Home Telephone Help

12-40 — elektor december 1982 home telephone help used (see figure la) may differ depending on the type of tele- phone in use. If your system is already operating, you will already be aware of the wiring connections referred to. However, if in doubt, the easiest method of checking is to undo the handset microphone and speaker covers and make a note of the colour coding used. This can then be tracked back down into the main body. Figure la may be of some assistance here. In order to prevent the possibility of feedback the connections to the speaker should be exchanged (reversed phase) as shown in figure lb. The power supply for the mini line amp is derived from the microphone line as a dc voltage exists at this point when the hand- set is lifted. The emitter of T1 is connected to the negative line while resistor R2 is connected to the positive. Care must be taken to ensure that connections here are correct. Readers have advised us of prob- lems encountered with the use of old sur...