I've searched hard but can't find a solution
I am using a smartphone as head unit. The 3.5mm output has 2 RCA plugs. The 2 RCA inputs are split to 2 el cheapo amps. One for front 2 x 5", one for back 2 x 6x9" The amp power is direct off the battery. The amp grounds are direct to the battery. When one amp is plugged in all good and quiet. As soon as I attach the second amp RCA input to the splitter (home made) I get buzzing through all the speakers. I have substituted the RCA cables so its not a cable issue. The gain setting does not have an influence. The amps both work and play fine, except for the buzz. Should I ground the RCA plugs on the input side since the phone is not grounded anywhere? Do I need to modify the split from the 2 inputs to the 4 outputs with some diodes or something. Any suggestions for a mechanically inclined dude?