Johnny B Good wrote:

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The advice note attached to those Quad 405s was simply a reminder that
the supply voltage would still remain 240v with very little danger of
the supply ever being matched to the notional 'Harmonised Supply
Voltage' of 230v.

I don't know the history, but it seems it was the only bit of BBC
equipment marked thus. The inference being they didn't take kindly to
being set to 230v.

One possibility might be Quad Acoustical taking advantage of the tighter
voltage tolerance required (for whatever reason) to save transformer
materials costs otherwise demanded by a "Universal" higher primary
voltage design supplying a voltage agnostic circuit (voltage regulators
and/or final output stage) in the form of extra iron and copper to keep
hysteresis losses at an acceptable level.

If you have to go to the trouble of closely matching a mains transformer
primary voltage to the supply voltage due to other considerations such
meeting a maximum output power for a given acceptable level of
distortion, you might as well extract the full benefit of minimising
transformer costs whilst you are at it. (i.e. Don't miss a trick! :-)


** The Quad 405 and 405-2 were designed to accommodate a +/- 10% variation from the set voltage without change in performance - says so in the 405-2 manual.

However, the set voltage needs to match the typical incoming supply voltage for this to work out.

Quad 405s are *not* unusually sensitive to supply voltage.


..... Phil