Circuit Description: Fig. 16.5 shows a preamplifier circuit derived from the tape recorder circuitry already described. The oscillator stage in this circuit uses a complementary pair comprising one AC 176 and one AC 128 transistor.
Performance: The distortion measured at the collector Q4 of transistor (AC 128) in the playback position is shown in Fig. 16.6. The measurements were made at a speed of 3 ¾ ips, although these characteristics vary little with speed. At a speed of 7 ½ ips with the volume control at maximum, the output voltage is 6.55 V for an input voltage of 400 μV. The total current drain on playback is 25 mA.