Wireless Headphones (Receiver)

To arrive at a suitable headphone re- ceiver that meets the requirements of being light, battery-powered, and offer- ing good-quality reproduction, a Ferran- ti ZN415 was chosen. This IC contains a complete AM detec- tor, an output amplifier, and operates from a single 1.5 V battery. The circuit shows the ZN415 in its stan- dard application as a medium wave re- ceiver. Circuit CI-Li is, however, tuned to a frequency above the medium wave band. The output stage drives a high- impedance headphone without any problems. The circuit draws a current not greater than 5 mA, which ensures a good battery life. The tuned circuit, Ci-Li, receives the signal from the transmitter described in the preceding article. The inductor con- sists of 40 turns 0.2 mm dia. enamelled copper wire close-wound on a 20 mm dia. ferrite rod. For optimum reception, CI must be adjusted with a non-metal screwdriver. Note that the transmit fre- quency lies somewhere between 1,700 and 3,400 kHz. 0 1,5V <5mA * see...