Noise From Reverb Wire

[jimsz]

Hi guys, I've recently being hearing scratchy sizzling popping noises and first began to attribute it to tubes. After swapping in known good tubes from another amp, it was found that the noise persisted. I opened up the amp and started prodding around with a chopstick.

Finding the red wire from the Reverb unit and where it was soldered onto the board, I could push on that connection and the noise would stop. I could touch the connection and re-create the noise, pushing a little harder and the noise got a little louder.

Just above that connection are (2) 100K resistors, both coming from V4, which I think is also part of the Reverb circuit. I could also recreate the noise where the (2) resistors are soldered together, just not as loud as the other connection.

Attached is the layout where you can see these connections in and around the Reverb input/output jacks.

[selloutrr]

resolder the connection.

[jimsz]

That was the first thing I did, but it didn't seem to make a difference. I'll try again and do a more thorough job. I noticed that even rubbing the chopstick along the 100k resistors also recreated the noise, perhaps those components are hooped?

[selloutrr]

if you have a spare and any doubt just replace it. you can remove the resistor from the circuit and meter it. then test it again with a hair dryer on high to heat it up and see if it is indeed drifting when voltage is applied.

scratching popping noises can usually be traced to tubes, a cold solder joint, or a dirty contact.

some points in the amp will transmit noise when poked this is natural.

it's possible you have not located the problem.

[aclempoppi]

Yeah, I would also suspect bad solder joints. I've experienced this with older Fender amps that have developed waves on the board. The waves stretch the below and above board wires and components, enough to break the joints. Although your amp is newer, pushing on the board is kind of doing the same thing. I would inspect(continuity) or reflow all of the under-board connections associated with this movement of the eyelet.

[jimsz]

Thanks guys, I'll spend some time backtracking through the circuits and re-soldering connections. I would assume that once I found the culprit, the noise that I can recreate on those connections should stop?

Strange thing too, is that I can merely touch the connection with the chopstick in just certain spots of the solder to recreate the noise. Funny how a wooden chopstick can do that.

[jimsz]

Soldering the connections at these points didn't work, I also tried replacing the 100k resistors but no luck. Backtracking the circuits towards the 200k resistors on either side of the bias adjust that connected to the power tubes, I found that if I pressed on the board in that area, I got a lot of noise and hum. I resoldered those connections and it appeared to go away. Pressing down on the board, the noise did not reappear. I let the amp run for a couple of hours afterwards and it seems fine so far.

I'll let it run some more, do some more prodding around and if all is good, I'll put it back together.

[iknowjohnny]

One thin i have learned when it comes to this sort of thing is that common sense goes right out the window. Stuff like this can make zero sense. It can seem like a certain area is where the noise is located via chopsticking and you eventually find it was no where near there. It's almost always a bad solder joint, but often hard or impossible to see w/o a lot of magnification, or in the worse cases not even noticeable then. Look for bad solder connections and anything thats even remotely suspect. On some amps i've ended up nearly hitting every solder joint in the amp till i found it. (ain't that just typical that it ends up being one of the last ones you hit ! )

But in any case, i've seen the same thing before where a wire seems to be causing it but turned out to be something else that was the problem and somehow it just caused that wire to become sensitive.

[Structo]

Something else that can happen is if the leads to a component are too tight, when the amp heats up and cools it can stress where the lead is connected to the component.
Especially on resistors. So over time or even one heating/ cooling cycle it can cause an intermittent connection on that component.

When soldering in resistors it is wise not to have the resistors leads straight to the eyelet or turret.
But then again, most of us do exactly that.

[jimsz]

Tom, that is very interesting about the resistors and makes a whole lot of sense, too. Based on the construction of a resistor, it's easy to see how the expansion and contraction of the board, eyelets, etc. during the heating and cooling of the amp can literally loosen the legs of the resistor from it's mounting inside if the resistors are mounted to the board that way. Kewl.

[Structo]

Yeah, some guys go as far as to put a bend or zig zag in the resistor lead before wrapping the ends on the turret or inserting it into an eyelet.