I'm using 2 multiplexer chips (both 74HC4051) to switch between different analogue guitar effects powered by a 9V battery. http://playground.arduino.cc/learning/4051
The resulting problem is a loud low digital hum/buzz with about half of the effected signal also going through (can hear guitar playing). Maybe a Ground Problem?
I've tried using both separately and they are both working on their own. I'm certain the 9V shouldn't be a problem as it works using 1 multiplexer.
The Select Lines are wired together on each multiplexer as I want the multiplexers to be switched together so i'm still using 3 digital pins (8, 9 and 10) using digitalWrite to select y0 to Z for both multiplexers. Also declaring 3 variables (s0, s1, s2) and pin modes (8, 9, 10). Very simple code.
Setup: Input Guitar Jack > Z Input (Multiplexer 1) > Y0 > EFFECT
Y0 Input (Multiplexer 2) > Z Output > Output Guitar Jack
^ This should mean that the first multiplexer acts as a demultiplexer which I shouldn't think would be the problem as it's the same problem using y0 as guitar input jack and Z as output to effect input.
I have got 1 multiplexer working with NO HUM/BUZZ so I have:
Input Jack > Circuit > Potentiometer Volume Lug 2 > Z (IN) > Y0 > Output Jack
Using a simple circuit like this: http://www.beavisaudio.com/techpages/HIW/HIW.png
multiplexer wired like so: Vcc - 5V S0 - Digital Pin 8 S1 - Digital Pin 9 S2 - Digital Pin 10 Vee - Grnd (Arduino) E - Grnd (Arduino)
(using same code as above)
Although I've tried different circuits and it's the same problem so must be to do with the multiplexers.
Would massively appreciate if someone could help me out and am happy to give more information.