I have akg K 701 headphones. I want to know what is the difference with amp and without it. Can i produce music with amp that is not so good or i need expensive amp?
I guide you to HeadRoom's amp section:
As long as you can achieve the loudness levels you want and avoid any unwanted noise than an amp may not be necessary. For better control of the mini speaker that is the headphone driver a good amp be it something built into a receiver, soundcard, or even a standalone amp may be in order.
So if you AKG K701 get loud enough and you do not hear excessive noise while listening then you may not ever need an amp.