Last month I had the pleasure of taking a deep dive into the Cayin N7 DAP music player - it's an impressive music player, to say the least, but boy did I leave out one of the best things about it - how it sounds with the C9 amplifier.

The Cayin C9 amplifier is a portable headphone amplifier that pairs perfectly well with Cayin's DAP lineup (and any DAP with a line out for that matter). The N8ii and the N7 are premium music players packed with quality features and more importantly some magnificent sound fidelity. So if they're already high-end music players, how does the C9 make them better?

Hang tight kids, we're going on a high-fidelity adventure.

There's not much to talk about here other than the I/O selection. On the front of the amplifier, you'll find the Line/Pre selection switch, which appropriately switches the amp from Line mode to pre-amp mode (input). You have both 3.5mm unbalanced and 4.4mm balanced inputs. a High/Low gain switch, the volume knob, the power on push button, the solid-state/tube switch, the class A/AB amplifier switch, and the 3.5mm unbalanced and 4.4mm balanced outputs. On the back of the headphone amp, you'll find a 4-LED battery indicator and the lone USB-C charging port.

Now to the real star of the show, the C9 with the N7 music player. I've already spent a lot of time talking about the N7 DAP, so if you want to learn more specifically about the sound quality, be sure to check out our full review of the N7 here.

For my testing session, I had the Cayin N7 DAP paired with the C9 Portable Headphone Amplifier, connected to the Meze Elite headphones with a Black Dragon Premium Cable for Meze Headphones. I also used a Silver Dragon Portable Mini IEM V2 Cable to connect the N7 music player to the C9 headphone amplifier via the line in/out ports.

Personally, I preferred the sound of the Class A setting for more genres except for Rock. Class A is a more refined and smoother sound, with Class AB is less so, with more impact - much like a slight bass and treble boost (a common EQ setting for rock music). That being said, Rock was more exciting and dynamic and likely can be said for genres that need a larger sound and space.

Tubes versus solid-state settings will depend on the user and the genre specifically. The tube circuit does provide a warmer and smoother presentation over the solid state. Combined with the already natural presentation of the C9 amplifier, and genres like Jazz, R&B, Folk, Classic Rock produce a musical and vintage aura. It makes an already intimate song even more so, the richness of the tube makes for the perfect setting for those who like to get lost in the music. The solid-state on the other hand provides trades out the richness and smoothness of the tube for what I like to call Cayin's signature sound: natural-sounding, clean, and detailed, with plenty of representation in the low mids and bass.

Classical already sounds great on the N7. The genre sounds detailed, incredibly transparent, and has great separation. I A/B tested one of my main testing tracks, the finale to Mahler's 8th symphony: "Symphony of a Thousand." On the first listen I played directly out of the balanced output from the N7 (high gain setting, class A). The music was expressive, really shining in the top-end clarity, but leaving a lot to be desired in the low mids. Keep in mind that it didn't sound bad, but comparatively speaking, you know how something sounds based on how you've heard it on other systems, right? So for instance, with this piece in particular, and classical pieces with large choral ensembles in general, the low mids are a very important frequency range for choral works. The human voice has a lot of natural resonant tones that get lost in classical recordings because they either get masked by other competing frequencies in the string sections or the high frequencies (sopranos, descants) overpower the lower ones (exacerbated by forward or more analytical-sounding audio gear).

Cymbal crashes at the end can sometimes sound harsh or painful when listening to more forward-sounding audio gear, especially at high-volume listening levels. Switching over to the C9 output with the tube circuit and class A amplification, the mids suddenly come out of the woodwork. The C9 adds the weight and size of the choir that was missing in the N7 alone. It was there, I just never felt the size of the ensemble. The high-end detailing is retained, but the harsher frequencies are hidden behind a larger and taller soundstage, allowing the performance to play with more gravitas.

For me, that's the real value of the C9 - it isn't making bad recordings magically sound good, but rather making already great-sounding recordings retain the impact and presentation of the original recorded performance. It's subtle and not-so-subtle at the same time - this difference between a great DAP music player and realizing what makes it even better. It's not that anything is missing or lacking from the original N7, but it's certainly not end-game sound quality. The C9 gets it there.

Vacuum Tube or Solid-State: Your choice of timbre: vacuum tubes or solid-state. The C9 has a tailored-designed, fully balanced 40ch dual timbre circuit. It comes equipped with a quad set of Toshiba 2sk209 JFET and a pair of KORG Nutube 6P1 double direct heated triodes. They're applicable to both single-ended and balanced phone output.

• Vacuum Tube Timbre Circuit: This is a redesigned timbre circuit featuring the two miniature double direct heated triode (DHT) Nutube 6P1. Applicable to both single-ended and balanced output, with carefully implemented NFB, reduces THD+N to 0.03%. It delivers a euphoric and energetic presentation with the utmost delicacy.
• Solid State Timbre Circuit: The solid-state option is a fully discrete buffer and amplification audio circuit. It's designed around two matched pairs of high-quality, low-noise audio frequency Toshiba 2sk209 JFET. They deliver a warm and rich timbre that is realistic and engaging.

Dual Input Mode: Choose between line input and pre-amp input.

• Line: receives fixed voltage audio signals from the line level output and functions as a headphone amplifier with local volume control.
• Pre: receives variable voltage audio signals from the pre-amp output  

Fully Discrete Headphone Amplifier: The C9 is equipped with high-quality 4-ch JFET and BJT-based fully balanced headphone amplification circuits for portable applications. To achieve the desired audio performance, the input signal is handled by a quad set of WIMA coupling capacitors and two matched pairs of LSK289 DUAL JFET differential amplifiers. The final output stage is composed of a matched quad set of doubled BJT in parallel, providing ample power for IEMs and headphones.

Effective Heat Dissipation: Cayin attached PBS (Pyrolytic Graphic Sheets) to components inside the C9 amplifier that generate the most heat. This was carefully designed for effective heat management to divert and dissipate heat energy efficiently, right down to the placement of the components themselves. The C9 portable headphone amplifier maintains consistently low temperatures due to this design.

Replaceable Battery Tray: The C9 amplifier contains a reliable power supply from 4x Sony VTC6 3000mAH 18560 Lithium batteries, with 8-12 mOhm low internal resistance and 30A maximum continuous discharge. Four batteries in series provide +/- 8.4V direct power. Dedicated power protection and management to ensure that all four batteries will be fully charged at the same pace. The C9 is compatible with QC3.9 and PD-compatible Fast Charging through the USB Type-C interface with an LED indicator to display charging and battery capacity status.