Comparison FiiO KA13 vs FiiO KA17

DAC model — a digital-to-analogue converter installed in the amplifier.

In accordance with the name, the DAC is responsible for converting a digital signal (for example, coming to the optical input or USB, see "Inputs") into an analogue format, with which the amplifier directly works. The presence of such a converter in an external "amplifier" is important, given the fact that many popular signal sources — such as smartphones or built-in sound cards — are equipped with fairly simple and inexpensive DACs with low sound quality; on external equipment, this quality can be much higher. And the quality of the conversion and, accordingly, the characteristics of the output sound directly depend on the characteristics of the DAC: even the most advanced power amplifier will not “save” a signal converted with significant errors. Accordingly, knowing the converter model, you can find detailed data on it — from official specifications to practical reviews — and evaluate how an amplifier with such a module meets your requirements.

The number of audio channels supported by the amplifier; only specified if the number is greater than one.

Since we are talking about dedicated headphone amplifiers, the term “channel” is used in this case in a slightly different sense than is usual in audio technology. This term most often means a set of two traditional channels (left and right), which allows you to provide full stereo sound in headphones. Simply put, the number of channels is the number of stereo sound sources that can be connected to the amplifier at the same time, and the number of headphones that can simultaneously output the signal from these sources. However, in addition to this, other types of channels can be provided — for example, monophonic. However, anyway, each channel uses its own signal source, its own headphone output (or other playback device) and its own set of adjustments.

Thus, on a multi-channel amplifier, several people can simultaneously listen to different sound sources in headphones; and some models are capable of reproducing individual channels also on external acoustics. At the same time, such functionality complicates the design of the device, increases the likelihood of interference and significantly affects the cost (including due to the need to take measures to compensate for interference). Therefore, there are relatively few multi-channel models nowadays, and these are exclusively stationary solutions (see "Type"), designed mainly for professional use....r>
Also note that the number of headphone outputs can be greater than the number of channels; in such cases, several connectors are “attached” to some channels at once, usually of different types (for example, Jack and XLR), which allows the user to choose the option depending on the headphones at hand. Theoretically, the outputs of one channel can be used simultaneously, but it's ok to clarify this possibility separately.

The sampling rate of the digital-to-analogue converter (DAC) installed in the amplifier. Recall that such a converter is responsible for converting digital audio into an analogue audio signal, which is then processed by the main amplifier and fed to the headphones (or other analogue audio device).

The sound in digital form is most often recorded as follows: the original sinusoid of the analogue audio signal is divided into separate sections (samples) — “steps” of a certain length and height, and each of these steps is encoded with its own set of numbers. The sampling rate determines how many such steps there are in a certain section of the original audio signal. Accordingly, the higher this frequency, the more accurately the digital record corresponds to the original signal; on the other hand, an increase in the number of samples per unit of time increases the volume of files and increases the requirements for the hardware power of digital circuits.

Specifically, for a DAC, the native sampling rate of such a module is, in fact, the maximum sampling rate of the incoming digital signal that the converter can effectively handle. With higher input values, the sound quality will at best be limited by the capabilities of the DAC, at worst, the amplifier will not be able to work correctly at all. Anyway, higher numbers in this paragraph (ceteris paribus) mean a more advanced and high-quality converter; on the other hand, this moment significantly affects the...cost, and you can evaluate all the capabilities of a high-end DAC only on audio materials of the appropriate quality.

As for specific numbers, the lowest value that can be found in headphone amplifiers is 44 kHz. According to the laws of physics, it is this sampling frequency that is the minimum necessary for the full transmission of all human-audible sound frequencies (16 — 22,000 Hz), and it is this frequency that is used in the Audio CD format. Many models provide values in 96 kHz and 192 kHz (this is already enough to work with different types of DVD-Audio), and in the most advanced devices this figure can reach 384 kHz and even 768 kHz.

Rated headphone output(s) provided by the amplifier.

Rated is the highest average power that the device is capable of delivering for a long time without overloads; individual “jumps” of the signal may have a higher level, but this indicator is the main one. The sound volume of the headphones connected to the device directly depends on it: with the same characteristics of the “ears” (primarily sensitivity), the high output power of the amplifier allows for a higher sound pressure level.

There are special formulas and tables that allow you to calculate the minimum power level required to achieve a particular volume. For example, to achieve 95 dB (the minimum required level for listening to music in silence at a satisfactory volume), headphones with a sensitivity of 100 dB will need 0.32 mW, for 105 dB (recommended level for powerful sound like rock concerts) — 3, 16 mW, and for 120 dB (the recommended level for watching movies with special effects like thunder, explosions, etc.) — already 100 mW.

At the same time, when choosing by this parameter, note that the actual power of the amplifier at the output will depend on the impedance of the headphones. This paragraph usually indicates the highest power value — with the minimum allowable resistance; for "ears" with numerous ohms, the power will be less, sometimes quite significantly. Therefore, when choosing, it is more convenient to use not a total number, but a specific power value for a parti...cular resistance (see below). The second nuance is that for multichannel amplifiers (see "Number of channels") this parameter can be indicated in different ways: in some models, the power is given for the full channel load mode (that is, we are talking about a guaranteed maximum per channel), in others — for half load or generally for working with one channel; such details should be clarified separately.

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.

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 presence of a display in the design of the amplifier. Usually, this is the simplest single-colour screen — either in the form of a segment display capable of displaying a limited set of characters (like screens in electronic watches), or in the form of an LCD matrix, suitable only for text and basic graphic information. However, even such equipment provides additional convenience: various data can be displayed on the screen that are not available for simpler indicators. Typical examples of such data are conditional volume level, actual output power, selected signal source, error notifications, etc. On the other hand, it is worth noting that the display (like any additional electronics) is a potential source of interference; so many high-end amplifiers are not equipped with screens for this very reason — for maximum sound purity.

The presence of a metal case in the design of the amplifier.

This feature has both aesthetic and quite practical significance. In other words, it not only gives the case a stylish and solid appearance, but also has a positive effect on its strength and reliability. And since aluminium alloy is most often used as a metal, the weight of the structure is also small. The main disadvantage of this material is the higher cost than another popular option — plastic; however, against the background of the overall price of the device, the difference in the price of materials is often insignificant. So in most modern headphone amplifiers, the cases are made of metal.