Probably best to ask in my hardware dev thread, or better yet on a support thread.

If I build an upgrade, and I'm very much planning on it, there won't be any custom controller required and the boards will be volt-adjustable. These are mandatory features for any miner I will ever build.

My hosting is set up with 3phase, where I have pulls from two phases dropped to a two-pole subpanel on each shelf breaking out customer circuits (at 208V). There are current meters on each leg at the junction box so I can keep everything reasonably balanced, also shows me what shelves have available power for new gear. Not fancy at all but works out pretty well.

Maybe we should start a thread about hubs so I stop getting "new post" emails that aren't about 2Pac sales?

If you got a decent soldering iron, buy an $8 hub off eBay and beef up the rails. That's how I get powered hubs.

Or do that thing he just said.

Dang that's a sexy hub. From where do you conjure up these things?

Maybe. Does it have any active parts or does it just link two jack "rails" and only send data down one? Also is the spacing the same between the hub it was built for and the one you want to use a 4A bridge with?

I should probably one of these days get back around to my high-power-handling hub project. Maybe if 2Pac assembly goes smoother than expected, but that's going to depend a lot on whether or not the guy helping starts being more effective.

For extreme overclocking I definitely recommend VH's new cgminer driver over Novak's. The original ramp code, while still better than nothing, was still pretty hard on the works as far as step current is concerned (which can cause the USB voltage to bottom out or trip the voltage controller and break hashing). VH's new driver exactly emulates the S5's smooth linear power increase and should make hitting the high frequencies quite a bit easier.

The new 2Pac also has hardware improvements to isolate the buck controller from voltage ripple resulting from high power use by the ASICs, so with both that and the better driver overclocking on those is a breeze. I hacked a basic version of this into "Max", the uber-test-Compac we pushed almost to 500MHz back in the day.

As Biodom mentioned, a larger heatsink will also do a better job of cooling when you get into high power ranges. Somewhere in here I posted a mechanical diagram of the heatsink which gives screw positions if an overclocker wants to make his own heatsink. There are also several examples of over-spec heatsinks posted throughout.

Technically not a correct answer, since the PSU doesn't accept 3-phase power. Only a single "phase" is used per PSU; whether that's 240V line-line (or, less likely, line-neutral) or 208V line-line is up to the end user's particular implementation. Of course this is based on a strict parsing of the OP's question, which may not read as he intended it to mean.

But the part about any AC over 200V is right, so pulling 208V from a three-phase installation works just fine.

The PSU will only take in a single hot line. If you span two legs of a 3-phase system for 208V it works just fine. My entire hosting is set up like that.

That's not a general-case truth. I see that error on solo.ckpool with a suggest-diff 4, it calls "share above target" for all submitted shares initially (and all submitted shares are at least diff 4, which the pool is asking for). I also don't see that error on Eligius with an initial diff of 4096 when the stick is only submitting a couple shares an hour.
Seems like "share above target" for a share not above target is a really poorly named error message, so either I'm misunderstanding your explanation or it's incorrect.

Also, admittedly, I've never used BFG. The only time I've ever seen "share above target" was on VH's cgminer fork when mining at ckpool. I don't know how BFG behaves. And honestly anymore I recommend VH's cgminer as outlined in the 2Pac thread; Novak's original Compac code was a rehash of the Icarus driver, and the BFG driver isn't much different, but VH's Gekko driver for cgminer is fully custom-built and handles the sticks much better overall.

Did you let it run for very long, or turn it off immediately? I got the same error testing 2Pacs on solo.ckpool, but after a minute or so it started accepting shares regularly. Not sure what's the cause.

Stencils arrived this morning so we got started on surface-mounting. By tomorrow I'll have about 600 sticks with ASICs mounted, and will have started on the topside components. All heatsinks are drilled and tapped and ready to be installed. Overall, we're right on schedule.

I also happened to fetch some materials to play with anodizing a bit if I get some spare time in the next couple days.

Just making sure it's being read correctly, the "-O2" is dash oh two, not dash zero two. I have no idea if that's related to your issue or not.

Bitfury stuff loves to run in strings. Remember they built 48V single-wide strings for their own DCs and apparently got along well enough.

I don't know how cheaply an S7 could be had these days, but they can be undervolted to downclock around 0.23J/GH and still get a decent hashrate, about a 25% efficiency boost over stock. Less power means less heat means less fan noise, still not S3 silent but probably 10-15db quieter than stock full-blast. Efficiency also means a longer viable lifetime before power costs obsolete 'em.

If you're looking for quiet PSUs, I also recommend the 4K setup. You'll have to scrounge up 120mm fans, but a bigger fan means less noise for the airflow. Server PSUs are good for high power, efficiency, reliability and cost savings but tend to have small noisy fans; the 4K setup uses external fans so doesn't have that problem.

The two-chip shipped with voltage set for 100MHz stable. Looks like you need to turn it up, getting ~100 errors per minute. Should level out to 22GH, about 300WU

The plain silver heatsink is because my regular supplier of heatsinks wasn't gonna be able to provide a bid until March, and after the procurement agent I handed the request to did a little bit of legwork and then forgot about the whole thing, I just bought a bunch of cut-to-length on short notice and got a guy drilling them out here in the shop. Nothing fancy, sorry.
The blank side of the stick won't be blank on the production version. Both US and bitshopper versions have a full-logo silkscreen and whatnot like the original Compac, I just didn't care to do all the manual mirror-image edits for that layer in time for the prototype sticks.

Yeah, that's in the Q&A section in the first post.

I built it on an older Debian fresh install, needed libncurses5-dev and libusb-1.0-0-dev to compile and work properly.