SMSL, like many other chinese amplifier and digital-to-analog converter (DAC) manufacturers, continue to come out with newer, lower cost and high performing devices and today we are going to review the new SMSL HO100 and DO100 headphone amp and DAC units. This "stack" was sent over by Aoshida Audio for review.
The SMSL HO100100 headphone amplifier sells for $149 USD and can be purchased here: https://aoshida-audio.com/products/smsl-ho100
The SMSL DO100 DAC retails for $239 and can be purchased here: https://aoshida-audio.com/products/smsl-do100
Non-Sound Stuff
Like many recent headphone pairings, these two form an ensemble when stacked on-top of each other with the exact same chassis dimensions and appearance. Both boxes are rather small at 150mm x 128mm x 39mm each. That's just about 6 x 5 x 1.5 inch in US non-metric units. Each of these are dressed in black with a glossy glass finish on the front, and connections on the back featuring grounded IEC-standard power plugs.
Both units feature balanced XLR and non-balanced RCA connections. The amp only has inputs, making it not viable as a pre-amp to powered speakers. The DAC however can be used as a preamp to speakers as it also have volume control functionality.
The DO100 DAC includes a lot of input connections, however. There is a USB-C input that is primarily what I used, connected to my desktop PC, and also coaxial and toslink optical connection inputs. Just above these ports is a detachable antenna for bluetooth 5.0 connectivity (LDAC, APT-X HD, AAC are supported).
The DAC also features a remote which can control the volume, choose inputs, and swap from one of the several digital filters included with the ESS ES9038Q2M DAC. This units a pair of the mobile version of the 9038 DAC, and is outputted through 4 dual OPA1612 op-amps.
The headphone amp has flip switches for on/off, XLR/RCA inputs, and to choose one of the three gain modes. The front panel also has headphone output through a standard 1/4 inch unbalanced jack, or a 4.4mm balanced option.
Finally, my favorite part of this stack is the volume knob. While the DAC one is a stepped digital knob and not my favorite, it does the job and feels good enough, the headphone knob on the headphone amp is very well done. It's an analog pot but the size of the volume knob and its smoothness and the small level of resistance feels really nice while turning it. It's not the best knob I've tried, not even close, but it's a big step up from previous SMSL headphone amps in general that I've tried/owned.
Sound Stuff
For the majority of this review, I set the DAC filter to Linear, fast-rolling. I didn't spend a lot of time on other filters but for the most part, this filter, apodizing, and brickwall are very much the same, with the steepest cliff at the Nyquist frequency and least amount of roll-off.
For connection, I used XLR to XLR to give the setup a fully-balanced setup. This also bumps the output voltage of the DAC to the amp. In addition, I used both 4.4mm balanced and 1/4 inch unbalanced in my trials, however a lot of the times, I used 4.4mm when given the option.
Power Planars
My first test was to see how much power the headphone amp has. I tried a series of planars. My first use came with the Hifiman HE400SE. This is a budget Hifiman set that I absolutely love for its good sound, lightweight, and cost to performance ratio. The setup was able to drive these headphones pretty well. I was fine on mid gain, and thought the HE400SE was very punchy and dynamic, with good body. The 400SE has a little bit of a elevated upper-mids and low treble, and unfortunately, the SMSL setup was pushing the peaks a bit more than I'd like for many songs that present strong notes here. It wasn't necessarily fatiguing, but it was noticeable.
I then threw on the Audeze Sine, which is an older closed-back planar that also requires a bit more power than you'd expect. Again, this IEM has a forward mid-range and does peak in the upper mids around 3KHz. While some amps may soften this peak, the SMSL stack exemplifies it a bit, providing perhaps an uncolored sound that is more raw and unforgiving. All in all, this was not one of my favorite combinations I tried with this setup.
Finally, I took out the Hifiman Susvara, which demands a lot of current. Hifiman recommends 2-4 Watts at 50 Ohm, which is pushing the scope of the HO100's 3 Watt at 16 Ohm specs considerably. Still, the Susvara was able to get loud enough for my listening preferences (roughly 70dB SPL at 1KHz) at around 12 o'clock on the knob on mid-gain. The Susvara proved to be a bit challenging of a listen though, as I found the same sharpness in the upper-mids to be present here, although the sound was punchy and generally fine. After a little bit of an adjustment period, it wasn't too bad actually, and I enjoyed the listen.
I went back and forth with my normal audio setup, a much more synergistic pairing of the Bakoon AMP-13R and Holo Spring 3 KTE and compared to the incredibly cheaper (on a magnitude of scale) SMSL stack, and the Bakoon/Holo combination was warmer, more smooth overall with quite a bit more refinement across the spectrum. It's also quite a bit more powerful than the SMSL HO100, which helps give the juice the Susvara needs.
Sennheiser Tests
Power aside, I spent most of the time using the SMSL stack with a combination of Sennheiser HD600 and HD580 headphones, and a series of in-ear monitors like the Hidition Viento custom, Unique Melody custom, Empire Ears Odin, Tin Hifi P1 Max, and the Thieaudio Elixir.
For the most part, these series of IEMs and headphones have a generally warmer sound than the planars I wrote about above and the pairings seemed to work a bit better. They also demand quite a bit less power too.
The HD580 and HD600 were good combinations here surprisingly. Both are very similar headphones from Sennheiser with the 580 being a little more open and bright, while the HD600 a little more relaxed. Both were given a nice punchy low-end and more smoother sounding treble.
I spent a good chunk of an afternoon listening to various songs from Matt Nathanson, Sugarland, and the like, on the HD600 and the HO100/DO100 stack and found it pretty enjoyable for an entry level audiophile setup.
On many pop songs, I was impressed with the punchiness and impact that the setup provided the HD600, which isn't exactly known for its bass performance. The midrange wasn't hampered by this setup either, so I was generally pleased with the results.
IEM Pairings
The first time I look for when I plug a set of IEMs in is how much noise is generated from amp noise, and if the output impedance changes the frequency response of some of my IEMs. In this case, none of my IEMs seemed to have issues here as the backgrounds were very dark and no noise was present. Now that said, I don't have anything as sensitive as a Campfire in-ear like the Andromeda, or the Vision Ears multi-BAs, but for the various hybrid, tribrids or multi-BA IEMs I own, none had issues.
With the Odin, I was a little worried if I was going to lose some of the dynamics with this SMSL pairing. If you've read previous reviews, I absolutely love this in-ear, and it sounds really fantastic with almost everything I throw at it, but I was terribly disappointed with how it sounded off the Topping A90 headphone amp, however I have used it with the lower-priced A30 with good results. In this case, I enjoyed the punchy character of the HO100 amplifier here, and felt it was well done. While the treble is borderline a little bright and pairing with an already slightly bright upper-mids focused Odin may not be the best synergy out there, I still was able to comfortably listen to this set.
With a darker IEM that demands good dynamics like the Thieaudio Elixir and the Unique Melody MEST, I enjoyed them the most of the IEMs I have with me and tried with the SMSL HO100 and DO100.
Overall, if I was going to change anything here, I would reduce the overall gain of the LOW gain switch on the HO100 amplifier to give more range for in-ears. This could also be affected by using XLR balanced connectors which typically have more output voltage (from the DAC) than stereo RCA.
Overall
The SMSL HO100 and DO100 seem to be appropriately priced and offer a lot of performance for a relatively small price. I was able to power most all of my headphones, with only the most ridiculous power-hungry headphone (Susvara) not sounding quite as good as other pairings. And even so, I thought it was mostly due to a pairing of a brighter amplifier with a brighter headphone that really did it in.
The SMSL set tested here pairs best with warmer and darker gear, but I did enjoy this with more neutral-tuned headphones as well. I would be slightly weary of using it with transducers that lean a tad bright just due to listening fatigue over long music sessions. Other than that, I don't have any major qualms with the reproduction of audio here.
The new design style of these SMSL amp and dacs are much improved over their previous units and I enjoy the piano-black glossy finish that gives these a little bit of standout character over the previous industrial matte looks that look more like glorified project boxes.
Overall, this is a good set for an entry level setup, and it does not take up a lot of real estate either.
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