LOW LEVEL AMPLIFIER CIRCUITS
(1) Preamplifier For use With the 3 W and 10 W Amplifiers The circuit for a two stage preamplifier which may be used with the 3 W and 10 W amplifiers, is illustrated in Fig. 19.6. The first stage uses a low-noise BC 149 or BC 109 transistor and the second stage a BC 148 or BC 108 transistor.
The input stage provides matching for a ceramic cartridge and for radio, the resistor R1 being chosen to give the required sensitivity in the latter case. A capacitor C 12 is connected in parallel with R1 the value of the capacitance being chosen to give with R1 a time constant of 18 μs. The second stage provides comprehensive tone control, with 10 dB boost and cut at 100 Hz and 10 kHz. This stage is followed by a simple balance ...
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