Rustling noise help

[Meat&Beer]

Have you tried a different guitar and cable?

Once I messed around forever inside an amp trying to find this kind of noise. Turned out to be the guitar...

[matt h]

(deleted)

[bluesguitar]

I don't think this is the problem.

The only way to know is to measure it.

Good luck!

jelle

I wish I could. When I use my multimeter set to volts, with the black lead clamped on the chassis and touching the red lead to the board it acts like it doesn't recognize a circuit. Just keeps scrambling thru numbers and won't get a fix on one. I know my multimeter works, because I tested it on other things.

[bluesguitar]

Have you tried a different guitar and cable?

Once I messed around forever inside an amp trying to find this kind of noise. Turned out to be the guitar...

Unfortunately it has nothing to do with the input source. Does the same rustling/static with or without any guitar plugged in.

[jelle]

You are on the right track. Pull preamptubes, and test eyelets that connect to cathodes and grids. Also the pot side of capacitors. If you see more than 50mV or so...

Let us know, Jelle

[pablogt]

I had a similar problem last month. The noise would go when the amp was out of the wooden cab. It turned out to be a faulty i IEC power cord. It only made good contact when the amp was upside down (when out of the cab).

P.

[brewdude]

I had a weird noise in a D'Lite 22 that turned out to be the PA bias drifting way off and the tubes were drawing way too much current.

[Richie]

So many things can cause what your hearing. And looks like you have tried a few. You need to back up. Start at the 1st preamp tube, pull it, then listen, is the noise still there, if so go to the second tube.. same thing. even though when you pull the tubes, you may lose a lot of signal or sound, but if the noise is still faint there in the background, then its on to the output and power section.

This way you narrow down where the problem is. Also its not only preamp tube plate resistors that can cause this. its any of the CC resistors. One may be cracked and hard to see. it could be the output tubes. A loose ground or connection. but it looks like you are going through some of the advise that was given.
Also yes, a conductive board can cause the static noise. And it can effect the sound of the amp, depends on where the board is conductive, if it is real bad or not. Sometimes you may not hear it effect the sound of the amp that much,but just cause noises.

[Structo]

Good advice Richie

[bluesguitar]

So many things can cause what your hearing. And looks like you have tried a few. You need to back up. Start at the 1st preamp tube, pull it, then listen, is the noise still there, if so go to the second tube.. same thing. even though when you pull the tubes, you may lose a lot of signal or sound, but if the noise is still faint there in the background, then its on to the output and power section.

Thanks for the advise. I now have a lead @ V2 that supports a suspicion. This is what I was looking for. Something precise instead of the shotgun approach and never knowing what or where the problem was. Will follow thru and update later.

[Milkmansound]

my favorite technique is to isolate it to a particular gain stage

use an alligator clip to ground and ground the "audio" low voltage side of the coupling caps moving from the input stage over to the PI

this is even faster than pulling tubes

once its isolated to one gain stage, you have very few things to look at - starting with the tube etc

[bluesguitar]

Update: Resoldered the suspect eyelets in the V2 circuit. Unfortunately no improvement. I'm nearly certain that the problem is somewhere in this part of the preamp (V2). Want to pick some brains for clues. If this rustling/static is constant when taking the amp off standby, and playing a guitar does not affect it in any way, because with enough volume can actually play over the noise, would that rule out a component problem? Does this seem like a filtering issue? I could save myself the headache if I knew of a good amp tech, but I also want to get a better understanding of amp troubleshooting.

[Reeltarded]

Better to take it to someone who won't refuse to believe the problem could possibly be what it is, which sounds like waterboarding if you axe me.

Other suspect areas are recently replaced filters and bias caps.

[bluesguitar]

[quote="Reeltarded"]Better to take it to someone who won't refuse to believe the problem could possibly be what it is, which sounds like waterboarding if you axe me.
We prefer to call it enhanced interrogation. If you are referring to the conductive board hypothesis I would be more inclined to entertain that if I could get a reading with my multimeter. However, since I can not get a fix on a specific voltage when testing the waxed eyelet board and the multimeter acts like it does not recognize a completed circuit, I tend to conclude that there is no voltage being conducted on the board. Correct me if my thinking is faulty.

[martin manning]

When I use my multimeter set to volts, with the black lead clamped on the chassis and touching the red lead to the board it acts like it doesn't recognize a circuit. Just keeps scrambling thru numbers and won't get a fix on one. I know my multimeter works, because I tested it on other things.

The noise voltage could be so erratic that your meter can't settle on a value. What does it do when the red probe is not touching anything? If it's different when you touch the board that might mean that something is there. Do you have access to another meter?

Have you gone over all the solder joints related to the cap job?