Abstract: A system for deriving a voltage which is a logarithmic function of peak value of an audio signal, in which the audio input signal is amplified by means of an operational amplifier having bipolar feedbacks through a pair of oppositely poled rectifying junction devices operating over logarithmic portions of their response characteristics, the output of the operational amplifier being applied in opposite polarities to a second pair of rectifying junction devices to rectify a bipolar signal applied thereto, and to control current flow to a storage capacitor, the second pair of devices having a common load which provides a constant current source for slow charge of the storage capacitor in one sense, the second pair of devices providing rapid discharge paths in the opposite sense. In one embodiment either or both pairs of rectifying junction devices can be transistors.

Abstract: A differential amplifier is connected to an amplifier for comparing an amplifier input signal with the signal fed back by the amplifier feedback circuit. The output of the differential amplifier is coupled to a full wave rectifier the output of which controls an attenuator connected between a source of electrical input signals and the amplifier. When the amplifier is operating in its linear range, the differential amplifier inputs are identical and it does not produce an output. Under this condition, the input signal is not attenuated. However, in the presence of amplifier clipping, the differential amplifier produces an output which, after full wave rectification, operates to increase the attenuation, and thus reduce the amplitude of the signal applied to the amplifier; clipping is limited.

Abstract: A gain control or multiplier circuit in which an ac signal is applied through bipolar diodes having logarithmic response characteristics to the bases of bipolar transistors connected in series and having an output at their junction, the diodes being directly cross connected to the bases, and gain control signals of opposite polarities being applied to the bases, thereby providing a linear output from the transistors despite their non-linear response characteristics.

Abstract: In an amplification system comprising an amplifier, a loudspeaker, normally open contacts connected in series between the amplifier and the speaker, and a power supply for the amplifier having relatively long buildup and decay times of its output voltage in response respectively to the connection and disconnection of the power supply to and from the a.c. line, means are provided responsive to the connection of the power supply to the a.c. line for delaying the closing of the normally open contacts until after the power supply voltage has built up to its full operating potential for eliminating the transient audio signals from the amplifier associated with power supply voltage buildup from being reproduced by the loudspeaker. Means are also provided for opening the contacts quickly after the power supply is disconnected from the a.c. line for eliminating the distorted audio signals from the amplifier associated with power supply decay from being reproduced by the loudspeaker.

Abstract: A superheterodyne f.m. receiver having a manually tunable local oscillator which is electronically voltage tunable over a small range, and including a frequency discriminator for providing signal voltage and a.f.c. voltage in response to a received f.m. carrier, wherein is provided an electronic bipolar switch responsive to either positive or negative a.f.c. voltage of greater than a predetermined value for effecting grounding of a point of an a.f.c. circuit which applies a.f.c. voltage to the local oscillator, and which also includes an interchannel noise detector which also provides grounding signal for that same point of the a.f.c. circuit.