Problems with amplifier LM4861

[tinusw7]

Hi

I'm testing the LM4861 chip to amplify the audio signal that comes from the PWM output of a ATTiny85.
I'm using the amplifier as suggested in the typical application section of the **broken link removed**.
My problem is that there is a strong buzzing both when playing a sound and in quite mode. I've added a low pass filter to the PWM signal but that didn't help. I guess it must be the amplifier that adds the buzzing. Is there an easy way to filter/stabilize the amplifier output?

Thank you in advance.

Martin

 

[goldsmith]

Dear Martin
Hi
You can use a notch filter in your out put. do you have an spectrum analyzer? if yes you can see , that what is the frequency of those noises , and you can design a simple notch filter to remove them.
By the way , did you designed PCB for that , or probably used bread board????? and did you used shield wire for your input wire ? these are very important
Best Wishes
Goldsmith

 

[tinusw7]

Thank you for your answer. Unfortunately, I don't have a spectrum analyzer or an oscilloscope here.

Yes, I'm using a breadboard for testing. The microcontroller and the amplifier are placed next each other on the breadboard, but I'm not sure if the wires are causing the problem. Before the LM4861, I was testing with a TDA2822 and there there was no buzzing problem. I want to use the LM4861 because of its shutdown function.

My LM4861 is maybe defect (due to all my tests with different setup), I will get a new one and see if there is any difference.

 

[goldsmith]

My friend!
We have a parameter , that called , noise ratio and noise number , and that depends on the internal circuit of the IC s , probably , the noise ratio of that ic is higher than TDA . try with shield wire as an input wire.
Respectfully
Goldsmith

 

[tinusw7]

Hi Goldsmith

Thanks again for your help. I've been able to solve the problem: The shutdown input caused the buzzing. In the datasheet is written that when this input is set to Vcc, then the amp will shut down, but I didn't know that it has to be connected to ground to operate correctly. I simply left the contact unconnected which caused the bad output signal. After connecting to gnd all went well

Regards
Martin