For some reason people are more keen on sharing schematics than layouts. I don't know if you want to build a discrete amplifier or just make a 10 - 20 watt amplifier rather quickly. In later case I guess the fastest way is to browse through some chip power amplifier datasheets - like TDAxxxx series. They usually present an example circuit accompanied with a PCB layout. You say you want quality: Most of them are excellent quality for that power range and come equipped with short circuit/thermal protection and top quality constant current loads etc. I bet you couldn't build a better one from discrete components aside make as tight layout with equal thermal coupling characteristics. If part of your project is to explain how the circuit works you could do that with a chip amp too; the datasheet usually has a simplified schematic of the circuit.
If you want to build a discrete amplifier I suggest you do the layout yourself. It's a great way to learn why the layout is pretty important part of the whole circuit. It's pretty easy to come up with a schematic that runs ideally on paper. When you build it, it will have all sorts of interference since real-life components and wiring are never that ideal. Besides, you learn a lot more by making mistakes and trying to correct them. Making a PC board layout shouldn't be that time consuming once you get to it and know what you are doing.
By the way, I don't know if you really searched or just expected someone to do it for you. When I typed "amplifier PCB" to google I instantly found several pages that might have a suitable circuit.
http://members.hometown.aol.com/_ht_a/lmdmkm/25w/25wamp.htmhttp://www.audiodesignguide.com/Headphone_amp/headphoneamp.htmlhttp://hepso.dna.fi/misc/lm3875/LM3875_amplifier.htmlhttp://www.digisound80.co.uk/digisound/modules/80-14/80-14.htmhttp://www.tcaas.btinternet.co.uk/jlhesl.htmBesides these you could check out the pages of hifi amplifier projects like "Leach" or designs by Nelson Pass to name a few sources. Guitar power amplifiers are still plain power amplifiers and if you concentrate your focus only on guitar amps you miss a lot of information.
Edit:
The Joe Davidson's amp is basically a variation of very old "Leak" circuit; the first commercial solid state amp without output and interstage transformer.
http://home.vicnet.net.au/~vic3d/audio/leak/cctStereo70.gifhttp://home.vicnet.net.au/~vic3d/audio/leak/cctStereo30.gifI don't know who's responsible for the initial design of this topology, Hung Lin perhaps? You can vary this circuit endlessly, here's one example of what you should avoid (extremely bad design as is):
http://www.redcircuits.com/Page65.htmIt doesn't have the all important two gain stages - structure so it's an inverting amplifier and the result is very bad: Noisy, low input impedance, narrow bandwidth. If you look at that volume potentiometer configuration and understand how the gain is set in such a circuit you'll see that something is terribly wrong. The "Leak" idea is much better since it separates the feedback from the input signal. It is non-inverting which is superior than inverting.
I've seen the Leak topology used in countless amps (with different component values of course), for example this one:
http://www.ssguitar.com/index.php?action=dlattach;topic=195.0;attach=14;imageThe other week I traced out the power amp of my old Sansui and it has one too. I bet that if I could get my hands on old RCA manuals with transistor stuff they'd be full of these as well. This topology is pretty difficult to tweak and doesn't work with dual supply. I built one similar amp last summer (it still needs a preamp) and I wouldn't build anything with this topology again; the circuits with current feedback or long tailed pair input stages are usually so much better.
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