JFET Design Spotlight - Audio Amplifiers

“Audio amplifiers are many and varied. Ones used for music should have a very low intermodulation distortion and when overdriven should produce a minimum of odd alien sounds. Class A amplifiers tend to be preferred over most for their “warm” and realistic sound presence. Though not efficient, The Class A and class AB1 often fit this category for the most part. Class B amplifiers are more efficient but have a nasty problem with the impedance shift at zero crossover. Here is a variation in thinking that merges both types of design. Though having a class B output with complimentary devices exclusively drawing current from their respective rails, an output stage bias is always on allowing complimentary emitters to operate with no series resistor and is thus designated as Class BA. As with most sound worthy amps, the input stage is a Low Noise differential pair of Linear Systems LSK389A JFETs. Output offset is <10mV and can be dialed to 0.0V with a small offset Pot. This circuit is inspired by an instrument buffer circuit circa: 1957 of Henry Hall and Bob Fulks at General Radio Co.” – Kirkwood Rough

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