As aune’s new generation of fully-discrete class-A headphone amp, the S17 Pro has the features of twin JFET, R2R volume control, 2 levels of current to select from (50mA/100mA class-A quiescent current per transistor), output power as high as 7.5W, 3 groups of headphone outputs + 2 groups of preamp outputs, etc. It is a high-performance rich-sounding headphone amplifier with high power. JFET has high input impedance and rich and mellow sound like the vacuum tube. As for the S17 Pro, it’s not just JFET. It’s TWIN JFET, whose temperature rises are the same, performances are the same, and the mid-point voltage is stable. It is the ideal input transistor of a headphone amp. The S17 Pro final output stage uses two pairs of output transistors in parallel. The whole device has as many as 16 output transistors. Max output is 7.5W. It can drive all kinds of headphones and IEMs with ease. The S17 Pro specially designed two levels of class-A current: 50mA/100mA per transistor, and each channel of the S17 Pro has two pairs of transistors in parallel, so the quiescent current of each channel is as high as 100mA/200mA. The sound of a class-A amp is mellow, warm and smooth. The S17 Pro uses the R2R electronic volume chip from JRC and the dedicated op-amps to build the 4-way balanced R2R volume control. High control precision, great channel balance, wide soundstage, accurate positioning. The S17 Pro has two gain levels, and has set different output amplitudes. The low gain takes advantage of the class-A amp’s feature that the transistors are always working in the linear area, to drive the IEMs well and properly, while the high gain is as high as 7.5W and thus can drive headphones well with big power.