Someone shot me a PM concerning this amp even though I have had it less than a day. I ended up giving my thoughts and impressions as asked of me. It turned out to be a bit long so I felt I should post it since I know the question was asked and is bound to be asked again and again. Basically the "how does it compare blah blah blah?" question.
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The Fixup amp is a great portable amp because it really pushes the limit of performance/price, performance/size, and performance/battery life. It manages to sound good with not a whole lot of juice, but seems to do it very well when even compared to something like the Porta Corda (original) off a 9V, or the TA(latest).
A long time ago I remembered the CHA-47 as being a leader in portable amps (admittedly there weren't too many varieties of portable amps to choose from back in the day) in terms of having the right compromises and didn't think it could get much better in terms of portable performance. But I think things have managed to progress since then. The Cha-47 is a punchy amp but somewhat colored and far from the last word in transparency or neutrality. Strangely enough this amp is most like the SR Grado of amps in terms of its sonic characteristics. Indeed the CHA47 was originally meant for the Grado line of headphones but of course was still good enough to be used for other phones. In size, performance, price, looks, etc I think it hit a real sweet spot for the time being and was a favorite of mine.
The PC(original) came along and was a lean and mean good sounding machine, but had slightly hard highs and a 9V battery truly did seem like the minimum it can run off of. It had a good design and features to boot. Strangely enough the PC(original) sounds like the Beyer DT931 of portable amps. It became my next new favorite.
The TA(latest) was good for a 3 AAA amp, and goes loud effortlessly but may lack the last bit of detail and refinement compared to most amps discussed. I really liked the use of 3AAA's however.
The Fixup amp has some of the better qualities of both the CHA-47 and Porta Corda amps even off the batteries of a TA(3AAA). It is very punchy yet still has plenty of detail without being harsh. Can't compare with other Meta designs as I never heard 'em...the Fixup design is obviously custom variant or cousin meant to be tiny running off minimal power and is obviously not an over the top or full-fledged Meta design although it borrows elements from it.
I can't compare with a full-sized Meta but I think its a pretty safe assumption that other Meta variants can have more power and part selection and other design features that c/would make them a better performer sonically.
My AKG240S despite being marketed as easily powered, is still classic AKG in being pretty difficult to power and taxing of battery powered amps. It has low sensitivity and low impedance, so it is often both current hungry and just power hungry only second or third to its older bigger brothers like the K501, K240M in this respect. I could always clip many a portable amp with the AKG240S, and with the Fixup and an over-compressed album like Lenny Kravitz, I could get it to clip at moderately high volume. But even the Porta Corda and other 9V amps I've tried could clip in some circumstances even with twice the voltage. With the ER4S I think I would have a very difficult time getting the Fixup amp to ever clip without bleeding ears. I will need more time to see its overall performance with my Nimh AAA battery set which probably gives less than 4.5 volts because they are Nimhs. I have the 3 AAA super-mini so maybe the 3AA or 9V mini amp has more power reserve with also the bigger caps. Right now I'm using the same set of 3 AAA batteries on Queensryche Operation Mindcrimes with plenty of gusto with no clipping, but that is because it isn't a terribly compressed recording like Kravitz.
All in all even the super-mini is still good enough even with the K240S for most listening conditions and AKG's are always some of the hardest to please with portables(yes even the one AKG phone designed with portables in mind). I think the Fixup amp has a lot of potential to hit a new sweet spot in performance/price, performance/size, and performance/battery life in a portable amp. Also I like the novelty of having an amp so small, that is so deceiving of what it is capable of in sound...kinda like my Ety's, and I can see it as a new favorite portable amp as I continue to listen to it.
Anyhow I still haven't divulged too much on its sound and may do so after longer listening. Right now I hear a good deal of warmth compared to the PC, but not to the extent of distraction. Also a *very* suprisingly powerful and rich bass line as opposed to an almost overly tight bass of the PC(original). Although I don't think I can call it absolutely transparent yet, it definitely doesn't hide me from poor compressed or harsh bad sounding recordings either. Likewise it makes good recordings that much more enjoyable.
I took another picture of it...I think it is the coolest picture yet with it lying on top of some floppy disks.