Comparison LD Systems HPA 4 vs Behringer HA400

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.).

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 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.

Rated power consumed by the amplifier during operation. It is indicated only for models with a network connection and/or USB (see "Type of power"), since in models with a battery, the power is initially selected in such a way as to match the characteristics of the battery.

The meaning of this parameter depends primarily on the specific type of power supply. So, when working from an outlet, you can not pay much attention to power: even the most “gluttonous” modern headphone amplifiers consume less than 200 W, any outlet can handle such a load. The need to take into account the power consumption may arise only in specific cases — for example, when using an "uninterruptible power supply" or a voltage stabilizer, for which you need to know exactly the consumption of the entire connected load.

In the case of USB, in turn, it must be taken into account that USB ports of different versions (and even types) may differ in power supply to external devices. Therefore, when choosing here, you should make sure that the connector to which you plan to connect the amplifier will be able to provide the right amount of energy. For example, 10 W is a fairly solid indicator for such connectors; and for amplifiers of higher power, most likely, support for special USB Power Delivery technology will be required.