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Quad 405 Individual Rectification and Smoothing Upgrade (Q405IRSUPG)
Amplabs
The original Quad 405 mains transformer has two independent centre tapped windings that were, presumably, intended to provide a
separate rectified and smoothed supply, one for the left and one for the right. Effectively providing a dual mono-block amplifier
arrangement, albeit, there is still a common primary winding, but this would have had negligible effect. The idea of adopting a separate
left and right supply was probably abandoned due to, the cost, or physical size, of four large capacitors. In 1975 when the 405 was
launched, capacitors of suitable value and voltage, would have been impossible to fit inside the existing enclosure!
With some types of music, the dual supply (DS) arrangement can improve the effective ‘sound stage’, particularly in recordings where
‘bassy’ instruments like double bass and drums are separately miked and spatially separated. So with a 405, jazz, blues and rock on a good
quality recording (label), can sound cleaner with separate supplies for Left & right.
Another audible advantage of a DS amplifier is when you Bi-AMP. In Bi-amping, the tweeter and tweeter x-over components are driven
from one amplifier and the woofer and woofer x-over components are driven from another amplifier. The two amplifiers can conveniently
be the left and right channels of a 405. If the 405 has separate supplies, the chance of heavy bass passages modulating the tweeter
amplifier are minimized. You will of course have to be the proud owner of two 405s.
Currently, we can only offer this modification as part of a 405 full service or full service & socket upgrade. To request this upgrade along
with your 405 service, quote ‘405IRSUPG’ on your ‘service request’ form.
For ure listening pleasure
Dual Supply Modification: Four smoothing capacitors and two 30Amp Bridge rectifiers wired to separate transformer windings.
