How to apply external power to WT5001M02-28P audio module


After fiddling around with the WT5001M02-28P, i got it working on an arduino Mega.
Only when the volume gets (to) high, the sound cuts off. My idea was that the the cause of this was that the module was drawing to much power from the arduino.

I tried to resolve this by using a separate powersupply (9v battery with L7805CV) to power the WT5001M02-28P and use the following wiring between the arduino and the WT5001.

Arduino WT5001
GND ------ GND
PIN1 ------ Pin 17
PIN2 ------ Pin 21
Pin 18 ------ 5V +
Pin 23 GND

When using this pin layout and connecting the ground of the Arduino and the Module i hear some noise when the sample is started to play but then nothing anymore.
If i remove the ground connection between de Arduino and the module and move pin 18 of the module to the Arduino 5v pin it works fine (apart from the cut-offs).

Is there a good way to separate the powersource of the arduino ?