From: firstname.lastname@example.org (N. Thornton)
Subject: Re: Class B amplifiers: what are the large low-value resistors for?
Date: 16 Nov 2002 15:06:54 -0800
NNTP-Posting-Date: 16 Nov 2002 23:06:55 GMT
Kevin McMurtrie wrote in message news:...
> email@example.com (N. Thornton) wrote:
> >Paul Burridge wrote in message
> >> On Thu, 14 Nov 2002 17:34:21 +1100, "Phil Allison"
> >> opined thusly:
> >> This one hasn't: it's just a breadboard experiment. BTW, there's no
> >> reactive load, just a loudspeaker. Okay, I know even a loudspeaker is
> >> technically a reactive load, but we're only talking low audio
> >> frequencies here, so I guess it'd be purely resistive, yeah?
> >> What I'm outlining here is class B *audio* of a few watts. Sorry if I
> >> should have made that clearer.
> >I'm thinking you're not using class B here :) More like AB, which is
> >somewhat different. Class B would be simpler, and can in fact be made
> >to work without any problematic level of crossover distortion.
> >If you're willing to use geranium output trs you can do a much simpler
> >cct that's totally stable and sounds nice. I always do that for
> >quickie amps.
> >Use an LM324 opamp to drive 2 small 1 watt Ge output trs, no bias.
> >Just connect the bases together and hook them straight to the LM324
> >output. A few Rs for the opamp feedback, one output cap, and thats it!
> >It only works with geraniums though: silicons give terrible crossover
> >dist. And its runaway proof, despite the lack of any obvious runaway
> >Theres no thermal or short protection, and no capacitive load
> >proofing. Them is extra!
> >Regards, NT
> The LM324 itself has terrible crossover distortion! It's meant to
> deliver current in only one direction so there's a couple volts of slack
> in its push-pull transistors. That's what "Single Supply" means.
If that's true, can you explain why it worked nicely? I've heard some
attempted explanations, but I've never been really at peace with them
myself. I have used this cct btw, it isn't just a paper idea.