Volume control circuit for vehicle radio speaker - is insertable between receiver output and booster amplifier or loudspeaker to control speaker volume in dependence of ambience noise levels

摘要

The volume control device comprises a boom sound probe (A) which monitors ambient sound and applies the signal through a low pass filter amplifier (TR4, 5, 6) and integrator. The radio output is applied through a wide band amplifier (T1) and integrator to control together with the probe signal, two field effect transistors (T&11) connected in resistive cascade between the radio output and a booster integrated circuit amplifier (Ci 1, 2). For stereo systems two pairs of field effect transistors and two boosters are provided with left and right inputs (B1, C1) and outputs(B2 C2). The sound probe (A) is suitably mounted on the car structure, for example, sufficiently far from the radio speakers.