unit. Sundry extra fittings have been added, and these must be embodied in the manufacture of the unit as several large holes and slots are required in the main plate. It is, therefore, not practicable to modify an existing gramophone unit and add the few extra parts.
The pick-up head is used for recording and also for reproducing, though a special steel needle is required for the former, and this can be used from ten to fifteen times.
For recording, which incidentally is made on a specially prepared aluminium disc, the pick-up head is driven by a worm and pinion from the turntable shaft. In order to render the apparatus as trouble-free as possible, and to prevent damage to the gearing or stripping of the fine thread on the traversing screw, the pick-up arm is driven through a spring-loaded quadrantfaced with raw hide. This arrangement is quite satisfactory in practice and does not appear to give rise to slip.
The mechanism for bringing the traversing drive into use is integral with a switch, which, in the recording position, connects the pick-up in parallel with the primary winding on the output transformer, and in the reproducing position joins it to the input of the LF amplifier, which in an orthodox receiver would be the gramophone terminals. Any good receiver chassis can be employed with this special motor unit.
Provision is made, also, for recording from a microphone, in which case the output from the microphone is amplified by the LF stages in the usual way by joining the secondary of its transformer to the pick-up terminals of the receiver. With microphones giving only a small output, a pre-amplifier mav be necessary. To prevent acoustic feed back when the microphone used, it is suggested that a switch be inclnded to break the secondary of the output transformer, so disconnecting the loud speaker and this switch can be embodied in the one that brings the microphone into use.
Output Valve Switching
We think that in cases where a large power output valve is used, with the likelihood of damage to the valve accruing bv removing the output, load, it would be advisable to arrange this switching so that a resistance equal to the impedance of the loud speaker is connected across the secondary of the transformer rather than to leave it open-circuited. Holes for all the extra switches and for the microphone terminals are provided in the motor plate.
Apart from the microphone connections there are actually only two more wires for interconnecting the recording motor unit and the receiver chassis than are required for a standard gramophone unit.
The complete Linguapbone, Recordiogram embodies the gramophone unit described in detail, while the radio receiver is a five valve superheterodvne of more or less orthodox pattern. It is AC operated and includes a mains energised transverse current microphone; it costs 25 guineas.
Special steel recording needles cost 1s. for five and thorn-tvpe playing needles ten for 1s. Double-sided chemically treated recording discs are available in 10in. and in 6in. sizes, the former cost 9d. and the latter 4½d. each.
It is interesting to note that the metal discs do not require lubrication or treatment of any kind before or after recording, and they are instantly replayable by merely changing the needle.
The recording motor with all the accessories will shortly be available as a separate unit for AC operation, and the price will be £5 5s.