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From: "Phil Allison"
References: <email@example.com> <firstname.lastname@example.org> <email@example.com>
Subject: Re: 'Current Dumping' Amplifier Circuits ?
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Wed, 4 Dec 2002 08:35:53 +1100
NNTP-Posting-Date: Wed, 04 Dec 2002 08:25:05 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"Barry E Porter" wrote in message
> On Tue, 3 Dec 2002 09:26:29 +1100, "Phil Allison"
> >"Barry E Porter" wrote in message
> >> Back in 197something or other, I was the first person to be awarded a
> >> license by Quad to produce current dumping amplifiers, on condition
> >> that they were not in competition with the 405. (I was asked by a
> >> Japanese agent to incorporate them into an active speaker)
> >> One thing that soon became clear, was that the 405 was not optimised,
> >> mainly because the plastic case parts had cost so much to make, that
> >> the PCB size was very limited.
> > ** Lost me here. There are no plastic parts in a Quad 405 save for
> >driver transistors.
> > The case is all metal, an alloy heatsink casting and some folded
> >sheets IIRC.
> To be exact, the sides of the original 405 was a pressure die casting,
> which cost around 50k UKP in tooling.
** Gawd - that must include the heatsink too surely ?
During the production of the
> 405-2, a plastic moulding with threaded inserts was used. I gather
> that they switched between the casting and the moulding at various
> The point I was making, (while screwing the engine back into my son's
> car), was that the performance was not optimum, because the PCB size
> was fixed by the size of the case - Mike Albinson told me that, so
> it's more than just my opinion.
** Hang on, what did Mr Albinson tell you ? The performance was not
optimised OR that the PCB had to fit in the case ?
The latter is kinda obvious.
> This was also the reason that the output fell away so badly when
> driving a load of less than 8 ohms - something that was later improved
> with the 606, which had space for parallel output devices.
** The 405 was designed to use two rugged output devices - so it did.
Everything about the amp is sized for the dissipation that a 100 to 150 watt
per ch amp produces.
The original VI limiter was of simple design - it protected the
output transistors from failure under overload and shorts. This meant the
maximum available power fell off when loads below 6 ohms were used.
The later 405 - 2 version allowed higher peak currents (on a
short term basis) at low output voltages so very reactive loads could be
driven to full power. More rugged transistors were also used to get the
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