[Alex Pogossov]

In another thread Phil Allison commended Quad 405.
Its typical schematic is he
http://schematic.narod.ru/Audio/semi/Amp/Quad405-2.gif

Assuming that Phil knows how it works, and how R38, L2, R6, R20||R21 form a
perfect bridge, blah-blah-blah, here is a question:

What is the purpose of diodes D5 and D6 connected in series?
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In my opinion, any bridge to achieve effect, needs to be "well balanced".
With typical componebnt tolerances and temperature coefficients in practice
it is difficult to balance the bridge better than to -20dB (unless you do
not select components on test or trim one of the leg of the bridge).

Thus the bridge would typically reduce distortion of the output stage by
20dB (on top of what GNFB does).

I would prefer to reduce distortion in the output stage by design, rather
than making the power stage non-linear and then rely on the bridge.

I have always been impressed by smartness (non-boringness) of Quad design,
but would not be relying on the current dumping for performance.

Regards,
Alex