mcp4921 crashing arduino

Hello,

i created a CV output for my midi sequencer. I get the wanted Voltage on Pin8 of the mcp4921. I connected pin8 to the tip and the arduino GND to the ring.

When I now connect the mcp4921 to my synth the arduino crashes.

When I remove GND from the plug it works like it should be, is it 100% neccesary to connect the GND and why does it crash?

thnx

EDIT: i had to put a 220Ohm Resistor between ground and plug, than it works fine.