Under the hood.
You can already get a good idea of what to expect under the hood from the Design section of the review. Cayin been in business of audio electronics for almost 3 decades, especially with a focus on personal audio products in the last 7+ years. C9 amplifier looks like a combination of their best design elements combined together in one package. And speaking of the design in general, some already asked on Head-fi “why amplifier only?” and if “Cayin planning to release DAC/amp version of C9?” The response from Cayin was clear, due to DAC and sw/fw dependency, DAC/amps get outdated faster than a pure amplifier that can stay relevant for a much longer time and be used with many different sources. And here is what you will find under the hood of C9.
First of all, you have a dual Input mode where you either select Line Input with the incoming signal from the source being fixed and you vary the amplifier output using C9 volume wheel, a more traditional headphone amplifier operation. Or you switch to Pre-Amp Input where C9 functions as a power amp with a fixed max gain level and you adjust its output by varying the input from the source. Some DAPs offer LO with an adjustable output controlled by a volume wheel, thus a name of “Pre-Amp” since you are adjusting the amp volume in pre-amplifier input stage. And because Pre-Amp output will set C9 to max gain level, as a safety precaution in addition to a switch you also have to press and hold pre-amp activator button on the side of C9.
After the initial input stage, signal gets timbre treatment depending on a selection of either Solid State (2SK209 JFETs) or Vacuum Tube (Korg NuTube 6P1). Yes, C9 is Solid State/Tube amplifier, but that part of the circuit is responsible for “coloring” of the sound prior to the actual headphone amplifier section. And as I already mentioned, this sound “coloring” will be applied to either SE or BAL inputs and C9 has a clever design to process audio directly through single ended or balanced path, as well as being able to switch from BAL to SE and SE to BA, considering amplifier offers both of these inputs and outputs.
The amplifier gain control is done in two stages. Primary Gain control is between Low (0dB) and High (6dB boost) gain selectable from the front panel switch. Secondary Gain control uses 4-channel ALPs potentiometer (volume wheel) with a pair of MUSES Series low noise, low distortion resistance ladder electronic volume (MUSES72320). Especially when using sensitive IEMs while keeping the volume low, I never experienced L/R imbalance with C9 volume control.
And last, but not least, the fully discrete headphone amplifier section with a selectable (by a switch) Class A or Class AB dual amp operation (DAO) mode. Many are probably going to remember that Cayin featured Class A and Class AB in their E01 card for N6ii. With E02 there was not enough room to have fully balanced circuit and both A/AB, thus E02 only featured Class AB. Here, C9 will give you both Class A and Class AB.
So, how does C9 amplification translate into the actual output power? C9 is rated at 700mW (@ 32ohm) from 3.5mm SE and 2,600mW (@ 32ohm) from 4.4mm BAL output jack. Of course, depending on headphones, with higher impedance the rated output power will scale down accordingly since it is inversely proportional. Considering this is a portable battery-operated amplifier, the power output parameters are quite impressive. And speaking of battery, the rating it from 5.5hrs to 15hrs and will depend on a mode of operation. Vacuum Tubes consume more current and will drain battery faster in comparison to Solid State. And you should expect to drain more battery in power hungry Class A or when using Balanced connection.
Thus, you can expect to go from Balanced Tubes and Class A with 5.5hrs to Single Ended and Solid State Class AB with 15hrs of battery life. And don’t forget, we are talking about components that generate a lot of heat, especially combination of discrete Class A and Tubes that make C9 feel quite warm. That is a reason why Cayin paid close attention to component layout to improve the air flow, even attaching PBS (pyrolytic graphic sheets) to those parts generating more heat. But overall, my typical C9 use was Balanced, Tubes, and Class AB where I was getting a little over 9hrs of playback time.
I have talked about Korg NuTube 6P1 (a dual channel triode vacuum tube) back in my N8 review. Just as a recap, while NuTube operates exactly like a triode vacuum tube, the tech behind it is based on a vacuum fluorescent display technology, like LED. These NuTube modules require less power than a traditional vacuum tube, smaller in size, have a much higher reliability with 30,000 hours of continuous life expectancy, all that while still providing a sound characteristics of vacuum tube sound. And just like with a vacuum tube, there is a warm up period, thus when you switch to tubes there is a short “warm up” delay. And similar to N8, to eliminated microphonics associated with these tube modules, Cayin designed a custom-built shock-absorption silicone housing and a spring-loaded suspension system.