Today, we are looking at the new C9ii Portable Tube Amplifier. It retails for $2,399 USD.

Disclaimer: Cayin sent us the C9ii Portable Headphone Amplifier for this review. As always, this article reflects my unbiased opinion.

Cayin

Cayin Audio is a world-renowned audio manufacturer founded in 1993, marking its 30th Anniversary last year. As a premium Chinese high-end audio brand, Cayin has primarily focused on desktop HiFi equipment, covering every chain in the music reproduction path from CD players to speakers. However, the essence of their reputation lies in their tube amplifiers. Cayin’s product range spans from around $100 to just below $10,000 per item, answering various requirements and budgets. To date, Cayin has developed over 500 products, earning more than 70 awards.

“We deliver music diligently, and we are prepared to go a long way for that.”

In 2013, Cayin ventured into personal/portable audio, launching a series of Digital Audio Players. The N-series DAPs are designed to provide a high-quality audio experience on the go.

Recently, Cayin has increasingly focused on the portable market as well, with successful units such as the N5ii, the N3Pro, the N6ii, the C9, the RU6, RU7, the reference N8/N8ii, and the 1-bit N7. If you’re still interested in finding out more about the company, then you can do so here. We’ve recently taken the N3 Ultra out for a spin; if you missed that review, I suggest you read it below.

Today, we’re taking a closer look at the second iteration of Cayin’s C9, originally launched in January 2021. Since then, audio technology has advanced significantly, paving the way for the Cayin C9ii. Cayin states that they have been working on it for 3 years, and it is finally ready. As the successor to the original C9, the C9ii brings many improvements in both features and sound. With its versatile design, Cayin aims to deliver a one-amplifier solution for all your needs, offering multiple switches to fine-tune sound signature, response linearity, and more. Let’s dive deeper.

Cayin C9ii – TOTL NuTube Headphone Amplifier

The Cayin C9ii is a (trans)portable headphone amplifier packed with innovative features to satisfy audiophiles with different preferences. It offers triple amplification modes, allowing users to switch between Class A, Class AB, and Hyper modes. This versatility is further enhanced by the ability to adjust the anode voltage and choose from three different tonal options: Solid State, Modern Tube, and Classic Tube. With its modular design, rugged construction, and top-quality internal components, the C9ii promises to cover all the high-end fronts.

Featuring a dual NuTube design, the C9ii incorporates a pair of KORG Nutube 6P1 triodes. These miniaturized vacuum tubes deliver the warmth and musicality that tube enthusiasts like while maintaining energy efficiency and durability. In addition, Cayin has designed a discrete solid-state timbre circuit using Toshiba’s JFET transistors, offering an alternative/selectable sound signature that is precise and linear. Whether you prefer the smooth, rich tones of tubes or the clinical accuracy of solid-state amplification, the C9ii has you covered.

The C9ii’s battery-powered operation eliminates interference from AC power lines for a cleaner signal. The four Samsung INR18650-35E batteries provide ample power, with up to 17.5 hours of run time in solid-state Class AB mode via single-ended. The amplifier also supports fast charging via its USB-C port.

There is a lot to talk about this over-engineered amplifier, so we better get into the details. As a reminder, the C9ii is priced at $2399 USD and is available from Cayin’s official Aliexpress Store.

Specs & Highlights

• Gen5 Dual NuTube Circuit
• Hi-End Audio PCB with TOTL Components
• Fully-Symmetric Discrete & Balanced 3-Stage Amplifier
• Dual Amp Operation Class A & Class AB + Hyper Mode
• SS | Modern | Classic Timbre Toggle
• Adjustable Anode (Plate) Voltage
• Local or Large-Loop NFB Toggle
• Dual Input Mode – Line | Preamp
• USB-C – QC3.0 & PD3 Fast Charging Support
• Direct Battery PSU Module (Batteries forming an 8.4V PSU)
• Quick Release Battery Tray with x4 18650 Samsung 35E Batteries
• Power – SE: 1.2W into 16Ω | 700mW into 32Ω | 80mW into 300Ω
• Power – BAL: 4.1W into 16Ω | 2.6W into 32Ω | 320mW into 300Ω
• Dimensions ≈165x88x30mm | Weight 650g

Packaging & Accessories

The C9ii arrives in a sleek black box with a top-opening design. The model name is elegantly displayed in gold letters on the top flap, accompanied by Cayin’s sophisticated handwritten logo in the upper left corner. I really like Cayin’s calligraphic logo; it adds a touch of sophistication and luxury while perfectly complementing Cayin’s gold-accented signature design language. A particularly striking detail of the packaging is the spiral shapes on the top of the box, which adds an artistic flair with a rainbow glow resembling the bony labyrinth, also known as the cochlea.

Upon opening the box, the C9ii sits front and center, nestled in a foam compartment covered in enamel/art paper, enhancing the premium feel of the presentation. Underneath, a drawer-style compartment slides open to reveal the included accessories.

Inside this compartment, you’ll find two interconnect cables (CS-35C35II and CS-44C44), a white, sheathed USB-A to USB-C charging cable, a user’s manual, and two hi-res stickers. The package also includes four Samsung INR18650-35E batteries installed in the amplifier’s battery tray.

The cables included with the C9ii (CS-35C35II and CS-44C44) are crafted from high-quality OCC (Ohno Continuous Cast) wires in an 8-strand Litz structure. Each core features eight strands of enameled OCC conductors wrapped in a durable 200D braided protective layer. To further enhance performance, Cayin states that each conductor is shielded with a twisted OFC outer layer, effectively blocking EMI and RFI interference.

Overall, I really like the accessories included with the C9ii. The cables are well-made, feel premium in hand, and their design fits the amplifier’s aesthetic. At around 15-16 cm in length, the IC cables are just right for stacking the C9ii with DAPs or DACs, offering good pliability.

Design & Build Quality

Cayin is doing what Cayin does best: Delivering the finest quality materials paired with a design that combines aesthetic elegance and industrial flair. The tasteful use of gold accents throughout the unit adds a luxurious touch without feeling excessive. At half a kilogram, the C9ii is more “transportable” than truly portable, but as the saying goes, every rose has its thorn. I must say that I love the design of the new C9ii. It feels like the og. C9 has undergone a Pokémon-style evolution, returning with a more refined, beefed-up form.

The chassis of the Cayin C9ii is CNC crafted from 6063-T6 aluminum alloy. This aluminum type is commonly used in high-performance applications, such as bicycle frames, due to its excellent strength-to-weight ratio. To optimize heat management, Cayin has incorporated advanced thermal design elements such as high-conductivity graphite pads that link the internal PCB to the side panels, which act as efficient heat sinks. The width of the chassis has been increased from 160mm to 165mm to accommodate these CNC-machined heat sinks on both sides, ensuring an even temperature distribution.

The new design features more curved corners, a distinctive rack-like front panel, and switches that are more prominent and easier to use. In my opinion, the quick-release battery module stands out. It’s practical, well-executed, and adds a lot to the overall convenience. The windows into the NuTube circuitry have also been updated, allowing for a better, wider view of the glowing tubes inside. Cayin even incorporated a new gold-accented rear panel and lined sides, giving the C9ii a more handsome look over the C9. Clearly, Cayin’s engineers put a lot of time and thought into refining every detail of the C9’s successor.

Speaking of the battery module, the latch release mechanism is nothing short of ingenious. To remove the battery, simply pinch the two latch buttons on the sides while pulling on the battery module, which is marked by the gold accent on the back. They used a SATA connector here, which is very smart, making swapping out batteries fast & easy. Also, the module itself can double as a standalone 18650 charger. Just wow!

Now, let’s get back to the overall design. The front panel houses all the inputs, outputs, and most of the controls. On the left, you’ll find the SE and BAL inputs, along with the anode and gain switches. On the right are the timbre and mode switches, as well as the SE and BAL headphone outputs. The back of the unit has a single USB-C port for charging the batteries, and the entire back is removable, as aforementioned. The unit won’t work without the battery module, naturally.

The sides of the unit have a lineal/linear/lined design with the PRE and NFB buttons subtly integrated. These buttons must be held down for three seconds to activate, a thoughtful safety feature that prevents accidental activation, especially since accidentally turning on the PRE could potentially damage your headphones or ears. Details like these really show Cayin’s years of know-how in product design. Overall, the C9ii is a stunning piece of craftsmanship that combines aesthetics, functionality, and innovation in a single package.

The review continues on Page Two, after the click HERE or by using the jump below.

Page 1: Disclaimer, Cayin, C9ii, Packaging & Accessories, Design & Build Quality

Page 2: Audio PCB & Technology Inside, Power Output, Removable Battery Module & Battery Life, Sound Customization 101

Page 3: Sound & Performance, Comparison, Last Words, Summary