Headphoneus Supremus
Versatile, powerful, capable, and efficient DAC nicely exceeding all my expectations
Pros: -- Very versatile DAC/dongle with 12 distinct hardware sound rendering options
-- The stage expansion option is really impressive
-- Very good power with three versatile gain options and, more importantly to me, the capability to drive demanding low- impedance IEMs
-- All three outputs (2.5, 3.5, and 4.5) are provided, and nicely compactly arranged
-- Conveniently small unit, considering all outputs, buttons and options
-- Quite power efficient, given the capabilites
Cons: -- Instructions are only on Chinese/Mandarin
-- The mecha design is not exactly my preference (subjective) but reasonably subtle and well built
-- Volume buttions are not as tight as ideally could be (minor nitpicking)
So no any major grips really - rare with my critical attitude, hence 5 stars
A brief opinion (well, at least I tried to keep it short while reflecting on key points) to share my very positive impressions of this less-known DAC.

About the manufacturer:
Kuang Pai is a Taiwanese company that does not seem to make much efforts to sell their products in the West, so their do not have much published materials in English. I bought mine Plus4 from AE, and interestingly, the name of the company is not mentioned in the text (only in images), perhaps due to their Taiwanese origin.

I bought Plus4 with my own funds (and no any special discounts) for ca. $125 from Ali Express. One can seach "Plus4 DAC" on AE to find the only store that (currently) sells Plus4. I did use information about Plus4 from their site - that should be acknowledged.

Package, accesories and build:
Plus4 comes in a relatively small box:

Included in the package are the DAC itself, USB C to USB C cable, USB C to Apple cable, USB C to A adaptor, and brief instructions exclusively in Mandarin. Cables are black and thick, while definitely flexible enough not to cause any problems, while feeling nice.

Plus 4 is very solidly built of two pieces of black anodized aluminum. Three buttons (two for volume control and the middle one to switch modes) are slightly protruding - that some may like and some may not. Buttons are a bit loose to my strict judgment (and compared to Tanchjim Space) but not rattling as in Tempotec BHD pro.

Plus4 is surprisingly quite compact and light, given its capabilities
In the image above, shown from left to right are Kuang Pai Plus4, Tanchjim Space, Tempotec BHD pro and E44, Muse M3, JCAlly AP90 and AP20 (DAC with an in-built battery).

Plus4 is only slighly longer and thicker than Tempotec BHD pro and not much heavier, so it can be comfortably handled similar to small DACs/dongles.

Main features:
1. Nice independent volume controls (>100 steps, and more than enough for me).
2. Three gains, changed by the long press of the middle button. I usually run all my dongles in low gain, since I use IEMs. Yet, for Plus4, while changing the filters and inadvertently changing the gain, I liked how different the sound was in the high gain, so I plan to explore it more.
3. Six filters, that can be changed by a short press of the middle button, and displayed by one of the LEDs. The filters are subtle but definitely functional and distinguishable at least between extreme options, e.g. expanding and curtailing the treble. So far I liked the first one (blue light).
4. Last, but most definitely not least, is the two tuning options of "classic analogue" and "wide space" overall sound rendering, selected by pressing two volume buttons simultaneously.
The "wide space" (the expanded stage) is definitely engaging and, IMO, demonstrates that to a signicant extent, the perception of stage can be generated by DSP, likely manipulating phase delays.

3 gains, two stage options, 6 filters - 36 different options altogether!

Power consumption and management:
Plus4 consumes ca. 120 mA while working, and 100-105 mA, when idle. The working power is very reasonable given a lot of processing. Idle power could be less/better, but perhaps dedicated audiophiles do not run their sources idle :)
Importantly, less difference (e.g. compared to E1DA) perceived when externally powered - good on-board power management.
I do not have demanding headphones to compare and evaluate the voltage-limited power of Plus4 and my other dongles.

Summary of the sound impressions:
Plus4 is unmistakably Cirrus 43131/43198 in its sound rendering, and on top of that, it is definitely neutral for lean, crisp sound as a base. Then, different options, such as different stage rendering (more) and filters (less) add well on top of the neutrality for multiple synergies.
I really like an expansive stage option with most of my music, other than some chamber pieces with already good separation between instruments.
Plus4 can run demanding low-impedance IEMs, such as Audiosense T800.

Comparisons with several other DACs:
Muse M3 vs. Plus4
From my very first impressions - Plus4 does all that I wished M3 do - true balanced with all outputs, reasonable power consumption, not that bulky and heavy.
So by utility, M3 is just not competitive.
The only aspect where M3 wins for me is the design.
Then, convenience aside, M3 sound rendering is different (ESS): equally capable and interesting in its 7 variations, and quite complimentary to Plus4. M3 rendering can be perceived aa more engaging, at least based on initial impressions.
I used to like ESS rendering with its thicker mids and more emphasized highs, when I started in this hobby. I slowly grew to appreciate and prefer Cirrus neutrality now. Also, MQA-rendering chips did not help ESS perception for me.
Curiously, M3-II is now Cirrus-based and may be closely related to Plus4, but I do not have any plans to explore another Muse DAC....

E1DA SG3 vs. Plus4
E1DA is ESS-based, and with its touch of emphasis on bass, feels powerful and authorative. Plus4 is more natural and spacious, and emphasizes transducer's rendering more naturally. Plus4 also seems to manage the power better, being less dependent on external power to sound the best, at leaat with old smartphones, like S10.
Plus4 handles demanding T800 at least as equally well, as externally-powered E1DA - a mighty accomplishment.
The rivalry beteeen E1DA and Kuang Pai seems to propagate in their product descriptions. Kuang Pai emphasizes specifically no EM interference (definitely properly done by Plus4), while E1DAs, less so SG3, are quite prone to EMI.
E1DA's creator, in turn, criticized the amps used in Kuang Pai, as potentially clipping. I could not notice any clipping/distortions with my IEMs (mighty demanding headphones are needed to reach any clipping, if it is at all the case...)
So, overall, Plus4 solidly wins over E1DA for me, by being more versatlie, better managing the power and working better for my subjective sound preference.

Tanchjim Space and Tempotec BHD pro vs. Plus4
All three are Cirrus-based DACs that are quite close in sound rendering. While the pronounced difference with Space is its special treble rendered for more perceived air and spaciality. BHD pro (with its original firmware, I have not tried to change so far) is different by its gentle warmth.
I really liked both flavours of Space and BHD pro (and plan to use both along with Plus4). At the same time - as with all flavours - they may not synergize universally with all IEMs, while more neutral Plus4 can be appreciated as more compatible and emphasizing the transducer sound, but then it may take some time to get use to Plus4 neutrality for many.
The expansive stage option of Plus4 is definitely a win in all comparisons.

Overall impressions:
Kuang Pai Plus4 is a nice well-built, powerful, very versatile in its hardware options, compact DAC built around neutral Cirrus sound.
Given its great versatility, especially in staging, and in absence of any major pitfalls/disappointments - Plus4 is well worth its asking price, and 5 stars are fully deserved, IMO.
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