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Review: Firestone Fireye II headphone amp - full metal amp

post #1 of 17
Thread Starter 
As part of the ongoing series of headphone amp reviews, I just finished auditioning Firestone's Fireye II, a USB-only amp/DAC.

For all photos and RMAA measurement tests, please read the original review:
Firestone Fireye II headphone USB/DAC amp in review - full metal amp

In a follow-up to last month’s review of the Fireye I headphone amplifier review, TMA will continue our look at Firestone products with the unique Fireye II USB/DAC headphone amplifier. Unlike the Fireye I, this unit does not accept analogue inputs and it is not a stand-alone amp; it functions 100% from USB ports as a plug and play audio device, and thankfully has a manual volume pot for volume attenuation. Its specific use is to not create a clean audio signal for headphone listening from a computer, a job which it does quite well.

Amplifier Structure: Class A/B
Power Structure: USB or Optional 5VDC external power supply (available separately)
Headphone Impedance: 32 – 600 Ohms
Circuit Protection: Short circuit and temperature protection
Support Format: 16-bit, 32 / 44.1 kHz/ 48 kHz
USB Chip: CMedia – CM 108
DAC Chip: Cirrus – CS4344
Main OpAmp: TI – DRV601

Build and Packaging
The Fireye II comes as solidly built as its sibling, and as such, is a among the most well-made in its price class. Its heavy aluminium casing serves two purposes: to protect its innards, and shield the unit from radio interference. It comes with the same accessories and great cardboard box as the Fireye I.

There are a few visual differences between the two amps which are dictated by their respective uses. Unlike the Fireye I’s charging circuit, the Fireye II’s rear-mounted USB port interfaces with a computer to provide analogue signal to headphones. The front panel houses the same on/off lamp as seen on the Fireye I, but layout similarities end there. Unfortunately, the headphone output port took a step back in build quality from the sturdy metal port of the previous amp – it is now plastic. However, it keeps up with the family by installing only one contact per pole. The toothed horizontal volume pot is next to it and on the rear panel is an impressively busy affair which is packed by the following: a 5V input, power selector, and USB port.

It remains as easy to open as the Fireye 1, requiring only a small philips screwdriver and opposable thumbs. And it not only looks solid: it is. Dropping this badboy to the floor will result in broken tiles, dented wood, etc.; the Fireye II is a very solidly constructed piece of audio equipment. Even so, it comes in well-designed, well-padded, and compact cardboard box. Inside, the amp, pseudo felt bag, connection cable, and USB charging cable are packed neatly in soft, protective sponge foam. Not that anything would really damage the amp. The ‘felt’ bag is a good accessory, however, as it keeps the amp from suffering small scratches, or more feasibly, from gouging your computer or desk!

Again, for the price, there is little to complain about – it, not you, will survive the coming wars.

Features in Review
First and foremost, the Fireye II is a USB/DAC headphone amplifier. While it does not function apart from a computer, it is a much more competent amp than its simple signal booster sibling: the Fireye I. Firstly, the volume pot is a much-needed addition to any amp simply because allows your music to maintain a higher signal-to-noise ratio.

It still hisses with sensitive headphones, but not as much as its sibling, and much, much less than a computer’s audio output. Since its amp circuitry comes from internal digital conversion (a much cleaner process), it is a much cleaner, better source than a laptop or desktop. You can power the unit completely via USB, or when your headphones need a little more power, the unit can also be plugged into the mains.

A great feature which doesn’t get enough press is the ability to pass on a 16bit optical signal to an external DAC, computer, MD, hi fi, etc.. If your computer lacks optical output, the Fireye II is a good pass-through for digital components, effectively rendering your computer into a hifi component.


It is completely plug and play: merely connect it via USB and select it in your computer’s software or control panel settings and, voila! instant sound upgrade. On my Mac, it shows up as a C-Media sound card, which incidentally, is the same circuit which inside of the Nuforce Icon Mobile.

Audio Performance
Amplifying headphones won’t reveal as stark a difference in sound as upgrading them to better models. However, there are certain, universal differences which nearly all amplifiers exhibit when compared to un-amped sources. Low frequency signal integrity usually degrades horribly when driven from “naked” audio sources such as sound cards, and especially, portable audio players. Similarly, hiss levels and distortion skyrocket from computer audio output. The Fireye II does a good job of reducing/eliminating these artifacts, but it isn’t perfect.

Like its sibling, the Fireye II isn’t among the most itchily-detailed amps out there, however, the FEII will reward those who enjoy crisp mids and highs and a decently weighty bottom. No frequency belts out in exemplary tones, but for the price, this amp should be a great companion to many headphones.

Depending on the headphone you use, the FEII will perform differently. Most headphones sound good when paired with this amp, however, some ‘mate’ better than others. Very sensitive inner ear monitors (IEMs) reveal hiss, but not too much. Generally, bass performance does not fall off, and even with the difficult-to-drive 16 ohm Kenwood C700 torture test, frequency response remains respectable. But, in direct comparison to the MBP headphone output, the FEII has much less hiss, whine, and audible distortion than when powered from the headphone out of a computer.


When moving up in price and down in sensitivity, the Fireye II really begins to strut. The 64 ohm Ultrasone DJ1Pro has no hiss at all with the Fireye II, and maintains a great frequency response from 20Hz to levels above 15KHz though there is a pronounced upper treble roll off. This headphone is detailed and speedy, but has great bass performance, and if anything, slightly laid back mids. But despite its ostensibly sterile market of DJ’s and studio engineers, it is a stunning listen for many genres and pairs well with the Fireye II. However, this headphone will reveal slight bass distortion from both the amp and the MacBook Pro’s headphone output. The latter, however, is at times, quite bad.


This trend is largely true for any headphone and a good point in favour of the amp: it simply stomps the mediocre headphone outputs of regular computers. But moving much further up the scale, to the excellent Jerry Harvey Audio JH13Pro, the FEII begins to hit a wall. Jerry Harvey’s masterpieces haven’t been properly driven from any external amp I have tried, including mains-powered modules – it is a very hard to drive headphone which will cause most normal to mid-end audio equipment to suffer huge bass roll off, and conversely, an uncanny upswing in treble amping. While the JH13Pro sounds good from every amp I have paired it with, its presentation remains unique and is likely a product of impaired amping.


For all other headphones, the Fireye II sounds better than any PC internal soundcard that I have tried, and also tests better under load than most of them. While not perfect, there is very little detail loss in any frequency with all but the most difficult to drive headphones. The Fireye II simply sounds better than most on-board computer headphone outputs, has a cleaner output, hisses less and suffers less distortion.

On a side note, it is a smashing match with a MacBook Pro!

Like many amps which utilise volume pots, the Fireye II has a few quirks, namely channel imbalance. At very low volumes, it will amplify one channel 3-5 decibels louder than another and to compensate, the computer’s software volume will have to be attenuated, the amp’s volume pot raised, and both monitored for balance. This presents little trouble for headphones like the DJ1Pro, but IEMs and earbuds are sorely affected. Even at a very low software volumes, finding the ‘right’ balance is hard simply because the volume put must be set to about 20% of its full output before balance is set aright. Conversely, at the top end of volume, there is little to no difference in output levels after the pot is set to about 60% volume. I have yet to use any volume pot equipped amp which does not suffer some imbalance, but this amp has it slightly worse than a few others I have tried.

That said, the pot itself is stiff enough to deflect accidental turning.

Chart Disclaimer
My findings are based on an Edirol FireWire Audio Capture FA-66, a very good, but not excellent audio capture card. It is made for musicians on a budget, but still manages a decent array of input options and apart from a horridly constructed headphone output,has very decent recording circuitry. For recording from analogue sources, I use the balanced 1/2 inputs in either TRS or XLR connections.

Your mileage may vary. These are soft, but wise words which should be observed when using any amp. As you can see, the easiest headphone for to drive is the 64 ohm DJ1Pro which allows both the Fireye II and the MacBook Pro a lot of breathing room, but out of the external DAC, it hisses less and overall, is more cohesive.

Sound Conclusion
The Fireye II is a much more impressive audio circuit than the Fireye I. It has a cleaner signal, a dedicated volume pot, and does a better job of cleanly ‘driving’ headphones. While it lacks the Fireye I’s bass jumper settings, it doesn’t need them — at least when amping most headphones — as its frequency response is largely laudable. When put through the torture test of the JH13Pro, however, it falls as hard as any current portable headphone amp I have auditioned. The good thing is that most of those amps cost more and are built by more famous audio houses. While the Fireye II DAC/amp does not deliver staggering stereo separation, or universally low distortion lows, it thumps the headphone output of most computers and is a good companion to most headphones. For movies, games, and music — assuming you don’t mind doing everything in stereo — it is a great, comparatively inexpensive option.

For 115$, you get an amp which should stand up to any cataclysm. From its sturdy extruded aluminium chassis to well-laid out array of ports, it is a well designed amp. Of course, it is meant to be paired with a computer, a job which it delivers in spades; just plug and play, and instantly, your sound is upgraded from a hissy and often chaotic background hum, to clean, well defined audio. The Fireye II also acts as an optical pass-through for pairing with a Hi-Fi or other optical equipment.

Again, for the price, it performs admirably, faltering at the same places where other, higher priced amps also misstep and exceeding expectation in other areas. Against its market, it is one of the better options, but it lacks some refinement. The volume pot for instance, has too much play and may frustrate users who want to listen with sensitive inner earphones as well as headphones.

All things considered, this is a TMA Grab.


I hope you enjoyed the review. This amp USB AMP has been a constant partner to my MacBook Pro since about August, so I know a lot about it including strengths and weaknesses. If you have any questions, please ask away!
post #2 of 17
I really like this device. I'm selling it mostly because I was starting to use it with custom IEMs and the channel imbalance was a little frustrating. For the money, though, it's a GREAT starter piece of kit.
post #3 of 17
Thread Starter 
yes, I agree. But the channel imbalance gives me trouble even with the relatively insensitive DJ1Pro. For the money, however, you are right: it is a great amp.
post #4 of 17
It played fine with my ATH-M50 (50ohm, I think) and for $200 that is a heck of a starter setup for computer audio. Nice plus that you can hold onto it and use it as a USB/SPDIF converter when you upgrade to a bigger setup.
post #5 of 17
Thread Starter 
Actually, the SPDIF is great - literally better than my MacBook Pro's built in SPDIF which I have used for years! Recently, Amazon have started selling it for like 80$ or so, may I am wrong; but it seems a steal for anything less than 100$. But the imbalance issue is annoying and the hiss (though slight) with iems is also... off-putting.

Cheers in your new setup.
post #6 of 17
I think I paid $97 + ship from Craig at Whiplash. Just selling it off now to a new head-fier who needs a good start. It's a nice little device for the price. Plus packaged better by miles than anything else in that price range.
post #7 of 17
Thread Starter 
wow, you got a good deal. I think when I got it, the amp was still selling for more. It could be though that I did not check Craig. And, I don't live in the USA!
post #8 of 17
Would the Firestone Fireye 2 work ok with HD650?
post #9 of 17
Great review!

The Fireye II is indeed a marvellous DAC and a most worthy external soundcard for any personal computer audio environment.

I use mine with a pair of the superior Future Sonics Atrio M5s.

This is, in my opinion, the best in-earphone personal audio solution available today!

It blows my mind!
post #10 of 17
Thread Starter 
Originally Posted by trentino View Post
Would the Firestone Fireye 2 work ok with HD650?
It depends on what you want. The Fireye II is pretty linear for large loads and despite not being the most detailed of outputs, sound pretty good with big headphones. Personally, I think it is a great way to enjoy better signal processing than many onboard soundcards, however, some will be better sounding. But, probably none have digital pre amps like this one - that is a great feature.

I recommend the HD640 and the FEIII - very good for the price.

Originally Posted by Pipps View Post
Great review!

The Fireye II is indeed a marvellous DAC and a most worthy external soundcard for any personal computer audio environment.

I use mine with a pair of the superior Future Sonics Atrio M5s.

This is, in my opinion, the best in-earphone personal audio solution available today!

It blows my mind!
It may well be one of the best deals, especially as the price seems to have lowered to below 80$ at a lot of places. It is made well, sounds good, and does the digital output which is great.
post #11 of 17
Originally Posted by shigzeo View Post
...despite not being the most detailed of outputs...
I would wager that anyone other than a studio mastering engineer would not be able to notice any such deficiencies in detail in a double-blind trial.

Seriously, ther Fireye II is more than anyone could wish for, in driving earphones or headphones.
post #12 of 17
Thread Starter 
Well, its hiss with earphones is pretty noticeable. but still, for the price, there is not a lot of competition in either build, sound, or feature quality. Very good product, but certainly not perfect.
post #13 of 17

hey i want a external DAC to hook up my audioengine a5's to my imac. would this DAC do the trick? any suggestions i dont want to spend over $100.



post #14 of 17

The AudioEngine A5s are active (self-powered) speakers. The Fireye II USB DAC would supply them with a totally clean analogue signal, directly from your computer. This would therefore be the best possible way of driving them. In fact, a pre-amped signal from the Fireye would absolutely spoil them. Your AEs would undoubtedly completely out-perform what you would ever hear from them otherwise. Pre-amping is always a very wise move. Good luck!

post #15 of 17


Originally Posted by tombade View Post

hey i want a external DAC to hook up my audioengine a5's to my imac. would this DAC do the trick? any suggestions i dont want to spend over $100.



I just received my Fireye 2 today and am going to use it on my AE A5's as well. I'll be running from a PC. Is it safe to assume that it's simply plug and play? Also will it work with a Macbook Pro running Snow Leopard?

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