I promised to do a review of my two portable headphone amplifiers, the IBasso PB2 and the Headroom ultra-micro amplifier. To do this review I employed 2 headphones, the Sennheiser HD 650, and the Grado SR225i. All the equipment was run in for two weeks before commencing any evaluation. On order, and yet to arrive is a balanced silver cable for the HD 650, to take full advantage of the iBasso balanced output. Since this is going to be get very complicated very quickly, it makes sense to do this evaluation in several stages. My reference system is my Sugden Bijou CD and preamp. The headphone output of the preamp is such that the preamp is often used as a headphone amplifier in its own right. I have been playing about with hifi since the days of John Linsley Hood and I have got to the stage that an ‘upgrade’ is not really meaningful unless you get the same buzz when you return to a recording weeks later. A-B-A comparisons are all very well but unless you can identify A or B in isolation, then the benefits are a diminishing return. Understanding this philosophy explains why my reviews will not be in questionable detail.
I chose a number of diverse recordings, not the usual “simple" acoustic recordings, like Chris Jones, Krall and Melua which tend to sound good on almost all systems but the more complicated recordings with both classical and electronic instruments, that often sound muddled on poor systems. These included a Bach violin Concerto, Vivaldi's Gloria and a dynamic track from Rush’s “Counterparts" album. The two headphones are very different beasts, with the well-known diverse sound signatures. The Sennheiser's opulent output versus the revealing nature of the Grado.
In the iBasso amplifier, I selected the AD797 Op-amp and the normal buffer. On order I have 4x OPA627, which I hope do not turn out to be fakes. These are the same up-amps that are used in the now out of production headroom Ultra Micro amplifier. When it becomes available I will order the iBasso DB2 DAC.
It has to be said that neither amplifier, when fed by an iPod 5.5g is close to the Sugden system, even with lossless files. With either set of headphones the Sugden system is more involving, dynamic and natural. One is not aware, in an analytical way, of the frequency extremes but when you listen out for them they are clearly apparent. I think I'm trying to say that the sound is cohesive and unforced with either set of headphones. Let's move on to the portable amplifiers. I fitted a Kimber dock connect cable to iPod 5.5g and fed the single ended inputs of both amplifiers. In the case of the Headroom amplifier, with either set of headphones it is fair to say that the sound output is warm and polite. Bass notes go very low, are quite ‘obvious’ and are accurately rendered, treble is smooth and the mid-band is quite tame. Playing the Rush track, as the music escalated the sound didn't enthrall in the same way that the preamp gave out and the tunefulness of plucked guitar strings wasn't there. It seemed to be holding back. This amplifier did curb the sibilant treble of the Bach violin concerto with the Grados. The combination of the Headroom amplifier and the Sennheiser HD 650 was too warm for my liking but offset the more forward balance of the Grado headphones very well. Both amplifiers reproduced the ambience and separated the voices of the massed choirs in the Vivaldi work, a little more in the case of the iBasso.
Moving on to the iBasso with the supplied AD797 amplifiers installed, it is fair to say that this amplifier has a lighter touch. In combination with SR225i headphones it is getting close to sibilant with the close-miked violin solos. With the Sennheiser cans, it clearly has less bass extension and general warmth than the headroom amplifier but is able to convey the dynamics of the Rush album and the tunefulness of the bass-line that is more pleasing. It will be interesting to see how this amplifier works with a balanced output into the Sennheiser headphones. I have a feeling that the silver cable will be more revealing and the better dynamics will work well with this little amplifier. It is becoming obvious that there are obvious pairings here – Sennheiser/iBasso and Headroom/Grado for an even balanced sound both tonally and in dynamics.
In both cases these little amplifiers give more authority and ambience to my music than the direct headphone output of my iPod 5.5 G. Bass was clearly better defined, deeper with more weight and treble quality was more refined with better resolution. In the next phase I will take the digital output of the CD player and feed it into the DB2 DAC using its balanced output directly into PB2. It will be very interesting to compare that with the ‘Sugden’ sound. That is something for next month, with a little luck. I hope this is of interest. regards Chris
Edited by iVinyl - 3/20/11 at 11:21am