NuForce UDAC2-HP vs. FiiO E10 vs. Hifiman HM-101 vs. iBasso D-Zero

The uDAC-2's amp is unimpressive (to say the least), so I doubt the amp-only version is worthwhile.

Fiio makes mostly quality stuff, but I haven't seen measurements for the E10 like I have the E7. The E7 is good for the price, though.

The HM-101 looks good for the price, but it may have high output impedance. The spec isn't published but it's possible considering its power output. You should avoid high output impedance with your headphones. The uDAC-2 has a slightly high output impedance too.

I don't know anything about iBasso.

Personally, I think you need to spend more and get the uHA-4.

A high output impedance means the amp won't be able to feed as much voltage into low impedances. That means you're not going to get the full benefit of the amp. More importantly, however, is that most headphones don't have the same impedance at every frequency. So, because a high output impedance amp can feed more voltage into high impedances, wherever your headphones have high impedance is going to get a volume boost relative to other frequencies. Basically, an otherwise neutral amp ends up making your headphones sound different.

Neither the M50 nor the XB500 have much variation in their impedance curves (a graph of impedance at different frequencies). The HD518, on the other hand, has a very big impedance peak at around 100Hz if it's anything like its older sibling the HD598. That's not a good place to boost too much, because the bass could start to encroach on the lower mid-range and drown out detail. You might not notice a difference with the other headphones, but you might notice it on the HD518. You might even like it, but objectively it's not a good thing to have.

We really need 'output impedance' to be a mandatory measurement for every amp foisted on the Head-Fi public. I know there were valid reasons for high output impedance back with studio gear, but I'm willing to bet that there are a higher proportion of low impedance headphones among Head-Fi members than 600-ohm phones. HiFiMan orthos and a couple of others aside, most low impedance phones are easily driven, but a well-designed amp (and a reasonably powerful line-out from the source...) can really bring out their best.

Quote:

Originally Posted by Head Injury 

A high output impedance means the amp won't be able to feed as much voltage into low impedances. That means you're not going to get the full benefit of the amp. More importantly, however, is that most headphones don't have the same impedance at every frequency. So, because a high output impedance amp can feed more voltage into high impedances, wherever your headphones have high impedance is going to get a volume boost relative to other frequencies. Basically, an otherwise neutral amp ends up making your headphones sound different.

 

Neither the M50 nor the XB500 have much variation in their impedance curves (a graph of impedance at different frequencies). The HD518, on the other hand, has a very big impedance peak at around 100Hz if it's anything like its older sibling the HD598. That's not a good place to boost too much, because the bass could start to encroach on the lower mid-range and drown out detail. You might not notice a difference with the other headphones, but you might notice it on the HD518. You might even like it, but objectively it's not a good thing to have.

That's a nice setup on your sig!

Btw, I NEED the high impedance since im'm thinking of getting the dt990s...what would you reccomend then?