USB DAC/AMP to suit UE600's?

[Neug]

Hi,
 
This is my first post. My UE 4 SuperFi's gave up the ghost about two years ago. Since then i've been using cheap ear phones, but finally disappointed with their quality I bought some UE600's recently. I am really happy with them, especially on the iPhone 3GS were they seem to have better bass than on either the USB X-Fi Surround 5.1 Pro or IDT 92HD94 (internal sound card).
 
I'm just wondering why that is, is there some artificial boosting of bass on the IPhone?
 
I know the low impedance (9 ohms at low frequencies) of the UE600's can constrain bass but the internal sound card specs state 0.1 ohm output impedance (minimum! no maximum or typical stated) and the bass there isn't much better than on the X-fi (I hear they are 10ohm o.O output impedance). I'm waiting on word from creative to see what they say.
 
Getting to the point. Do the UE600's need an amp with a especially low output impedance to get the most out of them and if so can you recommend one for around $100.
 
Neug

 

[Neug]

I decided to measure the output impedance of the IDT, X-FI and Iphone 3GS.
 
The IDT measured 30.9 Ohms. The X-Fi was at least 40 Ohms (Creative said 33 Ohms). The Iphone measured 2.1 Ohms.
 
Looks like the IDT and X-Fi are approximately impedance matched to 33 Ohm headphones, the aim being to get as much power into them as possible. At the cost of audio quality. With the Iphone being a lot lower impedance, there seems to be a explanation for the better bass response. 
 
I hear 8 to 1 is the minimum ratio of speaker to output impedance, so i guess i'm looking for a USB DAC/Amp with less than 1.1 Ohms output Impedance. Can't wait to hear it.
 
Neug

 

[davidsh]

Actually the sound cards should have more/worse bass than the iphone. There's of course the possibility that the sound cards drop off frequency response at low frequencies. 
 
Can't personally recommend a certain portable amp. Most portable amps have low/very low output impedance though.

 

[Neug]

I went and bought a Fiio E17 because it seemed to tick all the boxes for me. Bass on it is well controlled even on Beyerdynamic Custom Pro One 
(switch position 4) headphones. It drives the UE600's superbly. Measurements showed ~0.05 ohm output impedance (Measure at 0.2V OC 1Khz). Really happy with the purchase, it beats all my owned devices easily for neutrality, noise, and sound quality. I had the opportunity to test it on Sound Blaster ZxR stereo line out>aux in. The neutrality is better than the Sound blaster ZxR built in headphone amp, at least for low impedance headphones. 
 
Neug

 

[davidsh]

Should have bougth the x3, can be used as DAC/amp as well