Breakup, distortion on only one note

[Stanz]

Wondering if anyone knew what the cause of this might be. The note that triggers the breakup is the same as an open B (2nd string), except that string won't actually cause it. But if I play that same note on the 3rd, or 4th string, the sound will break up with a scratchy sound. Wondering if the bigger strings giving a bigger signal may have anything to do with it. Also, an A or B on the 5th-7th fret of string #6 will also trigger it. This is on an HRM ODS and it does not matter if the OD is on or off. It sounds great otherwise.

Cold solder joint?

[heisthl]

Turn the chassis upside down and see if it still does it. If not you know it's physical.

[Bob-I]

I had this happen with a bass amp I built recently. Low A on the E string distorted. Turned out to be blocking distortion at the PI, very clear on the scope. I simply adjusted the signal generator to an A and watched it.

Every amp has a resonate peak. You've most likely hit it. You have to find the stage causing the issue and fix it.

[Stanz]

That would say to start by looking at V1 or PI as it happens whether clean or in OD.

When you are looking at an amp with a scope, do you tie in to the grid, either before or after the grid resistor?

[heisthl]

That would say to start by looking at V1 or PI as it happens whether clean or in OD.

When you are looking at an amp with a scope, do you tie in to the grid, either before or after the grid resistor?

wherever you want to measure, I rarely ever have a need to scope directly on a tube grid and wouldn't trust the display anyway. The "action" you want to see is usually on either side of the plate coupling cap which I guess would qualify as before the grid resistor.

[Wayne]

I had this happen to me once, and it turned out to be a loose fit btwn tube & socket on a preamp tube. As an added bonus, once I played the "magic note", the resulting distorted note would continue to play (even with strings muted) til I shut the damn thing off!

W