MASS-Kobo Model 475

Mass Kobo 475

Its Special

The Mass Kobo 475 (MK475) is a really special little amplifier. It is a solid state so don’t go about thinking it will wildly change your audio experience. However it does somethings really well and for those differences, it may be enough to justify its purchase.

Video Review


TLDR
This is a good amplifier that outperforms its specs. It sounds great, especially if you love sound stage and response. The best part is it applies its characteristics to all headphones and IEMs. The only downside is it doesn't play nice with very sensitive IEMs. Still the price is high but if you like a competent solid state amp with a wide and holographic sound, this may be for you.

Specs:
Model: Full-Balanced Portable Stereo headphone amplifier
Maximum Input Level: +16dBm (balanced), +10dBm (unbalanced)
Maximum Output Level (P-P): 7 V (balanced), 3.5V (unbalanced) (with 32Ω loaded, 1kHz, THD+N 0.5%)
　　　　　　　　　　 (RMS): 2.3V (balanced) , 1.2 V (unbalanced) (with 32Ω loaded, 1kHz, THD+N 0.5%)
Maximum Output without Distortion: 165mW (balanced), 45mW (unbalanced) (with 32Ω load, 1kHz, THD+N 0.5%)
Power Supply: AA Alkaline or rechargeable battery x 4
External Power Supply: Micro USB +5v
Size: 97mmW x 132mmD x 40mmH (not include protrusions)
Weight: 440g (with batteries), 382g (without batteries)

Introduction
The Mass Kobo 475 is a unique amplifier. In the current market of mass product portable equipment, what we have here is a small outfit from Japan hand making a really limited set of these amplifiers. x. It is a rarity in the world today, an amplifier that looks like from the last decade using AA batteries. All of this comes with a hefty price tag of over $1600 usd. The question is does it sound good? Can it power the latest headphone? Is it worth its hefty price tag? We will visit that in this review here.



Build Quality and Inputs
This is a really well built amp with a brushed aluminum shell that I like as it does not pick up fingerprints and scratches are not obvious, important for a portable device. It weighs about 500g with batteries. The batteries are 4 AA which can either be the usual Alkaline or rechargeable types. You have gain selection in the amp which requiring you to shift 4 recessed switches in the battery compartment. Personally I left it at low. All the controls of the amps are on the front panel. One of the best things I like is the decoupling of the power switch from the volume knob. Many portable amps today combine them, but it does mean readjustment of volume with each session. For the MK475, you will not need to change your volume as the power switch is separate. The volume knob is smooth with a good amount of resistance so it doesn't easily shift when rubbed.

For inputs, the MK475 accepts balance via a 4.4mm port. A switch can be flicked and utilising a Single Ended to Balance interconnect, it is possible to plug a single ended dac into the amplifier. For outputs, the MK475 accepts both 3.5mm and 4.4mm output.

The amp can be powered utilising a USB C on the front panel, this is strictly based on the older power protocol using USB A to USB C with no Power Delivery support. The MK475 will automatically switch between USB power and battery when required.



Equipment Chain:
Fiio M17 -> Balance Interconnect -> MK475 -> Headphones

Headphones used:
Simgot EA1000 (IEM)
Tangzu Wu Zetian (IEM)
Abyss 1266 Original
Abyss Diana Phi
DCA Stealth
Audeze MM500
ZMF Atrium Open
ZMF Verite Closed

Amps Compared
Brise Audio Tsuranagi
Enleum HPA-23RM
Xi Audio Broadway
Ferrum Oor + Hypsos
Topping A70Pro

Sound Quality:
Contrary to the specifications, as per the headphone list above, the MK475 works wonderfully with all the headphones I threw at it to a comfortable volume. Sound quality of the MK475 is comparable to any good solid state amplifiers like the A70Pro or Ferrum Oor. There are however 2 standout differences and 2 minor differences compared to the solid state amps I owned that can be noticed when swapping between them.

Soundstage:
The MK475 has a more holographic and larger soundstage then all the amps I have when compared. This is larger than even the current mode drive in the Enleum HPA-23RM. There's also more layering when compared to amps like Ferrum Oor. Overall, for a solid state amp, this may be the largest sounding amplifier I have heard so far. If I was to put a number, it would be about 10-20% larger. I do not have the Holo Bliss on hand in-case if anyone is wondering. For more information, do look up the video review as I describe how this estimation of size is done.

Mids:
The mids are a little laid back and less intense. This is the second notable difference when comparing between amps. The difference is not large but noticeable especially when compared to most amplifiers. If compared to more energetic amps like the Ferrum Oor or Tsuranagi, the gap can be easily heard by most that have tried.

Transient:
The transient edge on the instrument for the MK 475 is surprisingly quick and clean. This is noticeable only by a few headphones like the DCA stealth and Verite Closed. Most headphones I perceive are an ever so slight improvement in clarity for instruments.

Bass Impact
Bass impact is clean, incisive and quick. It may be due to the transient traits as the bass impact attack is really quick and impactful. The quantity of bass however isn’t more then other amps I compared to: The Enleum current mode do actually give more in quantity and power then the MK475. That said this is a slight improvement and requires extensive examination of bass in tracks to notice.

Sound Quality Summary:
The MK475 is an amp that sounds different compared to other amps. Its standout characteristic of soundstage itself may be worth the asking price. Well designed solid state amps have very little differences between them, and to make a marked improvement is no easy feat especially when compared to the likes of the Ferrum Stack or the measurement darling A70pro. The laid back nature may be a downside to some as it may seem like a lack of power, but after conducting tests with a large number of headphones, I find it a consistent nature and more of a presentation of sound by the amplifier. That should be noted as some may not prefer it.



Pairing of Headphones:
Abyss Series: I find this pairing not optimal for me. The improved soundstage is nice but the loss of some energy in the mids make it less exciting. If I am using the Abyss, I want it to be fun and exciting.

DCA Stealth: I liked this combination. The larger sound stage makes it really enjoyable. The slight improvement in transient and bass impact are also noticeable makes tracks even clearer and more dynamic sounding.

Atrium Open: Really nice combination. It makes the headphone sound even larger and smoother. I enjoyed this combination.

Verite Closed: This combination is a mixed bag. I like the clean transient edge and how instruments feel so clearly separated and distinct. My wife however felt it was really weird. I personally like it but it may be something that others may not agree on.

Issues with Sensitive IEM: (There's a update below)
I notice the amp is highly susceptible to electrical noise. This is not ground hum or hiss that is normally encountered with amps. The MK475 does not exhibit any hiss or hum even on the EA1000 which is rated for 127db/mw. However if you are powering it via a DAP or Handphone + Dongle, you will pick up the buzzing of the electric signals and capacitive screen. This electrical noise seems to be transmitted via wire and disregards placement of the amp in relation to the DAP. To use my M17 with the MK475 with the EA1000, it requires turning off the screen, airplane mode and only using the physical buttons to control. I am not sure if it's my version of the MK475, but it doesn’t show up in any other headphone except sensitive IEM like the EA1000 and Truthear Zero Red. I will try changing cables and maybe if there is a chance to use it with other daps or try another copy of the mk475, I will update this post. For now if you have a sensitive IEM, do try it before committing or have some way to refund.

Summary:
The MK475 to me is special. It gives an improvement to sound that I appreciate across a wide range of headphones. The fact it powers headphones in a way that the specs don't quite represent impresses me. If you have a chance, do try it out as I think the mK475 is something worth considering even at its price tag if soundstage is something you favor. For users of sensitive IEM, do try it out with your DAP and IEM before committing if possible.

Update:
I notice that balance mode reduces the electronic noise significantly. Using the truthear Zero Red (~100db/mw) on Single Ended and Balance yielded significant difference in the amount hum you can hear. On balance, it is not noticeable while on single ended it hums. I did notice that the hum is also mix of ground loop sound where if you touch different things, it has different sound and quantity. Overall a very messy situation with the single ended output.

Update 2
Using a shielded and grounded 4.4mm interconnect eliminates all the noise. The MK475 is highly suspectable to noise introduced through the wires. Other amps like Tsuranagi I tried are not that sensitive to it. I used a generic 4.4mm interconnect with no ground connection is terrible for sensitive IEM like the EA1000. Using a ddHifi BC44B grounded inter connect with my DAP eliminates it totally. You can use your sensitive IEMs after that