Think its been a while since there's been detailed activity here for an amp that uses A/C mains. Four or five people contacted me about the case & may be building σ22s.
If any are newish builders respect the importance of safety, I'll mention a few particulars of my build(s) below.
There are good threads/posts/URLs that detail A/C/mains safety in DIY & builders new to it should certainly seek them out. E.g. in these builds I used insulated connectors to IEC, a proper chassis ground stack (dedicated screw, lock washers/lock-tite, ring lug, nuts), removed anodizing at chassis ground screw & at parts of enclosure panel mating areas + underside of screws/threads & assured the entire σ22 exterior contacts safety ground.
If building σ22 and/or β22 it pays to carefully review their related info on amb's site & triple-check all your work before powering up. E.g. a swapped/grounded MOSFET, swapped/maladjusted trimpot, unintended ground/short, slipped probe, pierced solder mask during adjustment/testing are some things to avoid.
Anyway, in case anyone is considering 2-channel β22 in same case as above know there's significant time overhead to do it (& probably some cursing as well:)
It's a nice quiet build. Note copper underside of ε12/zobel network/RK40 board is the star ground w/only connection to chassis ground at its mounting screw by headphone jack. Every "module" can be removed w/o soldering which came in handy for tweaking/lowering the ε12 latch LED brightness:) Runs cool & allows trying higher biasing. BTW I post some other build & parts details here: