this case, I will use DC coupling because that will make it
easier to feed back to the input for best linearity.
The input opamp, IC3A, is a pre-driver and buffer.
When the input to IC1 goes below zero, the output of IC1
goes to - 6 volts, cutting Q1 off. At the same time, IC2
output goes to - 4 volts or whatever is needed to turn Q2 on.
IC2 output can go negative as far as - 55 volts. Assuming - 4
volts Vgs for Q2, the voltage across the speaker and R2 is
51 volts. Similarly, the source of Q1 can go to + 51 volts, so
the peak-to-peak voltage is 102 volts. The sine wave power
would be: E2/R = (.707* 51)2/8.1 = 160.5 watts. The 47 ohm
resistor at the OPA544 op-amp is just to isolate the
MOSFET input capacitance. I don’t know if it is necessary,
but it won’t do any harm.
The output transistors, Q1 and Q2, will dissipate an
equal amount of power, so you will need good heatsinking.
One possibility is a heatsink designed for a solid-state relay
(Mouser part #558-HE54), but a better idea is to put the circuit in a large aluminum box and use the box as the heatsink.
Most of the resistors can be 1/4 watt; the parts list is in the
schematic. This is a paper design, I have not built or simulated it, so if anyone builds it, please give me some feedback.
Class C is the case when both power transistors are
off for an appreciable part of the cycle. It finds use in RF
amplifiers, not audio amplifiers.
A class D amplifier is a switching circuit using PWM. I
am not going to cover that here. NV
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