Which is actually most likely just a S7 underclocked & undervolted..
Back in the 2016 I tweaked a S7 to perform 4.2Th/s at 1066W (at wall) power consumption by using methods in this guide provided by
.
I used one these hex files with PICkit3 for undervolting and underclocking a
S7, batch 9 and everything went smooth.
I sold that miner but I'm going to do the same thing again soon to a S7 when the S9 arrives and I rearrange my miners and PSUs.
Here is my setup:
Antminer S7, 640/670mV, 4.223Th/s (60 min avg), 625 Mhz
Power supply: Enermax Revolution 87+ 1000W
Voltage: 227 VAC
Current: 4,7 A
Power (at wall): 1066,9 W