Comparison HiFiMan EF6 vs Pro-Ject Head Box S

Rated power delivered by the amplifier when connected to headphones (or other load) with an impedance of 300 ohms.

By itself, the rated power is the highest average power that the device is capable of delivering for a long time without overloading; individual "jumps" of the signal may have a higher level, but in general, the capabilities of the amplifier are determined primarily by this indicator. At the same time, the physical features of the audio equipment are such that the actual power delivered to the load will depend on the resistance of this load. Therefore, in the characteristics of headphone amplifiers, data is often given for different impedance values. Specifically, a resistance of 300 ohms indicates the professional level of the “ears”, but this is far from the maximum indicator for such devices.

As for the choice for specific power values, it depends on the sensitivity of the headphones used, as well as on the sound pressure level (in other words, loudness) that is planned to be achieved by the amplifier. There are special formulas and tables that allow you to calculate the minimum required power for a certain volume at a given sensitivity of the "ears". For example, the minimum for normal listening to music in silence is considered to be a sound pressure of at least 95 dB, and for the most complete experience — at least 105 dB; with a headphone sensitivity of 100 dB, these volume levels will require at least 0.32 mW and 3.16 mW, respectively.

Rated power delivered by the amplifier when connected to headphones (or other load) with an impedance of 32 ohms.

By itself, the rated power is the highest average power that the device is capable of delivering for a long time without overloading; individual "jumps" of the signal may have a higher level, but in general, the capabilities of the amplifier are determined primarily by this indicator. At the same time, the physical features of the audio equipment are such that the actual power delivered to the load will depend on the resistance of this load. Therefore, in the characteristics of headphone amplifiers, data is often given for different impedance values. A resistance of 32 ohms allows you to achieve quite good sound quality by the standards of low-impedance headphones, while it is not so high as to create problems for the built-in amplifiers of smartphones and other compact equipment. Therefore, most wired general-purpose (non-professional) headphones are made precisely in this resistance, and if the amplifier characteristics generally indicate power for a certain impedance, then most often it is for 32 ohms.

In the most modest modern amplifiers, the output power at this impedance is between 10 and 250 mW ; values of 250 – 500 mW can be called average, 500 – 100 mW are above average, and the most powerful models are capable of delivering ...f="/list/788/pr-19429 /">more than 1000 watts. The choice for specific power indicators depends on the sensitivity of the headphones used, as well as on the sound pressure level (in other words, loudness), which is planned to be achieved by the amplifier. There are special formulas and tables that allow you to calculate the minimum required power for a certain volume at a given sensitivity of the "ears". However, in the case of 32-ohm headphones, it does not always make sense to "get into the calculations." For example, the mentioned 10 mW is more than enough to drive headphones with a modest sensitivity of 96 dB to a volume of more than 105 dB — this is already enough to listen to music at quite a decent volume. And in order to achieve the same "ears" level of 120 dB, which provides a full perception of the loudest sounds (like explosions, thunder, etc.), you need to give out a power slightly higher than 251 mW. So in fact, you have to pay attention to this characteristic and resort to calculations / tables mainly in those cases when you have to use 32 Ohm headphones with a relatively low sensitivity — 95 dB or less.

Frequency range supported by the output amplifier; in other words, the range that this model is capable of delivering to headphones or another analogue audio device.

Theoretically, the wider the frequency range — the richer the sound of the amplifier, the lower the likelihood that the lower or upper edge of audible frequencies will be “cut off”. However, when evaluating this parameter, several nuances should be taken into account. Firstly, the average person is able to hear frequencies from 16 to 22,000 Hz, and with age, these boundaries gradually narrow. However, headphone amplifiers often have wider operating ranges, and they are very impressive — for example, for some models, a set of frequencies from 1 Hz to 60,000 Hz, or even up to 100,000 Hz, is claimed. Such characteristics are a kind of "side effect" from the use of high-end sound processing circuits; from a practical point of view, these numbers do not make much sense, but they are an indicator of the high class of the amplifier and are often used for advertising purposes.

The second nuance is that any headphones also inevitably have their own frequency limitations — and these limitations can be more significant than in an amplifier. Therefore, when choosing, it's ok to take into account the characteristics of the headphones: for example, you should not specifically look for an amplifier with an upper frequency limit of the full 22 kHz, if in the headphones that you plan to use with it, th...is limit is only 20 kHz.

In conclusion, also note that an extensive frequency range in itself does not guarantee high sound quality — it largely depends on other factors (frequency response, distortion level, etc.).

The ratio between the overall level of the desired signal produced by the amplifier and the level of background noise resulting from the operation of electronic components.

It is impossible to completely avoid background noise, but it is possible to reduce it to the lowest possible level. The higher the signal-to-noise ratio, the clearer the sound produced by the device, the less noticeable its own interference from the amplifier. In the most modest amplifiers from this point of view, this indicator ranges from 70 to 95 dB — not an outstanding, but quite acceptable value even for Hi-Fi equipment. You can often find higher numbers — 95 – 100 dB, 100 – 110 dB and even more than 110 dB. This characteristic is of particular importance when the amplifier operates as a component of a multi-component audio system (for example, "vinyl player — phono stage — preamplifier — headphone amplifier." The fact is that in such systems the final noise of all components at the output is summed up, and for sound purity it is extremely it is desirable that these noises be minimal

Separately, it is worth emphasizing that a high signal-to-noise ratio in itself does not guarantee high sound quality in general.

The coefficient of harmonic distortion that occurs during the operation of the amplifier.

Any electronic circuits are inevitably subject to such distortions, and the quality and reliability of the sound at the output depends on their level. Accordingly, ideally, the harmonic coefficient should be as low as possible. So, as a general rule, a level of 0.09% and below (hundredths of a percent) is considered good, and a level of less than 0.01% (thousandths of a percent) is excellent. The exception is lamp devices: higher values \u200b\u200bare allowed in them (in tenths of a percent), however, this point in many cases is not a drawback, but a feature (for more details, see "Lamp").

It is also worth noting that a low harmonic coefficient is especially important when using the amplifier as part of multicomponent audio systems — for example, when listening to music from a vinyl player with an external phono stage. The fact is that in such systems the sum of distortions from all components affects the final sound — and it, again, should be as low as possible.

The presence of the Gain Control function in the amplifier — that is, adjusting the input sensitivity, or, in other words, adjusting the degree of gain. The higher the "gain" — the higher the final volume of the sound (with the same characteristics of the headphones and the input signal).

Most often, modern headphone amplifiers provide the simplest two-stage (High / Low) or three-stage (High / Mid / Low) sensitivity adjustment. However, even such a setting provides additional features for coordinating the signal source, amplifier and headphones. For example, the ability to increase Gain may come in handy when changing headphones to higher-impedance or less sensitive ones: a weak gain sometimes does not allow you to achieve the desired volume on such “ears”. Conversely, for sensitive headphones, a high degree of gain may be excessive.

Types of inputs provided in the design of the amplifier.

Modern headphone amplifiers can be equipped with audio inputs of both analogue ( mini-Jack 3.5 mm, Jack 6.35 mm, RCA, XLR) and digital formats (S / P-DIF with coaxial or optical connection), as well as USB OTG and USB type ports b. Here is a more detailed description of each of these inputs:

— Mini-Jack (3.5 mm). One of the most popular modern audio connectors. In this case, it is mainly used to connect to an analogue audio signal amplifier; this can be a line-level signal or sound from the headphone output from an external device (these nuances should be specified separately), while the connector itself most often has a classic three-pin format and is responsible for both stereo channels at once. Due to its small size, the mini-jack is very convenient for use in portable models (see "Type"). On the other hand, it is less noise-resistant than a 6.35 mm Jack of similar design, and has less extensive capabilities — in particular, it is almost never used for balanced connection. Therefore, in stationary models, this interface is much less common.
Separately, we note that other types of inputs can also be built into the 3.5 mm...type hardware port — for example, coaxial and/or optical (see below for details). However, the presence of a mini-jack is indicated only if this connector is capable of operating in a traditional analogue format.

— Jack (6.35 mm). An audio connector, in many ways similar to the mini-jack described above — in particular, it is also used mainly for connecting an analogue audio signal. The key difference is in the larger sizes. Because of this, Jack type inputs are used much less frequently, and mainly in stationary technology (see "Type"); but, on the other hand, a large diameter expands the possibilities of the connector. First, the connection is more reliable than 3.5mm jacks, with less chance of interference and accidental disconnection. Secondly, such inputs can even be used for balanced connection (although such a possibility is far from mandatory, moreover, XLR connectors are more often used for balanced connection; see below about them and about a similar connection format). Therefore, for high-quality stationary equipment, such inputs are considered more preferable than mini-jack.

— RCA. RCA is technically a type of connector that can be used for a variety of purposes. However, in this case, a very specific application is implied — in the format of a line input (for an analogue audio signal). In this format, one physical connector is responsible for one channel of sound, so this type of input usually consists of a pair of jacks — for the left and right channels. In general, linear RCA is practically not used in portable devices, but it is very popular in stationary audio equipment. It is somewhat inferior to more advanced standards (like XLR, see below) in terms of functionality and noise immunity, but this interface is often quite enough for both everyday and simple professional use.

— XLR. Initially, XLR is a connector of a characteristic round shape, with a set of contacts in the form of pins (and sockets for them) and an additional retainer on the outer ring. It can have a different number of contacts and be used in different formats. However, in headphone amplifiers, when talking about XLR inputs, they usually mean an interface for balanced connection of an analogue (line) audio signal. Such an interface usually consists of at least a pair of three-pin connectors — one for each stereo channel (a rarer option is one common six-pin connector, in fact a two-in-one version). As for the balanced connection, this is a special format that uses three wires per channel (instead of the standard two) and a special way to process the signal at the input. Due to this method, interference due to third-party interference in the connection cable is mutually canceled when it enters the amplifier; in fact, the cable itself plays the role of a noise filter. This allows you to work even with fairly long wires without compromising the purity of the sound. On the other hand, XLR connectors are quite large, and balanced format support affects the cost of the device. Therefore, in general, this interface is considered professional, it is installed in amplifiers of the appropriate level, mostly stationary (with rare exceptions).

— Coaxial S/P-DIF. A variation of the S/P-DIF interface that uses an electrical cable (as opposed to the optical cable described below). In general, the S / P-DIF format allows you to transmit several channels of sound through one connector at once, including working with multi-channel formats (although stereo is most often used in headphone amplifiers). And the electrical version of this interface is somewhat cheaper than the optical one and does not require special care when handling the cable. Its disadvantage is some susceptibility to electromagnetic interference, however, to compensate for this moment, the cable is usually made shielded.
Note that the S / P-DIF coaxial input most often uses an RCA jack as a hardware connector. However, this interface should not be confused with the analogue RCA described above: these are fundamentally different standards that are not compatible with each other. In addition, in some models (in particular, portable ones), this type of input can be physically combined with a 3.5 mm jack; in this case, one socket can work in different formats (depending on the selected settings), and a cable with a special connector (or an appropriate adapter) is required to use the coaxial interface.

— Optical S/P-DIF. A variation of the S/P-DIF interface that uses a TOSLINK fibre optic cable to transmit digital audio in stereo or multi-channel format (however, the latter is not typical for headphone amplifiers). The main advantage of such a connection over the coaxial one described above is complete insensitivity to electromagnetic interference. On the other hand, the optical cable is quite delicate, it does not tolerate strong pressure and bending.
It is worth saying that in some amplifiers — especially portable ones — the optical input can be built directly into the 3.5 mm jack, and to work with such an input, you need a cable with a plug of the appropriate design. The connector itself can work in different formats — depending on the settings and the connected cable.

— USB (OTG). Initially, USB OTG is a standard that allows you to connect various USB peripherals (such as flash drives) to portable gadgets like smartphones or tablets. However, in headphone amplifiers, this function has its own specifics, it should be specified separately in each case. So, most models with USB OTG are portable, and in them this input is used in the classic format — to receive a digital audio signal from microUSB, USB-C or another similar connector in a portable gadget (if the gadget initially provides such an opportunity). But in stationary amplifiers (see "Type"), the name "USB OTG" can denote an interface for connecting to a PC, if this interface does not use USB Type B, but another type of connector. These nuances should be clarified separately.

— USB (Type B). Interface for connecting the amplifier to the USB port of a computer and transmitting sound in digital form; in other words, a connector for using the amplifier as an external sound card. Formally, USB Type B is a strictly defined type of USB connector that has a characteristic square shape; it is this connector that is usually installed in stationary models. But in portable devices, this role can be played by ports of a different type — for example, microUSB; however, they are also referred to as USB Type B in such cases.

Anyway, the point of connecting an amplifier in the format of an external sound card is, first of all, that the built-in sound cards of modern computers usually have rather modest characteristics, and much better sound can be achieved on external equipment.

The total number of headphone outputs provided in the design of the amplifier.

Most modern headphone amplifiers are designed for individual use, but there are exceptions — you can find models for sale with 2 outputs and even 3 or more. The general essence of this design is obvious: it allows you to connect several headphones at once and use the amplifier for several listeners at once.

However, not all connectors can be of the same type. Among those there are classic mini-Jack (3.5 mm) and Jack (6.35 mm), as well as less popular balanced 2.5 mm micro-Jack, XLR and 4.4 mm Pentaconn.

— mini-Jack (3.5 mm). The most popular plug format among modern wired headphones. It is found in models of all price categories; and even high-end solutions that can be used with a more advanced 6.35 mm Jack, most often do not have a built-in Jack format connector, but a 3.5 mm plug and a complete 6.35 mm adapter. On the other hand, the acoustic properties of the mini-Jack are somewhat inferior to the "big brother"; therefore, this headphone connection format is found mainly among portable models (see "Type"), although there are also stationary amplifiers with such outputs.

— 6.35 mm (Jack). Plug format designed mainly...for fairly advanced technology, mostly stationary. The large size of the connector somewhat complicates its use in compact devices; on the other hand, due to this feature, the connection quality, reliability and noise immunity are much higher than that of the smaller 3.5 mm mini-Jack. And you can connect headphones with a mini-Jack plug to a Jack-type jack using a simple adapter; often such an adapter is even supplied with “ears”. Thus, 6.35 mm type outputs are found in most stationary amplifiers (see "Type") and are found even in some portable models.

— XLR. This connector is mainly for professional use, having a characteristic round shape, contacts in the form of pins (“pins”), and often also a latch on the rim for additional reliability in connection. This connector is used for the so-called balanced connection of headphones, which has a positive effect on the purity of the sound and allows you to use even long wires without additional risk of distortion. On the other hand, in the case of headphones, the need for such a connection arises relatively rarely, and there are not many "ears" themselves with an XLR plug — mostly high-end professional models. So in amplifiers, outputs of this type are mainly used in stationary devices (see "Type") of a premium level. Most often, a four-pin connector is used as such an output, often without a latch and/or reduced sizes. In general, in audio equipment, such a connector is less common than a three-pin one (see "Outputs"), but specifically in headphones it is the standard option — especially since 4 pins allow you to output both stereo channels through one jack (whereas three-pin jacks work in the format "one channel per plug"). However, there are amplifiers where a pair of three-pin XLRs plays the role of a balanced headphone output. At the same time, such connectors can be physically combined with 6.35 mm Jack outputs — in other words, a 6.35 mm jack is built right into the centre of the XLR connector. This makes the design more compact, but does not allow the use of both types of connectors at the same time.

— Pentaconn 4.4. Connection implemented by a 5-pin connector with a diameter of 4.4 mm. This is a relatively new balanced connection standard developed by Sony. Most often used as a line output for digital-to-analogue converters and amplifiers. Additionally, this connector can be found in multimedia players and even console consoles. The main advantage of the Pentaconn 4.4 standard is the ability to output an audio signal to sufficiently powerful high-impedance headphones. This standard is an alternative for not very practical Jack and XLR connections.