E.W.S. Subtle Volume Control or SVC is a device based on Scott Henderson’s idea, which provides better control of your overall volume than a traditional volume pedal. With subtle increases or decreases in volume, your audience may never realize that you’ve changed your volume.
The SVC goes in your amp effects loop. This allows you to control your volume without changing the gain you have dialed in at the front of the Preamp. The SVC can also be used between your last pedal and the front of the amp, but keeping your gain consistent while changing volume will not be as effective.
Because the SVC is not an effect, it does not require any power source such as batteries.
The SVC is designed to be placed on your pedal board and foot operated. Since the signal coming from the amp effects loop is low impedance, the cables running from the amp to the SVC will not degrade the sound.
I've heard this many times - during a live guitar solo, the bassist and drummer try to start the solo at a softer volume, while the guitar volume is much louder than it should be. Then by the end of the solo, the guitarist is completely drowned out by the band. Some guitarists use a traditional volume pedal to try to ride their solos to match the band, but because of the short throw of the pedal, their foot actions can easily be heard by the audience and it sounds very un-natural.
With the EWS SVC, changes in volume can be made in much smaller increments, giving you the ability to mix your live solos with the band just like they would sound on a mixed CD. Since the box is low impedance and placed in the amp effects loop, it'll only change your volume, not your gain. The potentiometer is only 25k ohms, so it can easily be chained to a traditional low impedance volume pedal used for faster swells and volume changes.