AF amplifier for HI=FI equipment - has second channel with band-pass filter and dynamic compressor to adjust signal level to audio sensitivity

摘要

The AF amplifier, for radio receivers and hi-fi equipment, consists of a main channel comprising two amplifiers and at least one secondary channel containing an audio band-pass filter and a dynamic compressor (6, 8, 9). The compressor increases the level in the selected frequency band at low volumes so that it matches the curves of equal audio sensitivity. At greater sound volumes this increase increases only slightly in relation to volume. The compressor consists of a gain-controlled amplifier (6), and amplifier (8) and a rectifier (9) whose output controls the gain-controlled amplifier. The amplifier's filtered output (7) is added (3) to the main channel's signal.