Comparison Pro-Ject Phono Box DS2 USB vs Pro-Ject Tube Box DS2

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.

Sampling frequency of the analogue-to-digital converter installed in the phono stage.

As the name suggests, the ADC is responsible for converting the analogue audio signal coming from the pickup into a digital signal, for example, for transmission via S/P-DIF (see "Outputs"). The principle of such a conversion is that the original sinusoid of the analogue signal is divided into separate fragments — "steps", and the data on each "step" is encoded in digital form. The sampling rate describes the number of such fragments per second of the original sound. The higher it is, the smaller the width of each individual “step” will be and the more accurately the digital signal will correspond to the original sinusoid.

In modern phono preamps, the sampling rate is usually at least 48 kHz — this is slightly higher than in the popular Audio CD standard. In the most advanced models, this figure reaches 192 kHz, which is comparable to high-end DVD-Audio.

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.

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.

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).

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.

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.

The coefficient of harmonic distortion provided by the phono stage when working with an MC 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.

The input impedance of the phono stage when working with an MC type pickup (see "Intended use").

The 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". However, in some situations, another impedance ratio may also be optimal; these points are described in more detail in special sources.

Variable input impedance models are available, see "Adjustment" for details.