C9 Reference Portable Headphone Amplifier

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Tailored designed Fully Balanced 40ch Dual Timbre Circuit. Toshi More details

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The C9 from Cayin is the perfect accessory to your favorite headphones whenever you're on the go. The portable headphone amplifier has the option to switch between class A and AB, tube or solid state, high or low gain, and plenty of other options and features. Pair the C9 with you favorite source for rich, organic sounding high-fidelity audio.


  • Tube/Solid State Dual Timbre
  • A/AB Class
  • 2600mW p.c. 32Ohms
  • Fully Discrete, Fully Balanced
  • Line Input – SE/BAL
  • Pre-amp input – SE/Bal
  • 4.4mm/3.5mm Input and output
  • SE/BAL Conversion
  • Electronic Volume Control
  • Modular battery USB-C QC3.0
  • 5.5-15 Hrs Battery Life
  • 160x80x28 (mm)


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 Butube 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.


Switch between Class A and Class AB modes instantly. You can customize the sound signature to fit your personal listening preferences, music genres, and headphone pairings.

  • Class A Mode: Low efficiency and low distortion. Musical, smooth, warm, and lush sounding.
  • Class AB Mode: Higher efficiency and more dynamic. Clean, tight, great extension and slam.


Choose between high and low gain modes. MCU controlled and optimized automatically.

  • Primary Gain: Custom designed 6dB voltage gain circuit.
  • Secondary Gain: Gain circuit in electronic volume control.

The C9 is designed with electronically controlled analog volume control with a 4-channel ALPS potentiometer with a pair of MUSES series low noise, low distortion resistance ladder stereo electronic volume.


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


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.


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.


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 provides +/- 8.4V direct power. Dedicated power protection and management to ensures 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.


Headphone Amplifier Specification

Product Information
Input: 3.5mm TRS, 4.4mm TRRRS Timbre Circuit (Tube): KORG Nutube 6P1 X 2
Output: 3.5mm TRS, 4.4mm TRRRS Timbre circuit (SS): Toshiba 2SK209 JFET X 4
Electronic Volume Control: MUSES72320 X 2 Input Differential Amp.: LIS LSK489 JFET X 4
Battery: Sony US18650VTC6 (3000mAh 3.7V) X 4 Charging: USB Type-C (QC3.0)
Dimension: 160 x 80 x 28 (mm) Net Weight: 550 (+5g)
Battery and Duration
Battery Duration
Timbre DAO Single-Ended (3.5mm) Balanced (4.4mm)
Class AB ~15 Hours ~10 Hours
Solid State Class A ~12 Hours ~7 Hours
Class AB ~9.5 Hours ~9 Hours
Vacuum Tubes Class A ~8 Hours ~5.5 Hours


  1. Test condition: Input of a standard line level audio signal, volume at 10 o'clock position, lo gain, connected to 32Ω headphones.
  2. Charging time might extend if the four lithium batteries are in different voltage (capacity).
Condition Standard Charger (5V-2A) QuickCharge 3.0
Time os 6 Hours ~3 Hours

Headphone Amplifier Audio Specification

Headphone Output
Setting Test Condition
Loading 16Ω 32Ω 150Ω 300Ω
Power 3.5mm SE Tube/Solid State 1200mW 700mW 160mW 80mW High/Low Gain
Power 4.4mm BAL Tube/Solid State 4100mW 2600mW 640mW 320mW High/Low Gain
Freq. Response Tube/Solid State 15Hz-60kHz (+0.5dB) 15Hz-60kHz (+0.5dB) 15Hz-60kHz (+0.5dB) 15Hz-60kHz (+0.5dB) High/Low Gain
Single-Ended/Balanced Conversion SE>SE BAL>SE SE>BAL BAL>BAL
Solid State 0.00% 0.01% 0.01% 0.00% @1kHz, 1Vrms,
THD+N Vacuum Tube 0.03% 0.03% 0.05% 0.03% A-Weighted
Solid State 120dB 114dB 114dB 123dB 20Hz~20kHz
Vacuum Tube 112dB 111dB 111dB 114dB High Gain, A-Weighted,
Dynamic Range Solid State 122dB 119dB 119dB 125dB 20Hz~20kHz
Vacuum Tube 118dB 117dB 117dB 120dB Low Gain, A-Weighted,
Solid State 120dB 114dB 114dB 123dB 20Hz~20kHz
Vacuum Tube 112dB 111dB 111dB 114dB High Gain, A-Weighted,
SNR Solid State 122dB 119dB 119dB 125dB 20Hz~20kHz
Vacuum Tube 118dB 117dB 117dB 120dB Low Gain, A-Weighted,
Solid State 75dB 97dB 114dB @1kHz,
Channel Separation Vacuum Tube 75dB 90dB 110dB A-Weighted
1.5V 3.0V 1.5V 3.0V High Gain
Line In 3.0V 6.0V 3.0V 6.0V Low Gain
Input Sensitivity 2.1V 4.2V 2.1V 4.2V High Gain
Pre In 4.2V 8.4V 4.2V 8.4V Low Gain
Output Impedance Tube/Solid State <50mQ <50mQ <50mQ <50mQ High/Low Gain


  1. Unlesss otherwise stated, all parameters are measured at 32Ohm loading.
  2. All parameters are measured when the battteries are fully charged.



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