I am trying to make a PCB for the attached schematic (mixer.jpg). Rather than run on 2 9V batteries, I would like to plug it into the wall using a +9 / -9V DC power supply.
Do I need both diodes and capacitors (D1, D10, C21, and C22 in the attached mixer schematic 1.jpg) near the power supply? Or do I only need 1 of each (D1 and C21) as in mixer 2.jpg?
Not sure if both diodes and both caps are necessary when batteries aren't involved.
Thank you for your help!