LF amplifier for portable radio equipment. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Audio equipment
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The main parameters:
- Rated frequency range, Hz.......40...20 000
- Rated output power, W, at a load with a resistance of 4 ohms with a harmonic coefficient of up to 2,%......4
- Input impedance, kOhm.......50
A feature of the amplifier is the use of a current stabilizer on a field-effect transistor V4 in the power circuit of the pre-terminal stage of the microcircuit (pin 1) instead of the so-called voltage boost provided for by the typical inclusion of the microcircuit.
This made it possible to obtain the highest amplitude of the amplified signal and at the same time reduce the harmonic coefficient to 2...2,5%. Further reduction of non-linear distortions is achieved by increasing the depth of negative feedback (NFB) by increasing the resistance of the resistor R3 from 56 to 82...100 Ohm
In the current stabilizer, field-effect transistors KP103I, KP103K, KP103M can be used. Resistor R4 * is selected so that the drain current of the transistor becomes equal to 2 ... 2,5 mA.
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