It is a bit difficult to make photos, by some reasons, I’m just helping the buyer as I like this amp very much.
Yamaha uses two pin socket and the ground is made the same way as here Massive sudden hum - frightening! - #15 by james_n
Actually, it was working for me, when I was using another Yamaha. But now it works strange when setup in another home.
No difference, if this ground cable is connected either to yamaha or to 5si - the hum disappears and then slowly returns and grows.