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From: "Phil Allison"
References: <firstname.lastname@example.org> <email@example.com> <3DKC9.467$Lq.firstname.lastname@example.org>
Subject: Re: Class B amplifiers: what are the large low-value resistors for?
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Date: Wed, 20 Nov 2002 23:20:36 +1100
NNTP-Posting-Date: Wed, 20 Nov 2002 23:10:09 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"Kevin Aylward" wrote in message
> *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.
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
> The only commercial audio amplifier I am aware of that used a pure class
> B output was the Quad current dumper.
** The Quad 405 used a class A stage to fill in the gaps for the
"dumpers" and so was a hybrid - same as the much earlier Crowns that used
a standard class AB stage to drive their particular class B "dumpers".
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