Digital Volume Control

Many of today"s HiFi amplifiers feature a "clicking" volume control, but this is only rarely a real stepped attenuator based on a wafer switch. In nearly all cases, this expensive system is based on a normal poten- tiometer, whose spindle is fitted with a mechanical construction to simulate the stepping move- ment. A normal rotary switch is not suitable for adjusting the volume of an amplifier because it briefly disconnects the input from the signal source when operated, and so readily gives rise to clicks and contact noise. Different problems crop up when designing an electronic volume control. Of these, distor- tion is probably the hardest to master, but reasonable results are still obtainable, as will be shown here. Basically, there are two methods for making an elec- tronic potentiometer. One is to create a tapped resistor ladder (which is not much different from a normal potentiometer), the other is to change the resist- ance of the two "track sections" such that the total re...