Is grounding with RCA is safe?

Hello, 
I would like to ask if grounding with RCA is safe? What I have done is I solder one end the wire to the surround area of the RCA male plug (not to it's core) and the other end to the ground prong on the 3-prong male AC plug. 

Then I plug the RCA male plug to a female RCA  on pre-amp , amplifier, DAC and the AC plug to the wall. 

I can hear the sound quality improvement and want to leave it like this. 

My question is if this setup is safe for audio equipment? 

Thank you. 

Huy