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Earphone_radio

2014-11-28 02:44  
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Earphone_radio
This circuit shows the ZN414Z (Fig. 2-14A) combined with an external amplifier to drive an inexpensive earpiece. This arrangement is generally cheaper than having the ZN414Z drive an expensive sensitive earpiece directly (to produce an ultra-miniature radio). The arrangement also provides for a volume control, if desired. Substitute a 250-Ω potentiometer in series with a 100-Ω fixed resistor for the 270-Ω emitter resistor. L1=80 turns of 0.3-mm diameter enamelled copper wire on a 5-cm or 7.5-cm long ferrite rod. Any value of L1/C1 that gives a high Q at the desired frequency can be used.