ELECTRICAL “PICK-UP”

Evening Star, Issue 19775, 27 January 1928, Page 2

ELECTRICAL “PICK-UP”

FOR THE eRAiOPHOttE One of the most interesting developments in gramophone design in the last years has been the introduction of the so-called “electric pick-up” by which the music from the gramophone is reproduced on a loud speaker operated by a valve amplifier, instead of on the ordinary gramophone reproducer. > The new system frequently gives a much improved quality of reproduction, and it also makes possible the production of a far greater volume of sound than can be 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, can 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. The orifice in the cap is enlarged until the cap takes the *orm or 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 verticlle on to the centre of the diaphragm, using as little solder as possible. Care must bo taken not to dent the diaphragm. The vertical rod is then bent over in the same shape as the needle arm, which is attached to tho diaphragm on the reproducer of an ordinary gramophone, and a needle-holder taken from an old gramophone reproducer is soldered to tho other end of it.

If no needle-holder is available a light brass screw connecter, which can be bought for about 3d, will do instead. Level with the edge of the receiver cap ft 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 attached to the needle arm on the ordinary gramophone reproducer. The connections for the apparatus are simple. One of the two wires in the cord from the headphone is connected to a the grid of the first valve in a valvo amplifier, and "the second wire is connected to the negative terminal of the filament lighting battery. If desired, the pick-up can bo attached to a wireless receiver by removing the detector valve from its socket, and connecting one of the conductors in the cord to one terminal of the primary of the first intervalve transformer, and the other wire from the cord to the second terminal of the transformer primary. In use the telephone earpiece can he attached to the tone arm of the gramophone by rubber hands, with the needle bearing on the record in the ordinary way. No needle, of course, is used in tho gramophone reproducer.