Tried changing the frequency and so far, it doesn't work well with any setting other than 650. I tried 600, 625. 636, and 675. For each one I lt it try to hash for about 30 minutes and each time the overall hash rate barely got above 2TH. Setting it back to 650 and it went back to about 11TH immediately.
My guess is that the chips on the 821 are pretty much set to only work right at the 650 frequency. Of course, I could be doing something wrong so maybe someone else will have success.
So it looks like one setting that does work well is the "--avalon8-voltage-level". I set mine to -1 (range is supposed to be -15 to +15) and it is running cooler by 10 degrees and the fan is staying around 65-70% with a hash rate about 9-10TH. (Plus, it is much quieter now.) I also changed the target temp to 90 which makes the fan run more like the 741s. I'll let it run overnight and take a screenshot tomorrow. It will be interesting to see if there are power use differences when HagssFin retests.
Here is what I put in More Options: "--avalon8-voltage-level-offset -2 --avalon8-temp 90 --avalon8-voltage-level -1"
I'm more than a little leary of setting the temp to 90. Most chips today are rated for -20 to 80C, with a few exceptions that go to 105C (rare exceptions). And because *specifically* the developers at Canaan, changed the 90 which the 741's use to 70 in the code.
I did see that overriding the voltage-level-offset made a difference, haven't tried the other, but for now, I'm going to leave mine running at a max temp of 70 and just work on keeping the inlet temp down.