For some time I've been looking for a decent piece of kit to travel with. Previously I tried a HeadRoom Portable Desktop amp/dac, but didn't like the overall sound, though the DAC was good. The Fostex, allowing digital output from an iPod or iPad to a high-quality DAC is more appealing, especially as it was reported to have a half-decent headphone amp. Something has to give in all this, and it is the headphone amp which, while decent with low-impedance, easy-to-drive headphones, such as my V-MODAs, Audio Technicas and Symphones Magnums (eg: Grados), doesn't do so well with high-impedance ones.
However, a rig that does well with both would require adding a good portable headphone amp, such as an ALO Continental or the like (or simply plunking down the $1200 or so for their complete rig). As I don't intend to travel with a pair of HD-800s or LCD-3s, but only the Magnums, I don't need anything quite so overkill.
As a physical device, the HP-P1 is quite chunky with a solid feel, being that it is made from aluminium, with a thin, but not quite rubber-like cover or coating around the body. The top is slightly indented in a way that suggests an iPhone or iPod touch should sit there. The bottom, for reasons presumably to do with the style, is concave. This gives it a unique and easily recognisable look.
For it to work as a bound rig with either i-device requires some thinner than usual rubber bands of the type often supplied with portable amps. I happened to pick some up in Tokyo while I was there, from one of the companies displaying at the Fujiya Avic show. However, the HP-P1 comes with a case in which it is supposed to sit, along with your iPod or iPhone.
The case itself is a confusing affair of straps and velcro that is fiddly to get the HP-P1 in and out of. This is where the stylish design becomes an issue, as it resulted in edges that catch on the case when inserting or removing it. The case has two ends, both with two velcro straps, presumably to prevent anything falling out when one needs to access a socket. One end has a small, permanently sewn strap between the velcro straps, meaning that the HP-P1 and iDevice have to be inserted in the other end. Wrapping around the side is a cover strap that, when opened, reveals a window for accessing your iDevice. Inside, between where both sit is a fixed internal strap that looks to to be intended to sit between devices. This is going to be a nuisance if you have managed to find a means by which to attach the HP-P1 and your iPod or iPhone together, but the logic of its presence makes a little sense as Fostex likely didn't imagine people would attach them together.
Also present is a belt loop, rings for a shoulder strap and a finger-sized net-covered pocket on the cover strap, presumably for adaptors, cables or IEMs, as that is all that would fit in it.
As for the sound, it's definitely an improvement as amp even with more lowly headphones such as the V-MODA M80s and RE-ZERO IEMs, though the latter, due to their sensitivity require an amp or they sound awful. I had hoped it would form a good transportable rig with my Symphones Magnums that wouldn't make me miss my home rig while I am travelling, but interestingly while it is possibly overkill for the V-MODAs, it was clear the difference between my main rig and the HP-P1 with the Magnum V4s. However, using it as a DAC to my Stax rig, tonally it was indistinguishable, only not as resolving or clean-sounding.
Another member described the HP-P1 compared to the CLAS as being "darker" sounding. My main rig is somewhat "old school" with the proverbial black background, unlike the more bright-sounding gear that is often produced now, with a more "hi-fi" sound, which tends to give people used to newer designs the impression that my, and similar equipment is "dark".
Indeed, plugging my Magnums into my iPod and then the HP-P1 to listen to Jamie Cullum, the iPod had the more aggressive "hi-fi" sound, and the HP-P1 opening up the space around Jamie between him and his instruments and presenting him less harshly and more smoothly. Now I had to try this again on my main rig and then I just had to stop writing to listen to the whole song all the way through...
So, back to the HP-P1. Worth meaning is everything on the back panel, which I mostly ignore. There is a small socket for USB charging and a 3.5mm direct line-out that isn't volume controlled to use it with a separate amp. My one gripe, the presence of an optical digital output as opposed to a coax S/PDIF socket is here too. Toslink isn't a great method for digital transmission and my experience is that some DACs sound a bit harsh using it as an input, depending on their design. A 3-position gain switch gets around the slight channel imbalance at the beginning of the volume adjustment, but I found I never had to switch it from high-gain though it might be a good idea with some IEMs.
Last is the filter switch, which changes between, respectively, a steep cut-off filter and a more superior one. The differences between the filters, for me, was subtle, with filter 2 sounding a slight touch smoother and less harsh than the steep cut-off one.
(Feb, 2012 Edit). I recently purchased a Triad Audio L3 to use with a pair of prototype Sennheiser HD-700s, as I wanted to give them a fair run. This also gave me the opportunity to better evaluate the HP-P1's inbuilt amp. Using the L3 with my Magnums, the Audio Technica W3000s and other headphones, the L3 provided a noticeable jump in overall clarity and soundstage. This nailed it for me as an extremely satisfactory (if extremely expensive) travel rig.
So, overall, I reckon the HP-P1 is a great piece of kit, if not an amazing one. I reckon it hits its price almost exactly in terms of features, capability and sound quality. With most people who carry headphones around using low-impedance models or IEMs, the lack of ability to drive high-impedance cans isn't a great deal of a loss. If you must, you can pair it, for a great deal more with a good portable or desktop amp if using it at work or the like. However, for a portable rig, it is rather chunky and arguably overkill for IEM users who might simply benefit from something like a Pico Slim for their needs. If they could simplify the case design, make it smaller, shrink the volume knob and provide a good case, it would go from very good to great.
Questions and Answers: (Feb, 2012)
Does it work with FLAC Player?
Yes, even with high-res files. I haven't verified if they pass through high-res files to the optical output.
Does it work from a computer?
Not as far as I know, only from compatible iPods, iPhones and the iPad.
Is the battery replaceable?
It's soldered in, but appears to be otherwise.
Can the firmware be upgraded?
Yes, but only by Fostex. I'm guessing that due to Apple's terms Fostex isn't allowing firmware downloads.