1.Bypass mechanic in potentiometer audio signal
The use of potentiometer Abal Abal (mostly brand @alpha) in the signal path (volume control) can cause loss of audio quality. To avoid the use of mechanical potentiometer is then used as an external resistor divider. Round results will not logarithmic, but the audio quality is still better than directly via a mechanical potentiometer.
2. Bootstrap CCS with N-JFET
Part bootstrap (R7; R8; C6) added an N-JFET (Q7) to improve the regulation of the flow to the VAS transistor (Q6). R8 is now working to set the size of the current Q7 Drain. More like cascade CCS (Constant Current Source) This configuration has its own characteristics. Bootstrap which has the character of a typical bass because there is interaction C5 impedance against frequency signal, then increased the quality of the current regulations with the use of a JFET, giving bass bootstrap code and has a linearity better than before.
3. Transition Miller Compensation
Using the transition configuration miller compensation (C4; C5; R20) thereby increasing local-feedback around the output, thereby increasing the linearity at freq 'tall and produces lower distortion than usual Miller compensation.
4. Output Compound Emitter-Follower
Previously, output using compound-pair configuration, this time added a further transistor as a pre-driver to increase the output current gain linearity. Here I do not choose a triple-emitter-follower to avoid adding variables Re & VBE varies with temperature, thus setting the bias current final Tr becomes more difficult. Because Tr pre-driver has dissipation is low, around 50mW, so it does not need to be placed on the main heatsink, thus simplifying and shortening the PCB track.
100W HiFi Power Amplifier circuit with Sanken Circuit Diagram