Drop + SMSL HO150X Review featured image

Drop + SMSL HO150X Review

Today, we review the Drop + SMSL HO150X, which is a desktop linear headphone amplifier with a balanced circuit design and preamp capability. It is priced at $179.

Disclaimer: This was sent to us as a sample in exchange for our honest opinion. Headfonics is an independent website with no affiliate links or services. We thank Drop for their support.

To learn more about Drop products previously assessed on Headfonics you can click here.

Please note, that this article follows our current scoring guidelines which you can read in more detail here.

Drop + SMSL HO150X Review featured image
Drop + SMSL HO150X Review
The Drop + SMSL HO150X linear headphone amplifier exhibits a reliably consistent performance and one that indicates how close it adheres to the concept of neutrality and also makes pairing a fun challenge.
Slide here to add your score on the gear!76 Votes
Dependable setup for transparency
Three-level gain for IEMs and headphones
Includes RCA pre-out sockets
Imaging placement is sometimes inaccurate
Reader's Score

There’s a handful of Drop products we reviewed in the past but not all of them enjoyed the same amount of craze created by the THX AAA 789 headphone amplifier.

After a lot of reviews and customer feedback came out, it was undeniable that a lot of enthusiasts recognized it for its so-called “wire with gain” quality.

Drop continued to collaborate with different manufacturers since. But having focused on other markets, the wave of the THX AAA 789 naturally died down. I only know one person who still has this amplifier around.

Well, Drop is now back with another exclusive headphone amplifier that adds virtually zero coloration to the sound called the HO150X. This is a partnership project with SMSL, a company that also shares the spirit of producing well-measuring audio equipment.

The HO150X sits somewhere in between the SMSL’s own HO100 and HO200 headphone amplifiers, picking up features that aim to bring back the acclaimed “wire with gain” sound of the THX AAA 789 to enthusiasts’ desks.

Drop + SMSL HO105X design

Tech Highlights

The Drop + SMSL HO150X is a compact fully balanced headphone amplifier with a pre-amp output capability. The goal of the design was to reach complete transparency from DAC to a headphone or essentially reach for the hallowed ‘gain on wire’ description.

Since we’re talking about SMSL, you won’t find THX amplification technology inside this amplifier. Instead, the company’s Precision Linear Feedback Circuit (PLFC) is proudly stepping up for the challenge.

A vital feature it inherited from its SMSL peers is driving power. Sharing the sway of the HO200, the HO150X will comfortably keep most gears out there sounding dynamicand with plenty of headroom.

The HO150X is listed at a hefty 6W for 16Ω loads, dropping down to 3W for higher 32Ω gear, and a pretty respectable 550mW into more demanding 300Ω headphones. Note, that both balanced and SE outputs offer the same rated output power measurements with a sub-ohm output impedance.

There are three hardware gain adjustments present to increase or decrease the headroom of the volume wheel to preference. 


Another advantage of the HO150X is its incompact form factor, a diminutive size that’s openly derived from its other SMSL heritage.

Doubling the power of the original HO100, owners of this amp may salivate after learning about the HO150X’s beefier circuitry without needing any extra physical space. After all, who doesn’t want more power?

Those who have bought the HO100 can breathe a sigh of relief. Having the two in front of me, it is safe to say that the Drop version is slightly less posh. Still, SMSL tastefully dropped elements from the original only to set the HO150X apart, and to ensure no appeal is lost.

The most obvious swap that happened is the missing luster of the front plate. The new material is a matte finish with a slightly rougher texture when touched.

What’s not discernible until I toyed with the two units next to each other is the cheaper impression I got from the HO150X volume wheel. It does follow the design of the HO100 but the build and rotating action are not as smooth.

Drop + SMSL HO105X rear panel


Interestingly, the HO150X pretty much covered the essentials of the THX AAA 789. I’m certain that someone from Drop or SMSL decided they wanted to stay on par with this renowned amplifier.

Prominently placed in the center, there is a 4-pin XLR socket on the HO150X in place of the 4.4mm of the HO100. Those who have already embraced 4.4mm balanced cables though will have to use an adaptor.

This happened to me when I tried to use the Sivga Nightingale and realized I had the wrong termination to match.

The HO150X has an extra pair of RCA sockets to add pre-out amplification to its list of tricks just like the THX AAA 789. Do note that the rear IO can get confusing since SMSL forgot to place a label beside the sockets.

To save you from having to read the manual, the RCA and XLR that are next to each other are the ones for input.

Drop + SMSL HO105X controls


Once plugged in, press the power button on the left side of the HO150X to power up the unit and make sure the button is lit plus wait for an audible click from a triggered internal relay in the beginning. Then you know the amplifier is properly turned on.

Built in the same form factor as the HO100, the HO150X mirrors its set of controls though it is missing out on the dedicated switch for selecting between the front and rear outputs of the pricier HO200.

In any case, the key advantage here for users is that by using straightforward analog toggles with clearly labeled functions, the HO150X turns into a very simple box to master.

Packaging & Accessories

While the first word you’ll most likely read on the cover of the HO150X is the ‘Drop’ badging in crisp and bold print, there’s still no denying its true origin. Easily relatable to how SMSL shipped all their other products, the HO150X comes in the same box as the HO100, only differing in the material used.

So, just like the HO100 unboxing, the inside of the package is pretty straightforward to unbox. An average-length power cable is the lone item on its accessory list.

Aside from that, there’s not a lot more going for accessories, so most of the weight is packaging foam and the unit itself.

Drop + SMSL HO105X accessories

Sound Impressions

The following impressions were created using the Audio Technica ATH-ADX5000, the HarmonicDyne Zeus Elite for my main headphone pairings, and the Burson Conductor 3 Reference for the main DAC pairing.


I was able to try the legendary THX AAA 789 some time ago from a friend for a few hours. Honestly, I found it a bit lifeless, even sometimes too clinical, for my taste. My impression of the HO150X however is a little bit more surprising.

To my ears, the HO150X is placing broad-sounding beats slightly above linearity. We’re talking minimal amounts here but the occurrence has an inviting entrance preserved by an adequately roomy stage.

The punch is a bit held back to supportively convey a dynamic beat. Wait for a tighter bass line however and the more honest side of the HO150X emerges. The timbre and bite are also crisp and detailed.

For a sub-$200 amplifier, I found the vocal presentation of the HO150X impressive. I can see the faithfulness to the source but thankfully it didn’t lean too far towards blandness. Breathier sections are also textured pretty well and not hard to find.

Shoutier parts can show unevenness in placement. The bigger image size of the upper midrange and its upswell in energy eclipses some of the images playing further back.

Interestingly, plucks of guitars were displaying a friendlier twang than I expected. I confirmed this by listening to two other reference amplifiers I have here and the HO150X turned out to be the nicest sounding out of the bunch.

I can’t say the same for electric guitar riffs since they feature a more uncolored ton at full pelt. Meanwhile, the flavor of the horns is a bit more steely than normal on brighter parts. However, with a dynamic quality that’s able to show the gap between what’s loud and not, a typical instrumental ensemble produced an airy and enjoyable show.

Staging & Dynamics

The HO150X is strong in its adherence to its “wire with gain” promise by keeping the staging width pretty accurate. Having the ability to create a spacious rendition on the right track, it only gets held back by the sometimes uneven image placement.

Briefly mentioned in the previous section, the HO150X sometimes scales voices bigger than normal, especially around the upper midrange. This and bass-heavy songs will use up more area of the soundstage.

But to be fair, it is quite a nitpick though since I’m only noticing it on tracks that I’m very well familiar with.

With a pretty decent resolve, a live recording is played back with enough height to diffuse and add to the realism of an exciting scene. It pushes the clapping of the audience out which causes the images to cluster instead of properly separating.

Click on page 2 below for our recommended pairings and selected comparisons.

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