ABSTRACT
A volume control is the most essential knob on a preamplifier, in fact the unhappily named ‘passive preamplifiers’ usually consist of nothing else but a volume control and an input selector switch. The simplest volume control is a potentiometer. These components, which are invariably called ‘pots’ in practice, come with various control laws, such as linear, logarithmic, anti-logarithmic, and so on. Anti-logarithmic pots are the same only constructed backwards so that the slope change is at the top end of the control setting; these are typically used as gain controls for amplifying stages rather than as volume controls. The control law of a linear pot can be radically altered if it has a centre-tap. This can be connected to a potential divider that has a low impedance compared with the pot track resistance, and the attenuation at the tap point altered independently of other parameters.
