General Information

The THX AAA-888 Offers Extreme Clarity

The THX AAA lineup of amps are known for their power and clarity. Unlike many amplifiers, THX AAA amps use a feed-forward error correction topology that removes common distortion issues. To put it simply, the amp measures errors in an early part of the system and corrects them in a later part of the system.

The THX AAA-888 is the most sophisticated iteration of the lineup. Its distortion levels are seriously low. Signal-to-noise ratio is 137dB, meaning that you’d have to crank the amp up to 138dB before hearing any hiss. And unless you’re trying to permanently damage your eardrums, you’re probably not going to do that.

Desktop Friendly

Despite its massive output capabilities, the SH-9 is actually quite small. At 7.3” on its longest size, you should have no problem fitting it onto most desktops. And as we said, it’s designed to stack with the SU-9. The stacked pair are a modest three inches in height.

Product highlights

  • THXAAA-888 Headphone Amp with THX AAA Technology
  • 6W into 16Ω, 3W into 32Ω
  • Frequency response: 0.1-500,000Hz
  • SNR >137dB
  • THD <0.00006%
  • Ultra-compact design that’s perfect for desktops
  • Balanced stereo headphone output
  • Balanced stereo line input
  • HIgh precision resistors for temperature stability
  • Pop-less design with high-quality relays
  • 256-level relay volume control
  • Switchable gain control
  • 1.9” LCD display
  • Remote control
  • Inputs: 1 balanced, 1 unbalanced
  • Outputs: 1 balanced, 1 unbalanced
  • Output power
    • 6W x 2 (16Ω)
    • 3W x 2 (32Ω)
    • 440mW x 2 (300Ω)
    • 220mW x 2 (600Ω)
  • Output noise: 1.9uV, A-weighted
  • THD+N
    • -123dB, 0.00006% (A-weighted)
    • -117dB, 0.00013% (20-20kHz, 32Ω, -3dB)
  • THD: -125, 0.00006% (1kHz, 16Ω, -3dB)
  • Input impedance: 47kΩ
  • Output impedance: Near 0Ω
  • Gain: Low (+0dB), High (+10dB)
  • Power supply voltage/frequency: AC100-240V, 50-60Hz
  • Power consumption(EN60065): 24W
  • Power consumption in standby mode: <0.1W
  • Size: 7.38 x 6 x 1.5” (187.5 x 154 x 40mm)
  • Packing size: 11.1 x 9.1 x 3.1” (282 x 232 x 79mm)
  • Weight: 1.7lbs (790g)

What’s included

  • SMSL SH-9 THX AAA-888 Balanced Headphone Amp
  • Remote Control

Latest reviews

Pros: Sound is super clean and detailed. Scales really well with different DACs. Doesn't sound super cold and clinical. Decent power output.
Cons: Not truly balanced. Missing a few EQ features the old SH-8 had. Gets toasty after a bit. Still a bit warm sounding amp compared to other good measuring amps.

What I always felt made the now old SH-8 special was that at the time you could get a nice balanced amp for only $190. It was on the fairly neutral and somewhat boring sounding amp on its default setting but it has an on board EQ so you could fine tune it a little or even use their SDB setting which gave the amp SMSL’s own flavor of sound. Power output was only a little under 800mW when using balanced so It lacked some power as well. The SH-8 was mostly my main amp for the last two years and I very much enjoyed using it daily. When I saw the new SH-9 amp announced I was really interested to see what the upgrade could bring to the table over the SH-8.

Thanks to ShenzhenAudio for hooking me up with a review unit. While I always appreciate stuff being sent in to test and review, It never affects the ratings of my reviews.

More info on the SU-9 plus the purchase link will be below!

Gear used

IPhone 12 Pro via RCA, SMSL SU-8/9, iFi NEO, Ikko OH10, ADV M5-5D, LCD2C and Dan Clark Audio Aeon flow “RT” closed.

Looks and Feel
Much like the SU-9 I recently reviewed, I really like the looks over the now old SH-8. The included lcd screen and included remote makes for a nice upgrade over the SH-8. The back of the unit is fairly simple with a XLR in or RCA in. I was slightly bummed the SH-9 has no outputs at all. I felt they could have had pre outs for at least RCA.

Accessories and unboxing
I had the exact same unboxing experience as the SU-9 I just reviewed. There is a remote included with the amp which is awesome. The older SH-8 didn’t include a remote which was always a bummer.

While I really appreciate the new UI over the old SH-8, it’s a little easier to simply use the remote to change things. I don’t mind that no physical switches were included on the device. It’s fairly uncommon for me to switch gains constantly and it’s easy enough to swap between the inputs or gains using just the volume knob if you're not willing to fetch the remote.

Volume knob
I really like the little relay system in place for volume control. This, from what I read, is a little rare and mostly in more expensive amps. There are two settings for the volume relay control. The default setting(off) means any single adjustment in the volume knob will activate the relay which results in a click noise. The second option(on) means you can adjust to a volume number you may know you like and then the relay will activate once and adjust the volume to your intended selection. I leave the setting to change with each volume step since I don’t like having to wait for a relay to activate and lower or raise the volume I want. It’s claimed to save the relay lifespan but I rather have instant volume changes. Plus I I've read these kinds of relays have super long lifespans.

These will be my impressions overall with the SH-9’s sound signature when used with all the iems/headphones and few DACs I threw at it.

Lows take an accuracy approach for the most part depending on the DAC. There is good quality and decent thumps in the low end. This isn’t a clinical low end and things still sound fairly dynamic and musical still. That being said, if you want to add bass to lean sounded headphones, this won’t really help much. Since the onboard EQ that the SH-8 had is missing, you will have to software EQ if you wanna adjust the general sound to a boosted low end if that’s what you want. Some DACs like the now old SU-8 sound a bit more low end boosted due to how warm sounding the SU-8 is.

Mids come through with extreme accuracy and on the three main DACs I used, they all tended to have a little recessed feeling with the vocals. This makes for a lower volume of the voices while instruments sound a little louder and closer to your ears. I personally like it this way so for me it was fantastic but for others it may differ.

The highs come through very detailed depending on the DAC used. This is also a very accurate sounding amp for the highs and things can come through either neutral or bright. On something like the SU-8 or iFi NEO, Things can sound warm and relaxed up top. When paired with something like the SU-9 you start to creep into a brighter top end. This of course will depend on what you have plugged into the SH-9 headphone wise. The SH-9 doesn't suffer from sounding super bright however like some prior well measuring amps do.

The common thing I noticed here was that the stage feels a little average on width no matter what DAC I use. The depth was what changed the most depending on the DAC it was plugged into. While it won’t go crazy deep, it still gave a nice deep feeling on both the SU-9 and iFi NEO. Imaging was great across all sources but I believe this is a little more dependent on the DAC than it is on the amp.

Single ended output/Balanced outputs
I decided to make this one section since one thing missing on the SH-9 is a truly balanced amp design. Sure, there are balanced XLR inputs on the back and a 4pin XLR jack on the front, yet it’s still a single ended layout inside much like their SP200. I have mixed feelings on this since the old SH-8 is a truly balanced design and SMSL decided to make their SP400 which costs about twice the amount for a truly balanced design. That being said, both the single ended and balanced jacks produce zero noise, to my ears, on my sensitive iems. I was fairly impressed by this. There are also 3 watts on tap for both jacks so I really like that it will power my current gear and most of the headphones I would plan to buy down the road. Very impressed with the power output for the price.

XLR vs RCA inputs
Well since the SH-9 isn’t balanced, one might be wondering why anyone would use anything other than the RCA inputs for the SH-9. While using XLR isn’t necessary, one advantage is that most DACs output higher voltage via their XLR outputs. So when something like the SU-8/9 are going XLR into the SH-9 you get a much louder volume vs RCA. While running RCA from the SU-9 had a volume of 32/99 for my M5-5D, switching to the XLR input made it so that 22/99 was the same volume that I liked. Something to think about if you’re choosing whether or not to feed the SH-9 balanced cables or not.

Iem pairing opinions


I use the OH-10 pretty much as my daily iem for either on the go or relaxed listening. The OH10 still retains it’s warm signature but you can hear a little more detail making its way into the iems. Soundstage sounds a hair narrower but depth is noticeably better. The OH10 does fairly well overall and I had no complaints listening to it out of this amp.

Campfire Andromeda and ADV M5-5D
I run both of these together since they both can pick up the floor noise/hissing fairly easily from an amp, especially when run balanced. I had zero noise from both the single ended and balanced jack. The balanced XLR jack isn’t really balanced but I was still curious if I would still pick up some noise. The original andros felt a little lean in the low end. I still think it does well for an all BA design. I just wish I still had the on board EQ settings that the SH-8 had so I could adjust the sound to fit the andros a hair better. Mids and treble sounded great as they should with the andros. The M5-5D had excellent bass and mids. I love testing gear with the 5D as it handles low end and mids well with it’s bigger DD driver. The other 4 drivers are all dedicated to the higher frequency range which means they get super bright super quick on clinical devices. This was no exception with the SH-9. With that being said, It was simply dipping its toes into sibilance at times. I’ve heard this set get very sibilant on other gear to the point I simply stopped using the 5D with that gear. Using both the SU-8 and iFi NEO helped calm the top end a bit with the 5D. Brighter headphones may wanna think about a warm amp to pair with the SH-9 if they don’t like their top end possibly hot.

Over ear pairings

Dan Clark Audio Aeon “RT” Closed/ LCD2C

I put the poor “RT” through the testing ringer quite a bit. It has started showing a bit of channel imbalance so it got sent off for repair pretty much the day I got the SH-9 in. The little time I got to listen with it was a great experience. It performed fantastically with the SH-9 overall. It lost a little low end due to the pairing at the time which was the SU-9/SH-9 stack. I will adjust my review when I get the Aeons back if things sound different with the other DACs that are warmer sounding. The LCD2C also sounded very good here as well. I barely use them these days since I like the balanced sound of the “RT” Aeons. I never liked what felt like a compressed warm sound signature that my LCD2C produced vs the Aeons. The 2C sounded cleaner than what I was used to once it was paired with the SH-9 stack. Still a warm headphone but I felt like I was getting a little more detail and clarity out of these. Both were easily driven by the SH-9 to volumes I personally like.

Overall thoughts
While I’m bummed that the SH-9 isn’t truly balanced and missing the on board EQ settings of the SH-8, I was still really impressed with the performance overall. My favorite pairing was with the SU-9 DAC. I think the SH-9 does scale really well with any DAC you plug into. I’m happy that for an extra $100 over the SH-8 you get a decent power output upgrade, a better display, the remote and easier to use UI. This is another winner in my book from SMSL and I definitely recommend the SH-9! All my headphones performed outstandingly and my angry/sensitive iems didn’t pick up any noise which was fantastic! Great job to the team at SMSL. Thanks for reading!

Last edited:
I've just taken delivery of the SH-9, well 4 days ago & very pleased with it I am too. It's so good to have a headphone amp with a proper remote volume control without breaking the bank. I bought it from Shenzen but through Amazon UK. It cost a little more than buying direct but I would probably have got hit with import duty anyway. The other good thing was delivery was expected to be between the 6th & 20th January 21. It actually arrived on 31st Dec which was a nice late Christmas present. I'm currently using it with the Topping E30 DAC but will probably buy the SU-9 soon. The only thing I don't like so far is the fact that the screen is so bright, even at its lowest setting its bright. I wish it had an option for it to time out, maybe that could be added with a future firmware update. The only cans I've used with it so far are the Quad ERA-1's & it drives them just great. 👍
The old SH-8 had the option to have the screen turn off after a few seconds. I don't know why the feature is missing on the SH-9. I personally don't mind the light and prefer it for my desk setup.
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