Because of the nature of power amp design and function (specifically power amp feedback, the science of which fills volumes if not entire libraries) the presence control affects upper-mid and high frequencies in a completely different way that than the normal tone controls found in the preamp stage.

Here’s where things get a little complicated, but hang in there with us. Turning it up actually does boost part of the frequency band. Technically, it’s a “high frequency shelving boost” control, which is much like the treble control on a traditional stereo. The presence control, on the other hand, resides in the power amp stage. These tone controls are generally “subtractive”-that is, they don’t boost anything they control the amount of frequency band removed from the signal. Your amp’s traditional tone controls-“bass,” “mid” and “treble”-reside in the preamp stage and thus accomplish their work before the signal reaches the power amp. The preamp stage comes first and is where most of the tone shaping happens the power amp stage comes second and provides the muscle that blasts your sound out into the world and makes the neighbors call the cops. Namely, that an amp consists of at least two “sections”-a preamp stage and a power amp stage. To explain what a presence control does in greater detail, let us note a fundamental basic of amplifier design. Nor does the presence control affect the tone in the same manner as the amp’s “mid” and “treble” tone controls. Saying that the upper-mid and treble frequencies become more present doesn’t exactly mean they become “louder” in the sense that an amp’s volume control affects all frequencies evenly. The quality of this livelier, wilder tone is typically described as being more “present,” thus the name. What does it do? Well, it controls “presence', which boosts upper-mid and treble frequencies in a specific manner that makes the tone sound notably livelier a little “wilder” than normal. One of the most confusing controls that has appeared on Fender amplifiers over the years is the 'presence' control.

Fender bandmaster reissue