Comparison FiiO BTR15 vs FiiO KA13

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 nominal impedance (impedance) of the headphones for which the amplifier was originally designed.

Modern headphones can have different impedance. In particular, among the most popular options are 16 ohms and 32 ohms, and advanced models have values from 300 ohms and even from 600 ohms. High-resistance is considered to be "ears" with a resistance of 100 ohms. These characteristics improve the purity of the sound, but require increased signal strength — and built-in amplifiers in handheld devices, computer audio cards, etc. usually have difficulty with this. Therefore, external amplifiers are often used for this very purpose — to effectively "shake" high-end headphones with high impedance. For the same reason, some of these amplifiers are not compatible with low-impedance “ears”: there are many devices that require headphones with an impedance of at least 32 ohms, or even higher, and in some models the lower limit of the operating range can reach 100 ohms. As for the maximum resistance, the range of its values is very impressive — from 32 ohms in relatively simple portable "amps" to thousands and even tens of thousands of ohms in high-end stationary models.

Anyway, you should not violate the manufacturer's recommendations for headphone impedance. If the resistance of the “ears” is too low, at best, the sound will be s...ubject to noticeable distortion, at worst, equipment failure and even fire may occur. Too high resistance, in turn, not only reduces the volume, but also worsens the frequency response.

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.

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 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.

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 a Bluetooth module in the amplifier for direct wireless communication with other devices - primarily with audio sources that also support this technology (for example, a smartphone, tablet or laptop).

The main convenience of Bluetooth amplifiers is, first of all, the absence of additional wires, which can create various inconveniences. At the same time, the range of wireless communication is usually at least several meters. On the other hand, during normal transmission via Bluetooth, the digital audio signal is heavily compressed, which worsens the sound quality. To correct the situation, Bluetooth models may include aptX technology, which increases the purity of the signal almost to the level of wired Audio CD (or even Hi-Res Audio - in the aptX HD version); however, such functionality significantly affects the cost, and sophisticated music lovers often easily notice the difference between aptX and a wired connection.

In light of all the above, Bluetooth does not make sense to install in stationary equipment, so nowadays such modules are used only in portable amplifiers (see "Type"). At the same time, some of these models are positioned not so much as amplifiers, but as Bluetooth adapters for wired headphones. Nevertheless, such a solution can be a good alternative to classic wireless headphones: decent wired "ears" in combination with a Bluetooth amplifier can provide higher sound quality at a comparable,...or even lower cost, and often such a set turns out to be even more "long-playing" in terms of work without recharging.

Initially, sound transmission via Bluetooth provides a rather strong signal compression, which can greatly spoil the impression when listening to music. To eliminate this shortcoming, various technologies are used (the most popular of which is the aptX codec). Of course, in order to use any of the technologies, it must be supported not only by the amplifier, but also by the Bluetooth device with which it is used.

— aptX. A Bluetooth codec designed to greatly improve the quality of Bluetooth audio. According to the creators, it allows to achieve quality comparable to Audio CD (16-bit/44.1kHz). The benefits of aptX are most noticeable when listening to high-quality content, but even on regular MP3 it can provide a noticeable improvement in sound.

aptX Low Latency. A specific variation of the aptX described above, designed not so much to improve sound quality, but to reduce delays in signal transmission. Such delays inevitably occur when working via Bluetooth; they are not critical for listening to music, however, when watching videos or playing games, there may be a noticeable out of sync between the image and sound. The aptX LL codec eliminates this phenomenon by reducing latency to 32ms, a difference that is imperceptible to human perception (although it is still too high for serious tasks like studio work with sound).

— AAC. A codec used primarily in Apple portable technology to improve Bluetooth audio. In this sense, it is similar to aptX...(see relevant paragraphs), but noticeably inferior to it in terms of capabilities: if the sound of aptX is compared with Audio CD, then AAC is at the level of a medium-quality MP3 file. However, this is quite enough for listening to the same MP3s, the difference becomes noticeable only on more advanced formats.

The type of power used by the amplifier.

In modern models, you can find mains power, battery and USB port. At the same time, some devices may provide two options at once (or even all three at once) — this allows you to choose the most convenient way of feeding, depending on the situation. In addition, there are amplifiers with support for Power Bank mode — this feature is also indicated in this paragraph, although it is not a type of power supply, but an additional function of models with a built-in battery.

Here is a more detailed description of each option:

— From the network. Powered from a conventional 230 V socket. Such power is very convenient from a practical point of view: the operating time of the amplifier is unlimited (as long as there is voltage in the network), and the output power can be almost any. The main disadvantage of this option is the actual dependence on sockets; however, for stationary models (see "Type") this point is not critical, so most of these devices use mains power (and most often — as the only option). There are also portable amplifiers with the ability to connect to the network — in such cases it is provided as an additional option that allows you to save battery power if there are outlets nearby (and most often also charge the battery during such use).

— From t...he battery. Powered by its own built-in battery. Such a power supply complicates the design of the amplifier, increases its weight and cost, and the operating time on a charge is inevitably limited. On the other hand, the battery allows you to work regardless of the presence of outlets nearby. Therefore, this option is extremely popular among portable amplifiers (see "Type") — especially since it is easier to achieve high output power with a battery than with USB power (which is also suitable for such equipment). But stationary solutions with their own batteries are extremely rare — and in them, usually, the battery is a “fallback option” in addition to another type of power supply (and in some stationary amplifiers, the presence of a battery also depends on the modification).

— From the USB port. Powered by a USB connector — usually the same one that is used as a source of digital audio signal. The features of such a power supply no longer depend so much on the specific amplifier, but on the device with which it is used. So, when used with a PC, such a connection is in many ways similar to connecting to a network: the operating time is unlimited, and the power of the amplifier can be quite high (although not as high as when using an outlet), but there is no talk of freedom of movement. Smartphones and other mobile gadgets, on the contrary, are autonomous, but their power outputs are not very powerful. On the other hand, it is most often not required for them, and the unequivocal disadvantage can only be called the moment that the amplifier additionally consumes the battery of the gadget. Connecting to a laptop combines the features of both options described above: the power supply is comparable to the USB ports of stationary PCs, while the laptop can work without an outlet.

— Power bank function. The ability to operate the amplifier in power bank mode — that is, an external battery for charging various gadgets, such as smartphones or pocket players. This function by definition means that the amplifier has a built-in battery (see above); the device itself is most often portable (see "Type"), however, there are also stationary solutions with Power Bank mode. Note that the specific battery capacity in amplifiers with this function is different; often it is very low, and the device allows you to “prolong the life” of the gadget rather than fully charge it. However, even this possibility can be very useful — for example, if you need to wait for an important call, but you forgot to charge your smartphone, and there is no charger or outlet for it at hand.