In today’s feature, Lynn reviews the SMSL PA-X Gallium Nitride, a compact, balanced power amplifier capable of delivering up to 250W into an 8Ω speaker load. It is currently priced at $699.
Disclaimer: I received this sample in exchange for my honest opinion. Headfonics is an independent website with no affiliate links or partnerships. I thank Shenzhen Audio and SMSL for their support.
Click here to learn more about the SMSL products we have previously reviewed on Headfonics.
This article follows our current scoring guidelines, which you can find in more detail here.
SMSL is known for producing a multitude of DACs and headphone amplifiers. I have reviewed several in my time here, and others within Headfonics have as well.
Some are used as entry points into higher quality DACs, while others are oriented more upscale, such as the SMSL PL-200 and RAWPro-DAC-1.
The PA-X Gallium Nitride is first and foremost an amplifier. It can also be used as an affordably priced mono-block when using one for each channel.
While the features may seem to be pedestrian, I was nonetheless looking forward to this unit for what it can bring to the table: XLR inputs for use with a top-quality DAC, and its use as a two-channel desktop amplifier.
Sometimes simplicity is better than overcrowding an item.
Features
The SMSL PA-X uses Infineon’s latest Gallium Nitride (GaN) FET, with a switching frequency of up to 1MHz.
Instead of a rolling, or slow frequency response time, this 1MHz switching carries out changes much more quickly, with a (reportedly) more accurately represented signature.
The Texas Instruments advanced volume chip, PGA2311, is used, with more steps in the volume control along with purportedly an ultra-low distortion.
With Class-D power up to 250Wrms x2 in 4Ω, and 200Wrms x2 in 8Ω (Mono 8Ω: 500Wrms x1), the PA-X can drive a variety of speakers while consuming a fairly low 40W of power (nominal).
The PA-X also possesses overheating and over-current protection for those times it is driven past its capacity, something I did not approach in testing. An SNR of 115 dB allows for a large, expansive sound combined with very low distortion (0.003% THD).
Other high-end audio components round out the PA-X, helping to promote the listening experience, high power output, and demands of an amplifier.
Design
For a long time, SMSL was known for plain black boxes housing their wares. Then silver kicked in with a bit more flair.
The PA-X is of the latter, shod with a black plexiglass front cover. I wish more of that front cover was taken up with electronic responses, such as EQ or bitrate. Something to break up the long frontal plate.
That front plate has the necessary information on the left side, with the amperage of speakers set, volume, stereo or mono, and input level.
The black volume knob to the right can be used for volume or accessing the sub-menus. The front plate sits a bit above the aluminum case, so stacking should be done with care.
Those sub-menus include amp mode (input including pure amp mono), load type (4Ω or 8Ω), UI style (universal or graphic, which uses pictures of the input), dimmer (user settable), brightness, and reset, which resets to factory settings.
The sides have black plastic slotted “vents,” which would have been used not only to offset the all-silver but provide a heat release area; if they were ventilated. They aren’t.
The back panel has the on/off switch that can be left on for standby, two sets of banana plug (or wires) speaker jacks, a dual RCS source input, and dual XLR inputs, which can be used for mono as well.
I appreciate the heft of the PA-X, which means it has a hearty amplifier section as well as a heat sink inside, but I would have liked a bit more flair to the design.
As it is, though, the PA-X can occupy a place on your desktop or two-channel system unobtrusively, which is sometimes the better route.
I/O
The PA-X is a basic desktop amplifier with only XLR and RCA inputs and one pair of speaker outputs. The speaker choices are either 4Ω or 8Ω and can be set from the sub-menu “Load Type.”
The volume knob, which functions quite well, can be used to access the sub-menus besides volume changes. The functionality of the knob within those menus is exact and without play.
Simplicity in looks and functionality, the PA-X is meant to focus on the sound quality coming forth.
Controls
The remote, which is always good on SMSL models, provides all of the functionality needed. You can access each of those functions with a dedicated button as well as mute, raise or lower volume, and sub-menu options.
The plastic volume knob does the same thing with clearly defined detents for each volume level change or sub-menu change.
Wired Connectivity
The main hookup used was through the dual RCA cables for everything from my MacBook Pro to the FiiO JM21, the HiBy R4, and the Oppo BDP-83.
The CDs sounded more vibrant than either Tidal or Qobuz, which added some bass weight as expected.
I connected two different DACs, through the XLR input, the iFi iDSD Pro and the Geshelli Labs JNOG2.
Each DAC provided different sound qualities as expected, but the increased variety of input options made both worth it. Coaxial into the iFi was via the Oppo, and optical to the JNOG2, also from the Oppo.
Packaging & Accessories
The SMSL PA-X Gallium Nitride comes in a svelte-looking black box, complete with a vintage, rough feel to it. Lifting the lid, you are presented with a well-protected unit and the accessories.
Those accessories include the plug-in, remote, and a dual RCA to 3.5mm SE jack cable. The warranty card is included, and a quick start guide.
The only addition I would make might be dual RCA or XLR cables. But since we all seem to have extra of everything, that is not an issue.
Sound Impressions
The following sound impressions were made using the HiBy R4, FiiO JM21, a MacBook Pro, and Oppo‘s BDP-83 as sources.
Outputs ran to my office KEF Q150s, and briefly through my main two-channel Klipsch Forte IIs. Pairing included the iFi audio iDSD Pro and Geshelli Labs JNOG2 as dedicated DACs.
Summary
To me, most SMSL units are known for a neutral(ish) signature that can lose note weight in some parts. While the sound emanating from within is vibrant, you might wish for weightier notes.
The PA-X delivers very good note weight to go along with a vibrant character that is neither too thick nor too thin in quality. I never had to raise the volume level too high, either.
Most of the time, I limited the source volume, so I could press the KEFs through the PA-X, with good results. I never came close to the maximum headroom of the PA-X, volume-wise, which speaks to the power in reserve.
The treble region comes across with good extension and a presence that ties nicely to the midrange, which sits even with both ends.
Punctuating bass notes held tight, with little decay adding to a sharpness that prevented note weight from becoming too elongated. The attack was quick as well, giving a good, succinct definition to the notes across the spectrum.
The PA-X has that neutrality, which allows it to pair with different sources, imbuing the character of the source or DAC nicely.
Timbre
The SMSL PA-X comes across with good note weight combined with a nearly neutral signature. There is a bit of warmth to the sound, but the Infineon GaN FET transistors keep the delivery speedy, making for that near neutrality.
Slightly longer decay would elongate the note weight even more, but under the circumstances, I do not miss that.
There are plenty of warm-sounding sources on the market, and when taken together, you can pair the PA-X with one of those to tailor the sound. Or pair it with a flavored DAC to suit your needs.
The PA-X tuning pushes the midrange slightly forward, but not at the expense of either end or near-neutrality. I did find that to get the best details out, the volume must be pushed higher than one might expect, but there is plenty of headroom for that.
The ability to pair with a comparable DAC makes for an enticing Opportunity to play around with the sound, too. This is where the iFi and Geshelli Labs came into play, and both represented a positive effect on the PA-X.
Staging & Dynamics
The 3D effect of sound emanating from the PA-X was to be expected and did not disappoint. This makes for an excellent two-channel setup that is neither too expansive nor too intimate.
The height moves well above the KEF Q150s and Klipsch Forte IIs, while presenting good width as well.
The depth of the soundstage complements both the X and Y dimensions with good imaging and instrumentation. Dynamically vibrant to a point, the combination of the soundstage and instrumentation complements each other, too.
I found the PA-X worked equally well in small and large spaces (albeit my unfinished larger room), taking on the character of the speaker and placement. This is probably too much for a small room, unless it is an office or workroom situation, due to the immense reserves of power.
Dynamically, there is good separation to go along with the note weight, which makes for a nice spherical aspect that punctuates in all three dimensions as well.
The more vibrant the source music, the more vibrant the presentation, with the PA-X essentially providing the avenue with which to listen.
Synergy
Power
In the older days (and today in some respects), power ratings were erroneous in presenting capabilities. A 500W “sound system” couldn’t drive bookshelf speakers without sounding thin and overextended.
Conversely, moderately powered amplifiers could drive what are considered hard-to-drive speakers with ease.
The 250Wrms rating of the PA-X is a mix of both. Gobs of power for harder speaker applications, but enough finesse to drive inefficient speakers, too. This power is provided with the blackest of backgrounds in delivery, too.
The PA-X never had an issue driving anything that came its way from the aforementioned KEF & Klipsch speakers. 250Wrms is nothing to sneeze at, and I do not doubt that the SMSL can drive most moderately power-hungry speakers.
I was able to hook the Forte IIs up and power them without trouble, just like the KEFs.
Pairings
You might decry the dearth of input opportunities on the PA-X. This would be an incorrect assumption, knowing how versatile the XLR and RCA inputs can be.
The ability to run analogue from a DAP, CD player, or cassette deck should not be overlooked. Throw in the XLR inputs and a comparable DAC, and the Opportunities expand almost exponentially. Knowing this, there is no reason for more options.
Running the BDP-83 through the RCA connection was not its best option, but completely workable, and the PA-X provided plenty of punch to the sound. Adding in the iFi iDSD Pro as the DAC afforded more options, which I gladly took advantage of.
The iFi iDSD Pro added the GE tube flair, giving excellent note weight and warmth to the PA-X that complemented the power quite nicely.
The iFi duo is “older” but still sees regular use in my systems. Adding the SMSL provides a bit of a different change, with the ability to use speakers instead of “just” headphones or powered speakers like the iFi iCAN Pro.
The Geshelli Labs JNOG2 is almost the polar opposite of the iFi, with a crisp nature that exudes accuracy and detail instead of the tube-like warmth and richness.
When paired with the PA-X, the JNOG2 showed good promise with genres that rely upon accuracy and crisp detail retrieval.
With the ability to have both the iFi and Geshelli Labs hooked up, using RCA (iDSD Pro) and XLR (Geshelli Labs), you have excellent alternative source options to meet pretty much all of the listener’s needs.
Using either the FiiO JM21 or HiBy R4 from the 3.5mm SE out into the RCA provided a good option, and one that allowed each source to show its merits.
