Firestone Audio Fireye HDB

REVIEW: Firestone Audio Fireye HDB


(From Firestone Audio site)

* Power Structure: Built-in 4-Serial Li-polymer battery power supply
* Amplifier Structure: Class-AB amplifier
* Headphone Impedance: 16 ohm to 600 ohm
* Circuit Protection: Output short / temperature protection
* High / Medium / Low Gain
* Duration: Continuous using for more than 8hrs when fully charged
* Way of Charge: To charge via External Adaptor
* Charging Time: 2.5 Hours

Audio Performance (Output 2Vrms , Balance in, Balance out):
* Frequency Response (20Hz ~ 20kHz): +0.02dB ~ -0.3dB
* Noise Level: -112.0dB
* Dynamic Range: 111.3dB
* THD: 0.0004%
* Stereo Crosstalk: -110.2dB

* Differential OPAmp: TI – LME49724
* Main OPAmp: TI - TPA6120

* Charge Input: 2.0mm DC jack (24V/0.5A) *1
* Line Input: 3.5mm phone jack *1, Mini 4Pin phone jack *1
* Line Output: 3.5mm phone jack *1, Mini 4Pin phone jack *1

* Weight: 302g
* Net Weight: 194g
* Size (H*W*D): 171mm * 112mm * 80mm
* Net Size: 122mm * 62mm * 19mm

MSRP: ~$300.

Warranty: 2 years

Official product pageLINK


Packaging & Accessories:

Not much to say here. The new HDB comes in just a nice paper box. Inside you'll find a 4-pin to 3.5mm single-ended short cable, a DC 24V/0.5A adaptor and 3 extra DIY 4-pin plugs. The short cable is of excellent quality as expected from FSA cables. It would've been nicer if there was also a single-to-single cable as well, and at least a carrying pouch or case.

Build & Design:

Build quality is simply perfect. The whole amplifier is made of aluminum, rather thick and feels very sturdy. The gold painted volume knob is plastic and so are the 3 switches. In the front side we will find the Gain switch along with the volume knob and the two different headphone line outputs, single 3.5mm and 4-pin balanced ended. The single output can accept both TRS single and TRRS balanced plugs (such as Hifiman's in-ear models). At the rear side, the Power switch, the charge input and the both line inputs, 4-pin balanced and single 3.5mm, with a switch to change between the inputs, and the charging indicator LED. As for the 3 switches, they might be rather small, but not fragile. The Gain switch goes from Low (middle position) to Med (up) and Hi (down). Personally, I think it'd be more logical to put them in order rather than having the Low in the middle.
As for aesthetics, my credits to FSA for the simple yet elegant and beautiful design. Not the lightest weight unit, but easy to carry on the go nevertheless.

Gain and Hiss:

While there's no EQ/Bass Gain option switch like the one featured in the previous HD (non-balanced) model, instead of that, the HDB features a 3 level Gain option. The low gain is powerful enough for most sensitive earphones/headphones, while the High gain should be needed for really demanding ones.
Hiss was slightly noticed and only with very sensitive IEMs.
There's also a noticeable clicking sound when both starting and shutting the power switch. It could be annoying depending of the headphone in use, so it's recommended to start the amp before wearing the ear/headphones.



So far everything looks good for the asking price, great and solid built quality and sleek design, with the necessary accessories pack (ok, it'd be better). But it'd be worthless if the sound quality didn't match the ~$300 price tag. Fortunately, I can confirm that FSA's new HDB balanced amp offers a beautiful and enjoyable full sound performance. Let's get into more details.

Gear used for the testing/reviewing process:

Input source (DAP):
SanDisk Clip+ (mainly), iPod Shuffle, Hifiman HM700

Interconnector cable:
Included balance-to-single input cable

Ostry KC06 (Silver), Hifiman RE-400 (Single version), Dunu DN-1000, Rock-It Sounds R-50M, Moe Audio SS01, Xiaomi Piston 2.0, and more.
Being a balanced amplifier, the HDB doesn't only supports 4-pin connections, but also Balanced TRRS 3.5mm ones, and so both Hifiman RE600(B) and RE400(B) were tested as well on their 'balanced' mode.

Earbuds and headphones:
Ubiquo ES703, ES903, Senn HD25, HD600

The Panda Audio Amp-S as a reference amp (with stock LME49860 op-amp chip) and Hifiman HM700 were used for comparison as well.

Single Output

The HDB presents a warm and very rich signature. A full and very deep sound, which is very enjoyable and truly immersive. It's not what you'd call a flat and linear reference or analytical amp for sure (that's something for the Amp-S or JDS O2, for example), but rather smooth and engaging, giving higher priority to great dynamics with a noticeable added fun factor. Simply put, it's just 'Musical'.

The bass is probably the first thing to be noticed. In short, it's perfect. It's very full and deep with incredible extension and excellent rumble. It doesn't offer a heavy-bass low-end, and in fact it's missing the Bass gain option that the previous HD model had; not a bad thing per se, but would've been nice to have. Despite the slight extra coloration, the quality is great, very tight with good speed (although slower when compared to the Amp-S).
As for the quantity, well, it'd depend on the output. It won't make warmer/bassier phones sound as a bass monster, instead will give them better control, speed and decay. The HDB tends to have a better synergy when paired with more mid-centered to brighter phones, as it adds the low end they can be missing.

The midrange is very rich and well textured. Neither more forward nor recessed, but it's given an extra thickness and sweetness that makes it much more enjoyable. Vocals, as well, may remain in a neutral position in the whole presentation, but come out much more natural and articulated; very catching and with much deeper emotion. Still, the mids are not the most open and effortless, again when compared to more analytical and brighter Amp-S. Yet, the HDB has the upper hand in terms of texture and 'musicality'.

As expected from a smooth and warmer amp, the highs aren't the highlight of the show. They are very well extended, but to a lesser degree when compared to the lows extension. Quantity wise the treble is not lacking but definitely smoothed down; which is not necessarily a bad characteristic. In fact, the HDB does a great job to tame down some of the extra harshness that trebly/brighter sets may have. It works great with some more edgy and aggressive sounding sets as the TWFK based IEMs such as the R-50 and DN-1000.

While not being a detail oriented amplifier, the HDB detail retrieval is nothing short of impressive. Instead of being thrown to the front, they are presented in a more dynamic and natural way. The stage is more than big; it's huge, very wide with amazing depth. Not just that, the depth this FSA new product offers is without a doubt of the best I've heard. Dynamics are excellent and both instrument and vocal well separated. Imaging is pretty good; not the best yet, but everything sounds well-positioned for a warmish signature.

HM700 + HDB:

As mentioned above, the HDB gave great results when paired with the Sandisk Clip+, as it's a very colorless DAP that shows no personal character. That's not the same case with the HM700. The new Hifiman DAP is already powerful enough and doesn't benefit from extra amping, and already has some very slight sense of warmth (just the typical from Hifiman's house). Not real improvement was found, aside of a bit of extra speed and depth.
This leads to...

HDB (w/Clip+) VS HM700:

Now, this is more interesting. While the HM700 has quite enough power to drive most of my current gear, it's obvious that the HDB is the much more powerful as with the 3 levels of gain is meant to drive even 600ohm headphones. That aside, when it comes to sound signature, the HDB is noticeable warmer and stronger towards the low freq. with a much fuller and wider sound, giving a more "out-of-head" feeling. The HM700 in contrast, has a softer impact and leaner/thinner midrange but also more forward when no EQ is used. Vocals are more frontal and intimate on the HM700, while more even on the HDB. Even though, the Hifiman's EQ works as wonder and can achieve similar effect as the HDB. Still, the HDB will sound more spacious and much bigger with greater dynamic range; it can also be more aggressive (not in an offensive/annoying way). In the treble dept. the HM700 is brighter and more sparkly against the smoother and more rounded FSA HDB.


The two similar priced amplifiers are the contrast to each other.
In either Mode 1 or 2, the Amp-S offers incredible speed and clarity. Clarity and airiness are the strength of the Panda amplifier together with very tight bass, yet deep sub-bass. Obviously, it's much brighter on the upper end and less forgiving. Quite the opposite in both bass and treble dept. As for the midrange they perform great but also very different. While the Amp-S sounds more open, airy and effortless, the HDB wins in sweetness and emotion. In the end, it comes to personal tastes as always. 


Best/Favorite Synergy:


Rock-it Sounds R-50M:

Being a TWFK based earphone, the R-50M is obviously a very bright and clear set with a rather soft bass impact. When fed through the warm and smooth HDB, the results are quite nice. It tends to control the extra harshness these TWFK can have and add it a beautiful bass response. While it won't transform it in a bassy phone by any means, R-50M does sound more dynamic and richer through the midrange with a fuller overall tone.

Ostry KC06:

So, how the well regarded great sounding KC06 matches together with the HDB.  Well, to be honest is simply... (grin smileys).....WOW!!! Yes, despite being the easiest to drive earphone I ever owned, the KC06 benefits a LOT from amping and the FSA HDB is no exception. These little and quite affordable in-ear set is taken to different and highest level (or should I say levels). First thing first, the bass is now REAL. The HM700 already improved the KC06 sound in this aspect, but the HDB makes a noticeable difference. While a un-amped Ostry has great bass control the quantities probably weren't enough. When plugged to this FSA, it's like listening to different and better beast. The mids as well sound much fuller and the whole sound is bigger, very spacious and incredible deep. And, the soundstage is rather huge with great dimensions. A perfect match indeed, regardless the HDB retail price.

Hifiman RE-600:

Fortunately, the HDB is able to drive both single and balanced TRRS 3.5 ended earphones. Personally, I do think that RE-600 is needed to be driven in a 'balanced' configuration to show its true form. With the HM700 the RE-600 offers a perfect balance from low to highs with great extension in both ends. Like with the KC06, a similar result is achieved with the HDB. While, the RE-600 is the least light in bass from the Hifiman in-ear line, is more than amazing when listened with the HDB. The low end is substantially more convincing with very good rumble and deeper sub-bass reach. The midrange might show huge improvement in texture, but that's because the RE-600 is already perfect in this area; yet, the mids can be more enjoyable. The soundstage also feels wider.


Ubiquo ES703:

This is a pair of earbuds that I got to like a lot, usually used at home and quieter places. With the Sansa Clip+ alone the ES703 are already very enjoyable, but still are like earbuds. When used together with the HDB the results are more than impressive for just a ~$40-50 earbud. The ES703 start to sound similar to open cans, reminding me in a way to one of my favorites earbuds, the well known Yuin PK1.


For their first balanced amplifier, Firestone Audio made a great product. A mix of excellent build quality, sleek design, and most importantly, superb sound, which is simply musically engaging. It has more than enough power, and the different balanced in/outputs make it a very versatile product. $300 is no little money, but a well worth buy, indeed. With the right matching equipment the HDB might take the music to another level.