SPEECH_COMPRESSOR

Published:2009/7/1 4:20:00 Author:May | From:SeekIC

The amplifier drives the base of a pnp MPS6517 operating common-emitter with a voltage gain of approximately 20. The control RI varies the quiescent Q point of this transistor so that varying amounts of signal exceed the level Vr. Diode Dl rectifies the positive peaks of Q1's output only when these peaks are greater than Vr ≈ 7.0 volts. The resulting output is filtered Cx, Rx. Rx controls the charging time constant or attack time. Cx is involved in both charge and discharge. R2 (150 K, input resistance of the emitter-follower Q2) controls the decay time. Making the decay long and attack short is accomplished by making Rx small and R2 large, (A Darlington emitter-follower may be needed if extremely slow decay times are required.) The emitter-follower Q2 drives the AGC Pin 2 of the MC1590 and reduces the gain. R3 controls the slope of signal compression.



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