1.  Technical Field of the Invention
The present invention relates to a drive apparatus for volume control devices typically for use in mixing system for mixing audio signals. 
2.  Related Art
On mixing systems utilized in concert or the like, a plurality of input channel audio signals are mixed so that required audio signal is finally produced.  The gains of the input channel audio signals are to be adjusted in various stages before in mixing.  More specifically, the audio signals just input to the mixing system undergo gain adjustment in header amplifiers in which volume control knobs are typically applied to the adjustment.  Subsequently, the signals undergo frequency characteristics equalizing as needed, and come under gain controls in fader amplifiers.  The gains applied to the signals in the fader amplifiers are set by input fader knobs provided for individual input channels. 
In addition to the individual input faders, other common faders might be assigned to a plurality of input channels.  The common fader is so called DCA fader, i.e., digital controlled amplifier or digital controlled attenuator fader, in digital mixer, and so-called VCA fader, i.e., voltage controlled amplifier or voltage controlled attenuator fader, in analog mixer.  The gain set by the DCA fader is multiplied by the gains set by the individual input faders, respectively, so that the actual gains applied to the plurality of input channels are determined.  The DCA fader technique is useful for picking up and volume control of sounds generated by large-scale instruments such as pianos and drums or by a part of orchestra. 
The sounds from a piano and other large-scale instruments are generally picked up by means of a plurality of microphones, which are assigned to individual input channels with the aim of balance adjustment.  Those input channels are further assigned to one DCA fader.  Accordingly, the balance among the audio signals picked up by the microphones is adjustable by means of the individual input faders, while the volume of the entire instrument is adjustable via the DCA fader. 
It is desirable that the input and DCA faders are adjusted to obtain preferable volume when they are operated to a pre-specified standard position, e.g., “0 dB.” If the DCA faders are adjusted in this way, when an input channel is to fade in, the operating personnel is merely required to operate the fader to the standard position thereof.  Subsequently, while monitoring the actual sound, the personnel can adjust the fader position precisely.  The volume adjustment at the standard position is preferably completed in the rehearsal process.  However, if someone wishes to keep a constant gain throughout moving a certain fader knob to its standard position, then troublesome operation is required, such as operating the volume control knobs at the header amplifiers or operating the other faders, simultaneously.