OKKO FX Master MasterWouldn't it be great if you could just turn up your amp for certain parts in your set? The MASTERMASTER system offers two switchable volume settings for every amp with an effects loop. It consists of two units: The small VCA UNIT (voltage controlled attenuator) is plugged into the effects loop of your amp and controls the volume in a way a simple potentiometer would do. It is optocoupler based, the signal doesn't pass any active or mechanical