An Unusual Head-phone Circuit--- with Volume Control

Radio Record, Volume V, Issue 14, 16 October 1931, Page 29

An Unusual Head-phone Circuit---with Volume Control

Contributed by

A.A.

H.

(N.Z.7A).

ARIOUS methods from time to time have appeared, showing systems for switching from the loudspeaker to the headphones, and vice versa. Here then is a hook-up comprising an L.S. filter together with an efficient phonecontrol which can be added to the receiver cabinet, if room, or plugged in as a unit to the L.S. terminals of the set. It is applicable to broadcast or shortwave sets. The writer has used this arrangement with entire satisfaction, listening to any station, far or near, with the phones with ease, or by means of a switch, putting the best into the speaker. Using the head set, the eardrums will never receive a shock, and with the fixed condenser the phones are isolated in the event of power being used from the mains. The variable resistance allows for any comfortable volume as is desired. In building the unit care must be taken to use only two terminals of the potentiometer, one fixed and the arm, and that the lead to the Fil. — is to the last valve. A second and similar condenser can he used in this lead, but this is optional. The speaker and phone connections are made to a D.P.D.T. switch, which is mounted on the panelling together with the potentiometer, while the output choke coil and fixed condenser may be fixed on the baseboard. The parts required are:-One output choke coil, 20 henries; one 2 mfd. fixed condenser (or two if preferred); one potentiometer, 400 ohms; one D.P.D.T. switch. | A. diagram illustrates the hook-up. At (x) a second 2 mfd. condenser can be adopted .to protect the L.S. from H.T. current. The D.P.D.T. switch and potentiometer must be mounted on the panelling or unit panel. If flex wire is

used keep leads separately as shown. All connections should be permanent. The switch will throw the speaker or phones or both out of action. In this hook-up several L.S. can be connected for use in several rooms.