Amplifier electrical hum

butterfingers1

butterfingers1

Apr 22, 2019
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#1
I have a two-year-old Traynor SB115 combo amp that began humming (lightly but still annoying) a week ago. It stops when I touch the bass strings or bridge. It is the amp, not the guitar or cable (I have other amps, guitars and cables).

Would anyone know anything about this? Thanks.
 
#2
Any chance that you've moved to a different location since this problem arose? Some common external variables (unrelated to the amp) that can cause this are are things like fluorescent lights and dimmer switches. I've also heard of people having this problem when their cell phone is too close....
 
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#3
I might know a thing or two about this. Don't be so sure it's the amp.

A little bit of structured troubleshooting will help determine where the problem may be located and just as importantly, where it is not. The fact that the noise goes away when you touch the strings or bridge (which are electrically connected) is a clue by itself, which suggests that the problem is external to the amp.

1. With nothing plugged into the amp (no bass OR cable), is the noise present or not?

2. When the noise is present, does it increase and decrease with the amp's input gain/volume control? If it does change with the amp's volume control, now do the same with the volume control on the bass. What are the results?

3. Does the noise change when you touch the metal shell of the 1/4" plug on the bass end of the cable? How about on the amp end of the cable?

4. Is the bass you are using active or passive? Are the pickups humbuckers or not?

5. Is the amp connected to a properly grounded AC power source? Is the power cable undamaged? If you are using a power "conditioner", remove that and try again.
 
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#7
agedhorse said:
I might know a thing or two about this. Don't be so sure it's the amp.

A little bit of structured troubleshooting will help determine where the problem may be located and just as importantly, where it is not. The fact that the noise goes away when you touch the strings or bridge (which are electrically connected) is a clue by itself, which suggests that the problem is external to the amp.

1. With nothing plugged into the amp (no bass OR cable), is the noise present or not?

2. When the noise is present, does it increase and decrease with the amp's input gain/volume control? If it does change with the amp's volume control, now do the same with the volume control on the bass. What are the results?

3. Does the noise change when you touch the metal shell of the 1/4" plug on the bass end of the cable? How about on the amp end of the cable?

4. Is the bass you are using active or passive? Are the pickups humbuckers or not?

5. Is the amp connected to a properly grounded AC power source? Is the power cable undamaged? If you are using a power "conditioner", remove that and try again.
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1. No noise.

2. Noise volume increase/decrease with all 3 controls - bass volume knob, amp gain and master.

3. Noise change when touching guitar plug, not when touching amp plug.

4. Passive Squier split coil precision bass.

5. Aha, I moved it and plugged it elsewhere, no more noise. Put it back where it was, moved wire a bit (it passes under drum stands), no more noise.

Wow, thank you so much. Yet I could swear nothing around the wire was touched.

Your further comments or explanations are most welcome.
 
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#9
No your point no. 5 fixed it. The amp electrical cord snakes its way under and around the metallic stands of a drum kit. Moving it around slightly made the hum go away.

I knew it was not the bass, plugging it in other amplifiers was fine. And plugging other guitars in the problem amp produced the same hum.

Moving and plugging the amp elsewhere made the hum go away. Bringing the amp back to its original location, with the electrical cord snaking somewhat differently, no hum.

The drum stands must have been interacting with the electrical cord, a slight displacement of the cord made that go away.

I’m a bit surprised, the cord is thick and in excellent condition, should be well insulated. The drum kit metallic stands are just inert metal, not live wires.
 
#17
byacey said:
I'm skeptical that the drum hardware had anything to do with your issue. I would look closer at your power cords for a possible bad ground.
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Agreed

butterfingers1 said:
Yet the amp has been plugged there for two years and this started last week. Now it’s gone with the cord snaking a slightly different way.
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Things always work properly until they don't.

butterfingers1 said:
I use surge protectors almost everywhere, in part as extension cords and in part to not wear out wall outlets with repetitive unplugging, easier to replace a loose extension cord than the wall socket.
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As I mentioned earlier, eliminate the surge protector (that doesn't do anything meaningful anyway) and plug directly into the receptacle.

butterfingers1 said:
Wouldn’t cord damage result in a defective (scratchy) connection, especially when handled and moved around, rather than a steady hum?

And no more hum since I moved the cord.
Click to expand...
No, not necessarily.
 
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#18
So then it would appear to have been coming from the electrical supply outside of the amplifier. The cord or the extension surge protector (hopefully not the wiring in the wall). Keep in mind this just appeared, and it is now gone after moving the amp around and back.
 
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