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Testing Ground

Kingsound M-03: A Qobuzism for this portable amplifier for electrostatic headphones with exceptional sound quality!

By Barry Moore |

The young Chinese brand Kingsound has distributed in France and Western Europe for less than a year. It has just launched the world’s first mobile amplifier for electrostatic headphones – and we are delighted to offer you a thorough testing! The device was developed to be compatible with electrostatic headphones produced by the Kingsound brand, but is also compatible with models crafted by other manufacturers. This amplifier proves itself to be exceptional within the field of headphone sound reproduction.

Electrostatic headphones are considered by some audiophiles to be the ultimate in terms of quality sound reproduction. Yet, this often comes at a cost to certain aspects of the device; particularly through the large size that these models bear, due to the necessity of containing bulky charged diaphragms to reproduce the sound.

The operating principle of this type of headphones imposes the use of a very high DC voltage; to stabilize these diaphragms by covering their electrostatic surfaces charges, and, to complete the whole circuit. It is also imperative to use audio signals with large amplitudes (which are superior to those provided by the power amplifiers) in order to generate the forces required by these moving diaphragms.

This means, therefore, that until the triumphant appearance of the Kingsound M-03, the usage of amplifiers had been confined to sedentary mains-powered charges. This allowed for easy disposal of high DC voltages for the polarization, as the diaphragms could take in the high amplifier signals sent by the amplifier.

We refer you to our testing of the ensemble pieces we have, thus far, awarded Qobuzisms to. It consists of the KS-H03 electrostatic headphones (which are used for the present testing, but Kingsound have also recently released a specialized portable model, the KS-H4), and the M-10 amplifier. If you desire further technical information about Kingsound before reading the above testing? we now offer you the present review below!


Available in several colours, the Kingsound M-03 amplifier for electrostatic headphones is built into a sturdy, anodized aluminium casing. It possess a simple, pleasing shape, and a functional, ergonomic design.

The M-03 comes with a robust carrying case (which weighs almost 500g), in which there is a vibrantly coloured chord, and two 3.5mm stereo jacks to connect to the source that you desire to amplify and listen to.

The front panel contains a volume control (which also acts as an on-off end position switch), two 3.5mm input jacks (one for connecting to the source, the other to more traditional pairs of headphones), and, finally, the specific connector for the electrostatic headphones. The latter connector will accept all models from the brand, but also those from other brands possessing a compatible connector. A small green LED indicates power is received.

On the back face one finds the micro USB connector, which is used for recharging internal batteries, and a USB A connector, which allows these batteries to provide power for other equipment (meaning that it is a power bank). A small blue LED flashes while charging the batteries.


Much of the interior of the Kingsound M-03 amplifier is occupied by two Lithium Ion Panasonic NCR18650A batteries, which can reach a total capacity of 6200 mAh, and the two transformers which facilitate the operation of the electrostatic headphones by raising the amplitude of the audio signals to 90V. This would not otherwise be possible for a portable, battery-powered amplifier.

Above, you can see the transformers (yellow to the left, blue to the right) which enable the polarization of the electrostatic headphones? high voltage diaphragms. On looking below, to the right of the Kingsound-B logo, the rectifier diodes and voltage smoothing capacitors can be found (these are of low value, because the current required for this polarization is extremely low).

A few components are found underneath one of the two batteries, including the battery charging circuit; an ETA9640 model produced by the manufacturer ETA Solutions, accompanied by a self-filter. Next to this self-filter the stabilizing circuit is found, which is associated with the yellow transformer, which will allow the electrostatic diaphragms to attain a high voltage bias.

Near the volume knob, you can see one of the two integrated circuits supplying the headphone amplifiers, which is in this case an MAX97220A model from the manufacturer Maxim. This circuit has a charge pump, which generates a negative voltage value - opposite to that of the positive supply ? which allows the signals to function, and to do so without disturbing the output coupling capacitors. It allows the model to avoid the disadvantages that come with bandwidth limitations in low-impedance headphones; namely bass distortion, and risk of sound warping.

This amplifier feeds directly into a standard pair of headphones through a 3.5mm jack, and also drives the step-up transformers which will communicate the high amplitude audio signals to the electrostatic headphones.


It was an incredibly special moment when the ensemble collective of the Kingsound M-03 amplifier and the KS-H3 electrostatic headphones began broadcasting the l'Allegro of the Suite Américaine by Dvorak in Hi-Res 24 bit/192kHz, as interpreted by the Festival Orchestra of Budapest under the leadership of Ivan Fischer. It sounded excellent; crisp, clear, airy, with a seriously deep midrange register, and a treble of exceptional finesse.

To find out more, then, we needed to listen further, and chose a recording that has always made a strong impression on us, the passionate Contredanses by Beethoven, as interpreted by Andrew Manze at the head of the Helsingborg Symphony Orchestra.

We could actually make out air bells, and, dare we say it, the sound seemed to resonate with more brightness, and on a slightly higher level, than through any other systems we are accustomed to listening with. Now, we must ask, as Shakespeare forced us to consider: is this appearance, or reality?

When registered with a Clio system of electroacoustic measurements, the amplitude frequency response of the M-03 - loaded on a 3.5mm output with a resistance of 32 Ohms - actually betrays a slight, gradual rise of the high register, from 5000 Hz to achieve approximately 1 DB at 20 kHz, as can be seen in the image below.

Of course, one could argue that the accentuation is of no real importance, but the way in which the instruments and harmonies acquire a high-pitched richness - a shine, a gain in level - is in no sense bad, but can in fact be thought about as facilitating a hedonistic escape from reality. As for the light fluctuations in the bass sound, do not panic, this begins at 30 Hz, which means that we have reached a frequency that is rarely found in musical transmissions.

We believe that it is our role to highlight this feature of the M-03 amplifier. However, this does not detract from the very high level of audio that we enjoyed during repeated listens to extracts from Peer Gynt by Grieg, as performed by the Berliner Philharmoniker. The famous In the Hall of the Mountain King contained a seriously cavernous introduction, and the final explosion shook our eardrums powerfully, with flawless reproduction. The recording was also completely free of lag when we played it in conjunction with the KS-H03 headset (and this is a rarity!); the key point being that the M-03 amplifier seems to do a lot better than its predecessor, the M-10.

By way of comparison, when we connected our own orthodynamique headset to the M-03, the return on this piece of tape was still incredibly strong (and, remarkably, it still had power to spare!). However, despite attaining a high level, it remains a bit below the specifically created electrostatic KS-H03 in terms of sound ventilation.

One of the most famous songs of the 70's, My Sweet Lord, taken from the album Let It Roll by George Harrison, reverberates beautifully through this high quality equipment. Harrison?s voice is crowned with beautiful light, while fine guitar chords are strummed in an aery, carefree manner.

On Nuit 17 à 52, a track taken from the album Chaleur humaine by Christine and the Queens, we were carried away by the sense of rhythm. The vocalist?s voice is restored with a mixture of sweetness and sharpness - fluidity is paramount ? and the band accompanies Christine with serious verve, without ever sounding intrusive. An enchanting listen.

To conclude, with the Kingsound M-03 amplifier for electrostatic headphones, the first portable model of its type, used in conjunction with the KS-H03 headset, you are invited to partake in sound reproduction of exceptional quality. Your music will sound bright, clear, fluid, and extraordinarily vivacious. We have, therefore, decided to award our highest prize: a Qobuzism for the M-03 amplifier. Congratulations Kingsound!

French Kingsound Site
Contact (To contact Audiophonics, the importer)

Our thanks to Audiophonics for the use of the M-03 and the KS-H03.


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