The circuit consists of an N-Channel MOSFET voltage follower T1 (common Drain) and current source T2 (NPN Darlington). Current source is set to 2.2 Amps. With 40V of supply voltage the circuit is able to deliver about 17W into an 8 Ohm loudspeaker. The amplifier will take 88W from the power supply all the time. Bandwidth (-3dB) is from 4Hz to 250 kHz. Rise time is 1.5 us. Output resistance is 0.16 Ohm. The circuit is very tolerant of different kinds of load. Input resistance is 10 KOhm (R0), but can be increased up to 100 KOhm (R4) by omitting R0. Input capacitance remains relatively high, about 1500 pF. For this reason, the preamp should not have higher output impedance than 1 KOhm to maintain high frequency limit about 100 kHz. An input potentiometer can be used instead of R0.
If the value of the potentiometer is 5 kOhm then the high frequency limit will be about 70 kHz. The power follower can be connected directly to the output of CD player, and for reduction of volume potentiometer 5 kOhm can be used.
Normally, the thermal coefficient of zener voltage of 3V type is negative, and so is Ube voltage of the Darlington transistor. As Ube is reduced by -2mV/°C, zener voltage also goes down with increasing temperature inside a box (but the zener is not on the heat sink of the MOSFET and should not be). In fact there was a fluctuation of 40mA at 2A constant current, from my point of view it is negligible. Of course the heat sink for T1 and T2 should be better than 0.5°C/W for each transistor, so four such heat sinks are needed for stereo.
If the value of the potentiometer is 5 kOhm then the high frequency limit will be about 70 kHz. The power follower can be connected directly to the output of CD player, and for reduction of volume potentiometer 5 kOhm can be used.
Normally, the thermal coefficient of zener voltage of 3V type is negative, and so is Ube voltage of the Darlington transistor. As Ube is reduced by -2mV/°C, zener voltage also goes down with increasing temperature inside a box (but the zener is not on the heat sink of the MOSFET and should not be). In fact there was a fluctuation of 40mA at 2A constant current, from my point of view it is negligible. Of course the heat sink for T1 and T2 should be better than 0.5°C/W for each transistor, so four such heat sinks are needed for stereo.
