Is it possible to get really great sound from a headphone amp and some good headphones?
I am looking for something in the 100 dollar range.
I'm assuming you mean for guitar, not general audio listening: Look for a (probably used) Korg Pandora PX-3. You can use a set of $10 ear buds with one of these and get very good guitar sounds. The total cost be well under $100. If you are really lucky, a used PX-4 is even better. There are also Behringer V-Amps for around that price.
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what are the differences between a px3 and px4?
Last generation versus current generation. I have a PX4 and recommend it, but new it's held steady at $199 for a two or three years now. If you see one for less, new or used, snag it.
I haven't used a PX3, but have friends who have and say it is worth the typical $50 to $85 bucks.
-=tension & release=-