6. Sound-Shaping Features

Generally, it's unfortunately quite difficult to draw conclusions about the actual quality of a preamp based on technical specifications. This is less because the values themselves are not meaningful. Rather, the problem is that there are no precise regulations for the measurement of the values, or many manufacturers do not adhere to them. This leads to most manufacturers not even providing the measurement conditions, rendering many specifications meaningless and non-comparable. Nonetheless, it can't hurt to take a look at the datasheet and examine the following details more closely. However, the final decision should always be made based on what you hear. This is especially true when looking for a preamp with vintage sound.

Gain Range

This refers to the amplification that a preamp can achieve. It should be 60 dB or better.

Equivalent Input Noise (E.I.N)

This is an indication of the noise behavior of the preamp. The amplifier itself is assumed to be noise-free, and the noise is interpreted as a source at the input. The noise voltage at the output of the preamp is measured at a high gain, e.g., 60 dB. The E.I.N value is then the measured noise voltage in dB at the output minus the set gain.

This value indicates how much noise the preamp itself adds to the signal.

Signal to Noise Ratio (S/N)

The signal-to-noise ratio indicates the noise at the output of the preamp relative to the nominal level of the preamp at minimum gain. The nominal level is the normal operating level of the preamp, i.e., the level to which the microphone signal is typically raised and then sent to the output. This is +4 dBu for professional studio equipment. A value of 94 dB means that the output noise is 90 dB lower than a useful signal at +4 dBu, namely -90 dBu.

The higher this value, the lower the noise of the preamp.

Dynamic Range

The dynamic range is the level range between noise and upper overload limit. Smaller signals are lost in the noise, and larger signals can no longer be reproduced without distortion. A larger dynamic range is desirable.

In conjunction with the S/N value, the maximum allowable input level can also be determined. If the dynamic range is, for example, given as 114 dB and the S/N value is 94 dB, it follows that the maximum input level is 20 dB higher than the nominal level, namely 24 dBu.

Total Harmonic Distortion (THD)

For transparent, color-free sound, this value should be as low as possible. In general, the value is higher for tube preamps.

Input Impedance

The input impedance should typically be at least 5 to 10 times greater than the nominal impedance (output impedance) of the microphone. A typical value is 2kΩ.