audio/computer geeks; HELP!

[Cameramonkey]

OK Computer/sound geeks. A tough one.


Got my hands on a donated PC with lots of horsepower (i7 2.8) to drive the facebook live camera at church. Trouble is on the audio output there is a nasty 60hz hum. Said hum doesnt exist on the USB sound card when plugged into the old laptop we were using. (just moved everything to the tower; same sound card and camera equipment on both computers) So it doesnt seem to be the cable or the sound card. Its gotta be internal. And I have tried every last USB port.


But where? And how to fix? Suggestions Warren? You ever seen it? ...


Ive been doing PCs and PC repair for over 2 decades, but this one has me stumped.

 

[Tanfodude]

It might be a corroded or dirty USB socket of the donated PC. But why are you using a USB sound card when PC normally have audio jack outlet at the rear. Have you tried the other USB sockets?

I'm not an expert. Just a gamer who builds his own HTPC.

 

[hoosierdoc]

https://forum.cockos.com/showthread.php?t=113721

might this help?

 

[snapping turtle]

Just an idea here take the power from where the audio amp is located and run an extension cord to power up the pc. I think what you have here is a difference in ground potential between where the pc is plugged in and the audio is plugged in.

I have seen seen this several times where we we powering a powered speaker in a gym from the soundboard. One came from one subpanel and the other from another. Maybe with the laptop changing the power input to dc it did not effect it as it laptop was itself AC ungrounded so to speak.(only the power supply was grounded. ) I used to extension cord trick to prove the problem to the electrical aub contractor showing them that the ground potential made a difference.

Low impedance signals (mostly mic’s) require runs away from power that can also cause the 60 H hum. I still think the issue is the two devices are not on the same ground potential. But as always check the run of the audio path keep Eing it away from lighting and other noise producing items. They should really be in conduits and properly shielded also.

 

[Haven]

Did you try turning it off and back on again?

[video=youtube;nn2FB1P_Mn8]https://www.youtube.com/watch?v=nn2FB1P_Mn8[/video]

 

[woowoo2]

Chances are it's a ground loop.
(Current flowing on the shield.)
You can....
Put a three to two prong adapter on the computers power cord (not recommended)
Install isolation transformers, or a direct box with a ground lift, on the inputs and outputs.

Are the audio in/outs 1/8" unbalanced?
Are you feeding a balanced mixer input?

Examples:

AV-HK1 ? ?HUM KILLER? Stereo Audio Isolation Transformer - Dual RCA inputs and outputs

https://www.amazon.com/JacobsParts-...coding=UTF8&psc=1&refRID=FW6MEW3NS1HHXSGDDQRM

Pro Audio | Jensen Transformers

Henry Engineering

 

[jkaetz]

Just to make sure I'm understanding correctly:
The audio source is a USB audio device connected to the donated computer?
What is the connection method from the audio device to amp? 3.5mm -> RCA?
How is the USB audio device powered?
The same audio device connected to another computer does not produce the hum?

I'm inclined to say try a new power supply in the donated computer. Everything after the computer's power supply should be 12v or 5v DC so the hum shouldn't be AC related. This should be similar to car audio which is all 12v DC. The hum in car audio is usually created by a ground loop and is usually solved by making sure that the amplifier and source devices all use the same power and ground path. You have a slightly different situation but your amps are likely powered by an AC -> DC power supply as is the computer. While it isn't possible to power the two together perhaps something weird is happening between the amps and the donated computer's power supply.

 

[searpinski]

Just to make sure I'm understanding correctly:
The audio source is a USB audio device connected to the donated computer?
What is the connection method from the audio device to amp? 3.5mm -> RCA?
How is the USB audio device powered?
The same audio device connected to another computer does not produce the hum?

I'm inclined to say try a new power supply in the donated computer. Everything after the computer's power supply should be 12v or 5v DC so the hum shouldn't be AC related. This should be similar to car audio which is all 12v DC. The hum in car audio is usually created by a ground loop and is usually solved by making sure that the amplifier and source devices all use the same power and ground path. You have a slightly different situation but your amps are likely powered by an AC -> DC power supply as is the computer. While it isn't possible to power the two together perhaps something weird is happening between the amps and the donated computer's power supply.

My suggestion as well.

 

[Cameramonkey]

I clipped the ground lug, removing the ground loop. Poof. No more hum.

laptop isn’t grounded, that’s why the laptop doesn’t suffer the same noise.

 

[HoughMade]

My electronics knowledge is from the tube era....so clearly, electrolytic capacitors to filter the hum. It works on my Philco 60.