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Cayin C9ii - Reaching New Heights
The fundamental purpose of a portable headphone amplifier lies in its core function: improving sound quality and expanding its ability to drive a wide range of loads. With many DAPs featuring significant improvements in circuit performance, can the C9ii still achieve the same level of popularity as the C9 did three and a half years ago?
This is a question that concerns many audiophiles. Some even ask us which amplifier offers better sound quality, the N30LE or the C9ii? The C9 portable amplifier became a phenomenon three and a half years ago, primarily due to its innovative design and unique and powerful features. Today, we take a closer look at the new design, features, and updates of the newly announced C9ii.
Reviews
"Overall, the Cayin C9ii is a showcase of advanced engineering, blending cutting-edge components and meticulous design to deliver a highly customizable and versatile portable amplifier. The C9ii combines flexibility, power, and performance in a single device. Each configuration has its unique strengths, and there isn't a clear-cut “best” option; it all depends on the headphones or IEMs in use and your personal preferences. Its tunable sound characteristics and high build quality make it a true all-in-one portable amplifier for audiophiles who demand the portable market's top-of-the-line amplifier.
If you're in the market for a portable amp that can do just about anything and offers a wide range of tonality adjustments, the Cayin C9ii might just end your search for amps. The Cayin C9ii is now in the Recommended list!"
Cayin C9ii Review - Headfonia Reviews
"As a result, C9ii became a “portable amp with everything including the kitchen sink”, giving us even more tools to enhance the sound quality and come up with new ways of improving the pair-up synergy between various DAPs and IEMs/headphones.
I know, some have a misconception of thinking that portable amps are just to boost the power of the source when driving demanding headphones. But there is so much more to it when it comes to IEMs as well.
DAPs come and go, but a portable amp like C9ii should last you a long time to enhance any source you pair it up with."
Cayin C9ii – Page 4 – Twister6 Reviews
1. Gen5Nutube 6P1 Vacuum Tube Audio Circuit
Cayin has used this vacuum tube in several products, starting with the N8, C9, N8ii, and N30LE, and now the C9ii. After years of continuous circuit experimentation and technical refinement, Cayin has equipped the C9ii with an adjustable plate voltage, in addition to the highly acclaimed Classic and Modern dual-tube tones. This adjustable plate voltage offers two levels: high and low.
1.1 Dual Tube Timbre Circuit
The Nutube Timbre circuit in the C9ii uses a three-stage amplification design, with core components consisting of a matched pair of Nutube 6P1 dual direct-heated triode (DHT) vacuum tubes and 16 audio-grade Toshiba 2SK209 JFETs. The first stage is a discrete buffer amplifier consisting of four pairs of selected Toshiba 2SK209 low-noise JFETs, one pair per differential gain channel.
The second stage is the tube voltage gain stage, which provides the primary voltage gain and determines the overall sonic character of the timbre circuit. It is the heart of the C9ii's timbre circuit and consists of a matched pair of Nutube 6P1 vacuum tubes.
The third stage is a buffer driver stage, and in this implementation, we used a source-follower circuit with a pair of Toshiba 2SK209 JFET transistors. Instead of conventional power resistors, four pairs of selected 2SK209 transistors are used in the source-load circuit to create a powerful constant current source. This significantly increases the power of the source follower and improves the current driving capability of the tube timbre circuit.
In addition, Cayin engineers have carefully designed two feedback and fine-tuning circuits to process the output signal of the tube sound circuit, resulting in two different sound characteristics leads:
Modern Sound: Introduction of a large-loop negative feedback system, with the overall gain determined by the large-loop negative feedback circuit. By incorporating negative feedback across multiple gain stages, total harmonic distortion (THD) is significantly reduced. The harmonic distortion characteristics and sound signature lean more toward a modern style, with greatly reduced thermal noise and a slightly cleaner tube sound. The original C9 was designed with a similar NFB circuit.
Classic sound: No significant negative feedback; each stage operates independently through local feedback, with the overall gain determined by the cumulative gain of the individual stages. The distortion characteristics of the tube amplifier circuit dominate the sound signature, resulting in a higher THD. The harmonic distortion distribution and sound signature reflect a classic tube amplifier circuit with relatively high thermal noise and a richer tube representation. The N8 DAP was developed using a similar NFB circuit.
1.2 Anode (High/Low)
Cayin introduces a new "Anode" function to the C9ii. The adjustable anode (plate) voltage (High/Low) expands and refines the vacuum tube's sonic palette. The principle is that applying different operating voltages to the vacuum tube's plate changes its operating state, which ultimately affects the sound signature of the timbre circuit.
This primarily manifests itself in changes in audio linearity, resulting in an adjustment of the superposition, spectrum, amplitude, and ratio of second-order harmonics, resulting in perceptible differences. Here's a practical scenario: For example, when using the classic tube timbre to hear extremely detailed vocals, some audiophiles might find the sound too dense, with too much focus on vocal imaging.
By switching the board voltage to the L (Low) setting, the sound characteristics can be relatively relaxed and better suited to the listener's preferences. The C9ii is not only a high-quality portable amplifier, but also offers numerous features, gain states, and tone adjustments to satisfy our users' subjective preferences, such as exploring their music library at different times/moods, with different IEMs/headphones, and with different music genres.
The C9ii also features a solid-state (SS) tone.We developed a discrete tone circuit using four 2SK209 transistors in a single-ended Class-A source-follower circuit. A powerful constant-current source is implemented using four discrete double-triode transistors, finely tuned to deliver clear, smooth, and fatigue-free audio output without harshness. It's important to note that adjusting the plate voltage has no effect on the solid-state tone. Thus, the C9ii offers four tube tones and one solid-state tone, for a total of five variations, whereas the original C9 only offered two.
To put the timbre options of our Gen5 Nutube 6P1 Vacuum Tube Audio Circuit into context, we summarize these options:
- Classic + Anode(H): The richest tube sound, with intense emotional depth, suitable for vocal music with lots of detail.
- Classic + Anode(L): Slightly lighter tube sound, suitable for vocals with thicker tones.
- Modern+Anode(H): Lesstube character, with moderate smoothing in the midrange and a slight sweetness.
- Modern+Anode(L): Minimal tube coloration without affecting resolution and definition.
- Solid-state sound: Balanced across the entire frequency range, musical without tube coloration.
2. Fully discrete, fully balanced differential headphone amplifier
The headphone amplifier circuitry of the C9ii differs significantly from the first-generation C9. While both amplifiers utilize a fully discrete, fully differential four-channel headphone amplifier circuit, the C9ii utilizes a fully symmetrical circuit architecture.
2.1 Fully balanced headphone amplifier
In the design of hi-fi audio amplifiers, a fully balanced circuit architecture contributes to higher fidelity and better performance by reducing distortion, improving dynamic range, increasing channel separation, and providing stable and consistent performance. Fully balanced circuits are expensive to implement, especially in compact, portable applications.
Since its advantages align with audiophile expectations, this is a great incentive for Cayin to incorporate this technology into the C9ii portable headphone amplifier. Cayin developed a three-stage amplifier circuit to integrate the fully symmetrical design into the C9ii: a differential input stage, a voltage gain stage, and a power driver stage.
Stage one: Symmetrical JFET common-source differential input amplifier. The differential input stage has been completely upgraded and now uses two ultra-low-noise, audio-grade dual JFETs per amplification channel: the LSK489 and LSJ689 from Linear Systems.
It should be remembered that there are 4 channels in a fully differential circuit. While these JFETs are supplied as factory-matched pairs, Cayin uses a transistor characteristic tracer to measure the matched JFETs and select the best pairs to ensure performance consistency of the C9ii audio circuit.
Second stage: Symmetrical BJT common-emitter push-pull differential voltage amplifier. This voltage amplification stage uses audio-grade BJT (PNP) transistors from Toshiba. We ensure stable operation and high-quality output signals by fine-tuning the parameters of the peripheral circuitry. This optimizes the harmonic distribution and leads to improved sound quality.
Third stage: Symmetrical BJT common-collector push-pull parallel current amplifier (emitter follower). The power driver output stage uses Nexperia's high-performance paired bipolar transistors in parallel, known for their excellent thermal stability and superior audio performance.
This significantly improves the amplifier's power handling and compatibility. From a user perspective, the overall improvement of the C9ii headphone amplifier over the first-generation C9 is comprehensive: The increased power handling makes the C9ii more suitable for driving larger headphones or in-ear monitors with multiple drivers. It offers better bass control, treble extension, and imaging.
More transparent sound reproduction with balanced musicality and a more complete and clear soundstage. When we began developing the C9ii, we expected our R&D department to push the boundaries of the original C9. After all, purely analog signal amplification technology hasn't made any significant advances in many years, and the C9 is a very well-received product with an impressive track record over the past 4.5 years.
Having finally finalized the circuitry and industrial design of the C9ii, it's hard to believe that the C9ii has exceeded our expectations and completely eclipsed its predecessor in terms of sound quality. We're thrilled and look forward to hearing the feedback from our users, reviewers, and fellow hobbyists.
2.2 Negative Feedback (NFB)
The C9ii features a built-in precision control circuit that allows the headphone amplifier to operate in various modes, including NFB/LFB, Class A/Class AB, Hyper, Single-Ended, and balanced input/output modes. NFB (Negative Feedback) is a feature introduced in the C9ii. This function applies to the three-stage headphone amplifier circuit mentioned above.
When NFB is set to the OFF position, the headphone amplifier circuit is controlled by a wide-loop, cross-stage negative feedback circuit. The feedback signal is sent from the power output stage to the negative signal terminal of the differential input stage and controls the overall gain of the power circuit.
When NFB is set to the ON position, the headphone amplification circuit is controlled by local negative feedback. The feedback signal is sent from the voltage output stage to the negative signal terminal of the differential input stage, primarily controlling the gain of the voltage stage and changing the sound characteristics.
When designing analog signal amplification circuits, feedback circuit design is an indispensable tool because it directly affects the overall gain, performance indicators, and output impedance. At the same time, the placement and structure of the feedback circuit within the overall design can only be determined by length tuning and optimization based on the engineer's experience and expertise.
With the NFB enabled (indicator light illuminated), the C9ii delivers a more spacious sound with superior dynamic range, excellent transient response, and relatively fewer harmonics, resulting in a more neutral sound with impressive detail and speed. With the NFB disabled (indicator light off), the audio output exhibits richer harmonics.
You'll hear a more coherent and full-bodied reproduction with stronger imaging and more structured and elastic mid-bass frequencies. There's no right or wrong with the low-frequency range setting; it's a matter of personal preference, and the adjustable low-frequency range allows the user to choose their preferences on the go.
We have thought through all the features and circuit designs that offer our users specific sound shaping options.
Timbre: 3 options (Classic Tube, Modern Tube, Solid-State) Gain Mode: 3 options (Class A, Class AB, Hyper) Anode: 2 options (High, Low) NFB: 2 options (On/Off) Input Mode: 2 (Line, Pre) Can you calculate how many sound variations are possible with the C9ii?
3. Power supply design
The power supply design of the C9 series is critical to its performance. The discrete headphone amplifier circuits of the C9 and C9ii are powered directly by batteries. The advantage of this design is that it avoids DC/DC voltage surges, which are considered the most ideal power supply environment in analog circuits.
The power supply system is carefully filtered and decoupled, using four WIMA metal film capacitors, 35 Panasonic POSCAP polymer tantalum capacitors, four Panasonic OS-CON polymer aluminum capacitors, and numerous COG-type MLCC capacitors. We know you're not particularly concerned with the "component arms race," especially when it comes to cramming dozens or even hundreds of capacitors onto a single PCB, which might seem like a component arms race.
So let's keep it brief here: We used a lot of WIMA metal film capacitors, a lot of Panasonic POSCAP polymer tantalum capacitors, a lot of Panasonic OS-CON polymer aluminum capacitors, and a lot of COG MLCC capacitors. There are actually specific reasons why we used these capacitors.
We're not attempting to break a Guinness World Record for the number of capacitors we can fit on a single circuit board, nor did we use so many different types for fun. Each capacitor serves a specific purpose and provides specific benefits to the sound, unfortunately due to space constraints. We'll highlight just two of them for you.
1. Panasonic POSCAP polymer tantalum capacitors
POSCAPs offer high capacity in a compact form factor, which is why we managed to fit 35 of them in. Yes, you heard right: 35. They're perfect for densely packed circuits where space is at a premium.
2. Panasonic OS-CON polymer aluminum capacitors
These capacitors provide long-term reliability and maintain their performance over extended periods, which is critical to the longevity of a portable, sometimes palm-sized headphone amplifier like the C9ii. Imagine this: In the year 2077, your grandson asks about the mysterious black box in your cabinet. You proudly pull out your C9ii, play him a song, and he's moved to tears—"buy better, last longer," perhaps as long as your favorite pair of Levi's.
The C9ii uses four Samsung INR18650-35E battery cells, which form a series circuit that directly powers the headphone amplifier. The C9 uses four Sony US18650VTC6 cells. With nearly identical internal resistance, the Samsung cells in the C9ii offer a nominal capacity of 3400 mAh, compared to the C9's 3120 mA.Depending on the operating mode, the C9ii offers a maximum battery life of 17 hours (in solid-state timbre, single-ended input/output, AB mode) and a minimum runtime of 8.5 hours (in classic timbre, balanced input/output, Hyper mode).
This represents a significant improvement over the first generation, primarily due to the improved battery cells. It's worth noting that different brands and models of 18650 battery cells can have a direct impact on sound quality due to differences in internal resistance, discharge capacity, and other performance parameters.
Feel free to try different battery brands to determine the differences. Both Samsung and Sony batteries have a cutoff voltage of 4.2 V. This means that the output power of both C9 generations remains unchanged unless the voltage is increased, as both rely on direct battery power for the circuitry.
In other words, the output power of both C9 generations is virtually identical, decreasing over time as the battery voltage drops. However, thanks to architectural changes, the C9ii significantly improves load driving capability compared to its predecessor. The dynamic output current increases significantly in response to changes in the music signals and backend load, resulting in stronger drive capability, a richer sonic presentation, a more complete soundstage, and more natural and fluid musicality.
Audiophiles can easily detect these differences by comparing the sound of the first and second generations using the same source, track, load, and operating mode. It's important to emphasize that the rated output power and the number alone do not equate to actual performance. Many products on the market boast high output power achieved through voltage boosting, yet produce a horrifying sound that is dry, lacks transient response, or sounds harsh or hollow in the highs at high loads.
The cause is often limited dynamic output current and power handling. This brings us to the reason why the C9ii does not include a P+ mode, which would require voltage boosting (DC conversion). Implementing DC conversion would undermine the benefits of direct battery-powered amplification, and direct battery-powered amplification is a fundamental design philosophy of the C9ii that sets it apart from other products.
The C9ii is designed for purer performance and retains the Hyper Mode introduced in the N30LE. This mode further adjusts the static operating current in Class A mode and pushes the circuit to its limits in various operating modes. This concludes the major design changes to the C9ii. For more technical details, please refer to the block diagram below.
4. Complete assembly, heat dissipation and standard recording cable
Next, let's look at other changes and adjustments. The C9ii continues to build on the strengths of the first generation C9, such as the Class A/AB operating modes and the pure power amplifier mode (ideal for use with a DAP that supports pre-out). The volume control is still precise and utilizes the MUSES72320V, which you'll find in many of our products. In terms of appearance and structure, the C9ii features two small handles that aren't just decorative.
Due to the differences in function switches and components between the C9 and the C9ii (the C9 required two-position switches, while the C9ii uses three-position switches), the toggle switches are now mounted above the control panel. Grips on the sides of the C9ii provide protection, ensuring that accidental impacts only affect the exterior without affecting the switches or degrading performance.
The side panels have been redesigned with a curved structure, improving grip and increasing the surface area for heat dissipation. The C9ii's heat dissipation has been significantly optimized. The primary heat source is the transistors in the discrete four-channel high-performance headphone amplifier circuit.
To efficiently transfer this heat to the metal casing with minimal thermal resistance, the internal structure contains heat-conducting graphene sheets with high thermal conductivity. Additionally, aluminum alloy heat sinks are used to improve heat absorption and ensure even temperature distribution.
This heat is ultimately transferred through the thermally conductive graphene sheets to the aluminum alloy casing for dissipation via a low thermal resistance path. Another important structural change from the first generation C9 is the battery change. While the original C9 required external tools (actually a screwdriver) for this task, the C9ii features a self-locking push-button switch and a precision-molded battery socket.
The battery module features a tool-free, self-locking design with a self-locking push-button switch for easy installation and removal. The connection between the battery module and the C9ii is via a SATA slot, ensuring a secure three-point attachment that is both robust and conveniently replaceable. Since portable headphone amplifiers must be paired with a source device, the quality of the source's line-out (LO) or preamp signal has a significant impact on the overall sound quality.
The interconnect cable included with the C9ii has also been improved after extensive subjective listening tests. The new cable is constructed of eight-conductor OCC (oxygen-free copper) (the original used a blend of four-conductor OCC and OFC). It features a mixed-strand stranded conductor structure, and each conductor is individually shielded with OFC (oxygen-free copper).
The 4.4mm to 4.4mm interconnect cable uses four-wire balanced transmission, with the shielding layer independently grounded to greatly reduce interference.
We really hope that we can offer you a new and enjoyable experience with our new C9ii!
