Hum when not touching a string or anything metallic, but only when the amp is connected to the mains

[LeakingLead]

Hi all!

So, I own an Ibanez GSR-200 and a Blackstar FLY 3 Bass amplifier, which is the only one I own. I've always used it with batteries, and I've never experienced any kind of issues, until I purchased the power supply for the amp as I don't want to be dependent on the batteries. The first time I tried it I immediately noticed a humming sound coming from the amp, which of course becomes even louder and quite annoying when I plug in headphones. It disappears the moment I touch a string or anything metallic like the bridge. So I tried another socket but no improvements; then I put back the batteries, turned it on and the hum was gone. Tried the power supply again and the hum came back.

I've read that this may be a shielding issue; could it be exacerbated by the power supply? Does it have something to do with the socket grounding?

Thanks in advance

 

[dwizum]

Touching something metallic (and grounded) on your bass and hearing a reduction in hum generally means that your bass's wiring is good, but it's not well shielded.

The brick style DC power adapters like that amp uses are often very noisy. There are electronic components inside the power supply to step your mains voltage down and convert it to DC. That process creates a DC voltage that usually has some noise in it, and it also creates some amount of EM radiation which your bass will pick up. It could easily be the case that your bass has so-so sheilding and the brick power adapter is adding enough noise to make the hum audible. By contrast, batteries essentially have zero noise. So when you run on batteries, there's no noise, even if your bass has mediocre shielding!

You can try adding more shielding (you didn't really indicate if the bass is already shielded or not). Or, try a different brick. That unit is spec'd for a 6.5v power supply, which is not very common, unfortunately.

 

[LeakingLead]

Touching something metallic (and grounded) on your bass and hearing a reduction in hum generally means that your bass's wiring is good, but it's not well shielded.

The brick style DC power adapters like that amp uses are often very noisy. There are electronic components inside the power supply to step your mains voltage down and convert it to DC. That process creates a DC voltage that usually has some noise in it, and it also creates some amount of EM radiation which your bass will pick up. It could easily be the case that your bass has so-so sheilding and the brick power adapter is adding enough noise to make the hum audible. By contrast, batteries essentially have zero noise. So when you run on batteries, there's no noise, even if your bass has mediocre shielding!

You can try adding more shielding (you didn't really indicate if the bass is already shielded or not). Or, try a different brick. That unit is spec'd for a 6.5v power supply, which is not very common, unfortunately.

Thanks for the reply. I've attached a picture of what it looks like behind the backplate and the battery plate. I'll try shielding it with some copper or at least some aluminum foil tape.

 

[iiipopes]

Does the noise go away when you touch the strings? If yes, then probably everything is normal. Strings are the best antennas for all types of noise. They all go through the amp. Unless you have abundant shielding, electronics like EMG that are designed to have a -100dB noise floor, or other electronic noise reducers, you are going to have in 99% of passive basses some noise.

 

[LeakingLead]

Does the noise go away when you touch the strings? If yes, then probably everything is normal. Strings are the best antennas for all types of noise. They all go through the amp. Unless you have abundant shielding, electronics like EMG that are designed to have a -100dB noise floor, or other electronic noise reducers, you are going to have in 99% of passive basses some noise.

Hi, thanks for the response. Yes, the noise goes away when I touch a string or anything metallic.

I'll try shielding with some copper tape, let's see how it goes.