Sound Impressions

M-03 – Tonality & Presentation

This is a powerful but clean sounding amplifier with a decidedly neutral to bright presentation though slightly source dependent in terms of final coloration. There is also an inherent upswing in its treble performance with more sources and headphones used with it, more so than amps such as the Duet or V5.

Treble bias

It is not completely flat then but the additional treble doesn’t really peak well into the brilliance region with a slow but steady rise starting from around 5k onwards. It will not give a splashy percussion sound, it’s not harsh in that sense but it will give you bags of extension and a slightly “hifi” sound with excellent headroom in the upper octave.

Bass articulation

The M-03 does have a tiny bit of roll off sub 30Hz so it’s more focused on mid-bass upwards. Nothing new for me when dealing with an electrostatic presentation and whilst I did find the bass on the Kingsound systems more satisfying than say the Baby Stax or 3030 systems it’s not really where I tend to focus when using these types of amps and headphones. Be assured that it is tight, fast and fairly well defined but doesn’t convey a rich thick texture more commonly associated with tube amps. It’s very much a solid state sound.

Coloration

Sources using the line-in will subtly change the coloration but not a huge amount. Warmer musical DAPs such as the FiiO X5iii offered a bit more low-end body and a smoother treble response whereas the AK240 yielded more midrange and top end detail, better imaging and a more spacious sound.

KS-H04 – Tonality & Presentation

Refined

This is a considerable step up in resolution and detail over the M10/KS-H02 pairing I reviewed back in 2013. It is not as warm sounding as this older pairing but it still flows smoothly and is far more engaging, precise and more in keeping with a modern electrostatic presentation.

Relaxed

If you find the typical Stax presentation a bit too analytical and clean, or the H03 too forward, then the KS-H04’s slightly more “relaxed” and smoother delivery might be a very welcome compromise. Certainly, from an easy listening experience, the H04 is built for longer listening sessions with an eye on detail than previous iterations.

Expansive

Gone also is the previous level of intimacy in the H02 staging and in comes a far more expansive presentation with top notch headroom, though, unsurprisingly, a polite low end that’s a little lacking in body if not in articulation and speed. It is not quite as “explosive” and open sounding in the mids as the ESP950 which I find very suitable for rock workouts, it’s a bit more neutral than that but its imaging is more accurate and quicker transients make the H04 excellent for complex orchestral, jazz, acoustics and even some modern RnB tracks on sparse arrangements.

KS-H04 – Bass

The K04 bass response is fast, articulate with good extension but a little light in body and texture though definitely superior to the previous H02. It has been a while since listening to older Stax systems but it does strike me as being a touch warmer in the mid-bass and smoother sounding than the older Stax 3030 SS and headphone combo.

It is this slight warm sheen that gives the H04 this lovely smooth tonal character that I think first-time listeners of electrostatics will enjoy. It makes the KS-H04 a more flexible headphone for modern pop and some RnB, adds a touch of PRaT and a little bit of fullness important for bass fundamentals.  However, if you are expecting slam then sorry I have really yet to experience that with an electrostatic system and the KS-H04 is no different.

KS-H04 – Mids

Mids are more to the neutral side than the Koss ESp-950 and a slightly leaner note though not by much. It is, however, a touch faster with more precise imaging and sounds more openly than the Koss ESp-950. The K04 mid-performance is more suitable to delicate but fast transients, rapidly changing spatial cues, precise instrumental placement, and separation.

Timbre on the mids of the H04 is very engaging actually and whilst it won’t yield a thick or rich sound there was a certain sweetness and pleasing tonality that made it flow. Vocals stay impressively controlled and refined with very little sibilance indeed for either male or female vocals.

KS-H04 – Treble

One can understand then the use of the H04 as the primary headphone to pair with the M-03 given the feedback that the H03 was the more analytical and brighter headphone and the H04 is the smoother more relaxed version, you simply do not want to push a good treble performance into a harsh one on this system.

Paired with the M-03 the balance it just right. The treble performance is superb. Fast, detailed, and highly articulate come to mind yet never overly forward or too harsh. Kingsound has taken a very slight edge off the H04 in comparison to the H03 retaining the sparkle but keeping it from being peaky and hot. It is very much an electrostatic experience without the harshness of an overly forward and strident dynamic or planar treble performance.

Matchability

IEMS

The M-03 is not an efficient amp and will not cater for your IEMs at all well. The noise floor and gain levels are simply too high for this type of listening and frankly I would call it borderline dangerous for your drivers and hearing if you even tried.

Tested IEMs included super efficient units such as the Andromeda, the usually power happy Vega, 32-ohm earbuds such as the Astrotec Lyra 6 right up to the 150-ohm 89dB RHA CL1 and oBravo’s planar IEM, the ERIB-5a. It was only when I got to something like the CL1 and ERIB-5a could I stretch to just one tiny movement of the volume beyond super low channel imbalanced levels to safely listen to anything from the line input. A step beyond that and you could damage your earphone and your hearing very quickly.

RHA CL1

The CL1 offered a very clean, neutral sound with a focus on the upper mids and treble offering excellent detail. At times the CL1 treble response came across as a bit brittle beyond 3-4k for some tracks and not enough low-end body on other tracks. Matching sources did play a role so warm sources such as the FiiO X5iii did compensate a little for the inherently neutral to upper treble brightness of the SS M-03. The M-03’s natural lift in the brilliance region offers supreme extension and there is a nice warm heft in its mid-bass response.

oBravo ERIB-5a

The ERIB-5a is a more relaxed and balanced sounding presentation and a bit more natural sounding than the CL1. On the flip side, this pairing is not as well extended or as detailed sounding as the CL1. Also, the same caveat applies with this planar IEM, do not move this more than one notch above the low volume channel imbalance or you could hurt yourself.

Dynamic Headphones

Again, there is a question of efficiency and gain in the M-03 power. At 32 ohms or on a moderately efficient planar level the noise floor is high and you will experience some background hiss though at a much lower level than IEMs.

AKG K872

The K872 is a wonderfully efficient flagship closed dynamic headphone at just 36-ohms but sadly this pairing is noisy with background hiss. You can get a bit more volume control though than IEMs tested but not a huge amount, around 2-3 notches higher than most of the IEMs tested. I did, however, get to a level where I could listen carefully to the presentation.

Tonality

The K872 sounded slightly harsher with its treble presentation than say the ALO Audio V5 tube amp and quite a bit brighter and cleaner than the Duet. Bass extension was good if a bit light. This pairing has plenty of energy, more so than the more efficient amps and t it also has excellent resolution and speed. I do prefer my K872 a little thicker and richer sounding but I also appreciate the speed and detail this pairing can offer.

Planar Headphones

Hifiman Edition X V2

This was not a completely zero noise floor with a touch too much gain making volume control tight though possible to get good channel balance and a firm grip on the presentation at comfortable listening levels. Noise is present though lower than the K872 so with the music flowing it didn’t present a huge issue unless I had some very quiet passages.

Tonality

Detail and resolution are excellent with the Edition X and M-03 pairing with a smooth top end, impactful and musical low end and a rich but detailed midrange. Vocals are natural and vivid sounding. If the M03 gain wasn’t so high and I had a bit more control on its volume beyond 1-2 notches this would be an excellent and very articulate pairing.

Hifiman HE6

Zero noise, black background, oh why am I not surprised. The M03 has more than enough gain to drive the HE6 to satisfactory levels. It is perhaps one of the nicest portable amp pairings I have heard with the HE6 since the mighty Bakoon HPA-01M. You can drive this combo to around 12 noon – 1 pm on the pot before it gets too loud so you won’t get any clipping or distortion.

Tonality

Tonally it’s neutral, surprisingly neutral. I say surprisingly because I was expecting this to be a bright pairing but it stayed neutral with a good low-end body and excellent extension on both ends with only the merest hint of splashiness around 5-7k.

This pairing has also got some decent dynamics, excellent resolution and a relatively controlled treble for an SS amp which has that little treble upturn. I still think you will get a bit more finesse and a natural richer sound with balanced desktop solutions or flagship tube amps with decent grunt but for a portable solution, the M03 hits the mark for me with the HE-6.

Select Comparisons

Koss ESP950

For this, I hooked up a Fong Audio $140 adapter cable for converting the Koss 5-pin Koss connector to the 5-pin Stax Pro bias connector. Worked a charm so I highly recommend it. There is no noise as expected from the ESL output of the M-03 and also a much cleaner and more dynamic presentation than the stock Koss E-90 stock amplifier. It also has far less noise in the signal with less squealing type electrical interference you sometimes get with Koss systems.

Tonality

With the stock Koss E-90 amp, you get a reasonably warm mid-centric presentation that’s musical but doesn’t really do the 950 any justice. It kind of sounds a bit veiled and closed in. The M-03 takes this classic to a better level with a cleaner more resolving presentation, great clarity especially in the mids with better top end extension and sparkle. Wonderful for guitar and vocal work and very spacious sounding.

It won’t add too much low-end heft but it’s there if needed. With this combination, if you want a slightly more muscular and vivid or forward midrange presentation than the more neutral KS-H04 paired with the M03 then I high recommend the ESP950. If you want to stay neutral with a bit more clarity and slightly smoother signature but no less detail then the KS-H04 is superb. Personally, I gravitate to the H04 when I want to listen to something a bit more complex and then switch to the Koss for modern rock with its mid-range performance.

Stax SR-002

Purpose

This is an electrostatic closed portable system and priced at around $400-500 depending on where you shop. You can buy a pro bias terminated version for a desktop This system has been around for years in the MK1 variant and rather hard to find. The MK2 came out in 2013 with some tweaks and improvements on the original including a new smoother design of its amplifier and a slightly more ergonomic and comfortable fitting set of earphones.

Functionality

It runs off AA batteries and generates enough power to run the SR-002 earphones but nothing more. If you want a sleeker smaller electrostatic in-ear setup though for the same money as the M-03 then this is it. The next step up is the altogether more comfortable, resolving, and detailed Shure KSA-1500 system at $2999. Unlike the M-03 the Baby Stax II cannot accommodate other headphones, just its own complimentary SR-002 earphones but it’s the most portable in the market today.

Tonality

Tonally the Baby Stax is all about the mids and vocal performance., It is warm, smooth and very inviting, much more so than the H04 which I would still classify as smooth and refined sounding. However, in terms of extension above and below, as well as resolution and detail, the KS-H04 is miles ahead of the Baby Stax MK2. You will find the performance of the Baby Stax more forgiving but ultimately more limited sounding than the M-03 and KS-H04 combination. Staging properties are just so so also with the limited extension of the Stax system, the headroom of the H04 is miles ahead.

Just a small FYI, you can buy the SR-003MK2 earphone which is the SR-002 earphone terminated with a pro bias socket and it will pair with the M-03 just like the H04. Cost is around #350 for the earphone alone. Sadly we do not have one in the office for testing but it is something we would be happy to review should it happen to get here.

Our Verdict

It is a shame I cannot find a trace of the KS-H04 for sale as either a kit or separate these days on the various retailer websites as it is a very competent electrostatic headphone. I can only conclude that its either a lull in stock or we are on our way to H05 already. If you do find one, even used, I would recommend you give it a try, especially if you enjoy a detail orientated yet smooth sound with a nice treble sparkle.

The M-03 amp, on the other hand, seems to be still knocking around and at its street price level of around $450 it’s very good value indeed. Certainly, a worthy and unique addition for those who want electrostatic performance as well as a just a really powerful portable traditional amp for planars such as the HE6.

It is not IEM friendly not by a long shot. This is a pure headphone amp both regular and ESL. The M-03 has a decidedly solid state and resolving sound with tight bass, neutral mids, and a little treble upswing but nothing harsh. It is a good compliment to the KS-H04 but I would also check out the M20 tube desktop amp if you want something a little fuller or richer and mobility is not a priority.

Together both the KS-H04 and M-03 make a solid and logical pairing with a nice smooth and effortless electrostatic sound that makes for a solid introduction to life without air being pushed in your ear. The price is competitive if the build quality is still not quite as compelling as Stax. Certainly, it has a number on Koss. In all, it’s a pleasing and enjoyable experience and shows that Kingsound is learning very quickly how to make good electrostatic solutions.

Technical Specifications

M-03

  • Frequency Response 2Hz – 24KHz (90V RMS out)
  • Gain 60dB (ESL)/22dB(3.5mm output)
  • THD+N 0.028%
  • Maximum output voltage: 300vrms (ESL output), 3vrms/1KΩ(3.5mm output), 125mW/32Ω(3.5mm output)
  • Signal to Noise ratio 112dB
  • Input impedance 20KOhm(analog)
  • Rated input level 0.3V(analog)
  • DC5V1A (output) 6200mAh (also a USB power bank)
  • Weight 0.45 Kg

KS-H04

  • Frequency Response 6Hz – 42KHz
  • Electrostatic Capacity 139pF
  • Impedance 115kΩ (at 10kHz)
  • Sensitivity 106 dB (at 100vrms)
  • Maximum output sound level 116dB
  • Standard bias voltage 550Vdc
  • Weight 0.3kg
  • One cable included 1m (2.5m optional)
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About The Author

Editor

Founder & Owner of headfonics.com. I first started reviewing in the late 80s (ouch!). Back then it was albums, rock concerts and interviews with a typewriter for the local rag. Now its desktop/portable and digital 2.1 audio on a rather nice laptop. How time flies.

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  • M. Ingels

    Nice review again, thank you. You can find them at audiophonics.fr.

  • bmichels

    Thanks for this review. Did you tried the M-03 with the STAX SR009 or SR007 ?

    • headfonics

      I actually have not and I am quite keen to see if the little portable unit can really drive the high-end Stax well. There should be no issues on power though.

  • Ck Teh

    I got them both a few months back from audiophonics for just 690+ euros.

    The stock pad is a little loose so I bought additional 3 pads for my ksh4.

    The first pad was an angled velour brainwavz but it changes the sound quality too much. (i got really confused and it sounded totally different with the stock pad)

    The second one was a sheep skin non-angled brainwavz. It fits very well with ksh4 and makes it looks extra premium. The sound quality was actually more neutral and slight improve in lower bass (and decreases the mid bass) and higher frequencies like 10-15k+ (slightly irritating for me)

    The third pad that I got recently was the shure alcantara pad. It fits perfectly to my ear with great sealing (the sheep skin was a little larger). The vocal is very fluid and natural but there is a slight bump on mid bass. (lesser body and slightly over punchy)

    • headfonics

      Dang didn’t know so many pads worked with the H04 🙂