I have a Hendriksen JazzAmp that suddenly started making crackling/popping sounds. At first I thought it was line noise from the guitar but it continued when I unplugged the guitar. Then it even continued faintly after I turned it off and then unplugged the power cord. So maybe there are capacitors involved somehow.
Is there any possibility this is a DIY fix? I know how to use a multimeter and solder. I do not have a favorite amp tech but if it needs professional help I’ll start looking.
Wasn’t sure if this is FQ or IMHO but I figured these symptoms are going to be well-known to experts.
Hard to find much info, but there are a few inside pics on-line.
OK, it looks like a pretty easy old school semiconductor amp design. Through hole components on a double sided board, op-amps, and generally simple design. Something that dropped though a time warp from the 80’s.
It looks very easy to work on, and nicely constructed. No surface mounted parts, clearly a conventional old school power amp. Looks to be made to be serviced. There is a black box digital reverb. That is not going to be so easy. But probably isn’t the fault.
I can’t find a schematic however. But given the simplicity, it won’t be hard to find your way around.
Try to isolate where the problem is. Can you turn the noise down? Does it change with the EQ settings? Sudden onset of such a failure could come from a range of places.
To fix you will need to know your way around the circuit. If there was a schematic it would be easier. A simple oscilloscope and signal generator would make life easier. You may well decide to get it fixed by a pro. Really anyone who can fix general electronics should be able to do so. Since it isn’t filled with glowing bottles, you don’t really need a guitar amp tech.
Have you looked into guitar-specialist forums? I’m on a bass forum which has a section on amps and electronics where folk completely geek out. I’d suspect you might readily get some specific response on a specialty forum than a general forum like the Dope.
But I ought to know better than to question the fanaticism of my fellow Dopers. Good luck!
I understand that. Like I said, the bass forums I frequent have subforms dedicated to electronics. If I had a question as to my pickup/mics/amps, that is where I would go, rather than here. Seemed to me that there are likely forums which are dedicated to guitar electronics.
But sorry, I’ll step out. Hope the OP gets his amp sorted out.
Very likely a capacitor problem. Electrolytic caps are known for failing over time. But without a schematic, it would be difficult to know where to start, and there don’t seem to be any available, at least from a cursory search. You probably need to take it to a repair shop that has a wider range of test equipment, unfortunately.
I’m most suspicious of the moving parts: potentiometers and jacks/sockets. They’re the most likely to get scratchy but also easiest to troubleshooy and repair/replace.
I’ve heard scratchy pots and this not that. Here is the sequence of events:
Plug the amp into an extension cord for power. There is also a bass amp plugged into the same extension cord. Household power, not my house.
Plug in guitar
Turn on power
Within seconds of powering up, a crackly popping sound starts. It’s irregular but does not stop.
Unplug guitar from amp to rule out RF interference or guitar electronics. Noise continues.
Turn down main volume to 0, noise stops. No surprise there.
Turn up main volume, noise resumes.
Turn down Gain to 0. Noise continues.
Turn off power. The same noise continues only very faintly, have to put my head by the speaker to hear it.
Unplug power cord. The same noise continues only very faintly, for about a minute.
It did not occur to me to have the bass player unplug his amp but I don’t think this is caused by any noise in the power.
This morning I plugged it in at my own house. No noise. At. All. It’s been on for a half hour and only a very faint hum, which I think is normal.
I have identified a couple of shops in my area that work on amps. I am not really equipped nor knowledgeable enough to do anything but the most basic work.
One other thing. It had been in the trunk of my car for 24 hours, with cool temps, 40°F or so. Not that cold, but I turned it on right away with no time to warm to room temperature. Could that be a factor?
Bad caps, bad pots, and a bad ground are the first things I thought of. RF interference from something nearby is also a possibility. Even with the instruments unplugged, RF can still cause noise in an amp.
I personally would probably take the “shotgun” approach and just replace all of the electrolytic capacitors at once. It’s much faster than troubleshooting your way around the entire amp. It also prevents you from playing whack-a-mole with different capacitors all failing within a short time of each other since they might have used the same type of electrolyte and were produced around the same time.
How old is the amp?
Could be.
Cold can change the capacitance of certain types of electrolytic capacitors. Cold can also exacerbate bad solder joints or a bad connection through an old connector.
Is it a tube amp or is it all semiconductor? Tubes can have issues when they are cold.
Try to keep your amp at room temperature, or at least something close to it.
If you’re not getting noise now, you might want to just wait and see if the noise comes back.
I don’t know much about guitar amps. But a coworker brought his amp in to work a couple years ago and asked if I could take a look at it. It had similar symptoms as your amp.
I took it apart, discharged the caps, and did a close visual inspection. I looked for any and all anomalies: corrosion, evidence of overheating, cracked solder joints, bulging or leaking electrolytic caps, fried or broken PCB traces, connector problems, etc. It was then I noticed tiny (very tiny) metal filaments on some of the potentiometers. They were tin whiskers! The (cheap) potentiometers had metal covers that were tin plated, and whiskers grew from them and made contact with other potentiometer terminals. I blew them out with compressed air, and it worked perfectly afterwards.
I am not saying this is the problem with your amp. But it’s something else to look for.
Electrolytic caps usually last longer than that, and you’re quite a few years past the era of the infamous bad cap problem. Unless the amp was stored someplace really really hot (like in a very hot attic during the summer) I would say caps aren’t likely to be your problem.
I left the amp in my garage overnight then brought it in and turned it on. Dead quiet.
I am now suspecting something in the other guy’s house in the environment, but I have used that amp there before and this is the first time it’s happened.
(I get noise from the lights in the next room, which we traced when turning the lights off, but that was being picked up by the guitar electronics and stopped if I turned the guitar volume down or unplugged it. So they just turn the lights off when I come.)
