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[Impression] FireStone Audio Fireye HD and Fireye Mini

post #1 of 6
Thread Starter 

Over the years, FireStone Audio has made its name with high quality small form factor desktop headphone amp and DAC. In fact, my very first desktop amp is the company’s Little Country 2 hybrid OTL amp. Recently, they also venture into the world of portable amp. Here we take a look at some of their latest offering, the Fireye HD and Mini, priced at US$399 and US$38 respectively.

 

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Spec

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Fireye HD

Amplifier Structure: Class-AB amplifier

Power Structure: Built-in Li-ion battery power supply

Headphone Impedance: 16 ohm to 600 ohm

Equalization: Built-in bass boost function

High / Low Gain

Circuit Protection: Output short / temperature protection

Duration: Continuous using for more than 8hrs when fully charged

Way of Charge: PC or USB charger

Charging Time: USB : 5 hours, DC Charger : 2.5 Hours

Main Opamp: TPA6120

Audio Performance (1kHz sine wave, 2Vrms output):-

Frequency Response (From 40Hz to 15kHz): +0.02dB~ -0.14dB

Noise Level (1kHz, A-Weighted): -114.0dB

Dynamic Range (1kHz, A-Weighted): 113.7dB

THD%: 0.0005%

Stereo Crosstalk: -92.7dB

MSRP US$399

 

 

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Fireye Mini

Amplifier Structure: Class-AB amplifier

Power Structure: Built in battery power supply

Headphone Impedance: 32 ohm to 600 ohm

Circuit Protect: Output short circuit / temperature protect

Usage Time: With 100% full battery around 24hrs, depending on volume used.

Charging Method: Using PC or USB adapter to charge

Charging Time: Fully charging (3hrs), fast charging (1.5hrs = 80%)

Main Opamp: TI - DRV601

Audio Performance (1kHz sine wave, 2Vrms output, 24-bit / 48kHz)

dB-Weighed Frequency Response (From 40Hz to 15kHz) : 40Hz +0.1dB, 15kHz -1.67dB

Actual Frequency Response: 20Hz to 20 kHz

Noise level (1 kHz, A-Weighted): -110.5dB

Dynamic range (1 kHz, A-Weighted): 110.4dB

THD%: 0.0068%

Stereo Crosstalk: -96.0dB

Housing Material: Shock absorbing flexible silicone

Housing Color: 5 colors available : Red, Black, White, Green, Purple

Dimensions: 40 x 24 x 9 mm (D x W x H).

Weight: 14 gram (without cables)

MSRP US$39

 

Accessories and Build Quality

Accessories wide, both amps come with a short USB cable for recharging and a short 3.5mm interconnecting cable. The FIreye HD comes with an extra fast charger that will shorten the recharging time to 2.5hours.

 

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Fireye Mini, next to similarly conceived Travagan's dogbone

 

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Build quality wise, both are excellent. The Mini has a soft silicone shell that isn’t meant to be crash-proof in anyway. But given it is designed as an inline amp for small devices, such as smartphone, it is still adequate - just don't sit on it. On the other hand, HD looks and feels like a premier product. The aluminium case has a two tone texture and gives a very classy impression. The only minor complain I have is that all the letters are silkscreen printing so they will wear off in time. It would have been much better if they are either lasered or anodized on permanently.

 

Battery Life

The Mini has a quoted battery life of over 24 hours and the HD has a quoted battery life of over 8 hours. I didn’t fully drain either one of them but the actual usage doesn’t seem to vary much from the listed spec.

 

One thing worth mention is that Mini doesn’t have a dedicated power switch. Instead, the amp turns itself on automatically when a headphone is inserted.

 

Gain, Hiss and EMI

Gain wise, Mini has a fixed +6dB gain and HD is about +7.4dB in high gain and -14dB in low gain. That being said, HD in low gain is best used with line level signal input.

 

Hiss wise, both amps performed extremely well with no detectable hiss when used with the very hiss prone Shure SE530. EMI wise, Mini performs excellently. This is a big plus since ultraportable inline amp like Mini is usually the choice of casual smartphone-as-source user. HD on the other hand doesn’t fare quite as well. EMI is noticeably loud, though not in any deafening volume.

 

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Size comparison (from left): JDS Labs C421, Fireye HD, Leckerton Audio UHA-4 and Fireye Mini.

 

Sound Quality

Basic RMAA measurement doesn’t reveal much issue with both amps. HD actually performance quite well, flat from 20Hz to 20kHz and has really low noise. Mini has a mild sub-bass roll-off under 100Hz and reaches -1dB @ 30Hz, but otherwise decent. Since the roll-off doesn’t change with load impedance, it is likely caused by input capacitor that is required by the opamp for DC blacking. Output impedance is measured at 10 ohm for both amps, mainly because of the added output resistors needed for both opamps to avoid instability issue. Because of the rather high output impedance, the current output is not particularly good on both. Enough for typical load, but low impedance load will likely suffer. All and all, neither amp are particularly suitable for low impedance or multi-driver load, such as multi-driver custom IEM that tend to be under 16oom and has a crossover circuit. More likely they will perform better with higher impedance load that tend to demand less current and have lesser tendency for impedance interaction that causes coloration.

 

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Fireye Mini

 

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Fireye HD

 

As far as subjective listening goes, HD sounds very clean, resolving and transparent, if not just a tiny bit more forward and gives it a tad of warmth and fullness that are easily missed if not listened very carefully. Even with the very slight forwardness, it still has an excellent overall soundstage. The only minor gripe I have is that the bass hits just a tab softer than I like - otherwise, Fireye HD is easily a top-tier sounding amp that can compete against O2, Meier Audio Corda StepDance or JDS Labs C421 alike.

 

Fireye Mini on the other hand is more comparable to FiiO E6 and digiZoid ZO2.3. Bass impact is noticeably less powerful than E6, likely because of its sub-bass roll-off. But otherwise, Mini offers a cleaner presentation with better resolution, layer and wider soundstage that is a lot closer to a mid-fi portable than an entry level. However, it is still an entry level sounding amp so it is not going to crash any of the really good sub-$100 amp any time soon. However, as an inline ultraportable designed to boost volume, it performs admirably.

 

EQ

Fireye HD comes with a bass boost switch. It starts around 1~2kHz, reaching around +2.5dB @250Hz and peak at +6dB @ 20Hz or so. It is quite a broad bass boost though audibly it is actually fairly mild and doesn’t affect the mid as much as the FR curve would have otherwise suggested. It is actually quite pleasant and non-intrusive.

 

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Fireye HD's bass boost

 

Ending

All and all, both Fireye HD and Mini come out strong in performance in their respective category / competition. The two things that really put them down are the high output impedance, and Fireye HD’s price tag. High output impedance means they will never be the best pairing with many higher end IEM that are low in impedance and in multi-driver setup. Fireye HD high price tag also puts it in a tough spot since the recent trend in portable amp world is ‘high performance + low price’. Even though Fireye HD is every bit as HiFi sounding (and looks much more classy), it is facing some really stiff competition from the $200~$300 range. To FireStone, my advice is to find a way to lower its price, which will make it a lot more competitive in the increasingly crowded portable amp market. Given that there are more and more higher-end IEM users willing to invest in portable amp, designing amp in lower output impedance is also the way to go. As for the user, I’ll advice using both amp with either single driver or high impedance headphone and earphone (*IEM included). That way, coloration or current demand will be much less of an issue. One thing I like about both amps is that they have quite high a gain while still remain almost hiss-free, so getting loud without much side-effect is a strong point for both amps. Mini’s immunity to EMI also serves as a great plus especially for smartphone user where headphone-out doesn’t have enough volume. HD on the other hand is best suited to drive full size. Though I am not sure how it will go with 600ohm load, I’ll bet most of the 250ohm and under should do really well with it.


Edited by ClieOS - 4/3/13 at 9:43pm
post #2 of 6

Nice thoughts, Tai. I think my impressions fall right in line with yours when it comes to both the Mini and HD, though I no longer have the Mini and bought it years ago, so I don't quite remember. It's nice to see some RMAA measurements too, as I don't have a computer setup that can take advantage.

 

I've been telling FSA that the OI is too high; we'll see if they respond accordingly in future iterations. However, they do have a balanced version of the HD coming out soon, which will be pretty interesting for full-sized headphone users on the go.

post #3 of 6
Shame about the OI, seems like the form factor is perfect for iem users but it's rated from 32 Ohm which seems like a strange decision.
post #4 of 6
Thread Starter 
Quote:
Originally Posted by noxa View Post

Shame about the OI, seems like the form factor is perfect for iem users but it's rated from 32 Ohm which seems like a strange decision.

 

16ohm is still fine, I believe. However, the fixed gain of 6dB is actually quite high and there might not be a lot of room for volume adjustment for very sensitive IEM.

 

Quote:
Originally Posted by tomscy2000 View Post

I've been telling FSA that the OI is too high; we'll see if they respond accordingly in future iterations. However, they do have a balanced version of the HD coming out soon, which will be pretty interesting for full-sized headphone users on the go.

 

It is possible to implement TPA6120 with very low output impedance by using inductor instead of resistor. I have seen it on another amp and the result is quite good. But it isn't a standard implementation. The output resistor on the Mini however is more like a precaution rather than a prevention. Unless the headphone is particular high in capacitance, the resistor can be omitted without issue.

post #5 of 6
Quote:
Originally Posted by ClieOS View Post  It is possible to implement TPA6120 with very low output impedance by using inductor instead of resistor. I have seen it on another amp and the result is quite good. But it isn't a standard implementation. The output resistor on the Mini however is more like a precaution rather than a prevention. Unless the headphone is particular high in capacitance, the resistor can be omitted without issue.

 

Isn't that what they did with the HUD-mx2? I don't know if the iFi iDAC does it too, since their reported OI numbers are all over the place, and I haven't bothered to check if the numbers got cleared up.

post #6 of 6
Thread Starter 
Quote:
Originally Posted by tomscy2000 View Post

 

Isn't that what they did with the HUD-mx2? I don't know if the iFi iDAC does it too, since their reported OI numbers are all over the place, and I haven't bothered to check if the numbers got cleared up.


I saw only reference that Audinst is saying the output impedance is 2ohm on some email reply. Do you know anyone actually did a measurement? I only ask because I saw the picture of its inner a while ago and didn't notice any inductor near the output (could have missed it, since the picture is on an angle).

 

Anyway, iDAC doesn't have resistor or inductor on the output since it uses MAX9722 on the output. You must be referring to iCAN - yes, it does have an air core output that help to lower its output impedance. It is the amp I was referring on the previous post.

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