Best portable amp?

Well, I wouldn't say it's a minimal difference, but it's not big at all. Especially with the BOSE (which are the smallest circumaural closed headphones out there) that are far behind any big size open headphone.
At least with these big sounding ones (all the best DDs). I guess with later, thinner models the difference will be much higher.
With the tone controls untouched, the difference is perceptible but not big. However, in the street and with the tone controls (treble down, bass up) it clearly helps to compensate the noise, although the BOSE have a good passive isolation.
In those environments the music looses bass and becomes very bright, so this controls help a lot. I know I can go for a good IEM that isolates much better, but I prefer to not isolate as much in such an active city like Barcelona. I have had a fright before...
With the phone the differences are very big, even without tone controls. The music sounds impressively so well that made me think I was at home with my valve amp and the big headphones.
However, I could only listen to it for half an hour in the store (Werner musica) and could barely listen for 10 min at home. Tomorrow I hope to have a bit more time in the evening, so... more news coming ;-)

 

Lovely photo!
I recognize all models except the Tosh in the top right and the Panasonic? in the middle top. Great collection of walkmans and headphones.
I had the chance to test the 550 for a few minutes at a friend's home and they sound quite good, but as all closed headphones, clearly behind open ones. I prefer the Q701 by far, as seems that they are almost identical to the 702 except for a little difference in bass and the cushions (much better in the Q701).
I'm curious to know how good does the Fiio sounds when connected to the line out of the DC2 and the D6C and compared to each headphone output...

 

Thanks for your detailed comparisons.
I'm glad to hear that they are almost the same as mine: tonight I put the super-DC2, super-DD9 and super-D6C on the table together with the 701C and my new RHA L1 headamp. I connected my Sennheiser HD650 which are well known for their absolute neutrality and for being most sensitive to amplifier changes and quality. The perfect headphone for this kind of testing.
I used three identical MAxell XL-II that were recorded with the same songs in the same way (vinyl as source, no dolby). I put the tapes in all them, hit play and switched the jack between them once volume was matched.
That made the comparison much easier.
Without amp, the best sounding is the D6C clearly. The bass has more body and power. The DC2 has the weakest bass but seems to have more definition and soundstage than the D6C. The DD9 wins in definition, though is not as powerful as the rest (but it's waay more powerful than the standard DD9).

When I connected the RHA to the line out or headphone out, there were different responses. With the D6C, the result was a bit less pleasant surprisingly, with less body in the bass, but a bit more stage. So the D6C is the only one that can withstand against the amp.
With the DC2, it gained a bit in bass (tone controls in the RHA at zero all time) and in soundstage. With the DD9 which seems to have the sharpest sound of all them, the sound was overall more powerful and wider.
With the 701C, as expected, the sound was waaay better. Much more powerful. however, it's surprising how well can this tiny player withstand against an smartphone. Quite well.
With the amp the mids have better presence and the soundstage is wider. And the sound has, overall, more 'punch'.
I also did a quick comparison to my professional DELL Precision laptop (which is supposed to have a top-of-the-line sound card) and it was clearly behind any of the walkmans even without the amp. Needless to say that with the amp the comparison was simply unfair.
So, in the end, the sound gets better overall (much better in case of a phone or a laptop), with more 'punch' and better bass. This is something I have experienced when travelling in train, using my iphone and the tiny and cheap CMoy, though with this amp I have a DAC (that can be used with the phone or a laptop), a battery (that can even be used to charge the phone) and tone controls that are VERY useful when travelling.

So in the end I'm very happy with it.

 

Well, I don't like the 702 so much too. What I said is that I preferred the Q701/702 much better than the 550, but to be honest the sound of the 702 is in "V" (like a EQ curve) and in the bright side and not so comfortable to wear for long sessions. The headband is made from cheapo plastic, after some time starts to hurt in the head. The cushions are too strong, not very comfortable. I remember to read that the Q701 has much better materials in this area.
Anyhow, the sound is a bit behind other headphones in my collection and I think this ones doesn't offer anything valuable to me now. If I want a flatter sound I have the HD650 and HD540. If I want a V sound I have the DT990 or the ELEAR.
If someone wants a K702, modified to perform with better bass, with only 6 months of use and original box, like new for 160 euros, contact me

I think you maybe misread my words Chris. What I said is that this amp offered better overall response: wider soundstage, clearer mid presence and better, punchier bass.
This happened with all walkmans I tested: DC2, DD9, DD33 and 701C. the only exception was the D6C that showed better bass through the headphone out than from the line out to the amp.
I couldn't have time to do a throrough test and only used one song yesterday night (Thriller by MJ, sourced from vinyl, US mint pressing) but seemed to me that the D6C performed better. Maybe the bass was less controlled in this case, now I didn't remember. there was not a big difference, but I'll check tonight again with more songs.

 

Oh, no, please don't apologize. No worries at all ;-)

It took me centuries to learn the difference between flabby and tight bass. I had bass-intoxicated ears for many years, starting with my recordings made on my first boomboxes and continuing with the MegaBass.
But in the latest years, thanks to some good decks, headphones, amplifiers and recording practices I learnt the difference. Now I can say I absolutely know how does the "high end" sounds, especially after hearing it in places like this:
http://www.walkman-archive.com/wa/2016/02/star-wars-on-reel-tape-duplicating-to-my-pioneer-rt-909/

I don't have very good ears, and I'm pretty sure you have much wide knowledge in this area than me and many others. Fortunately I think I know how a tight bass sound now
Back to the matter, this amp has a punchy sound and the bass is very well controlled. Not flabby at all. I never heard how your RS sound but I bet they are in a similar league.
Today I took it out walking in some quiet streets and I was impressed with the punch in the drums. Holy god, this thing literally beats you in the head. What a power in the drums!
Tonight I'll do a test between the D6C headphone output and the amp and let you know my thoughts

 

BTW: I think you'll enjoy this reading:
http://www.headfonia.com/review-rha-dacamp-l1-energy/

 

BTW: Is there a good site to buy short jack cables for this? I'd like to get one with a right angle connector. (I'd like something that doesn't cost like unicorn blood if possible... )

 

Toocool's SA in my RX505:

 

That's another possibility. Where to buy connectors and cables, then?

 

Thanks for the info! I'll look at them.

 

Very interesting Toocool. Thanks for sharing.
Yes, the RHA does a lot of things and that's one of the reasons I like it. I have read it has a cutting edge sound (Headphonia) so I wouldn't bother if the P-51 wins for a little bit. That means the RHA is almost on the edge, but with steroids. That's fine for me ;-)

I'd like to hear your P51 someday. It looks soooo tiny! Surprising how can such a tiny box sound so good.
Di you have the chance to compare it to the Chord Mojo or the Hugo? (That last one should be my amp indeed! )