Dual classes Power AMP

This is special power amp since it operates in class A up to about 15Wrms / 8 ohms and then automatically changes to class B up to 75Wrms / 8 ohms. The 15 Wrms is more than sufficient for living room loud listening levels and the class A experience is highly well appreciated by audiophiles. But in the case more power is needed (for party for example) there is no problem to use higher power. The high power supply capacity makes it capable to drive very low impedance loudspeakers. The Power Amp measurements can be seen here:  Power Amp measurements .

Here is the internal picture viewed from the top of chassis:

 The front plate shows 4 Leds (2 per channels).

  • Dual color LED: Green for power and Red for audio clipping (1% THD sine trigger audio level)
  • Blue color LED that turns OFF when audio amp goes outside class A level (thus class B)

The pcb assembly (1 per channel) of the LEDs indicator for class A/ B and clipping levels is shown below (interior side of front plate of chassis amp:

Since it is a high current capacity amp (2 x 500 VA transfo), there is an in-rush/anti-thump circuit for power up. The drive pcb uses regulated voltage driven by independent transformer for isolation from output stage. Here is below the schematics which includes DC voltage output protection (trigger level of +/- 3 Vdc):

See the  Design Details of Power Amp .

Some of the building steps pictures are shown here Power Amp building steps