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From: "Phil Allison"
References: <email@example.com> <firstname.lastname@example.org> <3DKC9.467$Lq.email@example.com>
Subject: Re: Class B amplifiers: what are the large low-value resistors for?
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Thu, 21 Nov 2002 09:29:08 +1100
NNTP-Posting-Date: Thu, 21 Nov 2002 09:19:01 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"Kevin Aylward" wrote in message
> Phil Allison wrote:
> > "Kevin Aylward" wrote in message
> > news:3DKC9.467$Lq.firstname.lastname@example.org...
> >> *Pure* class B dose not require temperature compensation. Temperature
> >> compensation is to compensate the *bias* current. If there is no bias
> >> current, there is nothing to compensate. The reason for this
> >> misunderstanding could be that is usually to say class B as
> >> shorthand, when in fact one rarely uses class B, it is always class
> >> AB, i.e. there is at least some standing current.
> > ** Many commercial power amps produced since the late 1960s
> > operate with the main output devices completely cut off at idle - or
> > pure class B. The Crown DC300 and DC300A were early examples along
> > with most later Crowns and Phase Linears and many clones.
> I meant *real amplifiers*:-)
** You know what that is do you ? I doubt it.
> Crown DC300's were crap, despite their reputation.
** That completley idiotic remark reveals a lot about you Kevin and it
is not good.
> > There was temp compensation built in to make sure that the
> > output transistors did not become biased on at high temperatures due
> > to their Vbe dropping.
> I agree that technically this is temperature compensation, but the
> phrase temperature compensation when applied to amplifier output stages,
> usually refers to protecting against thermal runaway.
** More precisely to stabilise the bias setting.
I don't see why
> they would bother to prevent the outputs being slightly on.
** Part and parcel of the design.
> unlikely that that could cause thermal runaway, and the more bias the
> less x-over distortion.
** The bias stability is designed without the output devices involved
so they must not become involved or it will be unstable.
It sounds like a right silly idea, probably
> because it was done 30 years ago when they didn't know any better.
** No arrogance is beyond you is it ?
> still remember using 100 watt transistor amp modules that used a driver
> transformer because the designers were too daft to realise that the
> product did not have any glass in it.
** Unlike yourself no doubt who has too many glasses in him.
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