Performance

Quantifying the performance of a headphone amplifier is always a hard thing to do because there are so many variables to consider. As benchmark amplifiers I have the Octavart "The One" Amp / DAC and the recently reviewed Travagan's Green. My test setup consisted of the Head-Direct EF1 hooked up to my Marantz CD6002 via a pair of QED interconnects, I swapped back and forth between the EF1 and the Octavart amp for some A/Bing.
Unfortunately the Travagan's Green does not feature an analog input and considering that the Marantz CD6002 is a $600 source, a direct comparison was not possible due to the vast differences between the integrated DAC of the Green and the CD player's much more expensive DAC circuitry. I tested the Head-Direct EF1 hybrid amplifier with the following headphones: Sennheiser HD 580 (mods: HD600 grills, Dowin DW12 cable, foam removed), AKG K701, Grado SR-60 (mods: added dampening material, re-cabled, metal grills, quarter modded pads) and Yuin OK1.

To start off with I plugged in the RCA manufactured tube and hooked up the amp to my CD player. I had the amp burning in for approximately 100 hours before I began my tests of it. First up I tried it out with the AKG K701s which have a reasonably high impedance of 62 Ohms. Their efficiency is really low hence hard to drive. The Head-Direct EF1 powers the AKG K701s to stellar results, the bass is incredibly tight and detailed, in this sense it is way ahead of all the other amps I have every owned. Bass extension wise this amp is a beast making every bass note clean and articulated. Tone decay was just spot on right through the entire sound spectrum.

I would not call the EF1 analytical because it has a warm and very musical presentation although it still carries lots of details. As you might have expected this hybrid tube based amplifier has a warm and forward midrange which suits lots of music really well. The mids are forward without being dominating, detail wise it is also way ahead of the Octavart. Overall this amp is very transparent without being overly analytical, it has the right balance to my ears. One of the things that surprised me a lot were the highs. The detailing and extension is just amazing. Clean and precise and not over emphasized like on some headphone amplifiers.

Sound stage wise this amp was near perfect, you can pinpoint the location of the instruments and voices in the music both in a horizontal and vertical axis. It really makes listening to music so much more enjoyable with headphones because you get a sense of the ambiance of the recording. Because the amp is so precise you get a clear sensation of layering in the music, you can easily focus in on the details in any frequency area. Like all the other performance aspects the Head-Direct EF1 clearly distances itself from the Octavart. No matter what headphone I had hooked up, there are of course minor variations with the headphones because some exhibit a bigger or smaller sound stage to begin with.