Since I would like to run it even lower, I set brd_ocp to 30 and kept osc at 30(both minimums based on the documentation), this nicely decreases the fan speed (and sound) as expected.
with 30/30 you have already increased the efficiency with reduced stability compared to ECO.
I think the binaries documentation is outdated? (Apollo UI ranges from 25-60)
So you can step to 30/25 if it's unstable?
One thing that I don't understand is why the minimum brd_ocp is 30?, would it be safe to run it at even lower numbers?, I'm aware that the hashrate will be reduced of course, but I'm mainly concerned about the hardware functioning properly at it's absolutely lowest value (for example, would it be possible to run it so low that the fans are not needed?).
In the end brd_ocp reduces the chip voltage and from some point the chip is no longer able to to keep up it's base load I think. Maybe <30 is too far out of specification?
A low power mode is also a nice idea for the apollo UI.
Also, I noticed there's another fan in the "official" power supply. Since I'm planning to run it with very low power, I wonder if that fan is even needed as that's now the main contributor of noise. I guess I could buy another PSU without a fan for this "silent miner" project. Any suggestions for one? So far I've found
this one, which should run without starting the fan until 220W so it should be absolutely noiseless.
Yes, the official PSU is really interfering with the quiet operation of the apollo.
Maybe futurebit will design a PSU with a bigger and quiet fan in the future?