State-of-the-Art analogue amplification for DAP
N8ii is a showcase of integration. We didn’t offer any innovation technologies per se, but we have integrated almost everything we did in past 2-3 years into N8ii. As a result of that, the amplification of N8ii is an significant improvement over the original N8. On the other hand, if you are familiar with Cayiin DAPs and C9, you probably can read throught his part very quickly.
Fully-discrete fully-balanced
We have designed a 4-channels discrete components based circuit to serve as the headphone amplifier of N8ii. Going discrete allows more room to fine tune the audio performance of a circuitry than the more popular op-amp based approach. There are never-ending choices and combinations of audio grade JFET (Junction gate Field-Effect Transistor) and BJT (Bipolar Junction Transistor), we can regulate the voltage of different components, or use different resistors at various point of the circuit.
Because the choices and customisations are unlimited, we cannot assume all discrete circuit are equal. The experience of the engineering team plays a vital role in the final outcome although generally speaking, a discrete-based amplification circuit, if implemented properly, should out-perform op-amp alternatives.
On the other hand, disrete circuit require more space, drain more power, and dispense more heat than op-amp, that’s why we didn’t use them very often in DAP development. The E01 and E02 Audio Motherboards of N6ii are discrete based but they have serious limitations: E01 is single-ended only with limited output at Class A, E02 is Class AB only. Fortunately, the compartmentalized CNC Aluminum chassis of N8ii disperses heat at very high efficiency, and the verical placement of Nutube created a lot of room (and breathing space) for the circuit, and we can install a huge battery to powe the discrete circuit. With all these in place, the discrete amplification circiut havs a brilliant head start and we are very please with what we have offerd in N8ii.
Last but not least, we have noticed the trend of very low impedance IEMs in recent year. When we optimize our N8ii amplification circuit, handling low impedance load is one of our agenda. We are happy with the outcome and we add rated output of 16Ω loading to provide more information for low-impedance IEM users.
Dual Amplification Mode
The Dual Amplifier Operation (DAO) implies the same amplification circuit in two distinctive mode of operations: Class A or Class AB. The difference between the two modes is simply the point at which the transistors are biased. “In the case of Class A, the transistor is biased so that over the entire cycle of the RF input, the transistor is operating within its linear portion. In the case of Class AB, part of the cycle of the input is actually turning the transistor off". (cf
Acquitek)
Class A being a faithful reproduction of the input signal at lower distortion, it has its technical merit over Class AB, that is if you can live with the inefficient and excessive heat. However we cannot jump to the conclusion that one is better than the others in real life. If you are looking for maximum clean headroom and appreciate contrast and dynamic in your playback, your properly prefer Class AB. On the other hand, if vocal is your main genre and you enjoys warm, smooth and “a bit of soul” in your music, then you probably will stick with Class A most of the time. That why DAO is desirable whenever possible as users can switch between these two modes instantly through pull-down menu, based on their personal preference, music genres, and/or matching with different IEM/headphones.
For speaker amplifier, Class A almost always offer less power than Class AB in the same circuit. That's because power supply become the bottleneck is similar implementation. With battery power DAP, we happen to have a slight advantage. When we devleop our C9 portable amplfier, we have achieved a DAO circuit that can operate in Class A and Class AB with the same rated output, and power supply played a very important role in C9 implementation. We managed to adapt our C9 experience to N8ii, making it another DAO circuit that deliver almost the same power at Class A and Class AB.
When we implement the discrete Class A amplification in N8ii, we have to make sure all four amplification channels are in near-identical gain. We have to manually match critical components and installed them to the PCB manually before reflow soldering. In addition, we must control the static current so that the discrete components will remain perfectly stable operation in saturation mode, therefore adjustments is need to compensate the deviation cause by discrete components. As illustrated in the PCB photo, there are
FOUR adjustable resistors in place. We’ll fine tune each assembled PCB manually to match our reference design. All these procedures involve extra resource and is very time consuming, that’s why discrete Class A is an expensive option, especially on compact devices such as portable DAP.
Dual Output Mode
N8ii DAP incurred the unique Dual Output Mode from the original N8. We regulate the operational voltage of headphone amplification circuit to offer P (Standard) and P+ (High Power) mode. For those who have been in the HiFi hobby long enough, you probably noticed that the critical factor of High Fidelity is electricity, i.e., power supply in your equipment. When we increase the voltage of our discrete headphone amplification circuit, it will not only deliver more power and improve its handling capability, but also changed the sound of the discrete components. In other word, your IEM probably won’t need the extra power of the P+ mode, but it won’t hurt to have an alternative sound signature from their DAP.
Unfortunately, even when cost is no object, we are still bounded by the law of physics. We cannot engage P+ mode and Class A simultaneously. This will drain very high current from the battery and generate heats that can’t be disperse effectively given the tight space available with N8ii.
anyone is like me ?
