The Robust Audio Amplifier


The Robust Amplifier is a combination of a current limited power supply with a high current low impedance power output stage.  Any short
circuit on the output is instantly current limited.  The output stage utilizes two high current transistors with no emitter resistors.  The two high current output transistors are uniquely biased off of emitter resistors of two additional high current gain transistors.  The amplifier was designed so that all three transistor associated with the power for each (+ and -) power supply rail can be mounted to the same heat sink without the need for electrical isolation.  The use of old CPU heat sinks works well.  Being that there is metal to metal contact between the transistors and heat sinks, the amplifier can be biased hot to eliminate crossover distortion.  This amp also features adjustable output stage bias.  The schematic shows +- 45 volts power supply, this is a maximum, 35v is recommended.


Robust Amplifier Schematic

The power is supplied by a split power supply circuit with an instant current limit built in.  This current limited supply protects the amplifier's output transistors from output shorts and current surges during power on.  This design utlities scable current sensing resistors.  You can choose the current limit that is right for you output transistors.

7 Amp limit use 0.1 ohm
  10 Amp limit use 0.068 ohm

Current Limited Split Power Supply for Audio Amplifier
Current limit circuit operation is as follows.  Current flow throug R17 creates a voltage, when this voltage reaches 0.7v Q12 turns on and turns off Q10.  When Q10 is off voltage develops across Q10 and this voltage is used to drive the OL (overload) LED1. 

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