Figure 15.

Principle of operation.

When examining the spectral density of the voice

area and the larsen area, it can be seen that the

dominant features of each exist in different fre-

quency bands.

To extract the larsen component, the microphone

signal is first filtered by a second order filter (formed

by two first order filters), then amplified and rectified

in order to produce the AGC control signal.

The first filter is generated by the capacitors on pins 5 and 6 ; the second filter by the R-C network on pin 7.

Figure 16.

Zin : 4 k

Ω

V7

A=

= 15

V5 – V6

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