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.
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)
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.
Gain (MM)
The gain provided by the phono stage when working with an MM type pickup (see "Intended use").
This parameter describes how much the signal level at the output of the phono stage increases relative to the level at the input. It is traditionally written in decibels; you can convert decibels into "times" using special formulas or tables. Knowing the gain, you can estimate the actual level of the output signal when using a particular pickup. For example, if the characteristics indicate 35 dB (56.2x), and the “head” outputs 5 mV, then as a result, the signal level at the output of the phono stage without additional processing will be 5 * 56.2 = 281 mV. Accordingly, the input sensitivity of the power amplifier with which this model is planned to be used should be less than 281 mV (however, 150 mV is considered the standard minimum for such amplifiers).
Note that the output level of MM cartridges is noticeably higher than that of MC cartridges, so the gains for them are generally lower (although there are exceptions).
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").
Input sensitivity (MM)
Input sensitivity of the phono stage when working with an MM type pickup (see "Intended use").
Input sensitivity is the lowest root mean square (RMS) signal level at the input, at which the phono stage is able to “perceive” this signal normally, process it correctly and amplify it. Accordingly, compatibility with the pickup directly depends on this indicator: the signal level from the “head” must not be lower than the input sensitivity of the phono stage.
Note that
MM pickups are noticeably superior to MC pickups in terms of signal power, so the sensitivity threshold for correctors for them is relatively high — usually about 4 – 5 mV. At the same time, there are correctors with a higher "threshold of perception" — more than 100 mW; they must be connected through special step-up transformers or other similar equipment.
Input impedance (MM)
The input impedance of the phono stage when working with an MM type cartridge (see "Intended use").
Input impedance is the AC resistance at the Phono input. This is one of the parameters that determine the compatibility of a phono stage with a particular pickup. The general rule is that the input impedance of an equalizer should be greater than the output impedance of the pickup. And the most popular formula for accurate calculations is "10:1": the input resistance should be 10 times higher than the output resistance of the "head". In some situations, another impedance ratio may also be optimal; these points are described in more detail in special sources. However, in the case of MM, the standard option is just 4.7 kOhm at the “head” and 47 kOhm at the input of the phono stage.
Signal to noise ratio (MS)
The signal-to-noise ratio provided by the phono stage when working with an MC-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 circuits for MC cartridges usually give a lower signal-to-noise ratio than for MM cartridges; this is due to the technical features of both.
