Review: Firestone's Fireye 1 Portable Headphone amp - Heavy Metal
Sep 7, 2009 at 7:45 AM Thread Starter Post #1 of 4


The Hiss King
Aug 9, 2006
I hope that some find this helpful. Be forewarned though, my usual testing equipment chose last week to die, so my hardware tests fail in any good comparison except to show a general trend with the sonic signature of Firestone's amp. I hope to get the numbers updated next week with much better back up statistics.

While this review is aimed at iPod users, my observations apply to any use of this amp, particularly when regards to hiss, bass roll off and loss of channel separation when driving low ohm phones.

My blog isn't huge and cannot sustain loads of traffic, so I cannot post pictures here. The original blog post with pictures can be accessed here:
Fireye 1 Portable Headphone Amp - Heavy Metal

Taiwan’s Firestone Audio is known for creating high-quality amplifier and digital-to-analogue products at reasonable prices. One of their constants is the use of sturdy construction materials and methods, a design decision which guarantees the longevity of their products. The Fireye 1 is an impressively constructed headphone amplifier which has a couple of unique features that will help you enjoy music and movies from your your iPod, laptop, or larger, hifi source.

Output - 150mW Stereo
Frequency response: 20Hz to 20,000Hz
Impedance: 16 ohms
Input - 3.5mm stereo headphone jack
Output - 3.5mm stereo headphone jack
Mini USB port (For charging)

Additional Features:
Pop Reduction Circuitry
Internal Mid-Rail Generation
Thermal and Short-Circuit Protection
Auto On with LED indicator
Metal housing protects against EMI and RFI interference
Power and Battery
Built-in rechargeable lithium Ion battery
Charging via computer USB
Fast-charge time: about 1.5 hours (charges up to 80% of battery capacity)
Full-charge time: about 3 hours
Music playback time: 
Up to 24 hours when fully charged

Build and Packaging
From the get-go, the Fireye 1 is a great device. While not pricey, it comes in a cute, but firm cardboard box which is compact and well-labelled and easy to open. 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 Fireye 1’s chassis is machined from a solid, heavy aluminium which can withstand heavy pressure from the outside. The ‘felt’ bag is a good accessory, however, as it keeps the amp from suffering small scratches, or more feasible, from gouging your iPod!

The amp’s package feels ‘complete’ and since the Fireye 1 has an internal battery, there is no need for fumbling with charging accessories or switching power sources. However, the Fireye 1 is easy to open. It is fastened by four screws, one in each corner, which when removed, give easy access to the circuit board which pulls out from a slotted vent which runs the length of the amp’s chassis. Replacing the battery should be duck soup (as long as you can obtain a replacement): simply grasp the plug firmly, pinch and pull like you would computer logic board connector. The battery rests on a slight sponge via adhesive, but anyone familiar with a spludger should be able to pry it up.

As for connection quality, the Fireye 1 is quite good, if not exemplary. In particular, the headphone out is a thick metal-ringed port which won’t likely snap or fold with pressure from the headphone jack. The input, however, is ringed by a plastic port which is less sturdy. Each connect via one contact per pole which is par for most manufacturers, but could benefit from the insurance which can be derived from extra contact points.

In a later review, TMA will cover the Nuforce Icon Mobile, a great portable from the makers of the excellent NE7M headset. While the amp stage is quite good on the Icon, it is less robustly built and suffers what an embarassing setback: recessed connection jacks. Unless all of your connections are super slim, you won’t get a full stereo image. The Fireye 1 is free of these problems. Each connection jack is flush with the chassis body, or in the case of the headphone out, extended by about a half-millimetre.

Features in Review
The Fireye 1 is an amplifier that in the literal sense, amplifies the signal. However, it is closer to what in the headphone world has been dubbed a, ‘booster’. Most battery-driven headphone amplifiers come with attenuation circuitry to control music volume internally, but the Fireye merely boosts the signal from the source at a static level. This has both good and bad points. Firstly, it means that your ears are protected from sudden volume bursts which happen when the attenuator or volume pot might accidentally be nudged up, a common problem with portable amps. While from a certain perspective, this is helpful for portable application, it has a couple of drawbacks.

Firstly, it means that in order to raise or lower the volume, you must do it from your source device which is problematic. Whether computer, iPod, other DAP, DVD player, etc., your device is either already attenuated at a line-out level, or is internally amplified. In the case of the line-attenuated device, utilising the Fireye 1 is tricky because most headphones whether sensitive inner earphones or large, insensitive headphones will be too loud. Since the amp’s circuitry is static, there is no way to comfortably adjust volume levels without adding another circuit to the audio.

Secondly, it means that any noise in the source circuit will be amplified. Sources such as computers, the iPod Shuffle, many iRiver players and older iDevices have audible hiss when plugged into sensitive headphones. Because the Fireye 1’s volume is static, you must set the volume on your source to a comfortably low level which usually means that the noise of the source will only get worse. Headphone amps which feature volume pots or stepped attenuators allow you to set the source to its highest volume which will give it the best signal to noise ratio. Then, the external amplifier will do its job of reducing hiss and attenuating sound levels.

Battery life, as quoted is a long 24 hours which I have been able to replicate. Some amps get better battery life, and others worse. 24 hours is quite good and since a fast 1,5 hours will charge to 80% the Fireye 1 is never out of use for long. There isn’t an ON/OFF switch. Rather, activation is automatic upon the insertion of headphones and source cable and is indicated by the glow of a green light when the battery is healthy, and a reddish light when the battery needs more juice.

What Firestone don’t advertise is the special Left and Right bass boost settings. After removing the logic board from its chassis, bass levels can be adjusted by moving jumpers from default (OFF) to +2, creative a hardware equalisation circuit which helps bass anemic headphones. The effect will be discussed a little later.

Otherwise, the Fireye 1 works as advertised, but just how well is the question.

Audio Performance
Amplifying headphones won’t reveal stark differences as will ditching your iBuds in favour of a cheap MEELectronics or Nuforce headphone. However, there are certain, universal differences nearly all amplifiers exhibit when compared to unamped sources. One is low frequency signal strength which often degrades horribly when driven from a “naked” (iPod or other DAP without an amp) portable audio source. Another is increased channel separation for the completion of a strong stereo representation in music.

All amps are known for a certain sound ’signature’. The Fireye 1 could be considered a smooth, rather relaxed amplifier which voices warm mids and lows, while slightly extending high frequencies. For lusty vocals and mood music, this amp is special, but for faster music which prefers resolution over mood, there are better optioins.

Performance will vary depending upon the headphones you use, but there are certain undeniable traits which the Fireye 1 exhibits.

The first is is relaxed low frequency presence. Unlike many portable amps, the Fireye 1’s output doesn’t bolster the weakly powered headphone amplifiers inside of iPods and other portable sources. In fact, when using sensitive earphones, bass output is less than when powered straight from man iPod touch 2G. This is not necessarily a bad thing, but it is unexpected. This loss of bass definition is termed ‘bass rolloff’ and is a common characteristic of many sources.

Certain genres benefit from relaxed, but full-bodied bass. One of these is American Hip Hop whose low-resolution bass lines can be jarring with too much edge and vibration. Of course, depending on mood, other genres such as jazz and vocal music can sound lovely when detail is turned down as it were.

When paired with the iPod touch 2G, there is a subjectively ‘stark’ difference when using the Fireye 1 and when not. The iPod touch is technically a very good sounding player which excels in electronic, classical, and rock genres, but which can comparatively suffer from unemotional playback. The Fireye 1 adds that emotion that the Touch may lack on one hand, and decreases edge and grit on the other.

For vocal music, the Fireye 1 is a great companion. Madeleine Peyroux’s Careless love sang with more melody and emotion than via the Touch 2G as did a number of similar artists. If your source is cold, the Fireye 1 may add a fuzzy blanket to the mix.

High frequencies aren’t incredibly emphasised, but in the bat-range, they take an upward swing of about 1-2db, giving certain music a slightly airy, detailed presentation. Instruments remain well separated even when driven by voltage-hungry low impedance inner earphones. However, Firestone’s amp doesn’t Despite this however, the Fireye 1 cannot ‘drive’ any headphone for any semblance of bass resolution. Simply put, no matter the sensitivity, no matter the impedance, there is audible loss of detail in bass. When setting the bass jumpers to ‘+’ settings, bass presence is increased at the expense of incurring some boom, but mids and highs in comparison, are reduced by about one decibel. Having used several amplifiers which feature selectable bass enhancers, I am impressed by the relatively fatigue-free change introduced by the Fireye 1’s bass jumpers.

Lastly, though certainly not least, is hiss. Firestone’s amp is not a deathly black. Its background is a constant sheen of white noise similar to a television which has lost its reception. Though not audible on less sensitive headphones, it is bothersome when paired even with the oft-maligned Apple iBuds. In other words, to hear music cleanly, you will need to have rather large, non-portable friendly headphones on. Of course, with Ultrasone’s DJ1Pro and the even less sensitive DT880 from Beyerdynamic, there is no hiss problem and the warm character of the amp fits either clinical headphone very well.

Chart Disclaimer:
My recording source has disappeared in a recent move. I will be replacing it soon with a decent Firewire FA-66 machine from Edirol which can capture much better than my current and barely passable MacBook Pro. Results from the chart below should only be used in comparison with other results which I have recorded. In other words, I have no faith in the MacBook Pro’s recording capability and expect both the Touch 2G and Fireye 1 to represent better numbers and plot lines which was proven when I ran RMAA using an M-Audio USB Transit and professional Sony recorder for recording. Thus, for comparisons’ sake only, the graph below should illustrate the sound characteristics in both sources for easily to detect signal patterns: frequency response, and channel separation.

As seen below, the Fireye 1 can sustain a decent channel separation when driving nothing but an outboard amplifier, but when presented with the torturous 16 ohm Victor (JVC) FX500, its channel separation suffers. Fortunately, the audible effect is much more subtle, falling inline with the performance level of higher-end portable sources. Despite this result, for a dedicated amplifier, this result isn’t inspiring.

Below, you can see the bass roll off when compared to the Touch 2G which shows less than 1 dbl at 20Hz. This is the main reason that the amplifier’s bass resolution is lower in comparison to the Touch 2G.

Your mileage may vary - soft, but wise words which should be observed when using any amp. My iPod Nano 1G using both Rockbox and stock Apple Firmware benefited less from the warm signature of the Fireye 1 simply because it is already a warmer source than the iPod touch. However, bass jumper settings gave new lungs to the bass rolled-off Nano. A final graphic expression of the bass rolloff of the Fireye 1 is when reproducing a 40Hz square wave. Crisp, resonant bass will generally be audible from sources and amps which can produce rectangular lines. Though my current equipment is poor, the shape of the graph will illustrate the point that the Fireye 1 expounds in its RMAA charts above.

Sound Conclusion:
The Fireye 1 is a good product with good intentions. Separate left and right jumpers for passive sound equalisation is unique in any amp, but particularly at its price. And, if your source is a cold, analytical player of any format, the extra warmth given by the Fireye 1 is helpful and inspiring to certain musical genres. Whether that source is an iPod, a laptop, another DAP, or a DVD player, the Fireye 1 has a steady, warm sound signature. Adding bass makes action movies com alive and otherwise bass deficient sources move. However, the lack of attenuation makes this amplifier a hard to define product. You won’t be able to use it with line out-equipment simply because it will be to loud for nearly any headphone, and as its static volume only amplifies the noise which comes from laptops, some DAPs and other hifi equipment, it is not a great pair for sensitive earphones.

Finally, the loss of bass definition illustrated above and a comparatively small sound stage makes this Firestone product merely a static-gained wire. It is a gain device with passive equalisation which works for a few applications very well, but for others not so well.

Firestone’s tradition of quality products is continued with the Fireye 1, a simple amplifier which does more for volume than overall sound performance. While selectable bass jumpers for both right and left channels is a great idea, it would be better if the amp itself didn’t suffer bass roll off as much as it does. While it helps audio like laptops, going portable with it is difficult since it will be too loud with a majority of sensitive earphones and with larger, current hungry headphones, may not have enough power to satisfy their large coils.

Nevertheless, an investment of 77$ brings an impeccably made product which has a few good features and convenient, well thought-out design. If only the Fireye 1 had a volume attenuator, it would be a much more usable product.

All things considered, it is worth a Tap from TouchMyApps.
Sep 7, 2009 at 1:28 PM Post #2 of 4


Member of the Trade: Twisted Cables
Jun 18, 2008
wow, a portable amp that doesnt allow you to use a Line-out; thats could have been thought through a little better. good thorougfh review though man kudos for tha. I certainly would not have been able to provide such dedication to reviewing a product that had little appeal to me.
Sep 7, 2009 at 1:39 PM Post #3 of 4


The Hiss King
Aug 9, 2006
Thanks for the comments Qusp.

Well to tell you the truth, I have seen and used worse, and the build of this thing will outlast any portable player, but yeah... I do wish that Firestone thought of incorporating an attenuator. That alone would make it worthwhile. Bass jumpers are a nice touch, but then again, with such poor bass roll off, it is hard to justify the its name as 'amplifier'

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