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Message-ID: <005901ccbc30$7b9de820$8f27f004@ctrask>
From: "Chris Trask" <christrask@earthlink.net>
To: <rsgb_lf_group@blacksheep.org>
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Date: Fri, 16 Dec 2011 13:22:47 -0700
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Subject: Re: LF: RE: Wellbrook Loop
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>
> A very interesting circuit concept - I hadn't heard the term
> "augmentation" before. (It looks to have something in common - and
> completely turned upside down - with the bootstrapping technique used
> to increase the input resistance of emitter follower stages)
>
> But, looking at the circuit of the preamp in Figure 6, I'm wondering
> if, instead of what is virtually two independent input stages, with
> their own separate transformers, you considered a differential
> push-pull feedback as a single entity.   Have a centre tapped
> secondary in the bases (with the centre tap to AC ground),  but with
> the primary connected between the two emitters, ie directly across the
> loop input.
>
> The two input transistors now operate in true differential mode,
> rather than as mostly-independent amplifier stages, and with only one
> feedback transformer, complexity and wire losses are reduced.   This
> will give even more decoupling of the loop from ground.
>

    That results in far higher distortion as the emitter signal voltages are
not symmetrical, and you cannot force them to be.

Chris Trask
N7ZWY / WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/