I wonder what do you call this opamp?
I have searched many times but I only find its symbol without any explannation?

 

Differential output opamp.

 

Balanced Line Driver? A common circuit is the SSM2142

 

Oh, thanks!
This is the first time I see this opamp. I wanted to know more about it but I couldn't come up with a name to search for.

 

Hello,

The LM733 or the NE592 are examples of the differential amplifier.
See the attached datasheets for more info.

Bertus

 

Hello,

The LM733 or the NE592 are examples of the differential amplifier.
See the attached datasheets for more info.

Bertus

Yes, thanks Bertus!

 

Hello,

The LM733 or the NE592 are examples of the differential amplifier.
See the attached datasheets for more info.

Bertus

The are indeed differential in/out amplifiers, but the are not op amps, and probably would not perform well with feedback from output to input.