In figure 1 we have this simple configuration that employs few passive components.
The control voltage determines the attenuation, typically between 5 and 58 dB when the input voltage varies between the nominal voltage of a zener and the triple of the voltage of the zener.
For a voltage of twice the zeners used the typical attenuation is 30 dB. This attenuation also depends on the specific characteristics of the components used.
See that the resistor in series with the source is important to limit current in the zener. The value of this resistor depends a lot on the dissipation of the zener used, but what we indicate is for the types within the recommended range of values.
It is important to note that the linearity of this attenuator is not the greatest, but as a general-purpose application for audio signals, it works perfectly.
It is important to note that this is an attenuator for small signals.
