In article , Serge Auckland
wrote:


The original 405 didn't provide enough current for anything other than
nominal 8 ohm loads. It struggled a bit even with 4 ohm loads. Given
that a nominal 4 ohm loudspeaker is allowed to go down to 3.2 ohms, and
many go below that, Quad felt they had to provide more current
capability, hence the 405/2.

More to the point, the original IV limiting using on the 405 was
particularly severe for reactive loads - rather common for loudspeakers!

If you take a 405 or 405/2 and use them on, for example, 11-15 ohms
LS3/5As, I would very much doubt there could be any difference in
sound, but with, for example, Mission 770s, which were quite popular at
the time, I would expect the 405 to struggle, whilst the 405/2 would be
OK. You may not have been aware that QUAD published a modification to
the 405 which turned it into a 200w/4ohm mono amplifier by paralleling
the two channels. I built a few of these to use with Mission 770s and
KEF 104/2s and they worked very well.

Perhaps also worth recalling that around this time HFN organised a detailed
set of listening comparisons. The results of which showed that the
listeners couldn't tell one amp from another when all were used with the
same system gain and none were being taken outwith their limits. The amps
tested included the 405 IIRC.


Slainte,

Jim

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