My JLH Class A circuit mods any good ?

[chris speakman]

First I have to say thanks for this brilliant site , I love it .
Anyway I've been experimenting with John Lindsay Hoods "69" Class A circuit .
First I tried it without the bootstrap capacitor on tr2 load resistors .
Pure Class A .
Sounds great at low level but unacceptable distortion at hi levels.
Next tried led / transistor constant current source for tr2 . Wow more punchy and aggressive sound , no didn't like that sound so tried adding a class A phase splitter / current driver . I see this current splitter idea in his original Wireless World 69 article . It makes sense to me , tr2 is now vas , tr3 is current driver / phase splitter . tr4 / tr5 outputs are biased in pure class A . I've built this circuit and it makes sweet music . Under simulation optimum bias current is 0.8 amps for ten watts output into 8 ohms . My question is this , do you guys like the circuit ? how would you improve it ?

 

[Ian Finch]

First, I'd be interested to know why you would opt for MJ(L)4281 for a class A amplifier when any low frequency power transistor will be more than adequate and less risky for stability. Also, how did you simulate the design - as the generic transistors that came with the sim. software or with specific component models?

 

[chris speakman]

Hi thanks for the reply , gone a bit over the top with the MJ4281's , I bought these a while back for use in the JLH "69" circuit . I've simulated with MJ3281's , 2N3773's and 2N3055's . I've used MJ4281's because I have some . I'm using Tina-TI version 9 , had to import the MJ's spice model , all the other transistors were already in there . Would be Interested if you could recommend a more suitable / less expensive output transistor . Thanks for your Interest , regards Chris .