I don't know where exactly is the problem.If it's my amp's problem or another.
But...
When my amp's input is grounded is dead quiet. My speakers are around 92db and I don’t hear anything.
When it is opened there’s a small hiss or fsss or whatever (I’m not very good describing these sounds) but not audible at listeners place. Not even at very close to speakers.
When I connect the interconnect cable with the preamp there’s an audible (not very loud-you must place your ear next to woofer) hum that looks like it is from a transformer interference. Say it’s sth like a bass mmmmmm. The strange thing is that this sound is the same when the power switch of the preamp is opened or closed.
When I reconnect the interconnect cable only from the preamp’s side it’s like the second purpose above. Like when the input is opened.
I thought that the problem was at the preamp. But I tried another preamp and the results were the same.
I’m a little bit confused.

But...
When my amp's input is grounded is dead quiet. My speakers are around 92db and I don’t hear anything.
When it is opened there’s a small hiss or fsss or whatever (I’m not very good describing these sounds) but not audible at listeners place. Not even at very close to speakers.
When I connect the interconnect cable with the preamp there’s an audible (not very loud-you must place your ear next to woofer) hum that looks like it is from a transformer interference. Say it’s sth like a bass mmmmmm. The strange thing is that this sound is the same when the power switch of the preamp is opened or closed.
When I reconnect the interconnect cable only from the preamp’s side it’s like the second purpose above. Like when the input is opened.
I thought that the problem was at the preamp. But I tried another preamp and the results were the same.
I’m a little bit confused.