The successor to the genre defining c9 throws in no feedback operation, local feedback adjustment around dual 6p1 nutubes, and anode voltage adjustment to reinvent the rule book, once again. In its rawest form ndash with no global feedback and the barest minimum around its nutube voltage gain stage, where the majority of an amplifiers signature is shaped ndash c9ii is an exercise in circuit purity. Its 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. A listeners 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 c9iis gen 5 nutube circuit in classic mode eliminates the use of global negative feedback, 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 here is where a good old linear open loop circuit based on immaculate parts gain matching raises the victory flag. And thats before class a bias and high operating voltages come into play, setting up c9ii for success. You can even play with nutube anode voltage for very audible sonic outcomes. Throughout, c9ii allows linearity specs to remain respectable even without error correction, because there are fewer errors to correct in the first place. Cayins biggest asset in that regard comes from a differential, balanced operation, where common mode rejection enters the picture to amplify the signal and block off non linear distortion and noise. While 6p1 nutubes are always going to be the start of the show, and adaptable to sonic preferences and tastes, dont ignore c9iis solid state input either. Four channels of single ended class a toshiba jfets work in a quasi complementary fashion. Just npns, without pnp mismatches, plus even order harmonics and square law make for a totally unique differential circuit in a portable setup. Once you find your ideal match from five possible permutations, the input signal passes through jrcs muses 72320 resistor ladder volume controls ndash kept far away from the input and implemented only after the driver stage to preserve fragile small signal integrity and excellent signal to noise ratio. This preserved resolution is handled all the way by a discrete transistor signal path. C9iis design is more than up to the task of preserving the signal ndash mere op amp ics need not apply. Instead of wasting their input stage advancements by entrusting the analogy job to commercial ics, cayins labour of love continued into its discrete, differential, analogy stage for common mode rejection. C9iis driver section counts on all the benefits that come with a discrete fet and bipolar design ndash low open loop gain and the resultantly lower negative feedback necessary, high slew rates, current handling and unity gain stability. Cayins headphone power amplifier section is inherently stable without going into oscillation caused by too much gain product. The utmost attention is paid throughout. Differentiating itself from even other amplifiers that cling to op amp layouts seeking thx certification but with inordinate amounts of gain and feedforward feedback, c9iis linearity remains excellent already in the open loop, owing to its high operating voltages and bias. Those ensure individual transistors are working in optimum condition. Distortion and noise are kept low, without resorting to the excessive use of negative feedback. Cayin designed a true balanced differential amplifier to further improve c9iis linearity, and you can count on common mode rejection at its best whenever you plug in via 4.4mm preserving its resolution. Its an output stage thats direct coupled to improve low frequency performance, and c9ii audibly plumbs the lowest bass depths. With the extension down low, phase reproduction in the audible human hearing range for taut, hard hitting and life like dynamics is excellent. At the tip of the power stages spear, large bipolar devices work in parallel emitter follower configuration to ensure excellent beta and current handling for a good reason, reaping the full benefit of cayins quad of 18650 batteries outputting direct dc and working without voltage boost conversion. These power transistors are linear enough in the open loop, running fully biased and at high operating voltages, that they can be removed from the global feedback loop with the push ...