AMP1's BOOST is a two-stage gain boost situated before the amp's channels. The Custom Control potentiometer on the side of the AMP1 controls the amount of gain in the BOOST, and thus primarily the degree of distortion. Turned up halfway, the signal becomes more transparent (similar to a treble booster) and receives more gain. After that, the BOOST itself also starts to overdrive slightly (similar to a Tube Screamer). A moderate increase in volume (which is more noticeable in the clean channel than in the overdrive channels) is associated with this because the sound becomes more concise, but the internal BOOST of the AMP1 is the wrong tool for a volume boost.

The 2ND MASTER VOLUME function of the AMP1 is suitable for a sound-neutral increase (or reduction) of the volume, which can be called up using the REMOTE1 or MIDI. Alternatively, you can use a minus booster or a volume pedal in the serial effects loop to control the overall volume.