Low noise and speech preamplifier circuit diagram

The circuit principle is shown in the figure below, using MC2830 to form a voice circuit. Traditional speech circuits cannot differentiate between speech and noise input signals. In noisy environments, noise is often caused by switches, in order to overcome this weakness. Speech circuits do this by taking advantage of different speech and noise waveforms above the noise level. Speech waveforms typically have a wide range of changes, while noise waveforms are more stable. Voice activation depends on R6.

Voice activation sensitivity decreases if the R6 changes 14K to 7.0K, from 3dB to 8dB above noise.
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