As already mentioned, E0x stands for ESS DAC, just like A0x corresponds to AKM DAC and T0x name goes along with PCM DAC from TI.
Following A01 and T01 with single ended and balanced outputs (headphones and LO), E01 took many by surprise with just a single ended headphone output. But due to a large size ES9038 Pro DAC and all the miscellaneous components associated with Class A/AB dual operational mode headphone amplifier, there was simply no room left on the board for a second DAC and balanced ckt. Due to overwhelming requests, Cayin revisited E01 design with E02 update to make it balanced.
But to make room, you have to make compromises. ES9038 Pro is a desktop quality larger size power hungry DAC. Thus, to make the design balanced, Cayin switched to a mobile version of 9038, using two ES9038Q2M. It is still audiophile quality DAC from the same family, but a smaller footprint with a more power efficient design. E02 uses two of these ES9038Q2M DACs, each functioning in mono mode, decoding L/R channel independently.
It is still densely populated printed wiring board (pwb) with 4-channel I/V converters, two dual channel low pass filters (LPF), two dual channel line drivers, and just enough room to squeeze discrete component Class AB mode amplifier per channel. Plus, now the headphone output is doubled as Line Out which I’m going to talk about later.
To get a better idea of the changes between E01 vs E02, here is side-by-side comparison of their design block diagram:
And to put it into a better perspective in terms of layout and management of board space, here is side-by-side comparison (pictures by Cayin) of their circuit boards.
Going balanced has many benefits, with a boost in output power being one of them. The headphone output of E02 Class AB amplifier is rated at 600mW (32ohm load) which scales down accordingly as you increase the load. Also, similar to E01 Class AB, battery playback with E02 is around 9.5hrs. This actually suggests that with a similar discrete amp design, desktop ES9038 Pro draws as much power as two mobile ES9038Q2M. Another battery statistic, when using balanced Line Out, playback can reach 22hrs, suggesting Class AB amp ckt drain on the battery.
I have a feeling when E01 was introduced, too many people were pre-occupied with its Class A/AB amplifier and dismissed the lack of Line Out. If you think about it, the intent of LO is to connect to external amplifier, and maybe having the option of internal Class A/AB was good enough for some. But if you need more power and want a clean undistorted output to drive external amp, double-amping is not the best solution. Thus, you need a dedicated LO.
You can argue that you can switch to A01 or T01 modules to use their Line Out, though now you are talking about LO from a different DAC and its corresponding sound sig. But there is more to that. If you look closely at design diagram of T01 (similar to A01), you will realize that its LO goes through internal amplifier.
T01 block diagram:
If you refer to E02 diagram I shared before, you can see that its LO bypasses headphone amplifier circuit. According to Cayin, this is their first unamplified balanced LO in N6ii family. And to make it compatible with either desktop or sensitive portable amps, Cayin provided a setting to select between 3 output levels: 4.1V, 3.2V, and 2.2V
I tested N6ii LO with ROMI Audio BX2 full balanced portable amplifier, which I actually requested specifically for review with N6ii, and also planning to review separately soon. BX2 is a very transparent and super clean Class A amp with a volume control, something which is important for pair up with N6ii w/E02 since you only have 3 fixed output voltage levels and no variable volume control from LO. BX2 is a transportable battery powered amp, and makes a great combo with N6ii w/E02 to drive my demanding headphones (Meze Empyrean, oBravo HAMT Sig, ATH-R70x, etc.). But, BX2 is too powerful, not exactly IEM friendly even when you set LO of N6ii to 2.2V, but for headphones it is perfect.
When E01 was released with 3.5mm HO, some people were upset they had to adapt their balanced cables to SE. When E02 was released with its 4.4mm BAL HO/LO, I already had a few people mentioning to me “too bad, there is no SE output”. It is hard to please everybody, but I have noticed that Andy (Cayin global rep) mentioned about adapter to use single ended 3.5mm TRS plug with 4.4mm BAL output. Since E02 has GND pin of Pentaconn jack tied to internal ground, as long as you are connecting 3.5mm TRS to L+, R+ and GND pins of 4.4mm TRRRS Pentaconn connector, it should work.
I wanted to put this to the test, and pinged Peter (Double Helix Cable), asking if he can make the adapter. I think he literally made it on the spot: a DHC pigtail 3.5mm to 4.4mm custom adapter (25awg occ silver litz wires, 4.4mm Eidolic connector with rhodium plug). Keep in mind, this is not a typical standard connection. Such adapters don’t exist because you can’t convert single ended to balanced, just doesn’t work converting L/R/GND to L+/R+/L-/R-. This is a custom adapter where L/R/GND is connected to L+/R+/GND of Pentaconn 4.4mm TRRRS connector.
And it did WORK!!! I was able to connect 3.5mm terminated earphones and headphones and use this adapter with 3.5mm external amp. As expected, when going from BAL to SE, the power output drops since I had to raise the volume by about 6 clicks (tested with the same IEM, volume matched).
Also, while using CFA Solaris with E02 and DHC 4.4mm single ended adapter, the background waterfall hissing of Solaris is cut down even below the level I hear it with E01. Thus, this adapter is also a good option for high sensitivity IEMs.