FiQuest headphone amp in review – Adroit audio evangelism


If you aren’t ready to take the wild walk on the DIY side, but still want to really get down and dirty with tweakable headphone amps, there are a very few options available to you. One of them is to experiment McGuyver style with cotton, fish, cookies, and an oiled grouse to achieve a truly experimental sound. But if lock picking DIY isn’t your thing, there are only a few choices on the market. Some such as Graham Slee, Firestone, iBasso, etc., offer headphone amps with user-replaceable op-amps and slightly modifiable circuits, but no one outdoes MST, a one-man operation out of Akihabara Japan. MST’ FiQuest project is as ground-up tweakable a design as is possible in a pre-fabbed design. In a way, it is the audio evangelist among portable amps.

Feel free to discuss the FiQuest in our forums.

Power Source: Rechargeable 12-series Ni-MH Battery pack
Frequency Response: 5Hz – 100kHz/ -0.5dB
Gain: +3dB/+12dB/+23dB
SNR: 109.7dB (Gain:L), 101.2dB (Gain: M), 96.1dB (Gain: H)
Crosstalk: 90.7dB
Total Harmonic Distortion+Noise:
0.0009% @1kHz/+12dB/1Vp-p/600Ohm,
0.0011% @1kHz/+12dB/1Vp-p/100Ohm,
0.0018% @1kHz/+12dB/1Vp-p/33Ohm,
0.0024% @1kHz/+12dB/1Vp-p/15Ohm
Maximum Output power:
1300mW+1300mW (12Ohm loading+External powered),
590mW+590mW (12Ohm loading+Internal Battery Powered),
Battery Life: 8 Hours (with Maxxed config.) to 20 Hours (Normal)
Battery Charge Time: 2.5 Hours
Recommended Headphone Impedance: 8-300Ohm

Build and Package
If the first thing that strikes you when you see the FiQuest is its size, you ain’t blind: it is BIG. In fact, portable amps don’t get quite … this large. For that reason, the FiQuest transcends the ‘portable’ world and ascends to can be loosely dubbed: ‘transportable’. It IS at home in very large pockets, backpacks, and purses, but does an equally good job atop a HiFi or a desk.

Like Graham Slee’s Voyager, size comes with a number of advantages, mostly build quality and ease of use. The FiQuest is a high-quality platform for the tinkerer. Nearly everything on the inside can be custom-ordered, and from a DIYer’s usability standpoint, it earns accolades. Everything from the volume pot to the power supply is easy to fiddle with and replace. Heavy, yes. Fiddley, not at all. And of course, it is strong. The FiQuest’s walls are machined from ~3mm thick extruded aluminium with as little lateral flex as a cryogenically treated body builder.


To open it up, you need a hex key and the ability to discern between clockwise and counterclockwise; to have fun, you just need tweezer-like fingers and a few op-amps. Thankfully, MST can supply you with the latter. This amp is designed to be tinkered with.

There is one concern, however, with the FiQuest’s design. The four bolts that hold the front and rear panels on will go through a lot of twisting. If you go DIY wild, eventually, they will strip the aluminium casing. In that case, I recommend replacing them with static bolts and thum-screws.


Features in Review
Things get really sick from here on in, and by sick, I mean ‘amazin’. Firstly, under the bonnet is a powerful battery supply and recharge circuit. The maxed version is rated for up to 8 hours of use while the normal version eeks out 20. The truth is that the maxed mode can actually play music for a little more than 9 hours. Considering the power under the bonnet, this spec, while trite in comparison to a long-running amp like the Graham Slee Voyager, is respectable.

The real DIY bit, however, comes from the fact that every op-amp in the amp is user replaceable. That means the main L/R op-amp(s), buffers, and ground channel amps can be changed to your liking. What that means for the end-user is many possibilities. It IS true that op-amps have very low distortion, and that on paper, most shouldn’t differ that much. But in an amp, powering very different circuits, the swap of a single op-amp can mean the difference between good sound and great sound.

I’ve settled on the simple combination of: BB OPA2111KP in the L/R socket and BUF 634P in the Buff channels. This combination affords me: very low levels of hiss and smoothly detailed mids with low end punch. It drives everything from my super-sensitive FitEar 333 to my gory 600Ω DT880 with the energy and overhead of a busload of zombies.

You can easily tinker it for max power or max finesse. But perhaps the most important DIY feature of the FiQuest is that its case can stay off whilst the amp is being overhauled. I’ve used a LOT of headphone amps and really enjoyed passing op-amps in and out, and on occasion, soldering here and there. For simple op-amp switching, having to reassemble, replace, and re-cap everything is Oprah-book-hour boring. With the FiQuest, if I want to make a quick change, I do it with ad-hoc expedience.

Note: remember to shut the power off when fiddling with the FiQuest’s insides.


I noted that the Graham Slee Voyager was one of the best if not the best portable amp I’ve heard for driving my rather finicky DJ1Pro headphones. The GSP amp has got loads of power and a house sound that deepens the bass even without the contour switch engaged. Well, the FiQuest follows suit: it packs punch for hard-to-drive headphones, and for easy-to-drive headphones, supplies plenty of volume and control.


I ordered the Maxxed version as per my desire to really push a lot of hardware and I’m glad I did. Despite splashing out up to 16V, and driving the 600Ω DT880 to nearly ear-splitting volumes, the FiQuest is beautiful for any variety of inner earphones and iems.

Firstly, channel balance is extremely tight. For reference, I’ve re-seated the volume pot to point to 0 at the letter v on the volume legend. With a twist to the letter o, it is perfectly balanced on my most sensitive IEM’s and reveals no static when adjusting. Of course, every pot will vary slightly, but even sensitive ears should be able to enjoy low-volume amped music. Moving up to any proper headphone, especially high Ω beasts such as the DT880 is of course, better. There is no channel imbalance even at the lowest of discernable volumes.

The 600Ω DT880 can be very quiet from a lot of sources, but at high gain on the FiQuest, they double perfectly as desktop speakers. There is no better layman term to describe the power that belts forth other than: OMG. Of course, since I don’t need another operation, I never twist the high gain volume past about 12 o’clock.

Another issue with a lot of portable amps is radio interference. The FiQuest possesses no special powers, but its thick case does reflect most noise. I don’t know if I am just lucky, or if the FiQuest is just really well battened-down, but I’ve yet to grab someone’s mobile phone call – shame that.

So, how does it sound? Well, that is the hardest part to describe. You see, it sounds how you want it to sound. I suggest hashing it out with MST before purchasing. I wanted a do-it-all, and that is what I got. But MST can tailor an IEM-ready FiQuest if you want, or a power-hungry DJ1Pro FiQuest for you.

With my headphones, the FiQuest re-invents a lot of sensuous listening experiences. After I discovered the magic combination of op-amps, it took over as my home IEM amp simply because it is grain and for the most part, relatively hiss free. Of course, with any sort of proper headphone, there is NO hiss at all.

At normal listening levels, the maxed FiQuest is an IEM dream. It pushes through deep resolution, for 95% of hard-to-drive balanced armatures, perfect treble resolution. Dynamic earphones are easy breezy for the FiQuest: control, width, power, and extension.

The bass toggle adds up to 3dB of bass in three steps. Most bass boosters add 8-10dB, often creating murky messes in favour of a thump. The FiQuest’s circuit, on the other hand, is subtle. What isn’t subtle is its handling of the DJ1Pro, a headphone that ‘responds’ well to different amps. Its 64Ω isn’t ‘hard to drive’ in terms of volume. Instead, its voice deepens depending on the output source. Amps that can pump out a lot of voltage tend to bring out more bass from the DJ1Pro’s speakers. The FiQuest falls in that camp: lows belt out in ferociously smart aural earthquakes – earthquakes which violate everything when the bass toggle is engaged.

Moving up to high Ω headphone such as the HD600 and DT880 is beautiful. There is plenty of volume, space, and overhead, and in default bass configuration, the FiQuest is neutral. There is very low distortion, so don’t expect your knife-edged 600Ω DT880 headphones to suddenly sprout the dark, smooth voice of the HD600. That really is the beauty of the FiQuest – it preserves the headphone’s original voice. Assuming you like your headphones, you’ll love the FiQuest.


The one issue I’ve sussed with the Maxed FiQuest is intermodulation. Certain low Ω earphones can force intermodulation into the signal that is especially evident at high volumes. It isn’t an op-amp related problem as I’ve tested many configurations back to back with the same issue. Most earphone do NOT force intermodulation, and it only occurs at volumes which would deafen a rock star. Among my earphones, only one causes this distortion: FitEar Private 333; and among my headphones, only the DJ1Pro at high volumes.

One other small issue is ON/OFF thump. The FiQuest is not loud as the ALO Rx or the Graham Slee Voyager, but there is a noticeable surge, so be careful to keep earphones out of your ears when turning the amp on.

Chart Disclaimer
This review’s RMAA measurements reflect the performance differences between the naked iPod touch 2G and the same iPod when paired with the FiQuest maxed and ALO Cryo line out dock. Since they are taken with my equipment, they should not directly be compared to other technical data. The data represents the ability of the amplification circuit to drive headphones. It is NOT the headphone response data.

RMAA Charts for the FiQuest are found in the forums.

Sound Conclusion
The FiQuest is a powerful beast of a portable amp that does every job well. It isn’t limited to IEM’s or to headphones. You will get great frequency response from it with even the hardest to drive earphones such as the FitEar Private 333, but it is even more at home with headphones like the 600Ω DT880. Because it is buttons-to-bottom configurable, its sound is hard to pin down. But, I can say that your money isn’t going into distortion – it is going into a powerful wire-with-gain amp. The one area that needs improvement with the current Maxed FiQuest is intermodulation with lowΩ earphones and headphones. While intermodulation doesn’t affect normal listening levels, it is audible, and isn’t brought out by my other amps.

So the ~349$ – 449$ question is: is the FiQuest worth it? For those who want/need a transportable desktop amp, it is. There really isn’t anything readily available that fits the requirements of both IEM’s and headphones. The combination of resolution and very low hiss makes it a great desktop IEM amp, but with the simply flip of its gain switch, it is transformed into a voluble amp for any headphone. Since it can be configured to your specifications, it is more ‘your amp’ than any other headphone amp on the market. MST has done its homework – at least mostly. Everything is easy to use and sounds great with the exception of intermodulation distortion. That fixed, the FiQuest will for myriad uses, be the most holy amp on the market.

MST FiQuest Summary
Title: FiQuest Developer: MST
Reviewed Ver: Maxed: for FitEar 333 and DJ1Pro: op-amp numbers:
  • OPA211
  • AD744JN
  • LT1028ACN


  • 634
Connection: Stereo Mini 3,5mm
Price: $350-450 Application: Portable/transportable
  • Excellent construction with good RF rejection
  • Easy to tweak
  • Great, linear sound
  • Lots of sound options available
  • Small ON/OFF thump
  • Intermodulation distortion
FiQuest can be ordered in June from MST Audio – more information to come

Headphone amps and DACs help your headphones get the most out of their transducers. Take a look through our headphone section for suggestions of good upgrade/sidegrade options, and our headphone amplifier section for suggestions on how to wring out the best performance from your beloved phones.

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