The following contains my impressions of the Firestone Audio Fireye HD and its performance with a range of headphones.
Rig as pictured running apple lossless files.
Fireye HD
High quality is in evidence everywhere with the Fireye HD, from the slick grey finish to the feel of the controls. A highlight for me is the unmistakable click of a relay a second after the power is toggled on or off. Placement of the gain and bass boost between the volume knob and the jacks is a little awkward but not a real problem in use.
Fireye HD + Shure SE215
Bass boost not required here, gain low.
Volume sensitivity is good with around 90 degrees of usefull travel. Noise floor is absolute zero, even with the ipod paused and the volume cranked to full on high gain there is no detectable noise.
Bass is a little heavy and the treble rolls of early but that's what the 215's bring to the party.
Overall it is the best performance I have heard from the SE215.
Fireye HD + Sennheiser HD650
Bass boost not required again, gain high
Volume range excellent with my preferred highest level at around 50% of travel on high gain
Ease and authority come to mind with this combination, there is synergy here for sure.
Sound stage is wide open with clean air between instruments. Bass is tight and strong, mids smooth and well placed, treble crisp and clear
Overall this was my favorite combination.
Fireye HD + HiFiMan HE500
Bass boost, in this combo I felt the sound was very natural and true without the bass boost. With bass boost engaged the sound was clearly colored but still fun and quite addictive.
Gain high, this time my preferred maximum level was around 80% travel
Bass is a little blurred in complex passages, mids are glorious really superb, treble is a little off like something has been lost but still passable.
Overall while the Fireye HD lacks the power and control of my balanced Violectric set up with the HiFiMan it is surprisingly competent.
Fireye HD + Beyerdynamic DT770 Premium 600 Ohm
For the first time I felt the bass boost was required to achieve a normal level.
Gain high, obviously approaching the limits of the Fireye HD preferred highest level was around 90% travel
Bass boost engaged the bass response is well defined and strong, mids are again enchanting with a tube like air and warmth, treble is beginning to show some ragged edges when pushed.
Overall performance here is ok but showing signs of pushing the envelope.
Verdict
Everything I have connected to the Fireye HD has performed true to its signature, the little amp has no obvious flaws or shortcomings.
Overall the Fireye HD is a high quality high definition unit with a strong and neutral character.