The Quad 909.
I recently had the good fortune to get a couple of good buys on another two Quad 909 amps. So my
left and right main speakers are now powered by three Quad 909 current dumping amplifiers, providing a total of 1500 watts.
The center channel speaker is also powered by a Quad 909 with a power of 500 watts.
Here is the revised amp rack.
On the left are the three Quad 909s driving the left and right main speakers. On the right is the Quad 909 driving the center channel speaker, the two Quad 405-2 driving the back speakers and the 405-2 driving the surrounds.
Before I installed the 909s I granted Seth's request to see "GUTZ"
Here is the schematic.
IC 1 is the very high performance but low powered class A amp, that provides error correction to the dumpers, T9, T10, T11, T12, T13 and T14. These push pull triples are biased class AB but towards, B so the amp is very efficient. The performance is entirely determined by the performance of the IC1 class A Amp. So the characteristics of the amp are class A. So it is class a performance without the hassle, inefficiency, heat generation and unreliability of a class A amplifier. It sounds too good to be true, but it its the truth.
Here is a view with the bottom cover removed.
The toroidal power transformer is center, with the four power supply smoothing caps around it. At the back with the fuses is the power supply control and regulation board. The amp boards, again with very low part count are either side.
Here is a view of a power amp board, with the triple push/pull output dumpers in the heat sink either side.
Here is a view of the power supply regulator control board.
The justly popular Quad 909 is the only one of
Perter Walker's Current Dumping amps in production. IAG (International Audio Group) own Quad now, and they basically are sitting on the patents.
In truth these amps could be produced in large quantities quite cheaply. The part count is low and there is no set up to do, just test it. Amps of this type could easily be produced to produce huge power outputs.
Even more tantalizing is the prospect that IAG could and should license this design. They would make lots of money. These amp boards would have the potential to revolutionize the performance of receivers. The amp boards are small reliable and not at all fussy. Heat generation is very moderate.
The boards are also ideal for active speakers. Peter himself used them in such applications, for the BBC in particular.
It is a real tragedy the wider audio and now the AV community can not benefit from Peter Walker's sheer genius.
