sustain ?

[shooter]

As I'm tuning my last build I noticed the lower frequencies sustain forever, while the high F's decay pretty fast.  Are the tubes the *main* factor or is it more a function of the RC networks in the amp?
Thanks

[HotBluePlates]

As I'm tuning my last build I noticed the lower frequencies sustain forever, while the high F's decay pretty fast.  ...

How do you know? What is the test signal?

...  Are the tubes the *main* factor or is it more a function of the RC networks in the amp? ...

I'd need to understand the answers to the questions above, as well as see a schematic, before I could speculate on why the amp does what you're describing.

[shooter]

here's the link for the build, post 1 has schematic.

http://el34world.com/Forum/index.php?topic=20104.msg210672#msg210672

When I was scoping it, I wasn't looking for decay, I'll try and *see* it over the next 3 days, I'm off work!

How do you know? What is the test signal?

I have a *song* I use - called test pattern
It starts by plunking both the fat n skinny E strings hard, then just listening, the skinny one is *done* in       ~ 5sec or so, the fat one, ~30sec.  The closer I get to the middle strings, the more *even* the decay.

[John]

Could just be that the thinner string doesn't vibrate as long.

[HotBluePlates]

How do you know? What is the test signal?

I have a *song* I use - called test pattern
It starts by plunking both the fat n skinny E strings hard, then just listening, the skinny one is *done* in       ~ 5sec or so, the fat one, ~30sec.  The closer I get to the middle strings, the more *even* the decay.

Are you using an actual guitar for this? Or a recorded sample?

If using an actual guitar, it could be like John says: as simple as your high E isn't sustaining as long (i.e., guitar issue). Either way, the wound strings make a bigger arc than skinny strings when they vibrate, and often seem to sustain longer. And when you pluck the D & G strings (or D & A strings), their more-similar diameters probably lead to similar-sustain.

Separately, pickup height (mis)adjustment can leave treble strings sounding weak compared to bass strings.

[shooter]

i.e., guitar issue

I was thinking that at work after posting.  I should have a player n his guitar this weekend, plus a sig-gen n scope, (already here!)
and ya, it's live, I have a previous build that I did go to and while the fat string takes longer, it's done in about 10sec, but the 2 amps are totally different also.

More experimenting....

[PRR]

Go beat a piano.

The top octave just goes "plink".

The long slow wound strings of a grand piano rumble forever.

More mass, less loss per second.

[jojokeo]

This could also be a parasitic oscillation characteristic as they can take/show in many forms, frequencies, and behaviors. Also, as HBP says regarding pickups - as the magnet gets too close from being raised too high the magnetism pulls on the string(s) causing them to stop vibrating faster than they would otherwise. But if you haven't made any guitar adjustments and you are getting this characteristic on your current amp but not on others it could be very likely the earlier statement regarding oscillation. Oscillations many times are not heard and out of our hearing's frequency range.

[HotBluePlates]

IIRC, Shooter doesn't play guitar. This is why I thought there might be an issue just with the guitar and/or how it's being played.

No doubt there can be electronic causes for lack of sustain.

[shooter]

Shooter doesn't play guitar.

I do play, just not musically It's all frequencies doing cool things when I strum

This could also be a parasitic oscillation

When I was scoping I didn't see any, but, I plugged in last night and as the bass note decayed I could almost hear it rise and fall as it decays.  hopefully tonight I can do some scope work and see.

[jojokeo]

IIRC, Shooter doesn't play guitar.

this is always a cause for wonderment to me with a few here and there

Shooter doesn't play guitar.

I do play, just not musically It's all frequencies doing cool things when I strum

stick with it shooter, we were all there at some point taking baby steps one at a time 

[HotBluePlates]

Shooter doesn't play guitar.

I do play, just not musically It's all frequencies doing cool things when I strum

I'm thinking you oughta just play each string separately and listen. There are things a player can do (intentionally or otherwise) which result or greater or lesser sustain when playing a guitar. Unless you're playing the amp quite distorted, there's a very good chance this sustain issue is happening at the guitar.

This could also be a parasitic oscillation

When I was scoping I didn't see any, but, I plugged in last night and as the bass note decayed I could almost hear it rise and fall as it decays. ...

Again, that could be normal, or at least a function of the guitar & pickups.

For instance, some Les Paul players aim to adjust their pickup height such that after a string's initial decay, there is a "blooming" or swell to the note followed by an octave-up ringing. This has little-to-nothing to do with the amplifier, but very much to do with the specific pickup used and the settings of its height and position of the adjustable polepieces.

[PRR]

> after a string's initial decay, there is a "blooming" or swell to the note followed by an octave-up ringing.

Sadly, I know more about piano dynamics than guitar. But strings is strings. And piano hammer impact is more defined.

On a grand, the impact an initial vibration is vertical, cuz the hammer swings vertical. But watch it. The vibration goes horizontal and oval. On a piano the vibration direction changes all through the decay, in part because "one note" is 2 or 3 strings tuned "unison", which is never an exact unison, so they affect each other. Also the true pitch is not the same vertical or horizontal because of how the string lays over the bridges.

I don't have a clear picture of an octave-up decay. But the 2nd harmonic is strong, and altho it is faster (more decay per second), the mid-node is truly frictionless (unlike the end nodes), so it may ring well.

[Ritchie200]

Also, not sure how loud you are playing, but even low volume will keep the bigger strings going longer for all the reasons given here.

Jim

[shooter]

I will be teachin myself guitar repair soon 

I've been using a creation I call "test pattern" for the last 8ish years, I have tried to *learn* and it don't stick!
test pattern is musical, I watch n listen to you music types, but my internal metronome is stuck!(on random), so I am a descent garage band one hit wonder, but don't ask me what chord that was cuz you'll get; "look at my fingers and you figure it out"
Anyway, it is the guitar, I hope to have a replacement by Monday, attached are scope shots I did today with explanation.
Hopefully I call this one good after I get PA drive choked down by half, I got the pre dialed for now.
thanks all
dave
 

[shooter]

adjust their pickup height such that after a string's initial decay, there is a "blooming" or swell to the note followed by an octave-up ringing

I played around some this morning and you described quite well what I'm hearing, there is still something mechanical off in the guitar, when you hit it hard, there's a *crack*, like a cold solder joint or minor arc, It follows the guitar.  so it's take it apart time.

Thanks PRR, I was surfing some and found a *visual* of strings and waves overlayed, I was bat-eyed and didn't save link!