Question:
Does anyone know what the presence knob on an amp is supposed to do?
Answer:
It controls a frequency in the high mids that's somewhat different from the treble knob. Something like between the mids knob and the treble knob. It's called the presence knob, because it simulates, in a way, the tone you would hear as you move away from the amp. Very sharp when you're close, and more mellow as you move away.
Answer:
Additionally, I believe the presence knob, at least on the Fender amps I've used, affects only the drive channel and is a post-drive EQ (whereas the rest of the EQ is before the drive stages)
Answer:
Actually, on most amps it affects all channels. Not sure why Fender puts it only on the drive channel. And yes, it's a post drive knob on most amps, in the circuitry it comes very late in the preamp, often after the master volume.
Answer:
On my hot rod deluxe, it makes a difference on the clean channel as well.
Answer:
i see, so it does different things depending on the amp that you're using.
thanks
Answer:
Originally Posted by RipVanWinkle On my hot rod deluxe, it makes a difference on the clean channel as well. Hmm...for some reason I thought it was drive channel only on mine.
Either way, I think across the board it's a post drive stage (regardless of channel) high-mid EQ adjustment.
Answer:
I'll check tonight at band practice
Answer:
If its a "real" presence control, on a tube amp, it will affect all the preamp channels, unless an amp was specifically designed to switch that circuit out with a channel switch... I doubt if any are like that, but you never know.
Its in the NFB (negative feedback loop) which feeds some of the speaker output back into the phase inverter (the tube that drives the power tubes) 180 degrees out of phase with the signal there, which decreses the signal strength at that stage. The purpose of the NFB is to provide greater clean headroom, don't ask me how though, I don't know. What it does is cut some of that signal from a certain freq and up, the freq determined by a capacitor in the circuit. Some amps have 'em, some don't. Vox AC amps don't (and can't) because they are one of the few amps that are designed from the ground up without NFB. WHen you turn up the presence knob, you are decreasing the amount of NFB from that freq and up.
Bottom line - it acts like an eq control (treble) but with some added characteristics - it increases the gain a bit (although turning up eq controls also increase the gain), and is said (and I agree) that it provides a smoother transition from clean to distortion, with it turned up, I think most amps will break up a little earlier. Personally, I turn mine up, and then tame the increased treble with the treble control, I just think it sounds better in the just-beyond-clean, and edge-of-distortion range of an amp.
Some mods I've seen for the presence circuit - changing the cap value changes the "crossover" freq of the circuit. Take out the cap, and then it becomes a NFB level control. For fun, when I was modding and hacking on a PV Bravo, I disconnected the NFB - WOW, that thing got loud ! It increased the gain by a bunch, sounded good though. That amp already has tons of gain on tap though. One of the mods I did on it ws adding a presence control, which IMO, really made it come alive. At some point, I'd like to experiment a bit with it....