It has been suggested that the voltage setting under the
Miner Configuration -> Advanced Settings tab that is in the new S3+ firmware is a left over from the S4 firmware and is of no effect to the S3+, however this is not the case. While trying to figure out the effect the setting had, I changed one of my slightly OC'ed S3's voltage setting to 0850 and left it there for as it seemed to slightly improve the speed it was hashing at. This unit (like the rest of my S3's) was powered by a 550W server PSU, and having left the unit to run for weeks, the PSU started restarting every so often, which none of the others ever did. I finally realised that the PSU was dead and the only difference in settings was the voltage, which confirmed to me that the setting surely has an effect on the S3+, thus this post.
I looked up the datasheet for the BM1382 chip that is used in the S3+ and found 2 sections that helped me work out what caused the fauilre of my PSU (and also led me to properly use the voltage setting to properly overclock an S3+).
1. The typical hash rate and power table
2. The input timing for the chip
The initial table has voltage settings and hash rates at each voltage, while the second table has the hash rates and frequencies to achieve them. Putting these together, I came up with the following.
I have added an extra row for each voltage setting of 0.75v and 0.80v as I found that with the two units I overclocked they had a higher HW error % at the frequencies in the datasheet. When I upped the frequency a notch, the HW error % reduced to acceptable levels. It goes without saying that you may need to add the added frequencies as they are not in the shipped firmware, here's alink to how you can add them:
https://bitcointalk.org/index.php?topic=699064.msg8370071#msg8370071Also worthy of note is that setting a chip voltage to 0.85 results in a (datasheet / theoretical) wattage draw for the S3 (32 chips) of 544 watts. Remember the server PSU that I was using on the over-volted S3 that I mentioned earlier was rated at 550 watts ..... no wonder it gave up its ghost! So ensure you have an adequate PSU powering your S3 before you begin. Addidtionally, it may be worth noting that a fully populated 6 pin PCI-e connector will carry a maximum of 24 Amps @ 12V = 288 Watts (though I normally assume they can only carry 22.5 Amps @ 12V = 270 Watts), so you may need to power your S3 with all 4 pins rather than just 2.
Finally, here's an image of one of the OC'ed units. The HW error % is a bit high on this, but the unit has hashed at lower rates for longer runs, and also higher hash rates!
EDIT: The lower part of the image is the poolside registered rate(s) after OC'ing.
EDIT: It pains me to have to admit that the same voltage OC'ing will apply to the bitmain variants that have the BM1382 chips, e.g the S2 and S4; the reason it pains me is I do not have one!
EDIT 2: I thought I'd also post this to compare with my earlier OC'ing of my batch 6 S3 in this post:
https://bitcointalk.org/index.php?topic=750220.0 (also in my signature).
When I ran the test in August 2014 at freq 262.5 with the old firmware, I achieved an average hash-speed over a day of 529 Gh/s with 200 errors (0.00187113284%). Having set the voltage to 0750 in the newer firmware, I have a hash-speed 528.53 and a HW error rate of only 46 HW errors (0.0004%).
So again, not only does the voltage setting aid in OC'ing, it certainly does help with running efficiently!
EDIT: 6th Dec 2014I had to post this. An update for the 262.5 freq @ 0.75 volts (0750 setting) after running for 2 days. There are only
96 92 HW errors and the % is still the same! The consistency you get from setting the voltage correctly is astoundingly repeatable / maintainable given what we've come to expect of ASIC rigs.
Poll
