Hi all, I'm planning on building the very simple phono stage as a first audio diy project. The schematic is here: http://phonoclone.com/diy-pho5.html It says that R1 should be set relative to the cartridge manufacturer's value. Is it possible to substitute a potentiometer here so this resistance can be tuned as different cartridges are used? What does it mean that there is an optional capacitor? Finally, I'm a little worried about noise from my power supply (a wall wart from the thrift store). Is there a way to add a filter to the power supply to clean it?