Hi,
Please review your posts.
I´ve merged both threads, because you didn´t respond to the first thread but started a new thread with a similar problem.
Both your posts discuss a problem of tying two supply rails together. Both your threads talk about 5V only.
--> similar problem.
Your information about different supply voltage obviously came after I have merged both your threads.
Merged thread or not... your information in post#6 is new information.
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Regarding your problem:
I assume the 5V ADC expects an input voltage of 0...5V from the pot (wiper). If you clamp the pot supply voltage to 3.3V, then obviously the 5V ADC can only see 0..3.3V.
Thus it´s input signal is limited to 0..66%. I assume this will cause problems.
There´s a lot of information missing, thus we have to guess a lot.
I assume the two effect devices do not work at the same time, they work alternating.. if so then an alternating switch could be used to select the effect device.
Klaus