Gain controlled amplifier with current and volts feedback - has variable voltage feedback resistor and variable input resistor to alter gain

摘要

The gain-controlled amplifier, with current and voltage negative feedback, has a first variable resistor in the voltage feedback loop and a second variable resistor in the input circuit to alter the gain of the voltage loop. The magnitudes of these two resistors are altered in opposite senses. The two resistors may be PTC or NTC resistors (self-heating or indirectly heated) or photoresistors or magnetically-controlled resistors or incandescent lamps. The input is applied via a capacitor to the first resistor and passes from there over a coil and second capacitor to the amplifying transistor's base. The second resistor shunts the transistor's collector/base junction and the second capacitor.