The Drop + SMSL HO150X was kindly provided free of charge in exchange for an honest review. I didn’t receive monetary or any other kind of compensation and I don’t use affiliate links. The regular price of the amplifier is $199 but currently is on offer for $179 and available exclusively from Drop.
Introduction
Do you remember the Drop THX AAA 789 headphone amplifier? It’s been over half a decade since the launch of this linear headphone amplifier that brought exceptionally transparent amplification to audiophiles around the world who were seeking the so called “wire-with-gain” kind of amplification. The THX AAA 789 was very successful because it did what it promised and performed well without any serious drawbacks except maybe the scratchy pot, the sharp cornered chassis and the bulky external power adapter. It sold hundreds of units and many audiophiles are still using it on a daily basis. After so many years in production the amplifier eventually became EOL and Drop decided that it was time for a successor.
Drop + SMSL HO150X
For its successor, Drop have partnered with SMSL, a ubiquitous audiophile brand that raised the bar for clean audio with its Precision Linear Feedback Circuit, achieving distortion levels as low as 0.00007%. Working closely with SMSL’s engineers, they took the output power of the brand’s highly regarded HO200 amplifier and fit it into the smaller HO100 form factor. They also made sure to fit in several requested features, including balanced inputs and outputs, a dedicated preamp circuit for active speakers, and an intuitive three-position gain switch. The final product is the Drop + SMSL HO150X linear amplifier.
So, what does it mean for an amplifier to be a “wire with gain”? The answer lies in what such a device gives and doesn’t give. It gives the ideal amount of signal to power a source to its full potential. It doesn’t give any unwanted coloration through its amplification. The SMSL’s aforementioned Precision Linear Feedback Circuit is meticulously tested to reach distortion levels as low as 0.00007%, while maintaining a flat, uncolored signal from input to output. It’s also due to the inputs and outputs themselves, both of which include balanced options that cancel out noise by carrying polar-opposite signals.
Appearance and build quality
The Drop + SMSL HO150X follows the usual SMSL studio-like design with some modern elements. The amplifier has a rectangular chassis, in black matte finish, with well rounded corners and edges. It is entirely made from aluminum alloy which is lightweight and offers good shielding against EMI. The volume knob is also made from aluminum and the potentiometer turns very smoothly. This is one of the best ever made Drop products with excellent craftsmanship and finish without anything negative of notice.
Well, except from the plastic push button that is used to power the amplifier and lights in an orange color when pressed. I would rather prefer the usual SMSL toggle switch with a separate indicator LED but I guess that they had to design something different to add some kind of uniqueness to the Drop iteration of the product. The Drop + SMSL HO150X dimensions are 15×12.8×3.9 cm only so it is super compact and can fit virtually anywhere.
Operation
This is a headphone amplifier so you don’t need a PhD in engineering to operate it. At the back side there are the XLR and RCA stereo inputs, that can be left simultaneously plugged and the RCA stereo preamplifier output which automatically functions when you unplug your headphones. The Drop + SMSL HO150X features a low noise, internal power supply and the only thing you have to do is to plug a power cord to the AC input at the back of the chassis.
At the front face you get 6.35mm and 4-pin XLR headphone outputs, gain and input selection toggle switches and the volume knob. Due to the small size of the chassis it was nearly impossible to fit an extra 4.4mm headphone jack and although I would have preferred it instead of the XLR, you may think otherwise and be happy with the current layout.
Power output and noise
On the amplification side, the Drop + SMSL HO150X packs a healthy 6W of maximum output power at 16Ω, 3W/32Ω, 550mW/300Ω, pretty impressive numbers for the size and certainly enough to drive any pair of headphones. The power output numbers provided by the manufacturer are the same for both the balanced and unbalanced outputs thus indicating that the amplifier does single ended only amplification and the 4-pin XLR output is there only for convenience.
The amplifier has three gain settings: Low (-12 dB), Middle (0 dB) and High (+12 dB) so it is very versatile and adaptable to various loads. It did well with every headphone that I have tried, from low Z planars, like the HIFIMAN Susvara, to high Z ones, like the Drop + Sennheiser HD8XX. I have also tested the low gain with various IEMs where the Drop + SMSL HO150X proved to be dead silent without any background noise and with good adjusting range on the potentiometer.
The amplifier is very efficient as it consumes considerably less than 30W and it stays pretty cool even under stress conditions. As per usual practice the amplifier was left playing music for about 100 hours before listening evaluation. All headphone and power cables are made by Lavricables .
Listening impressions
The Drop + SMSL HO150X performs exactly as advertised, it is essentially a “wire-with-gain” which provides plenty of undistorted power and has a sound signature which is impressively transparent, flat and uncolored with class leading fidelity. The SMSL HO150X acts as an intermediate between your source and headphones without subtracting or adding anything that is not already present in the sound making sure that what you actually hear is the combined sound character of your source and headphones.
At this point it is essential to focus on the second part of the above sentence where it says that the SMSL HO150X is not adding anything of its own to the sound. Sometimes such linear and transparent amplifiers are accused of sounding sterile and clinical or for adding artificiality and additional brilliance to the sound. Thankfully this is not the case with the Drop + SMSL HO150X and I assure you that it is not going to add any kind of brightness, harshness or anything else negative that is not already there.
Of course at the same time this is not the kind of amplifier that you can use to make your music sound warmer, fuller, more visceral, harmonious or anything else similar. This is not the amplifier to buy if you wish to manipulate the sound character of your gear.
On a technical level the Drop + SMSL HO150X is pretty impressive with a dynamic and impactful low end, fast transients, excellent clarity, great definition and expansive soundstage. It is really fascinating how successfully this low price amplifier can match with very expensive components without hampering their audio performance. You can use your flagship DAC and headphones with the Drop + SMSL HO150X stuffed right in between them and it will act as a transparent filter but at the same time it is unable to help the chain sound better and reach peak performance.
Comparison
Having reviewed both the SMSL HO200 and HO100, that are the parents that gave birth to the Drop + SMSL HO150X, I can positively report that the child successfully combines their best characteristics with just a few meaningful sacrifices. It is essentially the same size as the HO100 but it adds a preamplifier function and offers the same power output with the HO200 while only lacking the truly balanced circuit and the XLR preamplifier output of its father. Additionally, when compared to its ancestor, the Drop THX AAA 789, the SMSL HO150X is leaps ahead in build quality, it has a smaller footprint and better audio performance, mainly because it avoids sounding slightly sterile and bright as the Drop THX AAA 789 did.
In the end
Mission accomplished. The brand new Drop + SMSL HO150X is a successful fusion of the SMSL HO200 and HO100 which cleverly combines their best characteristics. It is a compact sized and very powerful headphone amplifier that is as transparent, flat and achromatic as only a “wire-with-gain” can be. Greatly surpassing in build quality and audio performance the legendary Drop THX AAA 789, this amplifier is tailor made for anyone looking for pure, undistorted power to drive the most demanding loads, without adding or subtracting anything else to the original signal and all these without the need to spend a fortune in order to achieve it.
Copyright – Petros Laskis 2023.
+ Flat, transparent and achromatic + Crystal clear and dead silent + Powerful without distortion + Great technicalities + Will not add or subtract anything to the original signal + Will not add brightness or sharpness + Small form factor + Balanced 4-pin XLR output plug + Balanced XLR input + Three gain settings + Preamplifier output + Internal power supply + Excellent build quality + Value for money - A 4.4mm plug would be more convenient - Plastic power on/off button - Not really balanced circuit
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