I've got a battery powered synth that uses two 9v batteries to make a split rail power supply (±9 and ground). I'm trying to use a regular AC-DC power adaptor to replace the batteries. The adaptor outputs 12v and I'm regulating it down to 9v with the LM317 voltage regulator. To get the required -9v I'm using the ICL7660 CMOS voltage converter. The problem I have is with the noise created by the power supply, when i hook up the synth it works, but there's some oscillations and artifacts on the audio output. Does anyone know if there's a way I can filter out this noise?
here's the circuit so far -