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FiiO AM2A - Medium Power Amplifier Module For X7

  1. Brooko
    FiiO AM2A - Warm Organic Sound : More Power For the X7
    Written by Brooko
    Published Sep 12, 2016
    Pros - Sound quality, power output, low impedance, easy to swap in and out, low cost
    Cons - Relatively low battery life compared to alternatives
    For larger (1200 x 800) images, click any picture


    A lot of you will see the style and information with this review as being pretty similar to the one I have done on the previous AM2, AM3 and AM5 amplifier modules. The reality is that a lot of the physical aspects are very much the same. So for similarity I can't do much about it. I can assure you however that I performed the same testing, and the same comparisons I've done previously. I reviewed FiiO's TOTL Android based touch screen DAP – the X7 – in early November 2015, the AM2 module in February 2016, the AM5 module in May 2016, and the AM3 module in July 2016.
    Please note that the X7 (with subsequent firmware updates) is now a much more complete DAP than when first released. I can now go artist, album, track, the DAC works beautifully, the blue light can be turned off, the battery indicator seems to be a lot more accurate, and with the release of most of the amplifier modules, there is plenty of choice for no matter what headphones you are driving.
    It is not perfect, and there are still some bugs to be squashed, but for overall SQ compared to functionality, I still find the X7 and its ecosystem of swappable amplifier modules to be extremely good value.
    By now, most Head-Fi members should know about the FiiO Electronics Company. If you don’t, here’s a very short summary. FiiO was first founded in 2007. Their first offerings were some extremely low cost portable amplifiers – which were sometimes critiqued by some seasoned Head-Fiers as being low budget “toys”. But FiiO has spent a lot of time with the community here, and continued to listen to their potential buyers, adopt our ideas, and grow their product range. They debuted their first DAP (the X3) in 2013, and despite some early hiccups with developing the UI, have worked with their customer base to continually develop the firmware for a better user experience. The X3 was followed by the X5, X1, X3 2nd Gen (X3ii), X5 2nd Gen (X5ii), M3 and X7. They also have a full range of amplifiers, DAC/amps, cables and are starting to develop earphones.
    FiiO’s products have followed a very simple formula since 2007 – affordable, stylish, well built, functional, measuring well, and most importantly sounding good.
    The X7 and add on AM2A module were provided to me gratis as a review samples. I have made it clear to FiiO in the past that I did regard any product they sent me as their sole property and available for return any time at their request. I have continued to use X7 and its modules for follow up reviews, and I recently inquired if I could purchase the devices from FiiO. They have insisted I keep the X7 + modules for my own use. So I acknowledge now that the X7 I have is supplied and gifted completely free of any charge or obligation. I thank FiiO for their generosity.
    I'm a 49 year old music lover. I don't say audiophile – I just love my music. Over the last couple of years, I have slowly changed from cheaper listening set-ups to my current set-up. I vary my listening from portables (including the FiiO X5ii, X3ii, X7, LP5 Pro and L3, and iPhone 5S) to my desk-top's set-up (PC > USB > iFi iDSD). I also use a portable set-up at work – usually either X3ii/X7/L3 > HP, or PC > E17K > HP. My main full sized headphones at the time of writing are the Beyerdynamic T1, Sennheiser HD600 & HD630VB, and AKG K553. Most of my portable listening is done with IEMs, and lately it has mainly been with the Jays q-Jays, Alclair Curve2 and Adel U6. A full list of the gear I have owned (past and present is listed in my Head-Fi profile).
    I have very eclectic music tastes listening to a variety from classical/opera and jazz, to grunge and general rock. I listen to a lot of blues, jazz, folk music, classic rock, indie and alternative rock. I am particularly fond of female vocals. I generally tend toward cans that are relatively neutral/balanced, but I do have a fondness for clarity, and suspect I might have slight ‘treble-head’ preferences. I am not treble sensitive (at all), and in the past have really enjoyed headphones like the K701, SR325i, and of course the T1 and DT880. I have a specific sensitivity to the 2-3 kHz frequency area (most humans do) but my sensitivity is particularly strong, and I tend to like a relatively flat mid-range with slight elevation in the upper-mids around this area.
    I have extensively tested myself (ABX) and I find aac256 or higher to be completely transparent. I do use exclusively red-book 16/44.1 if space is not an issue. All of my music is legally purchased (mostly CD – the rest FLAC purchased on-line). I tend to be skeptical about audiophile ‘claims’, don’t generally believe in burn-in, have never heard a difference with different cables, and would rather test myself blind on perceived differences. I am not a ‘golden eared listener’. I suffer from mild tinnitus, and at 49, my hearing is less than perfect (it only extends to around 14 kHz nowadays).
    This review is essentially about the AM2A medium power amp module released by FiiO for the X7. For a detailed look at the features of the X7, and a quick run-down on the AM1 (default) IEM module, I would recommend you read my X7 review or indeed any of the 30 something reviews on the X7 currently listed.
    This is a purely subjective review of the AM2A medium power amplifier module – my gear, my ears, and my experience. Please take it all with a grain of salt - especially if it does not match your own views.


    The AM2A arrived in the usual small black retail box measuring approximately 90 x 120 x 25mm. On the front of the sleeve is a picture of the bottom half of the X7 with AM2A module attached and some text telling you that this is the AM2A amplifier module. One notable addition now is the “Hi-Res Audio sticker”. On the rear of the box are QR codes which will take you to FiiO’s website or Facebook page.
    am2a01.jpg am2a02.jpg am2a03.jpg
    Retail box front
    Retail box rear
    The new "Hi Res Audio" indicator

    Removing the outer packaging reveals a plain tin box with a nice powder coated finish. Removing the lid reveals a black cardboard envelope, and under this is a foam cut-out with the AM2A module nestled safely inside.
    Inside the envelope is a warranty booklet in multiple languages, a full set of stickers (which match the ones from the X7), and 2 replacement screws. The stickers are a nice touch and show FiiO are thinking about their customers. If you’ve brought and applied stickers to your X7 already, the last thing you’d want is a new amp module with no adornments. Although I don’t use them, I can appreciate the foresight. The other new addition is a set of 3 “Hi-Res Audio” stickers (presumably so you can affix them to the X7 if you wanted).
    am2a04.jpg am2a05.jpg am2a06.jpg
    Powder coated tin
    FiiO Envelope with Accessories
    The module in its foam enclosure

    As far as the AM2A goes, the other nice thing to note once again is the rubber dust cover/protector over the connection pins. So far almost everything is a mirror of the AM2 and AM5 modules, and this includes the lack of specifications on the packaging. The good thing is that FiiO have already listed the specs for the AM2A in the X7 section on their website (although they are missing a couple of power output settings). One last thing before we conclude this section – the case is actually large enough to store 3 modules. So my suggestion for FiiO would be to modify at least one of their releases to give that option. If not, then you can modify yourselves (see below).
    am2a08.jpg am2a09.jpg am2a15.jpg
    Full accessory package
    Manual, screws, sticker envelope and Hi-Res stickers
    My modified case for carrying multiple modules

    The table below lists most of the relevant specifications. I have (as a comparison) also listed specifications from the default AM1 and also the AM2 and AM5 modules.
    AM1 Module
    AM2 Module
    AM2A Module
    AM5 Module
    ~ 64 x 25 x 16mm
    ~ 64 x 25 x 16mm
    ~ 64 x 25 x 16mm
    ~ 64 x 25 x 16mm
    Voltage amplification
    Current Drive
    TPA6120 A2
    S/N (H/O)
    ≥115 dB (A-Weight)
    ≥118 dB (A-Weight)
    ≥118 dB (A-Weight)
    ≥120 dB (A-Weight)
    THD+N (H/O)
    <0.0008% (32Ω/1 kHz)
    <0.001% (32Ω/1 kHz)
    <0.002% (32Ω/1 kHz)
    <0.001% (32Ω/1 kHz)
    Output into 16 ohms
    >200 mW (16Ω/1 kHz)
    >350 mW (16Ω/1 kHz)
    Not stated
    >800 mW (16Ω/1 kHz)
    Output into 32 ohms
    >100 mW (32Ω/1 kHz)
    >300 mW (32Ω/1 kHz)
    >420 mW (32Ω/1 kHz)
    >500 mW (32Ω/1 kHz)
    Output into 300 ohms
    >10 mW (300Ω/1 kHz)
    >30 mW (300Ω/1 kHz)
    Not stated
    >55 mW (300Ω/1 kHz)
    H/O impedance
    <0.2 Ω (32Ω)
    <0.5 Ω (32Ω)
    <0.3 Ω (32Ω)
    <0.5 Ω (32Ω)
    Peak output voltage
    >5.2 Vp-p
    >8.8 Vp-p
    >10.6 Vp-p
    >11 Vp-p
    Peak output current
    >250 mA
    >250 mA
    >250 mA
    >250 mA
    Channel Separation
    >73 dB (32Ω/1 kHz)
    >72 dB (32Ω/1 kHz)
    >73 dB (32Ω/1 kHz)
    >72 dB (32Ω/1 kHz)
    Play time
    9 hours+
    8 hours+
    7.5 hours
    6 hours+

    The AM2A has the same dimensions as the AM1, AM2, and AM5. The main differences are internal. The AM2A follows the same look of the AM2 and AM5 with a darker shade of the powdered titanium appearance. Otherwise they all look and feel identical. The AM2, AM2A, AM3 and AM5 colouring appears to be the same. There is white text on the back of each designating the model number.
    am2a13.jpg am2a11..jpg
    Headphone out and USB port
    Internal connector board

    Replacing the modules is extremely easy – just a matter of using the small hex screwdriver included with the X7 – undoing two screws, sliding one module out, and sliding the new module in. The fit on the AM2A is perfectly flush, and the only thing very apparent with the AM2A fitted is the change in colour (compared to X7). This of course disappears when used with a cover for the X7 (if owned).
    am2a12.jpg am2a14.jpg
    Side view
    Underside - with product ID

    Although you can’t see them, it is probably a good idea to mention the internal electronics (also see the table above). The AM2A was a user modification to the original AM1 low power amplifier, and because of its popularity among DIYers in China, FiiO decided to release it as another option. It uses a similar current drive AD8397 ARDZ OP amp (the AM1 was an AD8397), but swaps the original OPA1612 chip with the AD8620 from Analog Devices – which has a much higher output voltage. This in turn gives higher output into a 32 ohm load. The original AM1 output was 100 mW into 32 ohms, this modified amplifier module is 420 mW and the actual AM2 is 300 mW. Because of the higher power output, the decision was made to release it as an AM2S rather than an AM1A option.
    am2a17.jpg am2a18.jpg
    Colour difference of the amp module
    Which disappears when the case is used

    The AM2A continues FiiO's delivery of low noise and low impedance – ideal for both IEMs and low to medium powered headphones. Whilst the AM5 still has most powerful single ended output of the X7's amplifier modules into 32 ohms (AM5 = 500 mW vs AM2A = 420 mW), the AM2A with its 420 mW into 32 ohm sits closer to the AM5 output than the AM2.
    So the specs are listed above, but what does that mean in the real world? Once again my HD600 was the ideal test device – with its 300 ohm impedance and sensitivity/SPL of 97dB at 1 kHz / 1V rms. The HD600 isn't an overly hard load to drive – how would the AM2A handle it?
    To perform this test I used a 1 kHz test tone, my trusty SPL meter, and rigged up a harness so I could hold the HD600 and SPL meter in place – meaning I only had to swap the amplifier modules out to compare. To get a reasonable listening level for me, I pre-calibrated the X7 with AM2A module, and for my normal 65-75 dB listening level (A-weighted), found that 70/120 on low gain was my ideal listening level for music. I then set about comparing the 3 modules with this output in mind.
    The first test was using 70/120 volume, low gain, no EQ, and a 1kHz test tone:
    1. AM1 = 68.8 dB
    2. AM2 = 74.2 dB
    3. AM5 = 74.5 dB
    4. AM2A = 75.7 dB – quite staggering
    The second test was designed to tax the amplifiers, again using the HD600, low gain, no EQ and a 1 kHz test tone. But this time the aim was to get the SPL meter to hit 95 dB.
    1. AM1 = 120/120, and could only manage 93.3dB – very creditable all the same
    2. AM2 = 112/120
    3. AM5 = 112/120
    4. AM2A = 109/120
    So once again in real world testing the AM2A actually outperforms the AM5 amplifier into the HD600. This module has some pretty good power output!
    Although FiiO publishes their own real world tests with their modules, I also like to conduct my own. I noticed FiiO uses relatively easy to drive IEMs and ear-buds – and achieved “+7.5 hours” at 52/120.
    For my test I again used the HD600 and simply left it at 70/120 (which would be my normal listening level) and left the X7 running looped tracks. The screen was off, as was Wi-Fi and Bluetooth. Gain was low and no EQ. Mode used was FiiO's Pure Music mode. My test managed 7 hours and 20 minutes – so I'd suggest FiiO's figures a re pretty accurate. Of course your results are going to vary depending on the volume you use, the load you're driving, the amount of screen time you have on, and the apps you have running.
    SONICS (subjective)
    So here we are again, after covering the specs, build, power and effect on battery life. I'll repeat what I said last time - my ears are probably not as sensitive as many of you, I volume match very closely, and I’m subject to the same amounts of potential placebo as all humans. The swapping for the comparisons were as quick as I could make them to preserve auditory memory (same procedure as before – screws undone – swap units, adjust volumes to the pre-set levels, and listen). I varied between rapid swapping (portions of a track about 10-15 seconds) and longer listening periods (a full track at a time). The exercise was made more difficult by the low-volume bug that exists with the X7 currently (first seconds of a track when switching amps plays quieter).
    I used a mix of my usual test tracks - http://www.head-fi.org/a/brookos-test-tracks and concentrated mainly on tracks exposing detail, dynamic contrast, sound-stage, bass quantity and vocal quality. I'm just going to summarise here – rather than go through section by section – because a lot of the time the results were so close that in the end I was guessing.
    Remember this is pretty subjective!
    AM2A vs AM1
    The AM1 is definitely the leaner, more linear presentation. The AM2A is noticeably warmer and sounds more full. Bass also sounds a little weightier – not like having a boost on or anything, but more like the whole signature has more body and warmth. I tried to compare other things like sound-stage or imaging, and the volume delay just made it too hard to try and pick. For me - the main difference is simply tonality, with the AM2A being warmer and smoother.
    AM2A vs AM2
    The change here was a little closer, but again the difference was quite noticeable. The main thing that kept coming through was the warmer tonality of the AM2A (and of course the difference in power/volume). Overall the AM2A is warmer and smoother – its a bit like comparing the Gen5 iPod Classic to the Gen 7. The funny thing though is that its not a smooth syrupy or muddy sound – its just warmer. Still has good levels of clarity.
    AM2A vs AM5
    Similar to the comparison with the AM2, and once again the AM2A sounds warmer and smoother overall. In contrast the AM5 sounds a little more vivid or vibrant particularly through the mid-range, but also a little thinner.
    Really hard to call, and the funny thing is that I can get used to each of the modules quite quickly (within a few tracks), and then they each sound quite natural. If I had to choose just two modules of all of the ones FiiO has on offer at the moment, I'd probably go AM3 and AM2A. The AM2A for my higher impedance single ended cans, and the AM3 for IEMs or balanced operation. The two sound very different – AM3 is a lot cleaner and more linear than the warmer fuller AM2A, but that again is part of the reason for choosing these two. It would pretty much cover most bases.
    As usual I wanted to measure the output of the AM2A and compare it to the AM1, AM2 and AM5. The roll-off you'll see is the X7's DAC section filters, and I've once again included the very linear E17K for reference. As per my earlier SPL tests we can see the slight differences in volume, and also the relative linearity of each of the amplifier modules.
    am2afreqgraph.png am2aTHD.png
    Module comparison - frequency response
    My attempt at measuring distortion - FiiO's output is lower than I can measure

    I also wanted to try measuring the AM2A's distortion level - but unfortunately I was again undone by the quality of my sound card.  The measurements simply show the limits of the measuring device - as we know FiiO's measurements on proper equipment show lower figures than I'm recording. The good news is that the distortion figures are below the limits of audibility anyway - the AM2A is a clean and resolving amplifier section.


    Once again I'll keep this short, as I’ve pretty much already summarised everything – but once again to put it in a couple of sentences …..
    The AM2A module (like the AM1, AM2 and AM5 modules) has a great build, is easy to fit, and measures as well as it sounds (check FiiO's specs). It will cost you some battery life from the original AM1 and AM2, but this is because of the higher voltage output. And the cost in battery life does mean you'll have no problems driving headphones like my HD600.
    Tonally the AM2A is closer to the AM2 and AM5 than the more linear AM1 or AM3. It is a little warmer and fuller sounding than the AM2 or AM5 to my ears. At an approximate release price of USD 99.00, if you own the X7 and are looking for a fuller warmer sound, and particularly if you are driving full sized headphones that require e little more voltage, then IMO the AM2A is an excellent choice.
    Once again thanks to Sunny at FiiO for giving me a chance to try the AM2A.
      djvkool, cleg, mowglycdb and 4 others like this.
    1. View previous replies...
    2. csglinux
      Hi Brooko - Nice detailed review, as always! I hope you can indulge me with a couple of questions...
      1) I'm now in a position to compare am2 and am1 amps. I know I probably can't do this reliably with only one X7 given the time it'll take to swap the amps and adjust the volume but I'm going to take my best shot at it. Do you know if it's safe to hot-swap the amps on the X7? i.e., can I safely pull one amp out and plug the other in without powering off the X7 in between? I don't want my X7 to do a Galaxy Note 7 impersonation :wink:
      2) How did you make your FR measurements? Are these into an infinite-impedance load and if so, how do you do this? Is the X7 HO feeding directly into some very high-impedance SPL meter?
      csglinux, Oct 17, 2016
    3. Brooko
      Thanks.  I just hot swapped the modules I had.  It's probably not recommended, but it was the only way I could meaningfully compare without too much delay.  WRT to frequency measurements - it's just X7 as DAC, and then loopback to a soundcard (which has been calibrated to measure flat).  I now have some impedance adaptors - so I could probably redo the measurements next time under load.  These ones were just straight loopback though.
      Brooko, Oct 17, 2016
    4. csglinux
      Thanks Brooko! I will risk some hot-swapping in the name of science :wink:
      csglinux, Oct 19, 2016