I will list here all the amps I tried with my HiFiMan HE-6 planar headphones. (I will update this over the next few days until I have tried all the amps I can get my hands on ) These headphones want some power and so not every amp will drive them. Dedicated Headphone Amps (unbalanced 1/4 inch TRS jack) Beta22 - YES. Drives them very well. Sounded great. (3-channel Beta 22) Audio-GD NFB-10ES - YES. Plenty enough power. You may want to use a little EQ to reduce the highs some... the DAC in the NFB-10ES is merciless and any HF flaws in the mix will sound too bright. (Using NFB-10ES balanced headphone output.) Great sound. Audio-GD FUN - NOT OPTIMAL. Drives them to a good volume level but bass is a little lacking. The FUN will do in a pinch but I'd say it doesn't have quite enough oomph to drive them all right and proper. Doesn't sound strained, just not quite....there. Bottlehead Crack - NO. Cannot produce enough power into a low impedance load. Distorted sound and not very much level. (This amp not intended for low impedance 'phones) M³ - NOT OPTIMAL. Drives them but not very loud. If you are listening at moderate or moderate-to-low levels, this amp works fine. Turn it up just a little more... obvious clipping on vocals, etc.(ELPAC PSU for this amp, not a Sigma.) Cavalli-Kan Kumisa III - YES. Will drive the HE-6 to loud levels without clipping. Ray Samuels Hornet portable amp - NOT OPTIMAL. Drives them pretty loud but ran out of steam before I did; I wanted it a little louder, but the Hornet said "no!" (I tried HIGH and MED gain settings.) Bijou - NOT OPTIMAL. Turned the NFB up to get some more gain and the Bijou played pretty loud... but I wanted more. Bass was not quite as good as it should have been, but the overall sound was not "thin." Sounded good, within limits. Little Dot Mk III - NOT OPTIMAL. Sounded fine at low-to-moderate levels. Bass clipping when played moderately loud. Good sound at moderate levels, though. Musical Fidelity XCAN V3 - YES. Will drive the HE-6 to loud levels without clipping. Bass was maybe a little less extended than with the Beta 22 but otherwise sounded good. "Speaker" Amps (HE-6 connected directly to speaker output terminals of these amps) Sugden A25 - YES. Treble a little harsh sounding compared to Beta22; deep bass not quite as good as Beta 22. Overall, though, not bad. Dynaco Stereo 70 16 Ohm Tap - YES. Bass was a little wooly and sounded a bit rolled off at the lowest frequencies. Highs very "sweet" and tubelike but lacking detail. The Stereo 70 sounded just like it did on my Quad ESL-57's. AMC CVT-2030a - YES. The AMC CVT-2030 is an under-rated Class A hybrid amp- MOSFETs driving EL34 tubes. I really like the sound from this amp on the HE-6. There were audible differences over the Beta 22. The AMC amp had good bass extension - maybe not quite what the Beta offers, but was no slouch either. There was a little of that midrange and lower-midrange "roundness" that EL-84's are supposed to be noted for, it sounds like just a tiny bit of extra level and added dynamics from say 225 Hz to 800 Hz. Something like that. Just a touch of emphasis. This was coupled with a "sweet" sounding treble range. The overall effect was a kind of "lush" or "romantic" sound. For example, on cello the lower frequency aspects come through just a bit more and there is no steeliness at all in the treble so you get an effect of heightened "texture" of the bow rubbing on the strings. Or, on Fender Rhodes piano or Hammond B3 there was just was just a little extra punch to the percussive attack of the notes that gave the sound a kind of of palpability. The Beta 22 sounded more transparent, not clinical exactly, but lacking the romantic (coloration?) of the AMC. The overall sound of the AMC went very well with the treble emphasis of the HE-6. Tim Rawson F3 clone- YES. This is a copy of the Nelson Pass First Watt F3 amplifier, somewhat exotic. Tim Rawson, as far as I understand it, is a DIY amp builder that builds an amp then sells it to build another. Some criticize him for "stealing" Nelson Pass' ideas; Mr. Pass is gracious enough to provide schematics of his designs to the DIY amp builder community, with the understanding that folks will not grab his designs and go into manufacturing. So some people see Tim Rawson as a small manufacturer, and apparently he got enough static that he no longer builds clones of Nelson Pass designs. This is my understanding, I might be confused about all or part of this. At any rate, the amp I have is a Tim Rawson F3 clone. The F3 is a POWER JFET DESIGN. Currently, to the best of my knowledge, the F3 is the ONLY power JFET design currently available. JFETs have a much more triode-like curve than MOSFETs, and with longer flat areas and better load-line characteristics they offer lower distortion than a given MOSFET design. Nelson Pass likes very simple, low device-count designs. He likes low feedback and designs with inherently low high-order harmonics in their output. I've read that people say the F3 sounds like a very good SET amp, but with bass and clear treble. I don't know about that. But I will say that this amplifier designed around a silicon-carbide semiconductor (the power JFET) does drive the HE-6 very well. The sound was excellent. I couldn't A/B it against my reference Beta 22 at this point because I can't A/B balanced or "speaker" amps driving headphones yet. (Another box to build!) I will report more after I do the A/B. Suffice it to say that I really like what I heard from the F3 clone. The F3 is a Class A design; it is a 15 watt per channel amp that draws 200 watts off the AC line. Even though it is only a 15 watt/ch amp, it has very large heatsinks and it gets HOT. (See pictures below) RATINGS YES = drives them well, no evidence of clipping. NOT OPTIMAL = you can listen through this amp.... up to a point. All the "not optimal" amps played well to at least moderate levels. Some, like the Bijou and FUN played to moderate-to-moderately loud levels. NO = Just can't handle the HE-6 NOTES: Just because I rate an amp as a "YES" does not mean it is a great SOUNDING amp for the HE-6. I am not trying to judge that. All I am trying to do is see how well the amount of power produced by the amp suits the power needs of these headphones. The "NOT OPTIMAL" amps might be fine if you never listen loud. Try it and see. What's moderate loudness for me might be just right for you. I tend to like music a little louder than some folks, measurements I've made show that I like to listen at 85~87 dB sometimes maybe even 90 dB. Sugden A25 Dynaco Stereo 70 AMC CVT-2030a CVT-2030 insides Tim Rawson clone of First Watt F3 power JFET amp - looks like he builds his own cases by careful home-shop metalwork. Well done but not as fancy as some DIY casework I've seen. Does the job. Inside the F3 - not much in there. Still, even with all those square inches of heatsink this puppy gets HOT.