This section introduces one example using R core audio interstage and output transformer: 2A3 push-pull 20W monaural power amplifier. Maximum output of this amplifier is 20W that is quite enough for family use. The main features are excellent performances (low distortion, wide bandwidth, high output, and low noise level) that are difficult to be achieved by the single-ended amplifier, and good sound quality straightforward that is particularly characterized by interstage transformer coupled circuit.Rated performance of 2A3 push-pull 20W monaural power amplifier Maximum output20WFrequency bandwidth (1W)10Hz to 55KHz +0,-3dbDamping factor3.8Distortion factor (1KHz)1W : 0.055%, 10W : 0.6.%, 20W : 3.2%Residual noise level0.1mV (without weighting network)