Silence noise limiter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Audio equipment
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The silence noise limiter reduces the level of high and low frequency noise in a tape recorder or turntable. It is connected between the output of the indicated signal sources and the input of the AF amplifier.
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The device consists of an emitter follower (V1) and a control signal generation channel containing a two-stage amplifier (V2, V3) and a rectifier (V4-V7). The signal to the input of the AF amplifier comes from the load of the emitter follower through a voltage divider, consisting of a resistor R4 and elements C3, T1, R12, R13, V9-V12. Elements C3, T1, R12, R13 form a filter, the frequency response of which has a rise at medium frequencies, due to the resonance of the circuit, consisting of the secondary winding of the transformer T1, capacitor C7 and resistor R7. With small signals and in pauses, the filter is actually connected to a common wire through a small direct resistance of open diodes V11, V12, so the low- and high-frequency components pass to the output significantly weakened.
With an increase in the signal level at the output of the rectifier (V4-V7), a negative polarity voltage appears, which closes the diodes V9-V12, and the filter is disconnected from the common wire. As a result, the entire spectrum of the signal passes to the input of the AF amplifier.
The depth of noise reduction is regulated by a tuning resistor R13. The frequency response of the controlled signal divider can be changed by breaking the circuit of the oscillatory circuit with switch S1 (in this case, a series oscillatory circuit operates, consisting of capacitor C3 and winding I of transformer T1). Switch S2 is used to disable the squelch.
In addition to those indicated in the diagram, transistors KT3102E (VI), KT3102A - KT3102G, KT315V - KT315G (V2, V3), diodes D220, D223, KD521 can be used in the device. Transformer T1 - matching from a small-sized transistor receiver.
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