Purity Amplifier

 

Ratings

 

 

Pros

 

• Very neutral sound, which emphasises the character of any connected DAC.
• It’s a complete DAC/Amp and pre-amplifier device.
• Fully balanced circuit.
• It has a balanced 4.4mm input. Also, 4.4mm balanced headphone output.
• Remarkable power.
• Great design, very attractive, minimalist and functional.
• Completely flat frequency response.

 

Cons

 

• No gain selector.
• The potentiometer varies the voltage too much in the last quarter.
• The DAC used, although well implemented, is a bit basic for the price of the set.
• There is a slight difference between channels, although it is not significant.

 

Purchase Link

 

https://earmen-eu.com/collections/portable/products/earmen-st-amp

 

Link to the Store

 

https://www.earmen.com/index.php/products/earmen-st-amp

 

Introduction

 

Almost everyone is familiar with EarMen, a brand that was born out of an audio company (Auris Audio) dedicated for over a decade to developing tube amplifiers, working to perfect a neutral, natural and clean sound. Away from the madness of achieving the most perfect measurements that other brands strive to reach, EarMen is driven by delving into sound above all else. As a result of this working philosophy, the new EarMen ST-Amp DAC/Amp has been born. It is a fully balanced desktop headphone amplifier with the option of a preamplifier and integrated DAC. The same topology is used for the SE signals, so its quality does not lag behind the sound of the balanced output. TPA6120 operational amplifiers and an ALPS potentiometer are used. As DAC it uses the Sabre ES9280 chip, capable of decoding files up to 384kHz. Let’s see what other surprises this new product brings.

 

 

Specifications

 

• Inputs: RCA Single Ended, Balanced 4.4mm.
• Headphone outputs: SE 6.35mm, Balanced 4.4mm.
• Pre-outs: RCA Single Ended, Balanced 4.4mm.
• DAC: ES9280
• Audio Formats: DSD 64 / 128 DoP. DXD 384/352.5 kHz. PCM up to 384 kHz.
• Dimensions: 170x30x150mm (6.69 «x1.18 «x5.90»).
• Weight: 1100 gr. (2.42 lbs).

 

	SE in – SE out	SE in – BAL out	BAL in – SE out	BAL in – BAL out
Input	2V	2V	4V	4V
Output	4V – 0.5W @ 32 Ω	7.75V – 1.85W @ 32 Ω	4V – 0.5W @ 32 Ω	7.75V – 1.85W @ 32 Ω
THD+N	0.0025%	0.003%	0.0025%	0.002%
SNR[A-W]	>117dB	>121dB	>118dB	>125dB
Dynamic range	>117,9dB	>121dB	>118dB	>126dB
Frequency Response	±0.003dB	±0.007dB	±0.003dB	±0.006dB

 

 

Packaging

 

The EarMen ST-Amp came protected in a white cardboard box, as external custom packaging. The actual product box is black, textured, with dimensions 208x208x95mm. As usual it was protected by transparent cellophane. On the front side there is only the logo and brand name inscribed in silver ink. On the back side there is a large black label attached, containing the specifications, a description of the features, the logos of the formats it can play and some barcodes and QR codes. Removing the cellophane reveals the pleasant texture of the box. Inside is the user manual and the ST-Amp, protected by a grey foam sheet, on its top and a perfect mould for the rest of the sides. There is nothing else, except for a silica gel sachet. The presentation is totally minimalist and cable-free. It’s surprising that a product like this and at this price level does not come with any cables, not even power cables.

 

 

Construction and Design

 

The ST-Amp stands out because of its front design. Actually, the rest is a classic rectangular aluminium case. But it is the faceplate that adds to the charm of this product. It is a greyish-white colour, with a matte, subtly rough texture that looks like unpolished ceramic. In each corner there are 4 black Allen screws that add contrast. On the left side, there is the product branding, in black ink. On the same side, but at the bottom, is the metal toggle type on/off switch. Below it, there is a white LED indicator light. To its right, halfway down the large black ALPS potentiometer, there is another switch just like it. This time there is no LED and its use is to switch between pure amplifier mode (position A) or DAC/Amp (position D). The potentiometer is in the centre, is large and offers a good level of resistance to movement. It is positioned slightly at the bottom of the front panel and is also a good size in depth, making it easy to grip and position. It is subtly tapered and its base is an almost flat cylinder of larger diameter, on top of which is the small white bar indicating the position of the volume. Around it, on the faceplate, there are multiple bars to mark the volume level. As it happens, the potentiometer rotates beyond where these bars start or end. In other words, its travel is greater. To the right of the potentiometer, there is an oval with a sloping upper side, increasing to the right. This oval is recessed by a few millimetres and inside it is, first, the 4.4mm balanced headphone output, gold-plated; second, the 6.35mm SE headphone output, also gold-plated. Above the SE output, at the top, is the model name, inscribed in black ink.
On the rear face are the connections. Starting from the left, at the bottom is the balanced 4.4mm input. Next to it, the two RCA inputs, vertically. Symmetrically, the pre-outs are arranged, first the RCA and then the balanced 4.4mm output. All these connections are gold-plated. Next to it is the USB type B input for connecting a source, such as a PC. Then there is the input voltage selector (115V/230V). Finally, there is the power connector. The back plate is black and polished, fastened by means of 4 round-headed Allen screws. The body of the amplifier is also black, but with a slightly rough texture, which gives it a slightly matt look and prevents finger smudges.
Like the presentation, the design is minimalist, but the design of the front panel stands out in a big way. The very, very light grey colour of it, its matt ceramic touch, which gives it a very special roughness and feel, the toggle switches and the headphone outputs in that slightly sunken oval, give it an elegant, very special touch. All this, together with the large central potentiometer, stands out in a powerful way.
The design is very elegant and attractive, but it retains a very striking sobriety, which does not lose an ounce of robustness.
Finally, it is interesting that it has only three legs, two at the front and one at the back, in the centre. Each leg is a rigid cylinder with a semi-spherical rubber base of a smaller diameter.

 

 

Connectivity

 

The ST-Amp can be used as a pure amplifier or as a DAC/Amp. For use as DAC/Amp a USB cable can be connected to the following compatible operating systems: Win10, Win11, Android, MAC, iOS. It does not have ASIO drivers.
Can be used as a pre-amplifier, using the 4.4mm RCA or BAL outputs.
Can be used as a headphone amplifier, using the 4.4mm RCA or BAL inputs.
To power the device, it is necessary to select the corresponding input voltage (115V/230V) on the rear selector switch.

 

 

Operativity

 

The operation is very simple.
There is a toggle switch to turn the device on/off. There is a white LED below it, to indicate that it is on.
There is a toggle switch to select DAC/Amp or Amplifier mode. Set the toggle switch to D mode to activate the USB digital data input. Set the toggle switch to A mode to select the analogue input.
As a pre-amplifier, the front potentiometer drives the volume of this output.
In amplifier mode, the balanced input takes precedence. If it is switched on, the SE input is disabled. To listen to music from the SE input, the balanced connection must be removed.
The headphone output can only have one active connection. To listen to music from the balanced output, nothing must be connected to the SE headphone output.

 

 

Measures

 

The measurements were made using the device’s internal DAC.
One thing that surprised me about the EarMen ST-Amp is that it has no gain selector. Compared to a cheaper device like the ifi Zen Can, which has 4 gain modes. In this respect, the ifi is much better suited to drive more headphones, due to this fact. How does the ST-Amp cope? Well, according to my measurements, in SE, with the pot at 3h, the output voltage is 600mV. While on BAL, with the pot at 3h, the voltage is 1.12V. This implies that there is a lot of potentiometer travel for use with sensitive headphones. But that, on the other hand, the voltage increase is very large from this point on: in less than a quarter turn, the voltage rises by 3.5V for SE and 6V for BAL. A very big jump. The potentiometer is very smooth up to this point, then the increase is very large. That makes the last quarter turn suitable for use with high impedance headphones, but with little room to move.

 

No Load SE

 

With the potentiometer at maximum without load the voltage value is above 4V (4.29 at 1kHz).

 

 

15 Ω SE

 

Actually, the ST-Amp is quite good for low impedances per SE. It is capable of delivering 3.17V, which implies a power of 670mW and 210mA. A very high value.

 

 

33 Ω SE

 

The ST-Amp meets expectations and gives the maximum at this impedance: 4.22V is 540mW, more than specified.
With these values, the output impedance for SE is below 1Ω.

 

 

100 Ω SE

 

I have not made measurements at this impedance because as at 33Ω the voltage peak is already reached, at 100Ω the same thing will happen. So the power for this value of resistance would be 180mW.

 

No Load BAL

 

With the potentiometer at maximum without load the voltage value is above 8V (8.58 at 1kHz).

 

 

33 Ω BAL

 

It was a bit complicated to make measurements with low impedances, as the potentiometer at the high end of the range, with very little rotation modifies a lot of voltage, it was easy to reach the cut-off due to thermal protection. According to specifications it should reach a voltage of 7.75V, very close to the maximum. The truth is that I have reached 7.34V, which means a power of 1.63W, which is a very high value.

 

 

100 Ω BAL

 

For 100Ω per BAL the voltage is above 8V (8.4V at 1kHz).
The output impedance for BAL, averaged over all measurements, is less than 1Ω.

 

 

Respuesta de Frecuencia

 

I have made measurements with the potentiometer at 9h, 12h, 3h, 4h and maximum by SE. It can be seen that at some volume levels there is a slight difference between channels. While at maximum there is no difference.
On the other hand, it can be seen that the device has a completely flat frequency response from 5Hz to 40kHz.

 

 

Sound

 

To evaluate the sound of the EarMen ST-Amp I have used my PC with Windows 10 + Foobar 2000 as audio player. I have used the ST-Amp as DAC/Amp and as Amp, connected to the EarMen Angel (via 4.4mm balanced cable) and Aune X8 XVIII Magic DAC (via RCA cables). For comparison, I have also used the ifi Zen Can.

The EarMen ST-Amp can be used as a DAC/Amp (D-mode) or just as an amplifier (A-mode). My impression is that the general purpose of this device is its use as an amplifier. The DAC section is determined by a relatively basic chip in this respect. This is the ES9280, a DAC that is mounted in EarMen’s cheapest product, the Eagle. Supported audio formats are 384kHz via PCM and DSD128 DoP. Despite my preference, it has no ASIO driver. But its big advantage is that it doesn’t need a driver to be used on Windows 10 or higher.
As an amplifier stage, the ST-Amp is very neutral, which can be seen in its frequency response. In this way, it is very capable of allowing differences between the DACs connected to it to be observed. In that respect, it is easy to differentiate between the internal ES9280 DAC and the Aune X8 XVIII Magic DAC. The ES9280 offers a clean, flat and linear sound, with a simpler, cleaner and smoother descriptive capability. Already, from the low end, the bass texture is smooth, clear, with a punchy but rounded punch, technically quite acceptable. Texture and dynamics are aspects that I notice distinctive, for example, when used with the Aune X8. The OpAmps can be changed on this DAC and the ST-Amp is the perfect ally to demonstrate and bring out the small differences that the change of chips can generate. Compared to the internal ES9280 DAC, the Aune X8 XVIII has a much more pronounced texture in the low end, generating a more descriptive bass, with more body, texture and roughness, something that makes it much more appealing. You also feel that the lower range possesses a superior grandeur, as well as a more dynamic, richer and lusher midrange. In contrast, the internal ES9280 DAC seems more linear in all ranges, even somewhat airier, brighter and cooler. The Aune X8 is more forceful, physical and dense, with a warmer character and a more pronounced texture. That texture gives it an ornamental appeal that may be superior to the internal DAC, because it attempts to offer a richness of nuance that contrasts with the less distinctive neutrality of the ES9280.
By using the EarMen Angel as a DAC, connected via the balanced output to the ST-Amp, the cleanliness of the internal DAC is restored, but superior analytical virtues are added. The sound again gains in dynamics and texture, but with a somewhat cooler, more transparent and more precise profile than with the Aune X8 XVIII. As for the bass produced by the Angel, it has more punch and richness than the internal DAC. Its size is larger and both the accuracy and the level of resolution are better and higher. The level of transparency also feels enhanced, as does the sense of dynamics offered. Relative to the Aune X8 XVIII, the Angel feels cleaner and more linear, with a punchy weight and presence, but with a more natural and pure timbre. The Aune, on the other hand, stands out for its reinforced character, texture and bass presence, something that detracts from its cleanliness and neatness, but adds extra density, body and exuberance. Clearly, its sound is warmer, while the EarMen pair tries to maximise purity, neutrality, but without losing musicality, gaining in extension in the upper area, sounding cleaner and clearer in this part, with a sense of openness and transparency also more discernible.
As you can see, the ST-Amp stands out for being very neutral and makes it easy for the character of the connected DAC to be extended to the headphones. Just as the ifi Zen CAN, from any connected DAC, already imprints a warm, darker colour, typical of the brand, with the ST-Amp none of this happens. On the contrary, it seems to try to maximise the personality of each DAC and not the other way around. In my opinion, this is a feature to be taken into account. If you don’t want to add more colour in the sound chain, the ST-Amp is the perfect ally. And in that respect, the pairing with the EarMen Angel is a winning combination. In terms of dynamics, clarity and stage, taking advantage of the balanced connection and the Angel’s more neutral and wider purity, you get a larger sound, which expands in brightness and ornamental richness. While the Aune X8 XVIII seems more expressive in the low end, the Angel surpasses it in midrange, tonal richness, mid-note weight and treble informativeness. In this respect, the Aune’s density works against it. Whereas the Angel’s purity and grandeur is rewarded in the expressiveness of the upper mids and treble.
If I concentrate on one main aspect, the vocals, they sound more muted on the Aune, whereas with the Angel there is a superior liveliness and a higher harmonic extension, which extends the presence of the vocals. The range of the voices is more extensive with the Angel. Starting with the male voices, the accent on the lower part is more subtle, but also fuller. While its expansion towards the higher tones makes its overall representation wider and fuller than with the Aune. On the other hand, the level of dynamics is more obvious, the separation between elements as well. The instrumental distance and the silence between them is perceived as reinforced compared to the Aune. If the sensation of volume is focused on the lower part in the X8, the sonic amplitude stands out, from the mids onwards, with the Angel, generating a sound that is more fluid, clean, clear, luminous, rich in detail and resolution, but it is also more gaseous, volatile and wide. As I say, connecting the Angel is like turbo-charging the ST-Amp’s internal DAC, and my sonic preference is much closer to this set than connecting to the Aune, which is a more visceral point, with a more physical and corporeal punch, especially in the low end. The texture and density stand out, as opposed to the size, scene, expansiveness, transparency, level of definition and resolution of the Angel. And, in this duel, the winner is always the EarMen ST-Amp, something that indicates to me that it can still scale further in its final quality, as a superior DAC could even take the connected headphones to a higher level. And therein lies the greatness of this device. While the internal DAC is quite appropriate and sufficient for those who want to keep a clean and uncluttered desktop, the marriage with a pure, technically superior DAC will increase the final sound quality, without the ST-Amp being any limitation whatsoever.

 

 

Conclusion

 

The EarMen ST-Amp is a complete device. An extremely elegant and minimalistic DAC/Amp, which can also be used as a preamp. With a black aluminium body and a very light grey front with a matte ceramic texture, the ST-Amp stands out with a simple, but extremely attractive, striking and distinct design. It features toggle switches and a large ALPS potentiometer, attributes that allow for a high and pleasurable user experience.
As an audio device, EarMen continues to pursue musicality with technical, pure and neutral devices, with the intention of magnifying the sound as much as possible. The concept of the ST-Amp is functional and minimalistic, without too many options and connections. It cleverly features balanced 4.4mm inputs and outputs, supported by an architecture that is also fully balanced. In order to maximise the sound quality that such a construction offers, EarMen uses the same topology for the SE signals, so that they become balanced, but in a special way.
As a single stationary device, the ST-Amp is completely versatile and self-sufficient. Although the ES9280 DAC used may be basic, its implementation, neutrality and musicality are enhanced by the ST-Amp’s amplifier stage. However, I can’t help but notice that this product is a winner when used as an amplifier. In my opinion, what makes this amp so special is its purity and its ability to not add any kind of colour to the connected DACs. The ST-Amp seems to enhance the sound of the associated DAC, amplifying its characteristics and personality. It really is an amplifier in every respect, not only adding power to the sound of the source, but amplifying its essence and particularities. And, speaking of power, this Earmen has a very powerful SE output, with more than 0.5W demonstrated for 32Ω. The balanced output is no slouch either, and calmly reaches 7V RMS for 32Ω.

 

 

Earphones and Sources Used During Analysis

 

• PC Windows 10 + Foobar 2000.
• Aune X8 XVIII Magic DAC.
• EarMen Angel.
• Tempotec Serenade X.
• Hidizs MS5.
• KiiBOOM Evoke.
• KiiBOOM Allure.
• TKZK Ouranos.
• Kinera Celest Pandamon.
• TinHiFi C2.
• Letshuoer S12 PRO.
• NiceHCK F1.
• BQEYZ Winter.
• Rose QT9 MK2s.
• ISN H40.
• Yanyin Aladdin.
• Penon Globe.
• Rose Martini.