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Old 8th Apr 2012, 12:43 am   #34
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: JLH Class 'A' Amplifier

Quote:
Originally Posted by Radio Wrangler View Post
A past boss of mine got into a protracted argument with JLH over the advantages in noise floor of series and shunt modes of negative feedback, in the letters pages of Wireless World.
I have forgotten who was JLH’s antagonist in this debate. Later on though, JLH seemed to soften his position, and in his 1982 Wireless World modular design used a two-stage series-shunt circuit. In his 1997 book he focussed on the HF error inherent in the series feedback approach (which could be, but seemingly often was not corrected), but was neverthless quite complimentary of Baxandall’s 1977 treatment of the subject, even though the latter came down in favour of the series feedback approach.

Back in 1969 I guess it would have been possible to combine the Cambridge P40 Darlington emitter follower input buffer with a lower impedance version of JLH’s shunt feedback triple for gain and equalization, and so have had the best of all worlds. But that would have required 5 transistors, as compared with the 2 (Dinsdale) or 3 (Bailey) typical of series feedback designs.

Cheers,
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