Noise in audio chain

[Johnny90]

I am using audio wireless to connect my guitar to the guitar FX.
Setup is like this:
guitar -> analog audio cable -> RF TX -> air -> RF RX -> analog audio cable -> guitar FX
Receiving side is powered by single USB cable from PC.
It is very noisy.
But, if I power RF RX from the power bank (or use integrated battery on RX) it is much quiter (guitar FX still powered from USB from PC).

I tried some things to mitigate it:
Daisy chained USB (PC -> guitar FX -> RF RX)
Added additional capacitors between GND and 5V on RF RX
Disconnecting GND from audio cable on RF RX
Removed charging IC (4056) and disconnected battery on RF RX
Added 5V LDO between USB and rest of the RF RX

What I can try to fix it?
Will using balanced audio help?
Will adding ground isolator trafo help?
Would ditchng analog part help (using I2S to connect RF RX to the guitar FX) help?
Should I buy ferrite bead and put it around USB cable?
Maybe utilize LDO/powerpath/transistor?
Something else?

[magic]

So guitar FX is some analog to digital gizmo which has to be on USB to work, and the receiver is powered by USB and when you connect its power cable to the PC or the FX gizmo, it gets noisy?

Did you try powering it with a separate USB charger?

The problem is probably a ground loop involving the receiver's USB cable and the analog audio link. If this link can be balanced, it's likely to help.

[Johnny90]

So guitar FX is some analog to digital gizmo which has to be on USB to work, and the receiver is powered by USB and when you connect its power cable to the PC or the FX gizmo, it gets noisy?

Yes. USB is used for power and as audio interface (sound card)

Did you try powering it with a separate USB charger?

Yes. It gets different levels of noise.

The problem is probably a ground loop involving the receiver's USB cable and the analog audio link. If this link can be balanced, it's likely to help.

Thanks, I'll try to add balanced audio between RF's analog output and FX's analog input.

[MathWizard]

So what kind of noise is it tho, any idea? 60Hz hum, or some digital wackiness ? Or AM/FM radio getting picked up ??

[radiolistener]

What I can try to fix it?

To reduce noise that occurs when a guitar signal passes through multiple devices, the first and very important step is to identify the source of the noise. Determine at which stage of the signal chain the noise is being introduced. This will help in implementing effective solutions, such as improving cable quality, using noise gates, or optimizing the settings on each device to minimize interference.

[magic]

1. This is borderline necro.

2. Which part of "ground loop" you guys don't understand?

[Terry Bites]

RF getting into analog circuits can be demodulated an appear as noise.
Stop RFI getting into the analog inputs with a filter that cuts off anything you dont need.

You might just start by adding some ferrrite beads inside your fx boxes.
Maybe wind the fx box input screened lead around a torroid, com ca https://www.pa9x.com/wp-content/uploads/2023/03/200W-HF-common-mode-choke.jpg

[CaptDon]

5V LDO is useless, isn't its input 5vdc from USB? A 5v LDO can't output 5 volts with 5 volts in, it needs headroom. The USB output from your laptop is probably loaded with digital noise from internal EMI within the laptop. The added gain of the guitar FX unit to give you all the overdrive distortion you desire is also going to amplify any noise that is on the receive chain. Most of these RF guitar TX/RX devices simply use internal batteries to reduce noise in the chain. Batteries are the simple solution here. You will need to run the volume controls on the guitar hotter than normal to get a good signal to noise ratio. I am one of the old dinosaurs using the Audio Technica VHF ATW system. Battery beltpack with rack mounted receiver. None of the little 'guitar jack' RF dongles ever had the range or quality of sound that the old Audio Technica provides which is why I stuck with it.

[Johnny90]

Thanks for the replies!

I've tried to measure it, but it is tricky.
Sometimes noise will stop when I press scope probe to the ground of the device (like shielding of USB cable or audio jack).
Sometimes noise will start when I press scope probe to the ground of the device.

Sometimes noise will start when I move disconnected USB cable. It acts as an antenna and more noise will come when (disconnected) USB connector is placed close to the things like monitor (possible because of PWM backlight)

I've ordered ground isolator and USB power isolator from China and see if that will help.

[radiolistener]

you can't detect small noise with oscilloscope.
Audible noise from audio amplifier is about -60..80 dB, it is out of visible range for oscilloscope. It will show you ideal and clean signal even if you listen noticeable noise.
It is better to use spectrum analyzer to check the noise.

The first thing that you need to start is to detect which component introduce the noise.

[Johnny90]

My guitar FX is not "high gain", it is digital (analog signal sampled at "normal" gain, digital magic is applied, converted back to analog and sent to the headphones).
I am using is as basic USB audio interface (sometimes with guitar, sometimes like USB audio card without guitar).
It could be very quiet when only headphones and USB to the PC are connected.
To prove it I did my experiment with another USB audio interface (without guitar FX capabilities) and result is the same.

I think my noise comes from my wireless receiver.
It can produce noise even if not connected to the USB charger.
Touching it (or placing hand near it) can reduce the noise.
Moving it across the desk (while connected with USB to the PC) can produce various levels of noise (from none to some).

[ssashton]

If the receiver has the option of a balanced connection to your FX / audio interface, that may be a lot better than single-ended.

Else, I think the receiver, getting power from the USB, is polluting the ground line. The only option is to provide power from elsewhere.