VM 114 and Bluetooth shield RN52 hookup -> noise

Hi there,

I bought a VM114 amplifier to amplify the audio coming out of a RN52-Evaluation Kit board and send it to a speaker.
RN52-EK datasheet: http://forum.velleman.eu/viewtopic.php?f=2&t=12055&p=54096&hilit=VM114#p54096

My sound is noisy in the current configuration (see attached hookup schematic). The noise is not a random white noise, it’s more shrill noise.

After I read that topic: http://forum.velleman.eu/viewtopic.php?f=2&t=12055&p=54096&hilit=VM114#p54096 I disconnected the shield from the GND input of the VM114 (as sketched in the drawing attached). It was already noisy before then.

If audio is send directly from my phone (through the jack to the amplifier) there is no noise. If the audio is send from the RN52-EK to a (battery powered) Jawbone speaker there is no noise…

I guess there might be a hum loop somewhere, but where ?
The noise is coming from the power supply as it sounds different when I change the power supply. But it’s caused by the fact that I use the same power source for the Bluetooth shield and the VM114.
The capacitance near the LDO are good in theory. And I tried with different Cap and LDO’s and I still have the same noise…

Could someone help me to find out where it’s coming from ?

Thanks for your help,


Hi there,

I still didn’t figure out where this noise is coming from and how to get rid of it. Could someone help me ?

Please just give me your thought !