Mini-MosFet Audio Amplifier

Posted on Feb 7, 2014

R1_2K2 1/4W Resistor R2_27K 1/4W Resistor R3, R4_2K2 1/2W Trimmers Cermet or Carbon (or 2K) R5_100R 1/4W Resistor R6_1K 1/4W Resistor R7, R8_330R 1/4W Resistors C1_22 µF 25V Electrolytic Capacitor C2_47pF 63V Polystyrene or Ceramic Capacitor C3, C4_100 µF 50V Electrolytic Capacitors C5_2200 µF 50V Electrolytic Capacitor Q1_BC550C 45V 100mA Low noise

Mini-MosFet Audio Amplifier
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High gain NPN Transistor Q2_IRF530 100V 14A N-Channel Hexfet Transistor (or MTP12N10) Q3_IRF9530 100V 12A P-Channel Hexfet Transistor (or MTP12P10) This project was a sort of challenge: designing an audio amplifier capable of delivering a decent output power with a minimum parts count, without sacrificing quality. The Power Amplifier section employs only three transistors and a handful of resistors and capacitors in a shunt feedback configuration but can deliver more than 18W into 8 Ohm with <0. 08% THD @ 1KHz at the onset of clipping (0. 04% @ 1W 1KHz and 0. 02% @ 1W 10KHz) and up to 30W into a 4 Ohm load. To obtain such a performance and to ensure overall stability of this very simple circuitry, a suitable regulated dc power supply is mandatory. This is not a snag because it also helps in keeping noise and hum of the preamp to very low levels and guarantees a predictable output power into different load impedances. Finally, as the amplifier requires only a single rail supply, a very good dc voltage regulator capable of supplying more than 2 Amps @ 40V can be implemented with a few parts also. Switch off the supply, disconnect the Multimeter and reconnect it, set to measure at least 1Amp fsd, in series to the positive supply (the possible use of a second Multimeter in this place will be very welcomed). Those lucky enough to reach an oscilloscope and a 1KHz sine wave generator, can drive the amplifier to the maximum output...

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