This circuit is designed with a simple and low cost. The optimal working voltage for this amplifier is +55 Volts. But the advantages of this amplifier circuit can work with a voltage of 30-60 VDC.
While the maximum signal input voltage is 1 Volt. You can see the component values of this circuit are very easy to find even at home. The final amplifier transistor is arranged with Darlington to produce for high gain. With a voltage of +55 VDC, the output power produced is around 60 Watts.
This circuit is of the class B type amplifier, meaning that current will continue to flow through the transistor, even when there is no signal input. But the current can be adjust with a potentiometer trimmer. Potentiometer must be set to get the best sound possible without distorted.
But if the current too high, it will be wasteful of power and the final amplifier transistor becomes very hot. However, if the potentiometer is set too low, the final amplifier transistor will not be too hot, but the output sound will be distorted.
A few notes:
Capacitor C2 used to adjust the low-frequency tone (bass). If the value of the capacitor C2 is greater, the bass tone will be lower. Whereas capacitor C3 used to produce a higher frequency (treble). If the capacitor value is increased, the high-frequency response will be even greater.