Abstract: An amplifier (10) is disclosed including circuity for improving the amplifiers performance, particularly the common mode rejection of differential amplifiers, by adding the amplifier input signal to the power supply signals which power the amplifier. Voltage dividers (42, 44) are connected between the amplifier output (16) and each of the two power supply rails (26, 28). Each divider includes resistors (46, 48; 50, 52) selected so that the amplifier output is divided down by a factor equal to the gain of the amplifier. The junction signals (V.sub.J1, V.sub.J2) provided by the two voltage dividers thus each includes a component equal to the input signal. The junction voltages are applied to the amplifier power input terminals (18, 20) by respective transistors (60, 62), each connected in a voltage follower arrangement. One embodiment (FIG. 4) incorporates a servo amplifier (100) for DC offset stabilization.

Abstract: A low noise amplifier circuit (FIGS. 4 and 5) is disclosed including plural differential amplifiers having their inputs and outputs connected to common input and output lines (50, 52; 54, 56). In the disclosure, each differential amplifier is comprised of a pair of bipolar junction transistors (40, 42; 58, 60; 64, 66) of the same type. Parallel connecting of the differential amplifiers in the disclosed fashion reduces the Johnson noise introduced by the base spreading resistances of the individual transistors. Since differential amplifiers, per se, are connected in parallel rather than their component transistors, thermal runaway is not a problem.

Abstract: An equalization amplifier (30) is disclosed which includes two amplifier stages (32, 34) connected in cascade. The first amplifier stage (32) includes a low pass filter amplifier (40) having a pole frequency of F1 and a feed forward path (36) bypassing the low pass filter amplifier. The feed forward path provides the input signal to an adder circuit (42) where it is added to the output of the low pass filter amplifier. The effect of this addition is to provide the first amplifier with a zero frequency of F2, where F2 is greater than F1. The resulting sum signal is applied to the second amplifier stage (34) which also has a low pass filter characteristic. The second filter has a pole frequency of F3, where F3 is greater than F2. The equalization amplifier is particularly useful for providing RIAA equalization of phono cartridge output signals.