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Grounding issue with audio

Faradave

Member
So I bought this cheap ThinkPad t420 to use as an amp Sim. I guess I assumed every computer came with an audio in 3.5 mm Jack. This one did not so I had to buy a USB audio in. It also has headphones out. Well, this works for my purposes but there's some kind of grounding issue because it produces a loud buzz. I was only able to play for about 45 minutes, the lifespan of my battery because the buzz is some sort of grounding Loop issue. I'm aware of ground Loop isolators, but those cost money.

Even with the laptop unplugged, I had to use headphones because when I plug in my Amplified PC speakers which are plugged into my power mains, here comes the buzz again.

The only solution I could find was to take an unused power cable with a ground prong and plug it in, then touch the ground wire to anywhere on the chassis of my laptop.

What a rapture to be rid of that horrible Buzz but still I'm greedy and I want more.

That solved the issue fine and dandy but I don't like having this plug I got to plug in every time I want to play.

Can I assume that it would be bad to touch that ground to the negative or positive wire? You know what as I type out that sentence I realized what a bad idea that would be. Never mind. I was thinking I could just run a very short cable from the neighbouring outlet's ground to the negative of the outlet that is powering my laptop, but that's dumb that'd pop my breakers, right? Well what would you guys suggest? IF YOURE SO SMART! jklol

The only solution I can think of is to just have an extra plug for ground and then tape that cable to my laptop power cable so that its as if I only have one cable to screw with but then I still have to take that ground cable and touch it to somewhere on the chassis. I've been wrapping the wire around a USB plug and plugging it in. There's gotta be a better way....

I sure do appreciate yall's help!
 

Faradave

Member
Here's my best guess.... Here is what will be if yall don't correct me.

20200119_095947.jpg
I just plug that new ground prong into whatever Outlet and then attach the other end of the ground wire to a screw for this old monitor input.

Yeah.... This laptop has no HDMI port or 3.5 mm audio input but it does have one of those old VGA monitor inputs and one of those brand new modern DisplayPort inputs.... now the 420 in T420 makes sense.....
 

rjenkinsgb

Well-Known Member
Most Helpful Member
If it's only buzzing while the speakers are connected, I'd say it's a bad power supply design & some capacitive leakage in those that is causing the problem.
Can you add a ground connection to the screen of the speaker audio cable? It should have exactly the same effect as connecting a ground to the laptop while the speakers are plugged in.

That should cure the problem, if that is the cause?
 

Faradave

Member
I may have mis-spoke. Let me restate. When I use this device for input:
20200119_131817.jpg
There is a buzz whenever the laptop or any peripheral connected to it are plugged into my wall outlet (without the extra ground wire added). I must use that USB input/output because the laptop HAS NO OTHER, LENOVO......You can hear it through my PC speakers or through my headset or through the laptop's onboard speakers. That cannibalized ground wire is the only way to cure it.

Yea that would probably work but it's no more elegant than what I have.... I think, what do you mean when you say the "screen" of the audio cable?

If that extra added ground cable still has to come all the way up to the level of myself and my laptop, then it's probably just as good how it is. But if them's the breaks, I can live with that.

But what caused this? The computer sounds just fine, no grounding issues until you plug in that weird third-party USB input. How is that thing so poorly grounded that now your whole laptop has buzzing issues? I need to understand this
 

rjenkinsgb

Well-Known Member
Most Helpful Member
OK, I thought it was when the speakers were plugged in. You could have connected a ground to the cable screen at the speaker end, so you just had the 3.5mm plug.

If it's the USB audio device, get a different, better quality USB audio device... That's the easiest fix, or at least it will help pin down the problem. It sounds like the ground problem may be within that.

You mention "amp sim" - if you are trying to use it with a guitar, is there a possibility it's what connects to that device rather than the device itself?

If that is how you are using it, you could be better off with a proper audio interface that will accept a guitar etc. with much better quality and lower latency than a pc "sound card" type input anyway; eg. a Focusrite Scarlett or similar.


Another thought - is whatever you are connecting to the USB device also connected to mains power in some way?
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
I have a way of making it more elegent, but not another way to fix it. You could attach a ring terminal/screw to the exposed nut. Then add a wire pigtail to a singke pin connector like: https://www.mouser.com/datasheet/2/276/0003091011_CRIMP_HOUSINGS-133189.pdf''

I'd cannibalize a shielded power cord and just bring out the ground pin to the mate to that single pin connector.

The reason for using a connector is that something always yanks at the laptop power pin and you;d like it to disconnect.

A grounded adapter MIGHT also work.

USB+5 and GND, the ground is the main ground of the laptop.

You also might find that a resistor like 2.2 ohms in series with your added ground might be better.
 

Faradave

Member
Yeah, I could get a better USB device. I could also get a better laptop but I'm a cheapo.

Yeah the amps sim is for guitar. As for the device that connects to my instrument, it's simply a half inch to 3.5 mm converter. Male half inch, female 3.5 mm. All analog until you hit laptop. And no, my USB input device does not plug into mains. It's just cheap.

And thank you, simple stupid, that idea is more elegant. At this point I don't think the increase in elegancy will outweigh my laziness though. If you offer me $20, I'll offer you $10 to put it in my pocket for me. I will, however, try adding that resistor to my existing ground cable.

But yeah, thanks guys, I consider this issue fully explored and I can rest easy. I'm going to give you guys a break then I'm going to come back in hot with another one, okay? Cool.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Is the converter mono or stereo?
(Two or three total contacts on the 3.5mm plug)

What happens if you bridge from the metal body or sleeve of the guitar plug to the laptop ground, such as that connector screw?

If it has the problem with no separately powered devices connected, it has to be a problem somewhere around that area.
 

Faradave

Member
The one I'm currently using is mono, but both mono and stereo will produce The Buzz. Also, bridging that sleeve with my PC ground will not solve the issue. Which is unfortunate, if the problem was inside the guitar it would be easy to access and fix
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Very strange!

I have a cheap USB sound card in one of my parts boxes, I'll do some experiments tonight..
 

unclejed613

Well-Known Member
Most Helpful Member
"antique" port looks like a VGA video port.
 

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