Where does sustain come from?

[ted01]

OK, so I was messing around last night with my amp (a Dumble clone) and I cranked up all the preamp gain stages all the way but I set the level to the power amp section as low as it would go. The resulting sound was very distorted (in a good way) but the overall volume was quite low (you could easily talk over it and be heard). I had an Epiphone dotStudio semi hollow body guitar plugged straight into the amp, and I noticed that if I hit a single note, it would sustain just about forever. Somehow, I had it in my head that sustain was a byproduct of volume and the density of the wood of a solid body guitar. Clearly neither was the case. So, what are the factors that go into looong sustain?

ted

[gearhead]

The volume-dependent sustain is feedback sustain. It happens when your output volume (from speakers) vibrates your guitar and strings, which causes a continued input to the amp, and so on.

For the case you're describing, one reason could be severe clipping. If you can crank the signal up at an early stage, yet have a further stage that really limits the output of that further stage, then it will clip the signal into a square wave, and sound like it'll go on forever. The Big Muff Pi is a prime example.

There are probably some internal feedback loop stuff going on too, but others will have to chime in on those.

[skyboltone]

With high gain amps, the magnetic pickups on the guitar will interact with the magnetic fields produced in the amplifier itself. So even with the speaker some distance away, you can bring your guitar closer to the head and get changes in feedback and sustain.

As to a direct answer to your question. Sustain comes from heaven.

[Bob-I]

2 things

1) Skyboltone is right, sustain comes from heaven

B) The way you're setting your Dumble clone is all wrong, you'll upset the space time continum and the universe will shift.

4) This sustain comes from the compression that results from clipping. As the signal lowers, the clipping drops but the level doesn't. At times you'll hear changes in the harmonic content as the note sustains and the clipping changes.

On #2) I'm joking of course but I find that running the gains just to the point of saturation and not a bit beyond gives me the best dynamics and bloom. Typcally that's at about 1:00 on the gain dials, your mileage will vary.

[CaseyJones]

This is a trick question, right?

IT'S ALL IN THE FINGERS!!!!

[ted01]

Hey CaseyJones,

With all due respect (and I mean that, I've learned a ton from you), on this, you're just wrong. I can't play guitar. All I am doing is plucking a single open string to get what I'm talking about. I have the preamplification stages all dimed, and the feed to the final stage of amplification (a pair of EL34's) as low as it can go and still make a sound. The output level of the amp is so low that one could easily talk over it and be heard. The sustain is nearly infinite. I mean it just goes on and on. At that low level, I just can't see how there is enough SPL to cause the strings to vibrate sympathetically. This isn't a matter of a feedback loop in the amp, either. The note maintains its original frequency.

So I'm still interested in how massive gain at the pre level can cause what I'm hearing.

[drz400]

OK, so I was messing around last night with my amp (a Dumble clone) and I cranked up all the preamp gain stages all the way but I set the level to the power amp section as low as it would go. The resulting sound was very distorted (in a good way) but the overall volume was quite low (you could easily talk over it and be heard). I had an Epiphone dotStudio semi hollow body guitar plugged straight into the amp, and I noticed that if I hit a single note, it would sustain just about forever. Somehow, I had it in my head that sustain was a byproduct of volume and the density of the wood of a solid body guitar. Clearly neither was the case. So, what are the factors that go into looong sustain?

ted

Hand vibrato and control over the strings

[iknowjohnny]

Having spent what seems like a lifetime now tweaking a few amps, what i think is a big part of sustain is the circuit design being such that many variables are in perfect balance. This seems to not so much be a result of all the frequency tweaks people talk about like cathode resistor and caps, tone stacks, etc. But instead the voltages and other things being balanced just right. the reason i say this is i will sit here changing values and design aspects of the preamp for hours on end, and when i hit just the right combination the tone gets real squishy, the high end becomes smooth and all harshness goes away, and the thing then will sustain at low levels just like you say. I have had that happen with several different configurations, and unfortunately there is no one thing that anyone is going to be able to cite. it's just a certain balance of many things. when it happens there is usually a ton of harmonic complexity happening. But i'm unsure as to whether that is what is making it sustain so well or if it sustain and harmonics tend to appear together because that perfect balance tend to accentuate both. In any case, you will unfortunatly not find any one thing that causes it. driving tubes into distortion is of course the main thing here, but that only gets it happening to one degree or another. It's that balance of things that makes it sustain effortlessly and take off into high harmonic feedback fast.

[ted01]

Hand vibrato and control over the strings

As I said, I am not a guitar player. I am simply plucking a single open string while muting the others with my hand. There is no hand vibrato or control over the strings, period. I simply don't have those skills.

[Structo]

I remember when Norm talked about the feedback capabilities of the D'Lite amp.
I remember his post because I save all tidbits like this in a file.

I know that feedback and sustain are two different things but that kind of go together if you know what I mean.

It's just an interesting phenomenon.

Here is what he said:

OK, this is gonna sound like mojo BS, but here goes...

1. The amp MUST be fully warmed up, at least 20-30 minutes.
2. Set input volume at 2:00 (o'clock)
3. Set OD gain anywhere above 10:00
4. Engage PAB
5. Bring master volume up until the amp starts to feed back

Here's the strange part, once the amp begins to feed back, you can bring the master volume down pretty low and it will still get harmonic feedback. In fact, you can even bring down the gain levels. I have no idea why the amp will continue to get nice harmonics after being played at louder volumes, but it does!

BTW, a semi-hollowbody will feed back at lower volumes, especially if you get the distance and angle correct. If I sit about 3-4 feet from the amp with my Artcore AS-83 (Gibson Classic 57 pickups) and angle the guitar at 45 degrees from the amp, it will get feedback at conversation levels.

[pureoldsound]

I am by no means an expert on Dumbles or any other amps for that matter. Now my take on this like it was mentioned at the begining of the thread and on that quote, two things one cranked pre-amp and the other PAB. They have to compress and that will give you sustain, this is after all a cascading amp. If much of the gain comes from the pre-amp and not much saturation from the power section then compression comes from the pre-amp. Wether the preamp is balanced or not you are saturating that signal enough to develop significant clipping.

Compared to other amps, I guess sustain comes from the sum of many factors, Amp, tubes, guitar and player....

[Bob-I]

So I'm still interested in how massive gain at the pre level can cause what I'm hearing.

What? you didn't like my answer

I've watched this on a scope. The tube reaches saturation and clips. On a really high gain amp it clips several gain stages. Dumble are fairly tame with 4 gain stages, the first 2 being clean as opposed to Soldano and Messy Booger who use 5-6 gain stages.

As these stages reac saturation, and beyond they cimply cannot amplify any more. As the input signal drops, the stage clips slightly less but stays at the same volume, for a good long time. Eventually the note will either die, or physical feedback will take over and keep the note going forever.

All that said, I prefer to rin fairly meduim overdrive so that the gain stages are just reaching saturation, then use finger vibrato to extend the sustain. In reality, guitar music shouldn't sustain forever, the notes should have a natural decay (JMO)

[iknowjohnny]

Like i said above, tho maybe not very well, theres also some sort of fine balance between the stages and the power supply and who knows what else. But i have moved my pre circuit around over and over and sometimes will actually find a setup that sustains more with LESS drive than before. That is, less disortion yes more sustain. thats what i'm trying to get at. When the voltages are right and the cathode resistors and bypass caps and who knows what else all find a certain balance, sustain comes easier and without the need for as much drive. It's the kind that quickly turns into higher harmonics as it sustains. Thats how i know i'm really nailing the preamp because whenever i get it like that it tend to just be right in all respects....frequency balance, clean sounds, everything just becomes right. so IMO it has to do with more than just how much you drive the tubes.

[Jana]

Sustain comes from pixie dust. It's hard to explain how it works but it has something to do with the harmonic convergence of the disparate carbon particles when they entice the nickle ferrous compositions to bisect magnetic fields in a constructive manner. Either that or it's the beer.

[iknowjohnny]

Either that or it's the beer

I do believe you have nailed it oh wise one.