benadrian wrote:Presence, in guitar amps, modifys the signal in a different way than the standard tone controls.

Standard tone controls work in a passive manner by sending teh frequencies you don't want to ground.

The presence knob is in the negative feedback loop circuit. In most amps, there is a negative feedback loop that feeds a bit of the speaker output back into the circuit, but 180 degrees out of phase. This makes the tone flatter and cleaner. However, the resencs knob, as you turn it up) sends high frequencies in the negative feedback loop to ground. The result: less hig frequency in the negative feedback loop = less high frequency getting cancelled out and therefor more high frequency making it through the amp and to the speakers.

Cheers!

Ben Adrian

rayj wrote:Aha!

Thanks for this. Makes sense, now...

scott wrote:A "bright/normal" switch can make a big difference in the sound... just generalizing here, but it seems like on the Fenders I've messed with, the "normal" position will sound kinda dry/dead but bearable, and the "bright" position will sound more exciting but will be too harsh to be of much use and will result in almost immediate listener fatigue for anybody directly in the line of fire of the speakers.

Lemuel Gulliver wrote:

scott wrote:A "bright/normal" switch can make a big difference in the sound... just generalizing here, but it seems like on the Fenders I've messed with, the "normal" position will sound kinda dry/dead but bearable, and the "bright" position will sound more exciting but will be too harsh to be of much use and will result in almost immediate listener fatigue for anybody directly in the line of fire of the speakers.

So well-put! This is precisely the problem, just much better stated than I put it. I boost the presence as needed, and turn off the bright, because the amp's pretty bright as is.

As for the second problem--the thing rolling into some overdrive at low levels--that stopped happening. WTF? Why's this thing sound like crap one day and like heaven the next? I'm not moving it; I'm not playing often, for long, or that loudly. I've noticed the other amp sort of does this, but not nearly to this degree. It's like when I turn it on, I don't know what amp I'm going to get.

Thanks a lot for the help guys. It helps me to find the best sound by knowing what's doing what--whether the presence is boosting or cutting, etc.