Abstract: A low level, low power, direct coupled integrated class B amplifier having a dual channel three stage preamplifier and a pair of output transistors, one for each channel. In each channel, a DC negative feedback loop connects the collector of the last stage preamplifier transistor to the base of the first stage preamplifier transistor to regulate the DC levels, and a resistive AC negative feedback loop connects the output transistor collector to the first preamplifier transistor collector to reduce the gain dependence of the channel on the current through the output transistor, thus enabling very low idle currents for the output transistors and also providing low distortion output. The resistor in each AC feedback loop is a floating tub resistor to enable it to be taken more than 0.6 volts above the battery voltage. Common mode rejection is provided for at least two of the three preamplifier transistors of each channel.

Abstract: An integrated circuit direct coupled amplifier capable of operating from a single battery cell, has: a differential amplifier input stage having an input transistor and a second transistor; an intermediate gain stage; and an output stage. Signal is fed back from the output stage to the base of the second transistor of the differential amplifier, through a negative feedback circuit. Current sources are connected as loads in the collector circuits of the input transistor of the differential amplifier and the transistor of the intermediate gain stage. The current sources are biased by separate bias sources, to improve stability. The bias source for the intermediate gain stage current source also biases a current source for the feedback circuit. A starting circuit is connected to the bias source for the intermediate gain stage and provides self starting for the current sources.