Is it possible to modify the clock frequency of the S9? (I'd be interested in underclocking it)
yes you can.
I have 3 units S7, after halving day, my earning is drop and now i still using S7, for result is drop but help because the price is increase, but need to long time for RoI, I want to know, as my experience we need about 7 months to get roi, could you calculate how long can take profit if i using S9?
I can plug in three or four sets of numbers to this calculator
https://bitcoinwisdom.com/bitcoin/calculatorand give you an idea.
If you mine at kano.is
price of coin stays the same.
Difficulty averages 2%
your power is 0.08 cents
in 407 days you will be even
in 530 days you will be ahead
price of coin stays the same
difficulty averages 3%
your power is 0.08 cents
you will not break even
So a simple question is you power 8 cents? If it is maybe you make money.
You say you have s-7's so this means you have power supplies. Buying the s-9 is a tough cal if your power cost is 8 or more cents a k-watt in USA money.