So here is the story: I have a guitar and an fx processor (digitech rp250), but I get a little noise when I record/hear it (through the processor's usb cable) in my laptop or my desktop PC. The noise only gets hidden under distortion, and that too when you are playing a note. But if you play clean, or hear out the entire release section of a note, the noise is audible. This was two years ago. I tried to deal with it, and hoped to find a solution someday since I am a EE undergrad student.
I also get the noise when I feed the headphone out of the processor into the line in of the computer. I have attached a sample, please hear it closely and you will notice.
Now, when I feed the headphone out of my mp3 player into the line in of the laptop, I get noise-free sound/music. So, I concluded that there might be some ground loop issue - I thought that since the mp3 player is not connected to the mains power in any way, effectively working as an isolated voltage source with low output impedance, there was no noise. Whereas the fx processor was connected to the power socket through an adapter, and thus created noise.
So I thought a preamp would be a solution, a preamp powered through batteries. There would be no connection to the household power supply, and so I would hopefully have no grounding problems and therefore no noise. I thought I would finally be able to record a crystal clear guitar.
I have just created a very rough first iteration of the preamp, using the TL071 opamp in non inverting configuration with gain = 2, powered by two 9V batteries, and having just my guitar as an input i.e. no fx processor. When I plug the output from the opamp into the line-in jack of my laptop, I still get the same noise! I don't understand why. Please help me, this whole problem is frustrating.
I would've thought that the guitar might be faulty, since I have a very cheap one, but the thing is, that noise is never there when I listen to the opamp's output with headphones. The noise was never there with headphones with the fx processor's headphone out either. It is not there when I connect a speaker to the fx processor. It is only when I connect my guitar to the laptop/desktop, with or without the fx processor, usb or line-in, that it is there.
PS: In case this is relevant, my laptop is connected to the power socket through a two pin connection, not a three pin one. Assume that I cannot use three pin plugs for it.
I also get the noise when I feed the headphone out of the processor into the line in of the computer. I have attached a sample, please hear it closely and you will notice.
Now, when I feed the headphone out of my mp3 player into the line in of the laptop, I get noise-free sound/music. So, I concluded that there might be some ground loop issue - I thought that since the mp3 player is not connected to the mains power in any way, effectively working as an isolated voltage source with low output impedance, there was no noise. Whereas the fx processor was connected to the power socket through an adapter, and thus created noise.
So I thought a preamp would be a solution, a preamp powered through batteries. There would be no connection to the household power supply, and so I would hopefully have no grounding problems and therefore no noise. I thought I would finally be able to record a crystal clear guitar.
I have just created a very rough first iteration of the preamp, using the TL071 opamp in non inverting configuration with gain = 2, powered by two 9V batteries, and having just my guitar as an input i.e. no fx processor. When I plug the output from the opamp into the line-in jack of my laptop, I still get the same noise! I don't understand why. Please help me, this whole problem is frustrating.
I would've thought that the guitar might be faulty, since I have a very cheap one, but the thing is, that noise is never there when I listen to the opamp's output with headphones. The noise was never there with headphones with the fx processor's headphone out either. It is not there when I connect a speaker to the fx processor. It is only when I connect my guitar to the laptop/desktop, with or without the fx processor, usb or line-in, that it is there.
PS: In case this is relevant, my laptop is connected to the power socket through a two pin connection, not a three pin one. Assume that I cannot use three pin plugs for it.
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