Possible ground loop issue when using an audio interface with a laptop connected to its charger

[Mugetsu]

Hello guys, recently I made some post asking for some advice between Audient ID4 MKII and Topping E2x2 for just using them to connect my guitar to amps simulators (for example Neural DSP) and nothing else. At the end after more research, I went with the IK Multimedia AXE I/O One (got it two days ago) since it is tailored specifically for what I wanted and it is also cheaper ($130 USD vs 180 USD + for the other two).

The thing is that unfortunately I came across a problem that I never expected, I have a terrible hum or buzz (can’t really tell which one it is but it is bad) when opening amps sims plugins.

The connected devices are as follow:

Voltage regulator --> Laptop Charger --> Laptop --> Audio interface connected to laptop --> Guitar and Headphones connected to the audio interface

My first thought was that the problem is the audio interface but after a little more testing I realized that the hum/buzz is mitigated a bit if I touch the tips of the guitar cable, the tip of the headphones cable or the laptop itself and it is completely eliminated if I disconnect the charger from the laptop and run on battery, so my hypothesis is that problem is maybe a ground loop created when using the laptop with the charger connected.

This however doesn’t happen if I just open some Youtube Videos or music stored in my computer (audio interface connected to laptop and its charger), so the problem only happens when using Amps sims plugins.

My laptop is a Lenovo Legion 7 with an RTX 3080 Ti so it is a super hungry battery consumer device, hence I always use it connected to the charger since the laptop allows me to bypass the battery and just power the laptop itself. I’m using the original Lenovo 300 W charger that has 3 tips connector (grounded) so no cheap or bad quality charger is used. Using the laptop without the charger is a hard no for me.

Also, just to test and nothing else I connected the laptop charger to a cheater plug to see if lifting the ground would eliminate the problem but that didn’t work.

Has anyone come across with a problem like this?

Would using a different audio interface would give me a different result? The Axe I/O one encase is plastic vs a metal one in other audio interfaces but for this specific problem I don’t think it would matter much.

Do you guys think a possible solution could be connecting the audio interface to something like a USB Isolator?

Cheers and thanks for your attention

 

[DonH56]

Try this on the audio interface's or laptop's power cord to the wall:

https://www.amazon.com/Ebtech-Hum-Ground-Voltage-Filter/dp/B0002E4YI8

 

[phofman]

Do I understand correctly that a software inserted into your software chain (that DSP plugin) enables the hum? And that disconnecting the grounding/PE pin of the ntb power adapter made no difference?

 

[AnalogSteph]

Also, just to test and nothing else I connected the laptop charger to a cheater plug to see if lifting the ground would eliminate the problem but that didn’t work.

I think you may have exactly the opposite problem, your equipment ground is floating and at partial mains voltage due to leakage from mains filter capacitors.

Please verify with a multimeter that mains earth on the power plug connects to the outer shell on the DC power connector, and that the outlet is actually grounded (if possible - might be a job for an electrician).

The Axe I/O one encase is plastic vs a metal one in other audio interfaces but for this specific problem I don’t think it would matter much.

I mean, the heavy lifting is usually done by the PCBs these days but having a shielded enclosure can't hurt when you've got high-impedance nodes about, and an instrument input definitely qualifies as such.

This however doesn’t happen if I just open some Youtube Videos or music stored in my computer (audio interface connected to laptop and its charger), so the problem only happens when using Amps sims plugins.

I would think that amp sims probably have a bunch of gain + limiting, making every little bit of hum that much more obvious.

Do you guys think a possible solution could be connecting the audio interface to something like a USB Isolator?

Yes, assuming its power hunger does not exceed the ~300 mA that you can typically expect from a basic USB isolator... plus you would want a USB 2.0 capable one anyway (Topping HS02 or the like) as the interface is easily capable of exceeding USB 1.1 data rates. You can say goodbye to a good chunk of your money saved at this point.

 

[Mugetsu]

Try this on the audio interface's or laptop's power cord to the wall:

https://www.amazon.com/Ebtech-Hum-Ground-Voltage-Filter/dp/B0002E4YI8

The audio interface is BUS powered so only the laptop charger is connected to the wall. Thanks for answering, going to check that option.

 

[Mugetsu]

Do I understand correctly that a software inserted into your software chain (that DSP plugin) enables the hum? And that disconnecting the grounding/PE pin of the ntb power adapter made no difference?

Yes, for example, when I have my guitar and headphones connected to the audio interface (BUS powered) and the interface to the laptop with its charger plugged in to the wall and do anything like listening to music through the audio interface there is no hum even with all the devices connected, but the moment I open any Amp Simulator (not just Neural DSP) the hum appears and only dissapears completely if I disconnect the laptop charger.

Also yes to the second question.

 

[phofman]

but the moment I open any Amp Simulator (not just Neural DSP) the hum appears

That simulator is what software API - VST?

and only dissapears completely if I disconnect the laptop charger.

And if you stop the plugin (i.e. remove it from your audio chain)?

 

[Mugetsu]

I think you may have exactly the opposite problem, your equipment ground is floating and at partial mains voltage due to leakage from mains filter capacitors.

Please verify with a multimeter that mains earth on the power plug connects to the outer shell on the DC power connector, and that the outlet is actually grounded (if possible - might be a job for an electrician).

So the problem might be that even if I have grounded wall plugs in my house they're not actually grounded to a physical ground? That would be worse since that would mean it is not protected, right?

I Also checked other outlets in my house to see if the hum problem also happened in them an unfortunately it did.

I mean, the heavy lifting is usually done by the PCBs these days but having a shielded enclosure can't hurt when you've got high-impedance nodes about, and an instrument input definitely qualifies as such.

I put the interface inside a metal bowl to see if shielding it would help but that didn't work either.

I would think that amp sims probably have a bunch of gain + limiting, making every little bit of hum that much more obvious.

Yes, that is correct, clean tones configurations in amps sims produce less hum that configurations aimed for high distortion, some amps sims even have noise gates to diminish this, however this specific hum problem is beyond that since it is produced an external factor (like my laptop charger) and dissapears completely on battery.

Yes, assuming its power hunger does not exceed the ~300 mA that you can typically expect from a basic USB isolator... plus you would want a USB 2.0 capable one anyway (Topping HS02 or the like) as the interface is easily capable of exceeding USB 1.1 data rates. You can say goodbye to a good chunk of your money saved at this point.

Since the audio interface is BUS powered from a USB 2.0 Type C I would expect that the maximum current it can draw would be like 500 mA, right?

Topping is HS02 sounds like a plausible option, what do you think of this one?

https://es.aliexpress.com/item/1005009749759535.html

Supposedly it has an ADUM 3165 and it can be powered externally to.

Or is the Topping one the only realiable one when it comes to USB Isolators?

 

[phofman]

dissapears completely on battery.

I still do not understand - the hum appears only when your start the audio plugin, not when the laptop is switched to the power adapter, and disappears when the laptop is switched back to battery? That's highly unusual...

 

[Mugetsu]

That simulator is what software API - VST?

They can work as a VST plugin in a DAW, however, amp simulators also can work independently as standalone software to usem them directly without a DAW, which is what I using, so I literally open them like any other software.

And if you stop the plugin (i.e. remove it from your audio chain)?

If I close the amp sim software the hum dissapears (I guess it is because the guitar is not sending a signal anymore and there is no software to receive it.), if I disconnect the laptop charger from the laptop while using the amp sim the hum also dissapears.

 

[phofman]

OK, so the sim software sets high gain on the audio input, and the noise generated in the incoming low-voltage signal from the quitar pickup (the induced noise may be higher if the soundcard input is capacitively linked to the mains via the power adapter) gets amplified. Sth like that?

 

[Mugetsu]

I think you may have exactly the opposite problem, your equipment ground is floating and at partial mains voltage due to leakage from mains filter capacitors.

Please verify with a multimeter that mains earth on the power plug connects to the outer shell on the DC power connector, and that the outlet is actually grounded (if possible - might be a job for an electrician).

@AnalogSteph Just returned home with a multimeter to do some measurements and It seems that what you said is true. There was voltage between live and neutral in the outlets but not between live and ground so I decide to look further and found that there is only live and neutral in my outlet.

Do you think that getting proper ground would fix my problem?

 

[DonH56]

I have the same problem with my laptop when using an audio interface; lifting the ground solves the problem.

@AnalogSteph Just returned home with a multimeter to do some measurements and It seems that what you said is true. There was voltage between live and neutral in the outlets but not between live and ground so I decide to look further and found that there is only live and neutral in my outlet.

Do you think that getting proper ground would fix my problem?

A proper ground might not fix the problem but not having a safety ground is against code in the US and is a good thing to have where ever you live. Look in the box and see if there is a bare or green insulated ground wire floating (may have a wire nut on it) and if so attach it to the ground terminal of the outlet.

 

[Mugetsu]

I have the same problem with my laptop when using an audio interface; lifting the ground solves the problem.


A proper ground might not fix the problem but not having a safety ground is against code in the US and is a good thing to have where ever you live. Look in the box and see if there is a bare or green insulated ground wire floating (may have a wire nut on it) and if so attach it to the ground terminal of the outlet.

@DonH56 Ironically I also don't have a ground as previously stated but I also have the problem so the reason could be what AnalogSteph stated before (equipment ground is floating and at partial mains voltage due to leakage from mains filter capacitors). To be honest at this point I don't know why (obviously due to my lack of knowledge on these topics) I'm having this problem since my ground is already lifted due to the complete lack of it in my house xD.

Fortunately in all these years there hasn't been a single accident but I do agree that it is a serious topic that needs to be adressed.

Unfortunately I didn't see a ground cable but I'm going to check again tonight when I come back home.

 

[AnalogSteph]

Do you think that getting proper ground would fix my problem?

I would think so - but good luck getting a safety ground retrofitted in something that isn't typical US "whole lotta nothing" architecture, and I spot brickwork in your photo. Electrical work tends to make a huge mess and be a major hassle, that's why it typically is only performed during major renovations with nobody occcupying the space. I am aware that ungrounded outlets were common in the US far longer than over here, let alone other places in Central and South America also using NEMA 5-15 outlets, but realistically your space is something like 3 decades overdue for a rewiring.

You should probably ask an electrician to have a look at your setup (including breaker panel) and advise on how to proceed, as they should be familiar with local code requirements. You may get away with fitting appropriately-marked GFCI-equipped outlets. Then you'd at least have the PE connected to neutral. That makes a fairly dirty ground since it also has to carry return currents, so if you ever do get any ground loops they are likely to be quite obvious, but it should be a whole lot closer to a proper ground than what you have now.

 

[dagfinn]

The audio interface is BUS powered so only the laptop charger is connected to the wall. Thanks for answering, going to check that option.

You don't have the power adapter? The manual says nothing about bus power, but the power adapter is mentioned many times. It is probably running out of power, it has hardware features not in use when DAC only.

 

[Mugetsu]

You don't have the power adapter? The manual says nothing about bus power, but the power adapter is mentioned many times. It is probably running out of power, it has hardware features not in use when DAC only.

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Hello, the pictures you attached are from the Axe I/O, I'm using the Axe I/O One.

 

[Mugetsu]

I would think so - but good luck getting a safety ground retrofitted in something that isn't typical US "whole lotta nothing" architecture, and I spot brickwork in your photo. Electrical work tends to make a huge mess and be a major hassle, that's why it typically is only performed during major renovations with nobody occcupying the space. I am aware that ungrounded outlets were common in the US far longer than over here, let alone other places in Central and South America also using NEMA 5-15 outlets, but realistically your space is something like 3 decades overdue for a rewiring.

You should probably ask an electrician to have a look at your setup (including breaker panel) and advise on how to proceed, as they should be familiar with local code requirements. You may get away with fitting appropriately-marked GFCI-equipped outlets. Then you'd at least have the PE connected to neutral. That makes a fairly dirty ground since it also has to carry return currents, so if you ever do get any ground loops they are likely to be quite obvious, but it should be a whole lot closer to a proper ground than what you have now.

@AnalogSteph I live in Mexico, but yeah, your point still stands. I'll talk to an electrician to see what can be done, people here can be pretty creative when it comes to problem solving so I wouldn't loose hope yet with retrofitting grounding.

In the meantime I'll get an USB Isolator and see if that helps. Would you recommend one with an external power supply or one that can provide enough energy by itself to the audio interface?

 

[Mugetsu]

OK, so the sim software sets high gain on the audio input, and the noise generated in the incoming low-voltage signal from the quitar pickup (the induced noise may be higher if the soundcard input is capacitively linked to the mains via the power adapter) gets amplified. Sth like that?

@phofman Yes, it's like this:

Laptop Charger + Laptop + Amp Simulation Software + Audio interface + Headphones = No hum

Laptop Charger + Laptop + Amp Simulation Software + Audio interface + Headphones + Guitar = Super loud hum

Laptop + Amp Simulation Software + Audio interface + Headphones + Guitar = No hum

 

[AnalogSteph]

Sounds about right.

You're not the first guitarist to curse their studio with ungrounded outlets. Unfortunately, electric guitars are often badly shielded (especially those wired back in the olden days) while sporting high-impedance nodes in their circuitry, which can make AC disagreements between system ground potential and that of the users and environment rather audible indeed. (And we're talking roughly half the mains voltage in this case.) It may not even be possible to make them fully immune to such hum pickup if say the knobs are solid metal, though DIY improvements may still be possible.

I hope you're running humbucker pickups at least. Otherwise you'll have a free detector for monitor backlight current paths (and whatnot) as well.