Damn! I really didn't want to be sucked into redesigning dodgy circuits ..
Input/Feedback caps.
The bias for TR1/2 come from earth (and from an O/P which is supposed to be at earth). So earth (and O/P) is +ve wrt to their bases.
I like high I/P current OPA like 5532 for this very reason cos I can ensure a few 10mV across feedback/input Al. electrolytic caps. Good performance and reliability. I HATE i/p bias cancelling OPAs for this and other reasons.
Here, the wrong polarity means electrolytics will be leaky and unreliable. Tants can stand a few mV reverse with only small leakage which is probably why he's specified one. But if you have larger reverses, eg when the amp is switched on/off, after a few goes, Tants fail catastrophically and go SC. So the already wonky offset on the amp is made more wonky and amplified by the full gain of the amplifier. Maybe no Holy Smoke from the amp but from your Speakers instead.
I'm really a speaker man and only a pseudo amp, mike, DSP & LN guru.
Abe, are you building from an Avondale Audio kit? If you are using your own PCB, be warned that the designer has a poor grasp of stability issues (eg his comments about small caps, 47p etc) and your PCB and layout may not be stable if it differs. I'm assuming he's tested his extensively (ha!).
First I gotta say in da old days, I wrote my own Circuit Analysis programme and hence don't use SPICE etc. I think I can do response / stability stuff as good as any SPICE but can't do non-linear stuff. But can full SPICE do Safe Operating Area + thermal stuff? That's what you need for Holy Smoke propensity. Can the free versions do this?
Do Golden Pinnae amps sound different? Of course they do! Some (all?) if driving a real speaker load (a big guitar speaker is good) and sine swept at various frequencies & levels, you will see small bursts of oscillation on parts of the cycle. All dependent on thermal & time history too. On overload, some will take several milliseconds to come out. None of this is Golden Pinnae subtle stuff.
A marginally stable amp may go into full Holy Smoke oscillation depending on thermal, time history & load. Changing the O/P stage changes this.
Don't ask how I know all this (especially the Holy Smoke) BS.
I'm going to bow out now but I'd like an answer about SPICE.
Don't get me wrong. It's good to play. That's how we learn. But Holy Smoke is no fun especially from your prized speakers.
http://douglas-self.com/ampins/ampins.htm
Unfortunately, he's taken a lot of good stuff & put it into his books. Definitely worth getting. Don't agree with everything he says but you can rely on his measurements.