Power supply ground loop quick fix?

[xorophone]

Hello! I'm having some problems with noise when plugging my pedals directly in to my audio interface and I'm pretty sure it's caused by a ground loop.

I'm using a cheap Harley Benton Powerplant to power my pedals and I'm plugging the pedals into a Focusrite Scarlett 2i2 (1st Gen). The audio interface is powered via USB and the computer PSU is connected to the same socket as the Powerplant. As long as the Powerplant is plugged into the wall, I'm getting some beeping and clicking sounds (even if the Powerplant is turned off). As soon as I unplug it, the noise stops. I'm guessing the best way to solve this would be to use a DI box between the pedals and the audio interface to isolate the ground sources, but I don't have one yet and I'm looking for a quick fix. Is there a cable or something I can make to fix this problem?

Thank you!

Edit: Forgot to mention that the noise only occurs when I'm recording something using one of the inputs. I'm not getting any noise in the speakers.

[xorophone]

I just tried putting a passive reamp in the signal chain between the pedals and the audio interface (both the right way around and backwards to act as a DI box). The ground loop noise is still there. The ground lift on the reamp decreases it slightly, but there's probably less noise when I completely get rid of the reamp. Any other ideas? Do I need to get one of those USB isolators or something? They're very expensive.. Another thing to note is that the noise changes whenever my computer is working (for example if I click something).

As I mentioned earlier, the noise completely goes away as soon as I unplug my pedal power supply from the wall.

I also tried using a power supply filter, but that didn't make a difference. I'm pretty sure it's a ground loop since it's there even when the power supply is turned off.

[thermionix]

I certainly have zero expertise on the topic of digital audio, but I tend to think of power supply ground loops as causing hum (ie 60Hz) and not clicks and beeps.  I could very well be wrong.

[xorophone]

I certainly have zero expertise on the topic of digital audio, but I tend to think of power supply ground loops as causing hum (ie 60Hz) and not clicks and beeps.  I could very well be wrong.

Yeah, that confuses me as well. I'm getting a low constant clicking sound, high frequency white noise, a high pitched continuous beep and some random quiet beeps. I really don't know how to fix it.

[thermionix]

Where I live the kitchen and living room are essentially one big open room.  If I get my guitar pickup anywhere within about 1 meter of the (digital) control panel of the dishwasher, it picks up a high pitched whine.  This is with the dishwasher NOT running, mind you.  If I open and close the dishwasher door, the pitch changes.

Sometimes I think this would be a better world if the words "digital" and "audio" were never put together.  Music would sound better, and rock stars could still get rich from album sales, and concert tickets would be cheaper.

Before I rant any further, I guess my point is that computers and other such things might be injecting noise into your audio path electromagnetically.  Or maybe your situation is something completely different.  But stuff to consider.  Try moving devices and cables around, turn off monitors, see if there any reduction of noise.

[xorophone]

Where I live the kitchen and living room are essentially one big open room.  If I get my guitar pickup anywhere within about 1 meter of the (digital) control panel of the dishwasher, it picks up a high pitched whine.  This is with the dishwasher NOT running, mind you.  If I open and close the dishwasher door, the pitch changes.

Sometimes I think this would be a better world if the words "digital" and "audio" were never put together.  Music would sound better, and rock stars could still get rich from album sales, and concert tickets would be cheaper.

Before I rant any further, I guess my point is that computers and other such things might be injecting noise into your audio path electromagnetically.  Or maybe your situation is something completely different.  But stuff to consider.  Try moving devices and cables around, turn off monitors, see if there any reduction of noise.

Great idea! I'll try that tomorrow. Maybe I should put the side panels back on the computer too.. The pedal power supply is right next to it.

[thermionix]

Hey, costs nothing to try, right?

Cell phones definitely make odd noises when they go off near tube amps.  Maybe you're picking up some WiFi router noises?

[xorophone]

Hey, costs nothing to try, right?

Cell phones definitely make odd noises when they go off near tube amps.  Maybe you're picking up some WiFi router noises?

My WiFi router is very close to the power supply too, now that I think about it.. I've read some reviews on the Harley Benton Powerplant that I use and apparently It's pretty much useless in live situations because of all the noise it picks up. That would explain a lot.

I'll try moving everything tomorrow. I kind of want to get out of bed and try it right now, but It's 2AM here, so I should probably get some sleep.

I guess another foolproof method would be to temporarily use batteries to power my pedals, but then I'd have to solder a bunch of adapters, since none of my pedals support batteries. That would get pretty expensive too.

[Hatredman]

I guess you figured out it's not ground lopp, but if it IS, have you consedered a simple ground lift?

Scarlett Johansson uses a Burst Box with her Telecaster.

[xorophone]

Hey, costs nothing to try, right?

Cell phones definitely make odd noises when they go off near tube amps.  Maybe you're picking up some WiFi router noises?

I put the side panels back on the computer and tried moving everything around, but I couldn't hear any difference. Yesterday I actually connected my pedals to a clean amp and then plugged the line out from the amp in to my audio interface, because I liked the sound of the preamp. This made the signal A LOT more noisy, which I'm guessing is caused by yet another ground source being added to the path..? When I get rid of the amplifier the signal is good enough for now, but I'll continue researching my problem, since the noise is still there.

I guess you figured out it's not ground lopp, but if it IS, have you consedered a simple ground lift?

I tried using the ground lift on a reamp to get rid of the noise, but it didn't work. I don't have enough knowledge to know what the problem is, but I have a feeling that upgrading the PSU in my computer and maybe upgrading the pedal power supply would help. I don't have that much money though, so I'll have to play around with alternative solutions.

Scarlett Johansson uses a Burst Box with her Telecaster.

A burst box sounds like a great solution, but I'm having trouble finding big enough coils.

[Tubebass]

Have you tried powering the audio interface from a USB source unrelated to your computer?

[Tony Forestiere]

Have you tried powering the audio interface from a USB source unrelated to your computer?

Like an AC receptacle block for a phone charger? Cheap experiment. Good idea.

[xorophone]

Have you tried powering the audio interface from a USB source unrelated to your computer?

Since both data and power is sent through the same USB cable I'd have to make an adapter that separates them. It's a great idea and I might actually order some parts and try it out! I might even be able to power it from the pedal power supply by adding a voltage regulator. That might be even better, since I'm limiting it to one power source.

Thank you!

[anotherjim]

That kind of noise is usually associated with portable computers, in which case you should try them on battery. Desktop machines aren't usually a problem unless the AC supply ground is faulty - or the AC ground deliberately isn't used as it's one of those machines that's really just the guts of a laptop with the same type of isolated power supply.

There probably is some USB power device that passes the data through but replaces the power with its own supply (to save portable devices battery). A powered usb hub would do that too, but have been known to add latency to the audio stream or cause dropouts. Either way, you still have ground continuity. Probably to keep things cheap, USB doesn't impose ground isolation. CAT5, MIDI and S/pdif do.

If the audio interface has balanced inputs, a small mixer that has balanced outputs can solve a lot of connection noise issues and give you a better connections than most interfaces have.

[Ice-9]

Have you posted this issue on the Focusrite forum, technical issues like this are often answered answered quickly by the Focusrite staff. Very helpful people with their products in my experience.

[Addy Bart]

How about a DIY rechargeable supply like this:

https://mike-bland.com/2013/01/11/rechargeable-9v-power-supply.html

I've not put mine together yet but some pedals (commercial and boutique) just don't like the power at home.

Might not be relevant to the problem but I like to add the Huminator II between the power jack and the board on anything I build. Just be aware that the 100 ohms resistor in the circuit can drop the voltage too much if the pedal draws a lot of current - so if that happens put in a smaller value resistor.

http://guitar-fx-layouts.42897.x6.nabble.com/Huminator-II-Power-Filtering-td36872.html

[xorophone]

That kind of noise is usually associated with portable computers, in which case you should try them on battery. Desktop machines aren't usually a problem unless the AC supply ground is faulty - or the AC ground deliberately isn't used as it's one of those machines that's really just the guts of a laptop with the same type of isolated power supply.

There probably is some USB power device that passes the data through but replaces the power with its own supply (to save portable devices battery). A powered usb hub would do that too, but have been known to add latency to the audio stream or cause dropouts. Either way, you still have ground continuity. Probably to keep things cheap, USB doesn't impose ground isolation. CAT5, MIDI and S/pdif do.

If the audio interface has balanced inputs, a small mixer that has balanced outputs can solve a lot of connection noise issues and give you a better connections than most interfaces have.

Thank you, Jim! I've tried using a powered USB hub, but the audio interface doesn't get detected by the computer. I'm using a desktop computer, but the PSU is pretty old, and probably cheap. I've considered getting a mixer for other purposes, but I haven't made the investment yet. My audio interface does have balanced inputs, so I'll make sure to get something with balanced outputs when I get one.

Have you posted this issue on the Focusrite forum, technical issues like this are often answered answered quickly by the Focusrite staff. Very helpful people with their products in my experience.

I haven't. I'll try some of the tips from this thread first and then I'll post on the Focusrite forum if I can't solve it. Thanks!

How about a DIY rechargeable supply like this:

https://mike-bland.com/2013/01/11/rechargeable-9v-power-supply.html

I've not put mine together yet but some pedals (commercial and boutique) just don't like the power at home.

Might not be relevant to the problem but I like to add the Huminator II between the power jack and the board on anything I build. Just be aware that the 100 ohms resistor in the circuit can drop the voltage too much if the pedal draws a lot of current - so if that happens put in a smaller value resistor.

http://guitar-fx-layouts.42897.x6.nabble.com/Huminator-II-Power-Filtering-td36872.html

I'm planning on building a battery powered power supply in the future, so thank you for the link!

I've tried putting a power filter between the power supply and a pedal, but unfortunately it doesn't make any difference. Most of my pedals have some kind of power filter in them too.