[SOLVED] Noise in audio when Raspberry pi connected to same battery.

[MD_SHAHRUKH]

Hello everyone,
I have a doubt regarding power line noise in my audio. The audio circuit and Raspberry Pi are power by Li-ion battery pack of 11.1V
I am using 5V buck converter to power RPi and 11.1V for audio circuit. When I power ON the system, I have observed that RPi when starts the noise is added to my audio. If I disconnect the RPi the noise goes away.
I think the noise comes when powered the RPi.

Please suggest some techniques to reduce the noise.

Thank you

 

[barry]

Noise could be coming into the audio several ways. It could be radiated from your buck converter. Maybe you need shielded inductors. It could also be that the converter is dumping noise spikes right onto the 11.1 volt supply line (pretty likely). Have you looked at your power supply lines with a scope?
It could be a grounding issue. If the PI and your audio are using the same ground, make sure they connect only at the battery (-) otherwise the ground currents from the PI are going to get mixed up with your nice audio ground.
You could try putting ferrite beads in there to isolate the audio supply from the digital supply. That's an easy thing to try.

 

[KlausST]

Hi,

what is your "audio device"? Amplifier, linear, Class D,...
do you use analog audio signals or a digital interface?
how is your wiring? especially GND and audio signals

exact connection points, wire gauge, length...

Ferrite bead: It may improve but it also may worsen the problem. It depends on where it is placed.
Easy to try ... but I doubt it brings much improvement.

Klaus

 

[MD_SHAHRUKH]

Hi Barry,
I have tried the ground part, that is connecting both the Audio ground and RPi ground to Battery negative(-). But same noise is coming.

In the oscilloscope, the power I have checked across the battery. It is smooth.


Ferrite bead I don't have right now. But can you tell me what is the reason of the noise, the buck converter is a module and it is kept little away from the RPi and Audio circuit. I have put shielding braid above 11.1V line also. But no change in noise.

--- Updated Mar 23, 2022 ---

Hi Klaus,
The audio circuit is a linear amplifier using TL072 op Amp. The audio input is a contact microphone. The wiring for all the GND points are connected very close to battery (-) point or directly connected to battery negative (-). Wire thickness is 2.5mm and length to be less than 10cm for GND from audio circuit to battery (-) and around 15cm for RPi to battery (-).

 

[barry]

What does the noise look like? Wideband? Spikes? Is your microphone cable shielded? If so, where is the shield connected?

 

[andre_luis]

Wiring matters a lot on this case, are you using a descent cable between RPI and the input of the audio amplifier ? I mean, a ground shielded one ? In addition, did you check the audio out volume level with the command line alsamixer utility to ensure that it is tunned at the maximal possible? Doing this adjust, you somehow reduce the noise/signal ratio.

 

[Audioguru]

A schematic with parts values is VERY important to see the cause of the noise.
I am guessing that the "contact mic" is an electret type and is powered with a resistor connected directly to the noisy buck converter.

 

[MD_SHAHRUKH]

Q

What does the noise look like? Wideband? Spikes? Is your microphone cable shielded? If so, where is the shield connected?

Hi Barry, the shield is there at microphone cable and I have extended that shield till the input of microphone. And shield is connected to ground of microphone and negative terminal of battery.

--- Updated Mar 24, 2022 ---

Wiring matters a lot on this case, are you using a descent cable between RPI and the input of the audio amplifier ? I mean, a ground shielded one ? In addition, did you check the audio out volume level with the command line alsamixer utility to ensure that it is tunned at the maximal possible? Doing this adjust, you somehow reduce the noise/signal ratio.

Hi Andre, I am not using any digital filter. I have used completely analog circuit. And after that I will give that signal directly to ADC. I cannot do digital filtering.

The main issue is occurring when powering the RPi, when RPi is OFF then no noise is there in the audio.

--- Updated Mar 24, 2022 ---

Can you suggest how to measure power noise in my circuit. And if there is a noise, then ho can I reduce that noise, making thicker ground cable could help?

 

[MD_SHAHRUKH]

Hi, I have observed some voltage fluctuations in the power side, when the Green Led of RPI fluctuate there is a voltage minor voltage drop of around 0.5V max and the it is frequently happening. I have put one 1000uF cap, but not able to reduce the voltage fluctuations. The noise is at audible frequency so, there is the voltage fluctuations somewhere near to that frequency. While tracing the FFT, It is not very clear what frequency it is, and the noise is also not at any constant frequency also when listening.

 

[MD_SHAHRUKH]

Hi,
I am going to isolate the power supply using isolated power supply. But it is a costly alternative. I hope it will work.

 

[barry]

0.5V variation is ENORMOUS, it’s not “minor“, particularly if you’re powering your microphone directly from that power.

im not sure what ’isolating the power supply using isolated power supply means’. Do you mean two separate supplies? You could just try powering the audio through a regulator instead of right from the battery; that will minimize the effect of fluctuations on the battery voltage.

 

[MD_SHAHRUKH]

I had used 9-35V to 5V isolated buck converter where I have isolated the ground. And 11.1V to 12V isolated power supply. Both are by mornsun. But still not working. Getting same fluctuation.

 

[barry]

Can you show us a diagram/schematic/something? You've got two isolated "grounds"? That might be a problem. We REALLY need to see something other than words.

 

[Audioguru]

All circuit grounds must be connected together.

 

[KlausST]

Hi,

Still missing a wiring plan.
Unable to give tailored help.

You need to try on your own.

Klaus