Tube
Phono correctors, the working circuits of which are made on the basis of lamps.
One of the main advantages of such audio devices is the notorious "warm
tube sound", which many music lovers consider the most pleasant and natural. At the same time, this point is rather ambiguous. The fact is that the level of harmonic distortion in tube circuits is several times higher than in transistor circuits, but these distortions are quite specific — they are quite pleasant for human hearing and give the sound a characteristic "atmospheric". But the unequivocal advantage of lamp technology is a good margin for overload. On the other hand, such devices are much more expensive and more complicated than transistor ones, they require warming up after switching on, and the lamps themselves need to be changed periodically (on average, once every few years). As a result, there are relatively few such phono stages nowadays, and they are designed mainly for principled lovers of tube technology.
Frequency range
The range of sound frequencies reproduced by the phono stage. When evaluating this parameter, it is worth keeping in mind several important points. Firstly, in this case, not the entire bandwidth is taken into account, but the range in which the uneven frequency response of the phono stage (according to the RIAA standard) does not exceed the value specified by the manufacturer. Secondly, the human ear is only able to perceive sound within the range of 16-20,000 Hz (in some people, up to 22,000 Hz). Ideally, the audio system should cover this entire range — otherwise, some of the low and/or high frequencies may be cut off; but to provide a wider range from a practical point of view does not make sense. Nevertheless, there are phono stages with quite solid performance, for example, 5 – 35,000 Hz. These specifications are usually a "side effect" of high quality audio circuits and are advertised by the manufacturer for promotional purposes.
Another point to consider when choosing is the frequency range of other components of the audio system. For example, it is hardly worth looking for a phono stage with a lower threshold of 16 Hz, if the power amplifier only supports frequencies from 40 Hz and higher.
As a note to this clause, the RIAA ripple present in the frequency range may be indicated. In most models, it is from ±1 to ±6 dB; the lower the value, the smoother the frequency response and the better the sound.
Dynamic range
The dynamic range of a phono stage is the difference between the maximum signal level it can produce and the maximum level of self-noise (which inevitably occurs in any electronic audio device). In a sense, this parameter is similar to the signal-to-noise ratio (see below), but in this case we are talking about the difference between the maximum signal and noise levels, and not between the average ones.
The greater the dynamic range, the more advanced the phono stage is considered (ceteris paribus). In top models, this figure can exceed 90 dB and even 100 dB. We only note that in universal devices (see "Intended use") the ranges for MM and MC may differ — the first is usually higher, and it is given in the characteristics.
ADC bit depth
Bit depth of the analog-to-digital converter installed in the phono preamp.
As the name suggests, the ADC is responsible for converting the analog audio signal coming from the phono cartridge into a digital data stream — for instance, for transmission via S/P-DIF (see "Outputs"). The principle of such conversion is that the original sine wave of the analog signal is broken down into individual "steps," and data about each "step" is encoded in digital form. Each fragment has two main parameters — duration and volume level.
The bit depth of the ADC determines how accurately the volume of each individual digital "step" corresponds to the volume of the original analog signal. For modern phono preamps, the minimum bit depth is 16 bits — this (in combination with an appropriate sampling rate, see below) is sufficient for obtaining digital sound quality of Audio CD or even DVD-Audio. However, there are also higher values — for example, 24 bits.
ADC sampling rate
Sampling frequency of the analog-to-digital converter installed in the phono preamp.
In accordance with its name, the ADC (analog-to-digital converter) is responsible for converting the analog audio signal coming from the cartridge into a digital signal—for example, for transmission through S/P-DIF (see "Outputs"). The principle of such conversion is that the original sine wave of the analog signal is divided into individual segments or "steps," and data about each "step" is encoded in digital form. The sampling frequency describes the number of such segments per second of the original sound. The higher it is, the narrower each individual "step" will be, and the more accurately the digital signal will correspond to the original sine wave.
In modern phono preamps, the sampling frequency is usually no less than 48 kHz, which is somewhat higher than in the popular Audio CD standard. In the most advanced models, this figure reaches 192 kHz, which is comparable to high-quality DVD-Audio.
Output level
The highest root mean square (RMS) output level that a phono stage can provide. Actual level may be lower depending on input signal level and gain
Recall that a phono preamplifier usually operates in the form of a preamplifier, boosting a weak signal from a pickup to a line level for transmission to a power amplifier. The minimum signal level sufficient to feed the power amplifier is about 150 mV; however, phono preamps usually provide higher values. This is done on the basis that the higher the intrinsic signal, the less it is affected by external electromagnetic interference. The maximum for modern phono preamps is actually 2 volts on the RCA outputs, higher values can be found on the XLR outputs.
In addition, some nuances of matching the phono stage and an external amplifier are associated with the output level; detailed information about this can be found in special sources.
Output impedance
The output impedance in this case means the internal resistance of the analogue audio outputs of the phono stage. Without going into too much detail, the meaning of this parameter can be described as follows: the lower the output impedance, the less the voltage drops at the output of the phono stage (actual signal level) when an external load is connected.
There is an opinion that, ideally, the output impedance of the phono stage should be as low as possible (and the input impedance of the load connected to it, on the contrary, should be as high as possible). This is partly true, but in some situations, on the contrary, models with a high output impedance perform better. Therefore, this indicator in modern phono stages can be different — from a few ohms to several thousand ohms. The choice of the optimal value depends on the external load with which the device is planned to be used; there are many specific nuances here, they are described in detail in special sources.
Signal to noise ratio (MM)
Signal-to-noise ratio provided by the phono preamp when working with an MM type cartridge (see "Purpose")
This parameter describes the ratio between the average level of the output signal and the average level of the device's inherent noise. The higher it is, the cleaner the sound reproduction, with fewer extraneous interferences. On the other hand, it is worth remembering that the overall sound quality provided by the phono preamp depends on a number of other parameters. As a result, an advanced model with high sound quality may have a lower signal-to-noise ratio than a budget device.
Note that in universal phono preamps (see "Purpose"), the signal-to-noise ratio for MM cartridges is usually higher than for MC due to the technical characteristics of each.
Harmonic distortion (MM)
The coefficient of harmonic distortion provided by the phono stage when working with an MM type pickup (see "Intended use").
The lower this indicator, the less distortion the phono stage gives, the more reliable the output signal is. It is impossible to completely avoid such distortions, but it is possible to reduce them to a level that is not perceived by a person. So, it is believed that the level of harmonics of 0.5% and below is no longer audible even to a “trained ear”. However, it should also be borne in mind that the quality of the audible sound is also affected by distortion from other components of the audio system. Therefore, the harmonic distortion of the phono stage should not just be below 0.5%, but as low as possible. Values in hundredths of a percent are considered a good indicator, values in thousandths and below are considered excellent.
