ringing, buzzes and squeaks when connected to devices with their own power supply

When my audio interface (Scarlett 2i2) is connected to any device with a power supply independent of my computer, such as my bass amp, it captures ringing, buzzes and squeaks like this View attachment soundcard squeaks.mp3. The bass amp is earthed, but I get the same thing when I attach devices which are not earthed, such as my electronic piano. I have never been able to work out whether it is the computer power supply which is at fault, or the audio interface, or something else. Which would it be?
 
That's buss noise, and is the data inside your computer getting onto the ground system. It's a really common noise and is always an unfortunate combination of equipment. My colleague had a 2i2 that did exactly the same as soon as it was connected to his small mixer that went between the 2i2 and the active speakers. I tried everything I could think of. A large torroid in the USB cable to the PC helped a bit, but it was still there. I'm still convinced that the real issue is the 2i2 needing very near the limit of USB the PC can provide, as it also got better when I used a powered USB hub to supply the 2i2 its power. He never solved it totally, and I loaned him one of my old ones, which was silent. Oddly, he's now on a new computer and the 2i2 works silently on that one. Very, very strange - but we've heard it before.

If you have access to another computer, try it to rule out the computer. It almost certainly isn't anything you are doing, and it's not the interface as they're well respected - just an awkward combination.
 
Buss noise was never a problem for me when I first entered the digital realm.

Some years later I got a new PC, and was consequently plagued by that noise.

Similarly, when using my laptop, i would get that noise unless I ran it off its battery.

In the end I eliminated it quite simply: by switching to balanced leads between interface and speakers.
 
Thanks for your replies.

I found I had a USB cable hanging around with a ferrite core in it, but using it for the 2i2 made no difference. I also tried using a powered USB hub, but that made no difference either.

I also tried connecting the 2i2 to my laptop instead of my desktop computer. When I did this I got a massively loud 50Hz buzz through the input that was connected to the bass amp, even when the laptop was running on battery and disconnected from the mains.

I should probably mention as well that I get coil whine from the 2i2, which often quietens down when I give the box a tap, and I get a lot of noise in my signal if I record with phantom power turned on. In other words the 2i2 is not in perfect shape.
 
Last edited:
...
I also tried connecting the 2i2 to my laptop instead of my desktop computer. When I did this I got a massively loud 50Hz buzz through the input that was connected to the bass amp, even when the laptop was running on battery and disconnected from the mains.
...
This puzzles me. How is the bass amp connected to the 2i2? What are you trying to record? Hum is in the headphones?
 
This puzzles me. How is the bass amp connected to the 2i2? What are you trying to record? Hum is in the headphones?

I was just trying to use the easiest available configuration to reproduce the problem, but it looks like the connection from the bass amp output to the 2i2 has an additional problem, so it's not a good example. I have tried two other configurations — a DI box connected to the 2i2 and to the bass amp, and my digital piano connected to the 2i2 — and I did not get bus noise when connected to the laptop. I double-checked the piano connected to the desktop computer via the 2i2 and I did get bus noise. So, in short, I get bus noise only when the 2i2 is connected to the desktop computer and not when it is connected the laptop.

Could the desktop computer power supply be the problem? The one I have in there at the moment was not the cheapest of the cheap, but it was not exactly top of the range either. I just got a budget-priced Corsair model because it was said to be mechanically quiet.
 
Last edited:
I was just trying to use the easiest available configuration to reproduce the problem, but it looks like the connection from the bass amp output to the 2i2 has an additional problem, so it's not a good example. I have tried two other configurations — a DI box connected to the 2i2 and to the bass amp, and my digital piano connected to the 2i2 — and I did not get bus noise when connected to the laptop. I double-checked the piano connected to the desktop computer via the 2i2 and I did get bus noise. So, in short, I get bus noise only when the 2i2 is connected to the desktop computer and not when it is connected the laptop.

Could the desktop computer power supply be the problem? The one I have in there at the moment was not the cheapest of the cheap, but it was not exactly top of the range either. I just got a budget-priced Corsair model because it was said to be mechanically quiet.
It does sound like you are taking the 2i2 out of the list of variables but are the results with the laptop the same whether plugged in (aka "mains" power) vs. battery?

Have you tried using the 2i2 + desktop with nothing else plugged in that's also running off wall current, like maybe a dynamic mic or acoustic/electric guitar (not the magnetic pickup kind)? I.e., something that is not picking up EMF or recirculating noise via phantom power?
 
I think like Keith. It seems that the 2i2 is very sensitive to any current circulating in the interconnections. If you connect the bass amp - can you check to see if any current flows in the connection? would mean lifting the ground in one of the jack plugs and putting the meter on a milliamp current scale between the ground and lifted ground. Any flow here would suggest an access path into the 2i2 and if it's being sensitive or in a bad mood, could trigger the instability?
 
It does sound like you are taking the 2i2 out of the list of variables but are the results with the laptop the same whether plugged in (aka "mains" power) vs. battery?

Have you tried using the 2i2 + desktop with nothing else plugged in that's also running off wall current, like maybe a dynamic mic or acoustic/electric guitar (not the magnetic pickup kind)? I.e., something that is not picking up EMF or recirculating noise via phantom power?

Sorry, I should have clarified. I tested with the laptop when it was connected to the power supply, but I still got no bus noise.

As for the desktop computer, I only get the bus noise through the input on the 2i2 that is connected to a device with its own independent connection to the mains. So even when the 2i2 is connected through input 1 to something that causes bus noise, such as the output of the digital piano, I don't get any bus noise through input 2. And I don't get bus noise on the desktop computer when only a mic or a guitar is directly connected to the 2i2.

I should also clarify that I normally keep phantom power off because it causes a noticeable spluttering noise on the inputs (which is quite different from the bus noise). Obviously that spluttering noise with phantom power is one I would like to resolve too, but it is a less urgent problem than the bus noise since the mic I normally use can operate without phantom power, using a 9V battery.
 
Back
Top