Overview and Testing of the Hifiman EF2C is an inexpensive hybrid headphone amplifier with lamp warming

The first thing that needs to be said is: although the lamps are out of the Hifiman EF2C case, it is not a tube amplifier. This is a discrete transistor amplifier with lamps in the preamplifier, that is, its circuit is hybrid. In order to make a high-quality pure tube amplifier, you will need expensive components, primarily custom transformers and large high-voltage circuit elements. All this leads to an increase in the overall dimensions and weight of the equipment, as well as to a price increase and a decrease in reliability. Therefore, engineers Hifiman decided to make a hybrid compact device: a powerful transistor amplifier, but with a pronounced lamp color.

Hifiman EF2C

This is not the only similar model for the manufacturer, there is still a pure Hifiman EF3 amplifier, without the USB DAC function. As we found out, the chosen model of the DAC is not capable of revealing the full potential of the device, however, the model does not become more expensive, being just an additional option. We believe that the main purpose of the Hifiman EF2C is the warming of the line-level signal and its amplification by a discrete headphone amplifier.


Hifiman EF2C

The body of the device is made of aluminum, and the lid is glass, to show all the main stuffing. The upper part of the lamps protrudes outward. Lamps are in the sockets and can be removed and replaced by the user effortlessly.

lamps Hifiman EF2C

Two Chinese lamps 6J1 are used. This high-frequency pentode is designed for use in amplifiers in VHF and TV equipment, but is also popular in the world of audio equipment. The characteristics of this lamp make it a fairly successful means of obtaining lamp color. In other words, passing through the lamp, through the “magic of electrons racing in vacuum”, the sound will be guaranteed by the lamp.

Instead of Chinese light bulbs, the user can put analogues produced by the US, EU and Russia. Here, amateurs of experiments and improvements in equipment immediately open a wide field of activity. With the change of the lamp, the sound must change, because their characteristics are slightly different.

Hifiman EF2C

In the output stage, two pairs of p-n-p / n-p-n transistors with heat sinks provide 600 mW of power at a load of 35 ohms. (A strange load figure of 35 ohms is simply a consequence of the fact that the ceramic load resistor had a slight deviation from the nominal value.) The maximum span is 4.6 V (RMS) when connected to a line input. The calculation shows a power of 70 mW at a load of 300 Ohm. Passport signal / noise is 90 dB. The percent of distortions for tube equipment are not indicative, since the main contribution to them is made by the 2nd and 3rd harmonics.

Hifiman EF2C

On the rear panel there is a line input, a USB input and an AC power connector. By the way, the amplifier is powered by a weighty transformer BP with a power of 16 watts. The rectifier and the stabilizer are located in the body of the device.

CM102S + Hifiman EF2C

CM102S + is the USB controller released in 2005 (speeds of version 2.0, compliance with version 1.0 for USB audio devices) with an integrated 16-bit 44/48 kHz converter. Indicators: signal / noise – 97 dB, Kg + noise – 0.1%. Fortunately, this exotic chip is not used for analog connection to the RCA-input of the amplifier, its circuits are completely disconnected by the button on the front panel. The use of the CM102S + as a DAC can be explained by the manufacturer’s desire to make the sound completely different than everyone has become accustomed to – to hear something completely unrecognizable when connected. If so, this effect was fully achieved. At the first listening we had a question: what happens to the sound, why does the music fall through the volume on the bass? Strangely, this effect has not been described in any review of the device. A study of the documentation on the C-Media site showed that by default a special mode of dynamic compression is turned on, which fails the sound in peaks. In our opinion, such a sound is absolutely impossible to listen to. Therefore, if you really need a USB connection, the first thing to do is install the drivers for the C-Media controller and disable this mode. Jackdaw is turned on by default, but should be removed. This setting appears only after installing the drivers and is in a secret place:

With the applied codec with 0.1% distortion in the passport is strongly contrasted high-quality operational amplifier BB OPA 2604AU, having distortions of less than 0.0003%.

Hifiman EF2C

The NXP TDA1308 is an integrated stereo head amplifier in the AB class, with a 5 V power supply and a 32-ohm load, it provides 80 mW power, 110 dB signal / noise. The scheme of the device is rather unusual, with its own logic. The integrated amplifier is adjacent to the discrete one. Perhaps this is done for a stepwise voltage increase without the amplifier entering the nonlinear part. That is, so that transistor distortions do not interfere, and the listener enjoys the tube sound, as they say, in its original form.

Hifiman EF2C

Hifiman EF2C – price. Where is the best place to buy?

The recommended retail price for the Hifiman EF2C in the US is about $ 80,99. At this cost, you can order it on Amazon. Plus Shipping, so the total cost of Hifiman EF2C when ordering on Amazon will be about $ 100,00. I would not recommend ordering anywhere else except on Amazon. Since you are less likely to find cheaper, and if you do not take into account the fact that Amazon is probably the most reliable online store, it still very often provides free shipping.

Test report in RightMark Audio Analyzer

Test device Hifiman EF2C
Operating mode 24-bit, 44 kHz
RMAA version 6.4.1 Pro
Filter 20 Hz – 20 kHz yes
Signal Conditioning yes
Level change -6.1 dB / -7.0 dB
Mono Mode yes
Calibration frequency, Hz 1000
Polarity correct / correct

General results:

Uneven frequency response (in the range 40 Hz – 15 kHz), dB
– 0.75, -0.99
Very good
Noise level, dB (A)
– 96.4
Great
Dynamic range, dB (A)
96.3
Great
Harmonic distortion,%
1,043
Bad
Harmonic distortion + noise, dB (A)
– 37.2
Very bad
Intermodulation distortions + noise,%
0.932
Bad
Interconnection of channels, dB
– 61.2
Medium
Intermodulation at 10 kHz,%
0.779
Bad
Overall rating
Good

What good have the measurements revealed? The data we measured proved to be much better than indicated by the manufacturer in the device’s passport. The manufacturer indicated a signal / noise of 90 dB, and we got 96 dB. The manufacturer indicated 2% distortion, we received 1%. And this is with a sufficiently high level of the signal at the output, typical for real operating conditions.

The device has a flat frequency response, that is, no stalling of the high frequency is observed at all. At a low frequency of 50 Hz there is an insignificant decrease of 0.2 dB, at 20 Hz – by 0.7 dB. The high second, third, and further recession of subsequent harmonics – this is the lamp color. The RMAA program is designed for modern equipment with a typical harmonic ratio of better than 0.001%, so the algorithm for automatic evaluation of results found that this is bad.

However, it must be understood that this is a very rough estimate. Studies show that the most unpleasant distortions for a human being are synthetic nonlinearities that do not occur in nature and destroy the structural integrity of the signal, make sound unrecognizable (for example, inaccurate alignment of the zero point in push-pull amplifiers or rigid overload of the path). If the transfer characteristic has an ideal linearity at zero and smooth compression in the signal peaks, then such a sound is perceived by the person more organically. It somehow passes the internal filters, the perception of the voices of voices and instruments does not suffer. Audiophiles call the effect of lamp equipment “warming”. Does this mean that any tube equipment automatically sounds good? Of course not. Millions of disgustingly sound tube amplifiers were produced and continue to be produced, as are millions of equally repulsive transistors. It’s not a matter of ideology, but of a specific technical implementation, knowledge of the engineers, skills and experience in creating hardware.

Hifiman EF2C

When listening to the headphones Fostex TH900 Limited Edition Black was used. From interest, we measured the response at our stand, having obtained the following result:

frequency response Hifiman EF2C

The headphones have a rather low impedance of 25 ohms. At the same time, a reduced sensitivity of 100 dB / mW indicates that they are designed with a powerful headphone amplifier.

It is for similar headphones that the Hifiman EF2C amplifier is optimized to a greater extent. It is able to provide power over 600 mW, which is more than enough for much less sensitive headphones. For pure tube amplifiers, a low-resistance load is usually a big problem: it is necessary to match the output through a transformer, which introduces its non-linearity and reduces the return on HF. In the case of the Hifiman EF2C amplifier, the advantages of a transistor amplifier with low output impedance and the ability to work well for any load are used.

Hifiman EF2C

The expectations of a typical listener of transistor equipment are easy to predict. Having looked at the measurement results and 1% distortion, a modern person will expect a terrible distorted sound. However, the sound is absolutely normal, no special distortion is heard. The music is not very different from the transistor amplifier with 0.0002% distortion. If you listen, then, of course, the sound is insulated, it has its own lamp-like character. However, there is no distortion of timbre or suffering dynamics. The most interesting thing is that the change of the source of the linear signal is well audible here. For this amplifier, a qualitative output with a DAC with the highest parameters is shown. As for personal preferences, they each have their own. To buy a tube amplifier in a collection to the existing transistor ones is a perfectly normal idea. You can try to pick up analogs of Chinese 6J1 lamps and affect the nature of sound insulation.

Of course, if you raise the price once in 10, then the engineering talent would be easier to turn around and improve something in the product. First and foremost, you can redo the BP and improve the separation of channels, reduce the volume of the volume control. But even what happened turned out quite well. Quite unexpectedly for us, the Hifiman EF2C amplifier is quite successfully combined with expensive DACs, at a cost of more than $ 1200, and with expensive headphones – the difference with cheap ones is well audible. Therefore, the Hifiman EF2C is suitable for anyone who wants to diversify their collection of equipment with the tube sound of a headphone amplifier. It’s nice that the price for the Hifiman EF2C amplifier remains rather low: $ 200.

Video review of Hifiman EF2C



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