At 10:26 AM 10/11/2012, Alexander Winnig wrote: >First: Which voltage level should not be exceeded between both >microphone cables(Signal and Mass) *between *a telephone handset and >it's telephone? What kind of telephone? Is it an old-school telephone with carbon=20 microphone or a newer unit with electret mic? >Second: I have two AC signal sources with a maximum voltage of 1.2 Volts >each. Which circuitry is the one with the least amount of components >that combines them in an adjustable way without distorting them or >diminishing the overal volume? Balanced or un-balanced? If unbalanced, simply use a 1:1 isolation=20 transformer connected to one of the signals (primary), then connect=20 the secondary of the transformer in series with the other signal. If balanced, you need two 1:1 transformers. Connect each input=20 signal to the primary of one of the transformers, then connect the=20 secondaries in series. This output signal can be treated as either=20 balanced or unbalanced - your choice. If you can tolerate a 6dB loss, simply sum the two signals through a=20 pair of 2k2 or 4k7 resistors. The mid-point of the resistors is the=20 sum of the two individual signals. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .