Tips for tracking a crackle

[Jsnwhite619]

I built a Princeton Reverb 6-7 years ago for a guy, and it has something going on. Lower volume is fine, but when it's really cranked and shaking with heavy overdrive with humbuckers - my Les Paul can make it do it - it's a nasty crackle that shows up.

Any tips for tracking it down when I can only get it to happen when the chassis is mounted and the amp is screaming? I've slowed down a lot on the amp thing the past couple years, so any advice is welcome if it maybe saves me some time.

Thanks.

 

[corliss1]

Confirm it's the amp and not the speaker.

If it's the amp, confirm it's not the tubes.

If it is the amp, I'd hook up a dummy load (or just pull the power tubes) so I didn't have to listen to the noise at high volumes, and trace the circuit with a signal tracer/audio probe until I found where it was happening. That at least narrows down the area of the circuit where it starts to happen and you can go from there.

 

[Harmonic]

Tighten the speaker mounting screws. I had an amp crackle at high volume once because the screws worked loose.

 

[Peegoo]

@Jsnwhite619

How I'd approach this:

1. Remove the chassis from the cabinet.

2. Disconnect the onboard speaker and hook up an external speaker cab with a long cable. Put the cab in a closet or cover it with blankets and pillows.

3. Plug in a guitar cable (to open the switch on the input jack) and turn on the amp. Crank the volume.

4. "Chopstick" the amp: use a wooden chopstick to poke and tap on all the internal components and wires in the chassis. When you get close to the problem component or connection, it will let you know through the speaker; you'll get the crackle.

Look here:

 

[39martind18]

That's easy- I just park my car at Wally World and there the little SOBs are... Wait, you said crackle, not Grackle... I'll let myself out.

 

[Jsnwhite619]

What's the opinion that it may be a tube shaking and a pin is vibrating just right? It's a PR that I built with a 12" Cannabis Rex inside, so it puts out some volume.

But, basically, with my Les Paul plugged in and the amp on 7-8+, the B note on the high E string would make it happen every time. Nothing else did it. I've since wiggled the tubes, moved the amp around, and I can't get it to happen again now. Amp cranked, even tried a OC-3 octave pedal trying to vibrate it more, and nothing.

I'm wondering it one of the tubes was vibrating enough that the pin and socket were breaking contact and causing the noise?


Also, even though I built it, it has been a long time and I'm more of a Tweed guy. The speaker jack is a Fender flat mount. Is it normal for the ground sleeve on the plug to be loose and able to spin around on these? I normally use the regular Switchcraft for the Tweed amps, so I'm not familiar with this style. The hot tip is fixed, but the ground sleeve spins 360°. Wondering if that could be it also

 

[corliss1]

Normal on the jack. Unlikely to be a tube doing that but the only way to find out is troubleshooting.

 

[P Thought]

That's easy- I just park my car at Wally World and there the little SOBs are... Wait, you said crackle, not Grackle... I'll let myself out.

When I saw the thread title I pictured a Dr. Seuss book. . .

 

[Wally]

I've since wiggled the tubes

There could be a chance that there was a dirty contact in a tube socket and the wiggling corrected the problem. I would pull all tubes and clean and retension the sockets.
If it reoccurs, @corliss1 and @Peegoo give good advice.

 

[Jasonpatrick]

You know what else makes weird static when cranked? When the reverb pan transducer is loose inside the stack. @Wally
I’ve had several amps that came in with weird static issues which turned out to be this being loose. I super glue it and all is good

 

[King Fan]

Sounds like you cured it. Let me yada yada a bit just in case it doesn't stay cured. I think your suspected diagnosis is excellent:

But, basically, with my Les Paul plugged in and the amp on 7-8+, the B note on the high E string would make it happen every time. Nothing else did it. I've since wiggled the tubes, moved the amp around, and I can't get it to happen again now. Amp cranked, even tried a OC-3 octave pedal trying to vibrate it more, and nothing.

I'm wondering it one of the tubes was vibrating enough that the pin and socket were breaking contact and causing the noise?

IME this almost had to be harmonic vibration in 'sympathy' with the speaker on just the right frequency. As I've found from painful experience, sympathetic vibration can affect chassis, board, components, wires, sockets etc., not just the speaker / cab. And as @Wally says, you're right to link static-y crackle with loose springs or dirty/bent pins. More generally, the diagnostic steps suggested by @corliss1 and @Peegoo might've saved me lots of time when I had unsympathetic results searching for sympathetic vibrations...

 

[Peegoo]

I've also had two cases of amps on my bench making weird tones when cranked up that turned out to be something loose or vibrating in the volume pot or gain pot.

I replaced the pot and the problem went away.

 

[Jsnwhite619]

Time to report back. The ground wire was sketchy on the big reverb tube junction with the half dozen leads. I reset that spot. I honestly think that it was a small symptom - the reverb sounds better and more full now. Link Wray "Rumble" tone all day long.

But I flipped it and checked the sockets and the reverb tube socket had a few spots that definitely needed the tension reset, and while I was messing with it, a tiny piece of debris came up with my tweezers from inside the socket. Whether it was the ground wire or socket debris, or loose tension, I don't know. But I think it's cured. I loaned him one of my amps to use on the meantime, so I'm gonna let it run and heat up a bit before it goes home.

I'll make a separate post here later on several mods and tweaks I made on it and the results. He mainly plays humbuckers, and has had it long enough to know what he would like to change. So we changed it. Thanks everyone and @Wally was near the mark. I'd already cleaned and scrubbed the tube pins, but I hadn't close inspected the sockets. I think that was my mystery "High B" noise.

Also, I turned 41 this year. Anybody have a suggestion on bench mounted magnifying lamp or headset because my damn arms ain't long enough to work on this stuff anymore! . It's been a while since I've messed with anything, but man, I was going crosseyed! Thought I was gonna have to hold a magnifying glass on my teeth to get it done!

 

[Jsnwhite619]

I've also had two cases of amps on my bench making weird tones when cranked up that turned out to be something loose or vibrating in the volume pot or gain pot.

I replaced the pot and the problem went away.

Local buddy of mine restores vintage amps. Was telling him about it and said he has a deluxe Reverb that he just couldn't figure out what was going on. Finally pulled a hair out of the volume pot and that was it.

 

[elpico]

Also, I turned 41 this year. Anybody have a suggestion on bench mounted magnifying lamp or headset because my damn arms ain't long enough to work on this stuff anymore! . It's been a while since I've messed with anything, but man, I was going crosseyed! Thought I was gonna have to hold a magnifying glass on my teeth to get it done!

If you don't already have reading glasses, start there, but if you do, you are going to need a magnifier. Either a bench mount one or the visor kind can work. Because it only gets worse...

 

[Jsnwhite619]

I built this amp 6 years ago, and he's obviously had enough time for some likes & dislikes. He plays humbuckers mainly, and the C Rex has its share of mids, so that's what I went after. He keeps the volume on the low side and uses pedals, so any gain/overdrive reduction wasn't really a concern.

I did the opposite of most and lowered the mid resistor from 6.8k to 4.7k.

Reduced the .022uf phase inverter cap to .01uf

Swapped the NFB switch with a 50k pot that starts off at stock PR value. I can't remember what I originally had on the switch, but it was such a small difference, the pot gives way more purpose.

Apparently I built it completely stock to the original layout back then, and I added 1500R grid stoppers to the power tubes, and backup diodes to the rectifier. Things I would do automatically today, but I'll admit that this was a huge project for me 6+ years ago when I started building it.

All the tube pins/sockets/pots got a good deoxit and cleaning.

It's really clean and sounds great. It still breaks up and sings with humbuckers, but the bass/mid cut did wonders for the wooliness and the bass doesn't have to stay on 1-2 range with the Les Paul now. The overdrive is smoother as well, but he never uses it that high anyway. I hooked it to my 1x10 cab that has a 1058 Legend in there at the moment. WOW that is a dark and bass heavy speaker! I thought that already, but with the Tweed amps it doesn't seem as noticeable. Throw in the Blackface scoop and bass response and the C-Rex is down right chimey in comparison.

And for a testament to JJ tubes, this thing is 6 years old. He plays at church every week, hauls it from home and back each week, whatever extra playing in between, and it's still the same set of tubes he started with. I'm not saying that fresh ones wouldn't sound better, and the preamp section isn't glowing too bright these days, but there is no audible issues from the tubes. I told him it's like looking at bald tires - they're still going, but maybe start putting a little cash away for a tube fund soon.

 

[prairietelecaster]

My last couple of crackle/crunchy problems on different amps were cracked grounding points that weren't obvious, found by the chopstick routine. Re-solder time!
One vintage deluxe reverb that chopsticking generally found a crackle in a rather wide area, and I couldn't find what! Remelted every point I could find and problem gone. A bad joint somewhere!

 

[jaonline]

I built this amp 6 years ago, and he's obviously had enough time for some likes & dislikes. He plays humbuckers mainly, and the C Rex has its share of mids, so that's what I went after. He keeps the volume on the low side and uses pedals, so any gain/overdrive reduction wasn't really a concern.

I did the opposite of most and lowered the mid resistor from 6.8k to 4.7k.

Reduced the .022uf phase inverter cap to .01uf

Swapped the NFB switch with a 50k pot that starts off at stock PR value. I can't remember what I originally had on the switch, but it was such a small difference, the pot gives way more purpose.

Apparently I built it completely stock to the original layout back then, and I added 1500R grid stoppers to the power tubes, and backup diodes to the rectifier. Things I would do automatically today, but I'll admit that this was a huge project for me 6+ years ago when I started building it.

All the tube pins/sockets/pots got a good deoxit and cleaning.

It's really clean and sounds great. It still breaks up and sings with humbuckers, but the bass/mid cut did wonders for the wooliness and the bass doesn't have to stay on 1-2 range with the Les Paul now. The overdrive is smoother as well, but he never uses it that high anyway. I hooked it to my 1x10 cab that has a 1058 Legend in there at the moment. WOW that is a dark and bass heavy speaker! I thought that already, but with the Tweed amps it doesn't seem as noticeable. Throw in the Blackface scoop and bass response and the C-Rex is down right chimey in comparison.

And for a testament to JJ tubes, this thing is 6 years old. He plays at church every week, hauls it from home and back each week, whatever extra playing in between, and it's still the same set of tubes he started with. I'm not saying that fresh ones wouldn't sound better, and the preamp section isn't glowing too bright these days, but there is no audible issues from the tubes. I told him it's like looking at bald tires - they're still going, but maybe start putting a little cash away for a tube fund soon. View attachment 1406947

Nice looking amp!

 

[Jsnwhite619]

My last couple of crackle/crunchy problems on different amps were cracked grounding points that weren't obvious, found by the chopstick routine. Re-solder time!
One vintage deluxe reverb that chopsticking generally found a crackle in a rather wide area, and I couldn't find what! Remelted every point I could find and problem gone. A bad joint somewhere!

I went through with a magnifying glass and reflowed anything that looked remotely suspect - even if I couldn't make it crackle. I think I mentioned the ground wire that I think was causing it. Crazy that it took 6 years of regular use to decide to cause a problem. And this can looks like it did when it left 6 years ago. Guy has kept it immaculate, so I can't imagine rough handling being the issue.

Different note - he was asking about OD pedal suggestions, but I only have a Blues Driver and all I've ever had. I gotta say, it sounds freaking great with it and the C-Rex. Better rig than anything I own...haha. My Pearly Gates Les Paul with that whole combo after the couple of mods is like butter. The natural gain of the amp is a little bit lower and cleaner now with more mids removed, but holy cow - my Blues Driver has never sounded this good.