[sherby42]

I'm not really sure if this needs an amp. Yet it is 70 ohlms if it does need an amp what would be good under $100 that could be used portably.

 

[Origin89]

I'm using mine with the Digizoid ZO2 right now, and it definitely enriches the sound and give the phones a noticeable amount of energy. Now that I know amps do benefit the HD25, I'm currently looking for one with less coloration. It doesn't require an amp, but it does make an obvious difference. Depends what kind of sound you're looking for.

 

[sherby42]

Im looking for the sound to just be good and be portable

 

[sherby42]

bump

 

[AstralStorm]

In my (pretty short) experience with Sennheiser HD-25-II, it doesn't need an amp or really benefit from one. You'd need a really anemic source to not be able to drive that sensitive headphone at 70 Ohm. (supposedly 120 dB/mW, I'd assume @ 1kHz.)
Sennheiser Amperior is more problematic due to low 16 Ohm impedance - a high impedance output will limit its bass quality.
 
ZO2 is not exactly what I'd call an amp - it's a portable equalizer. It's never quite linear enough.

 

[chrislangley4253]

if you can't tell whether or not it needs an amp, i seriously doubt that it needs an amp.

 

[Origin89]

Well, they definitely sound weak out of my iPhone 4. Even with the volume all the way up I'm still wanting more. I bought the Leckerton UHA-4, so I'll see how that goes.

 

[chrislangley4253]

Quote:

I'm not really sure if this needs an amp. Yet it is 70 ohlms if it does need an amp what would be good under $100 that could be used portably.

well then, that was different than what you opened up with. I hope the leckerton works out for you

 

[sherby42]

fiio e11 just a good amp if i would get this headphone

 

[AstralStorm]

So iPhone 4 is a really anemic source. Oh well.

 

[Origin89]

Yea, the HD25s are listenable through the iPhone, but there's an obvious lack in energy compared to my laptop. 
 
To the OP, check out the JDS Labs cMoyBB - http://www.jdslabs.com/
 
or
 
Electric Avenue's PA2V2 - http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=pa2v2&_sacat=0

 

[harrisonhawk]

I was really happy with my Rockboxed Clip Zip straight into my HD25. Nice and punchy, great detail and soundstage compared to my iPhone and you can dial in a lot more bass/treble if you want with the EQ settings. I'm sure an amp will help but if you are on a budget then I can strongly recommend a Clip Zip (as long as you Rockbox it).

 

[AstralStorm]

cMoyBB is not a true cMoy, but a misnomer, as it uses a rail splitter as the virtual ground.
This will likely actually worsen noise and THD performance but make for less resistor matching, higher battery life. It might limit the current capability somewhat as well.
(Extra caution: TLE2426 has very bad current limiting behavior - large negative DC offset. Avoiding that requires large bypass caps which on the other hand require an opamp capable of driving capacitive load - the few faster ones known to me cannot do that. JRC4556 can though. TLE2426CLP is a bit stronger which helps as well.)
 
It cannot effectively drive very low impedances unfortunately due to lack of a dedicated current stage - trying that results in increased THD, actually worse than in a real cMoy since you'll overdrive the virtual ground as well.
In case of 70 Ohm relatively sensitive Sennheiser HD-25-II though, it shouldn't have problems.
 
Some on single stage amplifier opamps choices:
Old NE5532 or especially JRC4556 are a decent choice if your power supply is not too noisy (like batteries) and there's not too much DC offset. (well matched resistors, low gain)
OPA2277 and OPA2132 are bit more silent and lower DC, but quite a bit less capable in current department.
 
LM4562 is not good if you want to drive anything low impedance (< 150 Ohm) due to low current handling capability.
OPA2604, AD8397, AD8610 and AD8620 are also very poor for a cMoy, low on the current side and require extra stabilization and protection, possibly increasing output impedance and reducing power handling even more.