I analyzed S2 sound with various IEMs, including Oriolus Traillii which I’m intimately familiar with and use in my critical sound analysis, while playing a variety of my favorite test tracks, such as Agnes Obel “The curse”, Sandro Cavazza “So much better” (Avicii remix), C-Bool “Never go away”, Ed Sheeran “Shape of you”, Alan Walker “Darkside”, Galantis “Hunter”, Iggy Azalea “Black widow”, Indila “Boite en argent”, Dua Lipa “Love again”, Counting Crows “Big yellow taxi”, David Elias “Vision of her”, and Michael Jackson “Dirty Diana”. S2 had about 50hrs of burn in before starting my sound analysis.
Overall, I found S2 to have a neutral sound sig and a more natural tonality with a smoother top end extension. Also, I noticed the pair up synergy to be very dependent on IEM signature and S2 gain setting. For example, when using brighter tuned IEMs, I found it to pair up much better with low gain setting where it gives upper mids and lower treble more natural smoother tonality. Then, when using neutral and warmer tuned IEMs, switching to high gain improves the resolution and layering of the sounds, expands the dynamics, and even improves the soundstage width and imaging.
The overall signature is relatively neutral balanced without any noticeable bass boost or mid-forward push. As a source and in pair up with many IEMs, I found S2 to yield a very good vertical sound dynamics, nothing compressed or congested, which leads to a good layering and separation of instruments and vocals, despite a smoother presentation of treble. Noise floor was pretty low, and no hissing even with sensitive iems.
The soundstage expansion was relatively wide (not super wide) with most of the IEMs I tried, only limited by IEM’s own technical performance. But it wasn’t as wide with some of the more demanding headphones, one of the reasons I think S2 is better for IEMs or easier to drive headphones. The overall imaging was pretty good too, including accurate placement of instruments and vocals.
3.5mm vs 4.4mm.
I hear a nearly identical tonality, signature, technical performance, and even power output where I didn’t have to adjust the volume when using the same pair of IEMs with 4.4mm cable and switching to 3.5mm port with an adapter (4.4mm to 3.5mm); maybe just by a few clicks if I’m being picky. Also, the soundstage is just by a hair wider and with a slightly blacker background in BAL. Otherwise, nearly the same sound performance. It was a bit surprising at first, until I realized that the difference in power output between SE and BAL is not too far off, and probably even closer under the load.
Source pair up.
I compared S2 connected to my Galaxy S9 vs Hiby RS6, and found the sound to be nearly identical while connected to either my smartphone or RS6 DAP, using HibyMusic app. I tried the same with a handful of other DAPs, and found similar results. In theory, it probably makes no sense to use S2 with high end DAPs, but it can certainly enhance the sound quality of some entry level and even mid-fi models.
After I updated S2 to the latest fw 184.108.40.206 with added LO functionality, and while A/Bing 4.4mm output with LO enabled and disabled (volume set to 100), I found it doesn’t sound the same. What I mean, with S2 volume set to 100, LO off, and Cayin C9 amp (in NuTube mode) connected, I’m hearing some saturation in bass. Then, when switching S2 to LO which sets output to max volume and with Cayin C9 amp connected, I don’t hear that distortion. Thus, I have to assume that enabling LO doesn’t just set volume to the max, but does something different to avoid saturation/distortion. And, btw, as I was finishing up this review, Lotoo just released new fw for S1, adding LO functionality as well.
The sound of any source, either if it is a DAP, DAC/amp, or a portable usb DAC/amp dongle, is based on pair up synergy with different earphones and headphones. Afterall, you are hearing the sound of earphones/headphones connected to the Source. In this section of my review, I will go over how various earphones and headphones pair up with S2.
Beyerdynamic T5p 2nd (BAL) – definitely benefits from high gain setting, though soundstage here wasn’t as wide, but with a lot more depth, and with the sound extending more out of your head. The tuning is not bad, natural balanced tonality, with lots of clarity, good resolution, bass has a good punch but was lacking sub-bass rumble.
Meze Audio Empyrean (BAL) – again, needs high gain, and considering open back design, soundstage was still surprisingly on a narrower side with more depth/height than width. The sound has a natural tonality and overall flatter tuning, not as dynamic as I’m used to with other more powerful sources. Overall, this wasn’t the best pair up.
Audio-Technica ATH-R70x (SE) – this was a huge surprise. I don’t have balanced cable for these 470ohm open back headphones, only 3.5mm, thus driving them from a little less powerful single ended side of S2. I had it in High Gain and with volume pushing at 70/100. While soundstage wasn’t huge, though having a decent width and a good depth, the imaging was very convincing and 3D holographic. But what surprised me the most was the tonality, very clear, natural, resolving sound, with a great bass extension down to sub-bass rumble, detailed layered mids/vocals, and resolving airy treble. Surprisingly, a very good pair up.
FAudio Dark Sky (BAL) – wide soundstage, balanced tonality, needs to switch S2 to low gain. In high gain upper mids/lower treble are a bit peaky and harsh, switching to low gain makes it sound more natural and smoother.
Oriolus Traillii (BAL) – wide soundstage, holographic imaging, smooth natural tonality with a balanced sound sig. In this pair up, low gain makes the sound too smooth and organic. The Bird definitely benefits from high gain in S2 which expands soundstage a bit, improves layering and separation of sounds, improves resolution, and adds air to the treble.
VE EXT (BAL) – very wide soundstage expansion, mildly U-shaped sound signature, very powerful bass impact, natural detailed mids, clear natural treble. This pair up definitely needs high gain which widens the soundstage, improves resolution, and helps with retrieval of details.
64 Audio U18t (BAL) – wide soundstage, no complaints here, the sound is a little more revealing, leaning more toward the mid-forward signature. Bass is north of neutral, with a good quality and accuracy, typical of U18t. Here is another example where you have to switch to low gain to give mids and treble a more natural and less harsh tonality. High gain pushes it over the edge, while low gain brings it back to a more natural tonality.
CFA Solaris 2020 (BAL) – wide soundstage, great imaging, more balanced sound sig with a natural revealing tonality. Here, it is very important to keep gain at Low in order to maintain natural tonality and to eliminate any treble harshness. Going to high gain brings sibilance to lower treble, while low gain is like a magic switch that attenuates down that peak. No hissing.
UM Mest MKII (BAL) – very wide soundstage with 3D holographic imaging in this pair up, sound signature is W-shaped, thanks to upper mids being more forward instead of slightly recessed like in other pair ups. The tonality is more revealing, and surprisingly I actually enjoyed it more in high gain. With many revealing IEMs I switched S2 to low gain, but here high gain gave me bigger soundstage and improved resolution without causing any extra harshness.
EE EVO (BAL) – I’m going make this one short, I didn’t like this pair up because it created a weird hollow sound effect in mids/vocals. Bass was fine, powerful impact, deep sub-bass extension, and treble was clear and resolving. But mids/vocals sounded like they were coming from a tunnel with a weird echo-like effect. Tried it at both gains, the same effect.
EE Odin (BAL) – soundstage is pretty wide in this pair up, and the sound sig is balanced with a natural revealing tonality. Switching between low gain and high gain here doesn’t make difference in the tonality. Odin is tuned with higher resolution and brighter tonality, but it doesn’t sound harsh and maintains a similar natural revealing tonality at either gain.