Let's make this clear: Does the DT770 need an amp?

It's always been clear, with 250-ohms and average sensivity beyerdynamics are ones of the harder to drive cans around.

Both 80 ohm and 250 ohm versions NEED amping - in particular - deep bass takes lots o' juice - so do not not choose a cheapy amp. Portably, a RSA P51 would be a good choice......I have a number of Darths and use the older Corda amps eg. Prehead MkII, and HA-2 with them........a better, but more costly choice would be a Blue Circle SBH. If you're intending to use your dt770 for music (instead of gaming) I'd strongly recommend you send them to Headphile for his mods..

IMHO, in stock form the DT-770 pro (80 ohm) doesn't improve all that much when amped, provided you prefer to listen at moderate volumes. If you like to listen loud, some devices may not have the headroom.

the 80 ohm runs well from a strong sound card or portable amp. the 250 ohm needs at least a strong portable or small desktop amp

Well I auditioned a DT770 pro/80 straight out of my cowon i7 once,

I concluded that it sounds like pooey poo without a good amp.

without amp - you will get clipping. No question..........this is NOT arcane information, and not new.

YES it does. Bushguy is totally correct. You get large amounts of clipping from a portable device and a decent soundcard without an amp. EVEN with the 80 ohm pro.
IMO the 80 ohm one needs an amp more for the quality improvement, although it will go loud enough from most portable devices it will sound SLOW and you will get clipping.

Yes

the 80 ohm will sound OK out of a portable device and will go loud enough. Depending on the DAP it will clip (and i actually have heard it clip during burnin from a xonar DX and STX). But it really does benefit from an amp in terms of speed, you can warm up the mids and you can give the bass some texture.
It really makes the can more refined (if you can describe the 770 as refined).
The confusion comes from people comparing the 250 and 80 ohm from the same portable i think or associating an ohmage as how easy a can is to drive rather than how much power it needs.
The 250 needs an amp yet requires the same amount of power as the 80 (more or less).
the 80 will need more current though, which is where the problem comes from a non-mains-operated device.
The reason it sounds louder than the 250 (i believe) from a portable is most portables are rated at either 0 ohm or 120 ohm at the output jack. The 250 is furthest away in BOTH cases and thus there will be a less efficient energy transfer resulting in a quieter sound.
Both still 'need' an amp, but one needs it more desperately (because having headroom is good) and volume is frequently associated with how well a headphone is driven (but this isnt the case)
you can be happy with the sound of the 80 ohm from almost any device but it will under perform quite strongly in my opinion and if the device is really bad it will clip unbearably.

There's a night and day difference running my 770/80 out of my ipod and out of my compass. The bass is so bloated, the midrange is very recessed, and the highs can be a little harsh. They sound decent from my compass. The bass is tightened(control is important), the midrange is smoother, and the highs are much better. And more importantly, there is no clipping. Heck, they even sound better out of my motu 828. But IMO, using a good quality amp transform these from listenable to pretty good. You probable would guess that I'm not a big fan of these. I wasn't initially, but doing a couple of mods, a recable and decent amplification makes these sound pretty good. I still like my other cans better.

I agree completely with Moodyrn.

When I first got my DT770 Pro/250s, I plugged them into my Zune just for laughs and not only was volume an issue, but they may as well have been some cheapo $30 headphones. Then I set my sound card's built-in amp for high impedance and POW these babies came to life and after being persuaded by HeadphoneAddict's Travagan's product reviews, I picked up a Red amp (with AD743 opamps) and POW, once again these suckers got new life.

Summary:

No amp = lifeless (Zune)
Cheap amp = much better (HT Omega Claro Halo built-in)
Decent amp = great (Travagan's Red)
Jesus amp = even better?

On a side note, since it sounds like you just recently acquired your DT770s, I'd recommend burning them in for at least 50 hours; that also gives you some time to get an amp! I felt that the sound out-of-the-box and after about 50 hours was hugely different, with the latter mentioned being much better.

Sounds pretty clear to me.

Yes.