I analyzed C9 sound with Oriolus Traillii and Audio-Technica ATH-R70x 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”. I let C9 burn in for about 150hrs before starting my sound analysis.
Similar to my DAP reviews, I prefer to describe amplifier sound based on comparisons and pair ups, but not in the same way as DAPs. People buy amplifiers to replace internal amp stage of their DAPs with an external one through Line Out connection. In the follow up sections I will bring up a lot of brief pair up examples with various IEMs and headphones, as well as different examples of DAP comparisons with and without C9.
This sound analysis section usually serves as a summary of my findings in the follow up sections. And across all my comparisons I found a common improvement of soundstage being more expanded, both in stereo separation and improved 3D imaging. Also, as expected, overall tonality changed with a more natural fuller body sound, thanks to vacuum tubes, though solid stage amp also adds some organic coloring, though not to the same extent as tubes. Furthermore, while some might expect sound coloring with vacuum tubes to make the sound thicker and more saturated, to my surprise I actually found improvements in micro-dynamics with layers of sounds being more separated and less compressed (improvement in vertical dynamics).
The flexibility of C9 design gives you many different sound shaping options, like going between Class A and Class AB and of course, Solid State and Vacuum Tubes (Korg NuTube). I’m already familiar with Class A vs AB from E01 card, and quite familiar with AB from E02 card. In C9, you can clearly hear the difference when switching between Class A and Class AB where AB sounds tighter and faster with notes having cleaner edges, while A is smoother, more relaxed, with notes having longer decay. It is up to a personal preference, and I preferred AB since I like a punchier sound.
When switching between SS and Tube, the difference in tonality reminded me of switching between Class AB and Class A. SS timbre gives you a faster and tighter sound, with shorter and faster attack of the notes, while Tube timbre gives you a smoother and more analog tonality, also slightly laidback and less aggressive. The sound with Tube timbre still packs the punch, especially when you use it in combination with Class AB. That is a beauty of C9, you have lots of different options to customize your sound.
I’m sure some will be wondering about 3.5mm vs 4.4mm comparison. Here, I found tonality to be the same under consideration of using either SS or Tube, or Class A or Class AB. But 2 noticeable differences were the soundstage width, with BAL output sounding wider and more expanded, and the other one with BAL output having a blacker background which is also quite noticeable, most likely due to grounding of 4.4mm BAL TRRRS jack.
Also, I saw a discussion on Head-fi about different rechargeable 1860 batteries. Cayin already includes premium Sony batteries, and for comparison I “borrowed” 18650 batteries from Broadway S, “rolling” between stock Sony VTC6 3000mAh and replacement Panasonic NCR 18650B 3400mAh. I did hear with Panasonic the sound to be a little smoother and more laidback, while with Sony the pace of the sound was faster and the sound was a little more revealing. Of course, there is a little delay when you have to slide out the tray and replace the battery, but it was relatively quick for a “non-blind” A/B comparison.
As I was writing this review, a few people asked me if Interconnect Cables (IC) make a difference. Cayin includes a rather nice pure copper short ICs, both 4.4mm and 3.5mm, so I wanted to test it with a few other ICs I have on hand.
Cayin stock copper IC (CS-44C44), DHC silver IC (Clone 22awg OCC Silver Litz x4, coaxial cable with 2 conductors and rhodium Eidolic plug), Romi Audio encryption series Sensation IC (pure silver core with silver-plated copper shielding), and Eletech Iliad 6W IC (24awg, 6wire with a full TRRRS connection including GND, Monocrystal Silver & Palladium Plated Silver & Gold-Silver alloy). I know, it is just a short piece of wire, but nevertheless, there is some difference in sound that I hear, maybe not night’n’day, but I do hear it.
Cayin to DHC – DHC IC sounds a little dense and warmer, giving the sound a thicker tonality while Cayin original cable has a little more air between the sound layers, giving it a little brighter tonality.
Cayin to Romi Audio – the improvement is quite noticeable here, and I actually had to lower the volume a bit since it was louder, most likely due to lower impedance of Sensation IC. The soundstage is a little wider, the sound has more air and sparkle, bass is a little deeper, and it also felt like I’m hearing further improvements in vertical dynamics.
Cayin to Eletech Iliad 6W – the improvement is also noticeable with sound having more air and sparkle, bass deeper, but overall tonality was still natural and organic. One interesting observation which I confirmed multiple times is that in addition to improvement in width I also hear some improvement in depth. This is the only interconnect cable I have with a proper wiring that has both signal pairs and GND connected between the plugs.
I know for some the comparison to other amps using demanding headphones will be very important. Unfortunately, I don’t have too many demanding headphones, or too many portable amps for comparison. But I was using ATH-R70x (open back, 99dB sensitivity, 470ohm impedance, 3.5mm SE termination) which is my hardest to drive pair of cans. Also, I used N6ii w/E02 as my source while switching between C9 ($1,999), Romi Audio BX2 ($850), and XI Audio Broadway S ($1,599) amps. With C9 and BX2 I was using stock 4.4mm interconnect to N6ii, while with Broadway S which has RCA inputs, I was using Audioquest RCA to 3.5mm cable and DDHiFi single ended to 4.4mm adapter (the one which uses only L+/R+/GND side) to connect to E02.
All three, C9, BX2, and Broadway S were able to drive R70x without a problem with enough volume headroom. I had all three amps in low gain and approximated the volume % by looking at the volume knob. Under all these conditions and with ATH-R70x volume matched, BX2 was at about 20%, C9 was at about 50%, and Broadways S was at about 75% of volume setting. BX2 has too much power for IEMs and optimized better for demanding headphones, while Broadway S (Single ended) was optimized for IEMs. This puts C9 to be somewhere in the middle, optimized for both IEMs and headphones.
Using R70x and a few other IEMs, I found BX2 to be more transparent, clean, uncolored, and maybe even a little colder while C9 (SS timbre) and Broadway S were being warmer, richer and more analog in tonality and also having a fuller body sound. When I switched C9 to Tube, the sound became even more analog and smoother, pushing farther ahead of Broadway S. Of course, these types of sound changes will depend on your IEMs and headphones, their sound signature and power requirements, and their pair up synergy with these amps. For me personally, it was a clear choice. BX2 has too much power and Broadway S only one “coloring” option. C9 was versatile to use with either IEMs or headphones and it gave me different options of coloring the sound, using either SS or Tubes and Class A or Class AB.
Another thing to keep in mind. Something like Broadway S (I only have single ended version since it is more IEM friendly) is definitely not a portable amp, and also not in a category where you will carry it around. It will be transportable to move from one desk to another without interrupting the playback since you are not plugged into the wall. Romi Audio BX2 is a portable amp, though in comparison to C9 it is only solid state and Class A. And while BX2 is shorter than C9, it also 10mm wider and a little thicker which puts it in-between portable and transportable. For my own personal preference, the width of the stack up is one of the deciding factors between portable and transportable because it makes it easier to grip.