OK. I have sort of written on this topic before at EA, but these are different questions.

I haven't been able to play because of broken knee and time for about two months now. It felt like a new experience when I did so this evening. I was puzzled and now think you peeps can help me out.

I have two amps. The first is a Fender 4x10 DeVille. It is loud. The clean tone is just right most of the time. The Gain 1 is good. The Gain 2 is Crap. For punching it into 5th gear, I was using the gain boost function on my Boss Hyperfuzz, which is Crap except for that function. Problem: I've never really understood what this presence knob does. What does it do? It sounds like it is a finer control on the high end, but how does it work in relation to the tone knobs? Does it apply to the gain channels? To complicate things, it's got a "Bright/Normal" button. This button seems to work in conjunction with the presence. Can anyone tell me what these things are doing, if they are redundant, overlap, etc? Does this thing apply to the gain channels? I had a very hard time telling, though it didn't sound like it. But, the tone knobs apply to all three channels, so why wouldn't the bright work for the gains too? Basically, can you give me the Wikipedia low-down?

Second, and more importantly, my other amp is a Fender Concert from the early 90's. It's a beefy 40watts. When it sounds right, it is perfect. Problem: Oftentimes, when I hit low notes, especially on chords, there is some sort of break up that is not harmonic distortion or overdrive. The best I could explain it is that it sounds like someone blowing a Bronx cheer into a microphone or maybe what a Wookie fart would be. What the hell is it, and how can I fix it? I am not technically savvy. Is this something I could fix myself? Too, there is a rattle coming from the reverb cylinder. It sounds like the spring is making contact with the tube, so it is a noisy amp. How can I fix this?

I am poor.

Also, tonight, I began to wonder, how the hell do these footswitches work anyhow? The click between channels seems to lag. Is this normal? Do I need to really stomp on it or try to learn how to hit it a split-second ahead of time? Sometimes it's right on time, but others, there's a noisy pop and a lag. My timing isn't THAT poor that I'm not stepping on the thing at the right time.

I am whacked out on pain-killers and merlot right now, so please forgive a crippled and altered man his ignorance.

Help me, EA Forum Users, you're my only hope!

I'm only replying because of the picture you posted above.

Presence is just a name for another eq. frequency. On guitar amps, it sometimes sounds in-between mids and highs. It gets the name because it makes your sound more "present". It works alongside you tone knobs.

A bright switch is similarly another eq. control. It is basically a fixed treble boost which is either on or off. Used to be common on old amps.

I'm not sure if these apply to the overdriven channels. Use your ears. Also, use your ears when setting these controls - I wouldn't worry too much about what they are actually doing.

The problem with the Fender Concert amp sounds like a shagged speaker. Either that, or perhaps the speaker doesn't handle low-end well. Try the amp with a different speaker cab to confirm this. If it still sounds shit, then it might be something else. Regarding the reverb, you can open these things up and take a look. You could maybe attach a little foam to the springs if they are hitting somethingt or come up with some other simple solution. Guitar spring reverbs are often pretty crude.

The footswitch usually (this depends on the amp) controls a relay which does the actual switching between channels in amps. So, your footswitch switches the relay, and the relay in turn switches the guitar signal. Unfortunately there is sometimes an inherent delay with some amps. The delay time should not change though.

Thanks.

Rather than start another thread, I've got this question to ask the geniuses of this forum: My hotrod is starting to break up into an overdrive at levels that it previously didn't used to do this. Is this a problem that a simple retube could take care of? Else, I think it might be related to when I was warming the tubes in standby, and my dog knocked the AC adapter for the pedals in and out, and I saw a small flash inside one of the input jacks in the amp. What could this have been?

ha! roddy said "shagged" instead of "fucked."

I love your island(s)!!

[quote="Lemuel Gulliver"]Thanks.

Rather than start another thread, I've got this question to ask the geniuses of this forum: My hotrod is starting to break up into an overdrive at levels that it previously didn't used to do this. Is this a problem that a simple retube could take care of? Else, I think it might be related to when I was warming the tubes in standby, and my dog knocked the AC adapter for the pedals in and out, and I saw a small flash inside one of the input jacks in the amp. What could this have been?[/quote]

What you're describing sounds like a speaker. Tubes could be the problem too, but it "could" be a solder problem on the speaker wires, or elsewhere.

If you canb swap out the speaker for an external cab to debug it, that's the best approach, beyond that I'd go to an amp guy.

Regards,

Gary

damn this! i definitely need to look up for technical explanations in my dictionary...

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

Rodabod wrote:Presence is just a name for another eq. frequency. On guitar amps, it sometimes sounds in-between mids and highs. It gets the name because it makes your sound more "present". It works alongside you tone knobs.

Hey, Mr. Rod-

Is this control applying a Bandaxall (sp?) curve over the whole thing, or just pumping out some more standard EQ filter on the mids? Doesn't sound like 'air', but I'm not sure what that would sound like through the tubes and speakers anyway...

From what I've seen, presence controls aren't geared toward the midrange so much as the higher, more treble frequencies that the amp is producing. They are generally associated with how much "sparkle" the amp has.

Ben, sometimes the "presence" control actually *is* just another tone knob, with the negative feedback loop being there and in place but a separate entity altogether from the presence control. The Traynor YBA-3 and YBA-3A and also Sound City 120 are the amps that come immediately to mind, and I imagine there are others, where the presence control isn't in the NFB circuit.

The Presence control on my Hiwatt is pretty crazy, as far as how it's implemented in the circuit, but it's tied in to the NFB. Check it out.

I haven't checked the schem for the amp in question, the DeVille, but here's my stab at the questions...

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.

The presence control is most likely what benadrian described, a control that's in the negative feedback loop. It will affect all channels on a multiple channel amp, since it is implemented at the output of the amp (like literally, the presence knob's source is what's being fed to your speaker, the end of the chain) and at that point, it's impossible to tell what signal came from input one or two or fifty.

Presence controls seem, to me, to generally sound best either fully cranked up, or almost all the way up. That's just a trend I've noticed.

And as far as whether or not the bright switch and presence knob both have an effect at the same time, sure they do. If you're having trouble hearing the exact effects of one or the other or both, make sure that you've got your head directly in the line of fire of your speakers. Cause that's the only place you're gonna hear the highest frequency content of your sound.

scott wrote:The Presence control on my Hiwatt is pretty crazy, as far as how it's implemented in the circuit, but it's tied in to the NFB. Check it out.

That's pretty cool. For everyone else, it's a normal negative feedback loop circuit, but it also smartly contains a treble rolloff tone circuit earlier in the circuit.

As you turn it up, you get more high end from the NFB loop and you reduce treble roll off in the tone circuit. As you turn it down, you get treble roll off in the preamp AND tamed treble from the NFB loop circuit. Very clever!

Ben Adrian