OptiGain®is AMR's amplification circuit of the audio signal to a desired level in the most optimal way. In order to interface signals, often some form of gain is needed. Audio equipment requires both voltage gain and power buffering - voltage gain, where levels need to be increased and power buffering where loads (like speakers) need to be driven.

In power amplifiers a common approach is to design the amplifier circuit to have very high gain (which requires a large number of amplification stages and invariably adds noise and distortion for each added stage) and a large amount of negative feedback to set circuit gain. Often several such multi-stage circuits with their attendant negative feedback circuits are connected one after another.

In the AM-77, two stages are used for the OptiGain®circuit. First, the signal is amplified to the desired voltage using the excellent NOS 5687 thermionic electron valve. This is performed with exceptional linearity and drive without the need for a negative feedback loop. This solution is much more costly and difficult when compared with the more common and cheaper use of operational amplifiers (Op-Amps). The significant sonic performance over a circuit with negative feedback places it in rarefied company. So much so that the pre-amplification stage of the OptiGain Circuit sonically embarrasses many other standalone pre-amplifier stages.

This feed-forward error correction in effect completely removes the "solid-state" sonic signature of the power buffer stage. This leaves an amplifier that behaves sonically like an optimal, extremely high power (>160W) and very linear (0.09% THD @ 160W) single-ended triode amplifier with only two stages, which also has a constant high damping factor (over 15 from 1 Hz to 100 kHz).