Power Amplifier Class A 25W

Musical Fidelity would let you believe that this is a Class A design. However, in common with most commercial amplifiers, it is a class AB amplifier - it simply has a rather high standing current in the output stage, which results in the first 8 watts or so being class A.

This is a curious design, in my experience at least. It is a symmetrical design, using what appears to be two identical amplifiers - indeed there’s separate feedback paths for each. I guess that you could replace one half of the amplifier with a current source and it would work happily…

Several people have emailed to inform me that Tim de Paravicini designed the circuit - he is more famous for his valve designs, particularly single-ended, I’m told…

Each half is very simple - essentially a long-tailed pair feeding the output device which is connected in a common-emitter configuration. The two intermediate transistors (TR7/8 and TR5/6) are simply emitter-followers, providing current gain…

Read More Source:
http://www.mhennessy1.f9.co.uk/mf_a1/technical.htm
Thank you.

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