Posted on Jan 23, 2013 3454
This circuit is fed from the earphone jack of your receiver and goes to limiter control R6 and is then amplified by Ql: a common-emitter stage that has a voltage gain of only about 10, because of the negative feedback introduced by R3. The output of Ql is fed to a simple clipping circuit, consisting of diodes D1 through D4. The diodes, connected in pairs, act like Zeners with an avalanche rating of aboun V.
The two pairs are connected opposite in polarity to each other, so that the audio signalis clipped at about 1 V. The signal is then coupled to the output socket through an emitter-follower buffer stage built around QZ and an output attenuator control R7.