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.
Signal to noise ratio (MM)
The signal-to-noise ratio provided by the phono stage when working with an MM-type pickup (see "Intended use")
This parameter describes the relationship between the average output level and the average noise floor of the device. The higher it is, the clearer the sound is, the less extraneous interference it has. On the other hand, it is worth remembering that the overall sound quality provided by a phono stage 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 low-cost device.
Note that in universal phono stages (see "Intended use") the signal-to-noise ratio for MM cartridges is usually higher than for MC ones; this is due to the technical features of both.
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.
Input load capacity (MM)
The input capacitance of the phono stage when working with an MM type pickup (see "Intended use").
This parameter determines compatibility with a specific pickup. The selection rule in this case is as follows: the total capacitance of the phono stage and connecting wires must correspond to the capacitance of the “head”, in extreme cases, at least not exceed it (otherwise the sound will deteriorate noticeably). In order to simplify this matching, it may be possible to adjust the
input capacitance(see "Adjustments").
Noise canceling
The presence of a noise reduction system in the phono stage. The general purpose of such systems is already clear from the name; in this case,
noise reduction can work both with the amplifier's own noise (thus increasing the signal-to-noise ratio), and with extraneous noise from external sources (for example, the rustle of a needle on a record).
This function can be found in phono stages of various levels, from the most budgetary to the top ones. Accordingly, the quality of its work may also vary. Anyway, however, two points should be noted. On the one hand, noise reduction can really improve the sound, making it clearer. On the other hand, additional processing of the audio signal inevitably introduces its own distortions into it, and during the operation of the noise suppressor, the reliability and detail of the sound may suffer, and quiet fragments may “fall under the distribution” along with extraneous noise. Therefore, this function is often turned off.
External power supply
The presence of an
external power supply unit(PSU) in the device.
Most often, the meaning of such an arrangement is to move the PSU, which is a potential source of interference, outside the case, to the maximum distance from the components of the phono stage. This is especially true for high-end models. In some cases, an external PSU may also be provided to reduce the size and weight of the device; this moment, on the contrary, is typical mainly for correctors of the budgetary level.
