I think the problem lies with the cross-over, in multi-driver models.

Half an ohm is going to mess up a crossover that much?  I guess it's possible but how common would it be.

Yeah, I can attest to those ER4S adapters making the TG!334 sound like ass.

I'm sure it makes a lot of IEMs sound like like ass but I'm not sure how you'd separate the change in FR from the change in damping factor.

The graph up there shows about 0.7dB of difference between the Leckerton and the O2. Is it just the Zout that's higher than the 0.5 Ohm quoted by JDS Labs, or something else ? Your guess is as good as mine.

I think golden ears has an impedance plot for the W4 so the Zout's of those units can be calculated.

Too tired to bother with that right now though...

Howdy pirates!   

May I request some enlightment on my first post in this great forum?

I'm in the process of trying to sell my Yulong D100 Dac/Amp to "upgrade" to something better ampwise without compromissing on the Dac section(maybe a little). my budget is 3-400$.
At current state of head-fi equipement it seems to me that I can actually make an upgrade from the Yulong D100 while at the same time spending less... if I'm smart I might even get out of this with a small profit...

My headphone is a GMP 400 300Ohm and I plan to buy a Sennheiser HD6x0 or DT880 in the near future.
It will be used as a stationary desktop system just like the D100 with both of these Headphones and some IEMs.
It doesn't have to be only this, though... it would be nice if there was some portability factor in the equation.

I must say that what really drives me to move from the Yulong D100 is it's amp section which I find somewhat limited for my modded GMP 400 and not very transparent... compared to the little Sansa clip+ it has a certain treble glare (digital glare?) that is not natural and the bass and lower mids sound thinned-out, it is bright, unpleasently bright and I could go on and on my issues with this amp... it seems like it's trying to sound transparent but it really isn't.

The sonic attribute I most value is transparency.
My initial plan was to just go with the Odac/O2 combo and be done with it.
Further search and reading, however, suggested that there is better than the O2 within my budget.
Right now my plan is to get the Odac + ?? preferably solid state at max 300$. (Don't like the hassle of tubes and DIY...)

My long search for a suitable amp upgrade has brought me unexpectedly to the portable amp market...
I'm not sure if I'm doing my search right, and probably I'm not, but right now I feel like I need a definitive answer to the following question:

Am I right to think that certain sub-500$ portable dac/Amps like the UHA-6s, Dacport, Portaphile 627, can perform as good or better as most similarly priced sub 500$ desktop solid-state amps to drive most headphones?
Or am I wrong?

It's just that I've noticed a trend on Head-fi that is favoring much more portable amps discussions than SS full sizes in this price range...
And why is it that here at Changstar there's almost no amp talk other than portables and a few high-end fulls?

Are we watching to the take over of the sub-500$ SS desktop amp segment by the portable amp market or what?
Probably a silly question?

What should be the ss amp to get below the 300$ tab for someone who values transparency?
Before I would expect that a desktop solution like an m-stage or asgard would be the schiit to get, but now I'm not so sure...
Hard to believe that a portable can outperform a desktop with a good open headphone of >300Ohms...

Where lies the real value right now?

Could some experienced ears enlighten me, please?
Or rather fix up my mind?

My headphone is a GMP 400 300Ohm and I plan to buy a Sennheiser HD6x0 or DT880 in the near future.
It will be used as a stationary desktop system just like the D100 with both of these Headphones and some IEMs.
It doesn't have to be only this, though... it would be nice if there was some portability factor in the equation.

I must say that what really drives me to move from the Yulong D100 is it's amp section which I find somewhat limited for my modded GMP 400 and not very transparent... compared to the little Sansa clip+ it has a certain treble glare (digital glare?) that is not natural and the bass and lower mids sound thinned-out, it is bright, unpleasently bright and I could go on and on my issues with this amp... it seems like it's trying to sound transparent but it really isn't.

The sonic attribute I most value is transparency.
My initial plan was to just go with the Odac/O2 combo and be done with it.
Further search and reading, however, suggested that there is better than the O2 within my budget.
Right now my plan is to get the Odac + ?? preferably solid state at max 300$. (Don't like the hassle of tubes and DIY...)

My long search for a suitable amp upgrade has brought me unexpectedly to the portable amp market...
I'm not sure if I'm doing my search right, and probably I'm not, but right now I feel like I need a definitive answer to the following question:

Am I right to think that certain sub-500$ portable dac/Amps like the UHA-6s, Dacport, Portaphile 627, can perform as good or better as most similarly priced sub 500$ desktop solid-state amps to drive most headphones?
Or am I wrong?

Are we watching to the take over of the sub-500$ SS desktop amp segment by the portable amp market or what?
Probably a silly question?

What should be the ss amp to get below the 300$ tab for someone who values transparency?
Before I would expect that a desktop solution like an m-stage or asgard would be the schiit to get, but now I'm not so sure...
Hard to believe that a portable can outperform a desktop with a good open headphone of >300Ohms...

Where lies the real value right now?

Could some experienced ears enlighten me, please?
Or rather fix up my mind?

A (portable) headphone amp that can drive very low AND high impedance headphones is not easy to design.
Technically different demands need to be met:

For low impedance, meaning 8 to 32 Ohm (IE for instance) we do NOT need a high voltage (3V-6V power supply could do) but the design needs higher current capabilities. Preferably the internal power supply should have at least 2200uF on each power rail if portable AND split power supply. It also must have a very good S/N ratio. These demands imply a low output resistance as well < 2 Ohm as IE monitors tend to be all over the place in impedance in sonically critical areas. The gain of the amplifier is between 1 to 2 times.

For medium impedance (40 to 120 Ohm) we need a power supply voltage of about 9V-12V and not a whole lot of current capabilities. Most headphones in that range prefer a low output resistance, but some headphones simply sound better on higher output resistances. This feature will not be present and the output R will generally be between 1 and 10 Ohm. Most simple amps (C'Moy type) will be capable of delivering enough voltage and current and have low enough S/N ratios. The gain of such an amplifier needs to be between 2 and 5 times in general.

For high impedance headphones (250 Ohm+ e.t.c.) you need a higher voltage (say 1 8V-24V for portable or even higher) but you do not need a lot of current. 100uF power supply caps on the voltage rails would do already, SN/ratio isn't that important. output resistances between 1 and 50Ohm will do. If you want to drive say HD800 or K(Q)701/2 a 100 Ohm output resistance (or in that neighbourhood) would probably give the best sonic results. The gain needed is between 3 and 10 times.

It's why it pays to have different amplifiers for different circumstances/sources/headphones.

I cannot say which amp meets all the criteria as your choice would, beside the technical demands, also depend on preference and some subjective things as well.
How much you are going to spend does not equal how well it is going to sound (subjectively).
What sounds good to person A may sound crap to person B.
So giving proper advice appears harder as it seems  .
There is no one correct answer nor solution (even-though some are of the opinion only theirs IS)

Has anyone tried the JDSlabs CMOY or PA2V2 for the HD-650? It'd be nice to get an extra portable amp (under $100) for my DJ100 and HD-650 to use around the house.

I love the Total Airhead but it's kind of awkward to fit in a pocket. The E11 i'm just not too thrilled about. My DJ100 just isn't the same with it, but still pretty good.

I don't think there's a headphone the Airhead can't drive (OK, maybe not so well with IEMs) well enough. Sure maybe the K1000 or K400.

It gets loud enough with my Sextett (and sounds good), but struggles a bit with my K601.