C9 uses a custom-designed fully balanced 4-ch dual timbre circuit with the Toshiba 2SK209 JET(Quad Set) for solid state, and a Korg Nutube 6P1 Double Direct Heated Triode for tube mode. You can use either mode for both Single-ended and Balanced Headphone Output
The Redesigned timbre circuit gives you a livelly, euphonic, and delicate presentation using two miniature double Direct Heated Triode (DHT) for both Balanced and Single-ended output, with carefully implemented NFB that reduce THD+10 to 0.03%. Cayin's innovative installation process eliminates the microphonic effect of vacuum tubes.
The solid state circuit delivers a warm and rich timbre that is realistic and engaging. It uses a fully discrete buffer and amplification audio circuit designed around two matched pairs of high quality, low noise Toshiba 2SK209 JFET op-amps.
C9's dual amp operation mode lets you switch between Class A and Class AB operation instantly. Class A mode is less energy efficient, but provides the lowest possible distortion, and a warm, smooth, musical sound. Class AB offers longer battery life along with a clean, tight low-end presentation.
C9's dual input mode allows you to optimally receive fixed or variable volume signals, and bypass the C9's volume control when connected to a device with its own volume control.
Line: Receives fixed voltage audio signal from line level output and functions as a headphone amplifier with local volume control
Pre: receives variable voltage audio signal from pre-amp output and function as a power amplifier: volume is controlled at the source equipment
The amp also isn't limited by your input source. You can use balanced headphones with a single ended source or single-ended headphones with a balanced source, seamlessly.
One of the biggest problems portable audio fans face is battery degradation on their high-end devices. Usually a battery replacement means waiting weeks to receive service from the manufacturer. C9 gets reliable, replaceable power from 4x Sony VTC6 3000mAH 18650 Lithium Batteries.
I am using this with my Astell & Kern SE300 and Meze Empyrean II Headphones. The A&K can "drive" the Empys, but the addition of the amp brings them to life. Highly recommended.