When I connect the effect pedal to the same wall wart feeding the 9v to 5v converter feeding the Arduino (using a Y adapter for effect pedals), the noise is so bad I can't even hear the guitar signal anymore.
I assume I should place ferrite beads on the 6 lines going from the Digi-Pots to the effect pedal PCB,
Sounds like you have grounding problems. Have you connected the grounds together of the two systems?
The problem with effects peddles is that they often have what is called "ground lift" resistors fitted. This means that the signal ground for the audio is not at the same potential as the ground for the electronics of the peddle. I faced that problem when I built a common power supply for five assorted peddles for my son. In the end I had to make a separate mains power supply for each peddle built into a box.
Without a schematic for the peddle it is hard to be definitive as to what to do. The simplest solution might be to have two isolated power supplies and opto isolate the digital pots, but I appreciate that is not the most elegant of solutions.
Remember my earlier comments on the floating earth which i suspect your pedal employs.. so I suspect you'll need a floating psu.What does the noise sound like ? Hum ? hiss ? warbling?Allan.
So does this mean I need to configure a floating power supply connection for the Arduino setup?
How can I accomplish that by tapping into the 9v alread going into the effect pedal
2 wallwarts are a pest, but not terribly expensive.
He recomemded to try upping the input voltage to 12v, and using a 7809 voltage regulator for supplying 9v to the pedal's PCB and a 7805 to supply 5v to the Arduino.
Googling "isolated DC to DC Converter" is coming up with lots of results. Is there an IC I could use for this, or is it more complex than that?