IMPROVISED PICKUP

Radio Record, Volume I, Issue 27, 20 January 1928, Page 3

IMPROVISED PICKUP

LLUWCTRIFIED GRAMOPHONE, One of the most interesting developnients in gramophone design in the last year has been the introduction of the so-called "electric pick-up’ by which the music from the gramophone is reproduced on a loudspeaker operated by a yalve amplifier, instead of on the ordinaty gramoplione reproducer, The new system generally gives a much improved quality of reproduction, aud it also makes possible the production of a far greater yolume of sound than can he obtained from the ordinary gramophone. This is a distinct advantage when the instrument is being used for dancing. Although the commercially made electric pick-up devices are fairly expensive, a simple experimental pick-up, capable of giving excellent results, cau easily be made from an old wireless earpiece. The earpiece is detached from the headband, and the diaphragm beneath the cap is removed by screwing off the cap. ‘he orifice in the cap is enlarged until the cap takes the form wf a locking ring, which can be replaced on the earpiece to hold the diaphragm in position. The centre of the diaphragm is carefully burnished with sandpaper and a length of bus bar, or some similar rigid metal rod-~an old bicycle spoke will do well-is soldered vertically on to the centre of the diaphragm, using as little solder as possible. DO NOT DENT DIAPHRAGM. Care must be taken not to dent the diaphragm. The yertical rod is then Lent over in the same shape as the needle arm, which is attached to the diaphragm on the reproducer of an ordinary gramplione, and a_ needlieholder taken from an old gramophone reproducer is soldered to the other end of it. If no needie-holder is available a light brass screw connecter, which can be bought for about 8d., will do instead. Level with the edge of the receiver cap a light supporting hinge should be attached to the bus bar in the manner in which the supporting hinge

at the edge of the reproducer is af tached to the needle arm on the ordinary gramophone reproducer. ‘The connections for the apparatus aré simple. One of the two wires in the cord from the headphone is connected to the grid of the first valve in a valve amplifier, and the second wire is cote nected to the negative terminal of the filament lighting battery. If desired, the pick-up can be attached to a wires less receiver hy removing the detector valve from its socket and connecting one of the conductors in the cord te one termial of the primary of the first inter-yalve tramsformer, and the other wire from the cord to the second ters minal of the transformer primary, In use the telephone earpiece can be ate tached to the tone arm of the gramoe phile by rubber bends, with the needle bearing on the record in the ordinary way. No needle, of course, is used in the gramophone reproducer.