Comparison FiiO BTR5 2021 vs xDuoo MT-604

— Portable. Amplifiers designed to be carried all the time. They are small enough to fit in a bag or pocket and are powered by either a built-in battery or a USB port (see "Power Type"). Such devices can also be used as stationary ones, but constant use in this format is hardly justified: the functionality and power of portable amplifiers are generally quite modest, and with similar characteristics, they are noticeably more expensive than stationary counterparts.

— Stationary. Amplifiers designed to permanently stay in one place. They use power from outlets and do not have such size restrictions as portable models, which makes such devices more advanced. So, they can provide higher power than portable ones, the ability to work with professional high-impedance headphones, numerous different adjustments, high-quality signal processing circuits, multi-channel layout, etc. Of course, the specific functionality of such an amplifier may be different; however, if the headphones are not planned to be used “on the go”, and the sound quality is crucial for you, you should pay attention to this particular variety.

Amplifiers in which at least part of the element base is built on vacuum tubes (as opposed to most modern models that use exclusively transistors).

The main advantage of this technique is the notorious "warm tube sound" — a special soft coloring of the sound, which is appreciated by some audiophiles. At the same time, purely formally, tube amplifiers are noticeably inferior to transistor ones in terms of performance — in particular, they have a narrower frequency range and a higher harmonic distortion coefficient (see below). However, it is these distortions that give the "tube" sound its characteristic colour, they are more pleasant to the human ear than the "cold" errors in transistor technology. So this point in itself is not a disadvantage, and some consider it an unambiguous advantage.

It is also worth mentioning that tube amplifiers are more resistant to overloads and allow for a smoother frequency response. In addition, the lamps can be made open, which gives the device a special style. On the other hand, such an element base has a number of serious drawbacks. Firstly, it turns out to be noticeably more expensive than a transistor one. Secondly, the lamps are quite bulky and fragile — this makes them difficult to use in portable models (see "Type"); and although such solutions also occur, they require special care in handling. Thirdly, after switching on, it takes some time to warm up the elements. Fourth, lamps...have a more limited lifespan than transistors. In light of all this, tube headphone amplifiers are now much less common than transistor ones and are intended mainly for principled adherents of such technology.

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.

The capacity 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. In this case, the "height" (level) of each step cannot be an arbitrary value — a specific value is selected from a specific list. The bit depth determines how many options this list contains: for example, an indicator of 16 bits means a list of 2 to the power of 16, that is, 2 ^ 16 \u003d 65536 level options. Accordingly, the higher the bit depth — the closer the level of each sample will be to the level of the corresponding section of the sinusoid, the smaller the deviation from the original signal in cases where the original level falls between fixed values. Thus, a high bit depth has a positive effect on the quality and reliability of the sound; on the other hand, it significantly affects the volume of audio materials and the requirements for processing power of the equipment for their processing.

Specifically, for a DAC, the native bit depth of such a module is, in fact, the maximum bit width of the inc...oming digital signal that the converter is able to effectively handle. With higher input values, the sound quality will at best be limited by the capabilities of the DAC, at worst, the device 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 values, the standard options in modern headphone amplifiers are 16 bits, 24 bits and 32 bits. The first value is used, in particular, for the Audio CD format, the second is found in the lossless APE and ALAC formats, and 32 bits may be required to work with FLAC and certain high-end standards.

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 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.

Rated power delivered by the amplifier when connected to headphones (or other load) with an impedance of 16 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. And 16 ohms is a rather low resistance indicator even for low-resistance "ears"; such characteristics are provided mainly in general-purpose headphones designed for pocket gadgets with low-power amplifiers.

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". At the same time, it is worth noting that at 16 ohms, even the most low-power modern “amps” are capable of delivering about 20 mW — this is enough to drive headphones with a sensitivity of 88 dB (far from the highest figure) to a vo...lume of 105 dB (the minimum value recommended for a complete listening experience). And in most amplifiers, when operated with a given impedance, they provide much more power. So paying attention to this point and going into the calculations makes sense mainly either with low sensitivity of the "ears" (less than the mentioned 88 dB), or if you want to end up with a level above 105 dB.