Cayin announced the E01 Audio Motherboard today. We didn't put Nutube into E01 Audio Motherboard, but we offer something better, in our humble opinion. The E01 Audio Motherboard is a discrete component based pure Class A (Switchable to Class AB) DAP audio system. We consolidated our N8 audio system into A01, and we pushed the envelope or our N6/N6mod design to become the T01, the E01 on the other hand, is new Frontier that Cayin has decided to venture into with determination and decades of analog audio experience. This is our ultimate audio design within the physical and electrical limitation of N6ii architecture.
The DAC section of E01 Audio Motherboard is designed around the ESS ES9038PRO. This is an 8-channel DAC chipset and we have set it up to output in differential current mode. To optimize the output performance, we have connected four DAC output channels in parallel as an audio channel. The stereo output will then go through IV conversion and LPF circuitry as in other current mode output DAC design.
When we formulated our Audio Motherboard roadmap, we have set our mind to offer Pure Class A headphone amplification at some stage, and after two general-purpose full-features Audio Motherboard A01 and T01, we think this is the perfect timing to introduce a special purpose limited-feature Audio Motherboard, and E01 become the perfect platform for this plan. To put this into the context of DAP, we have designed an innovative, first of its kind, Dual Operation Mode circuit that allows user to switch between Class A and Class AB instantly through menu control.
Since it is not possible to implement a Class A headphone amplifier with off-the-shelf highly-integrated Op-Amp, we have to build the E01 headphone amplification circuit with discrete components. We use low-noise audio grade JFET (Junction gate Field-Effect Transistor) and BJT (Bipolar Junction Transistor) and the result is a jaw-dropping portable system that offers impressive current output capacity and outstanding control a difficult load.
One of the very tough requirement to implement Class A amplification with discrete components is to make sure amplification in each channels are in near-identical gain, and this can only be achieved with manually matched critical components such as BJT and manually installed them to the PCB before reflow soldering.
The other critical point is to make sure the static current are well-controlled so the that BJT will maintain perfectly stable operation in saturation mode. There are loads of factors that will affect the static current: the resistors in peripheral circuit, the internal resistance of the PCB itself to name a few. The difference may sometimes cause a slight deviation in the static current and affect the operation of BJT, not necessarily significant from electrical safety perspective, but audible in audiophile application. Therefore, in order to ensure the stability and consistency of the static current, we have added two adjustable resistors in the circuit. After we stuffed the PCB, we need to test and fine tune these adjustable resistors manually in order to make make the static current of the PCBA is consistent with the reference value defined by our R&D Engineers.
In view of these manual procedures in the E01 manufacturing process, and the relatively high BOM cost due to discrete components (when compare to highly integrated Op-Amp), the production capacity of E01 will be fairly low when compare to the A01 and T01 Audio Motherboards.
The N6ii with E01 can playback 7.5hour continuously at Class A mode, and 9.5 hours continuously at Class AB mode. This is consider impressive battery duration for power-hungry ESS DAC chipset and Class A discrete components.
The suggested retail price of E01 is US$419.00 and it will be available through our international distributor network before Christmas 2019,
Pre order already in thanks to Phil@AudioConcierge... 
