The single speaker amplifier circuit uses current feedback, rather than the more popular voltage feedback. The feedback loop is from the junction of the speaker terminal and a 0.5-0 resistor, to the inverting input of the NE5534. When the input to the amplifier is positive, the power supply supplies current through the TIP32 and the load to ground. Conversely, with a negative input, the TIP31 supplies current through the load to ground. The gain is set to about 15 (gain = SPKR 8 0/0.5 0 feedback). The 0.22-!LF capacitor across the speaker rolls off its response beyond the frequencies of interest.
Audio-power-amplifier - schematic

Using the 0.22-!LF capacitor specified, the amplifier current output is 3 dB down at 90 kHz where the speaker impedance is about 20 0. To set the recommended class A output collector current, adjust the value of either 130-0 resistor. An output current of 50 to 100 mA will provide a good operating midpoint between the best crossover distortion and power dissipation.

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