Posted on May 17, 2012

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.

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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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