Amp hums, then doesn't.

Sounds like the old 60 cycle hum.

Is the furnace on when it hums? Since it is just now getting cold, I'd guess furnace. But any appliance can sometimes cause this.

Can you lift the ground on that amp? Try that. If there is no ground lift switch, pick up one of those cheap little things at the hardware store that allows a grounded plug to be plugged into a non-grounded outlet.

If this doesn't work, I guess it could be something in your amp, but that is unlikely.

 

Maybe it is 60 cycle hum, maybe not.

But do not defeat the ground on your amp. It is there for a reason and it is dangerous to defeat it.

60 cycle hum is usually caused by a ground loop or insufficient grounding. If you have something else plugged in to AC that is connected to your amp, such as an effects unit or if you are going out to an external amp, start by disconnecting that to isolate the problem. Try different guitar cables.

If you can't seem to isolate the problem, it may be the amp.

 

could it be the instrument cable????

 

Maybe it forgot the words. Seriously, though - it should have a good ground connection on a correctly-wired power circuit. That's the first thing to check. You can get a circuit checker at a hardware store. It will show whether it is properly grounded. I recommend NOT using a 3-to-2 wire adapter, especially if there is 3-wire power available.
- Mike

 

Why is it called 60 cycle hum? Does it occur at 60 Hz?

 

It could be an amp problem.

When it is humming, does the hum respond to the volume control?

When it is humming, if you disconnect the guitar cable so that nothing is plugged into the amp, does it continue to hum?

 

If it were in the output stage, it would not respond to the volume control. Try unplugging everything from it when it's humming and see if goes away. This will help isolate the problem.

 

It could be. You don't happen to have florescent lights nearby or a light dimmer. These would be prime suspects as an external source.

 

Amazing! I am having almost the exact same problem! I have a Crate BFX-50 amplifier, and it has recently been causing lots of problems for me. I wouldn't describe the sound as a hum at all, but sometimes when I play there will be a buzzing / overdrive-ish sound even at very low volume levels. This occurs with three different basses. My problem is also similar in that if I turn the amp on and don't have a problem, then I can play for hours but if I turn it on and there is a problem, then sometimes leaving it on for an hour will help but other times not. It seems to me that this problem only occurs in my dorm room. However, this may not be the case. Most of my playing is in my room and since the problem is intermittent, it may be that I have just been lucky playing in other locations. Oh, and the problem that I have is frequency dependant. It is usually worst around the 3rd fret on the E string and the 12th - 16th frets on every string, but sometimes it occurs on nearly every note. I have no idea what to do about it, but buying a new amp is definitely not an option for me.

 

chhogg,

What you are describing sounds more like a cabinet buzz. Sometimes these seem to be electronic but are really just some loose screws perhaps. If I understand you correctly, your amp buzzes only when playing. Mike's hum is there regardless.

 

Michael,

The more I think about your scenario, the more I think it may, if fact, be a problem with the amp (somewhere in the preamp stage). This is not to say that the amp is falling apart. Electronic components do fail. Most of the time, to part itself is only 1 or 2 dollars, but the labor charge to replace the part sometimes exceeds the value you place on the amp. Kinda like a car, if you could fix it yourself...