C9ii – The successor to the genre-defining C9

The successor to the genre-defining C9 throws in local feedback adjustment around dual 6P1 Nutubes as well as its discrete solid-state output stage. That’s before anode voltage adjustment allows Cayin to reinvent the rule book, once again. 

In its rawest form – with the barest minimum error correction around its Nutube voltage gain and transistor output stages – C9II is an exercise in circuit purity. It’s a simple circuit that outperforms any complex one, especially in portable form factor.

With Hyper mode, where operating voltage and bias get pushed to the linear open-loop maximum, and fully balanced differential operation, Cayin equipped C9II with the means to operate at its maximum in every possible mode of operation. 

The vast majority of an amplifier’s tuning comes from its initial input and voltage gain stages. Here, we see how far Cayin has come since C9 was released in 2021.

Gen5 Nutube 6P1 Vacuum Tube Audio Circuit

Cayin has applied this vacuum tube to multiple products, including 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 anode (plate) voltage feature and the highly praised Classic and Modern dual tube timbre. This adjustable plate voltage feature offers two levels: high and low.

Fully-symmetric Headphone Amplifier

Cayin has designed a three-stage amplification circuit to embrace the fully symmetric design into C9ii: a differential input stage, a voltage amplification stage, and a power driver stage. 

• Stage One: Symmetric JFET Common-source Differential input amplifier.
• Stage Two: Symmetric BJT Common-emitter Push-Pull Differential Voltage Amplifier. 
• Stage Three: Symmetric BJT Common-collector Push-Pull Parallel Current Amplifier(emitter follower).

Dual Tube Timbre Circuit

Modern Sound: Introduces a large-loop negative feedback system, with total gain determined by the large-loop negative feedback circuit. By incorporating negative feedback over multiple amplification stages, the total harmonic distortion (THD) will be reduced significantly. 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 large-loop negative feedback; each stage operates independently through local feedback, with the overall gain determined by the cumulative gain of each stage. The distortion characteristics of the tube amplification circuit dominate the sound signature, resulting in a higher THD value. The distribution of harmonic distortion and the sensor signature exhibit a classic vacuum tube amplification circuit, with relatively more thermal noise and a richer vacuum tube presentation. The N8 DAP was designed with a similar NFB circuit. 

Anode (High/Low) 

Cayin introduces a new feature, “Anode” to C9ii. The High/Low adjustable anode (plate) voltage further enriches and refines the range of vacuum tube timbre. The working principle is that applying different operating voltages to the plate of the vacuum tube alters its operating state, ultimately affecting the sound signature of the timbre circuit. This mainly manifests in changes in audio linearity, and it will adjust the overlay, spectrum, amplitude, and ratio of second-order harmonic, resulting in perceptible audible differences.

• Solid State sound: Balanced across the entire frequency range, musical without tube coloration.
• Classic + Anode (H): The richest tube sound, with intense emotional depth, suitable for vocal music with a lot of details.
• Classic + Anode (L): Slightly lighter tube sound, suitable for vocals with thicker tones.
• Modern + Anode (H): Less tube character, with moderate smoothing in the midrange and a slight sweetness added.
• Modern + Anode (L): Minimal tube coloration, without affecting resolution and definition.

 Negative FeedBack (NFB)-Integrated precision control circuit

A listener’s ability to adjust every parameter including tube anode voltage and the feedback loop around Nutubes means up to five potential sonic signatures are possible.

The operation of C9II’s Gen 5 Nutube circuit in Classic mode reduces negative feedback to a bare minimum, increasing immersion with a simpler and faster circuit that avoids time lag and transient intermodulation distortion.

Distortion figures also increase on paper but are of a low-order variety that is less jarring to the ear, compared to the complex intermodulation associated with unabated feedback levels.