A op amp and transistors Q1 and Q2 exponential converter to generate an exponential gain control current, which is introduced into the rectifier. A reference current of 150 pA, (15 V and RZO = lOO-k), is attenuated by a factor of two (6 dB) for each increase of tension in the control voltage. Capacitor C6 slows secure changes to a period of 20 IDS constant (C6 x IR) such that a sudden change in the control voltage will produce a gain change smooth sound. RI8 ensures that for control voltages of the circuit will go to great attentuation full.The rectifier bias current which would normally limit the gain reduction around 70 dB. RI6 attracts more courses of the rectifier. After about 50 dB of attentuation to -6 dB / V slope, with the increase in slope and the attenuation becomes much faster than the circuit to close completely at about 9 V control voltage. Al should be a low noise, high intensity, scanning speed, op. R13 and R14 in place around 0 V bias to the output.
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