Using Multiple Multiplexers - Problem (Switching Between Guitar Effects - 9V)


I'm using 2 multiplexer chips (both 74HC4051) to switch between different analogue guitar effects powered by a 9V battery.

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:

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.

Thanks, James

Sounds like either a missing ground somewhere, or a need for shielded wire somewhere. Hard to say without seeing a schematic and your wiring. Is the hum like 60/120/180Hz buzz? You can download Visual Analyzer and use a microphone into your laptop, use the spectrum analzer feature to see the frequency of the hum.

yes it’s 60hz buzz/hum and a slight oscillation, pretty sure it’s a ground problem as when I remove a ground connection the hum gets louder however I’ve checked and re-checked the ground connections and they should be fine unless it’s because there are multiple grounds (the 9v powered effect circuit and the multiplexer grounded on the arduino/powered by 5V).

Could it be current drain/Not enough time to get through each multiplexer?

Here is the schematic I’m using for the effect circuit:

And I have attached a rough schematic of the 2 multiplexers and Arduino, ‘Circuit 1’ being the above schematic: (sorry it’s hand drawn, the connections aren’t too complex though).

Any help is greatly appreciated,



All the Gnds need to be connected, not clear if you have that or not from your description or the schematic - best to resize those before posting to 900-100 wide, 2327 is too big. The mux chips need 0.1uf caps from their Vcc pins to Gnd.

What are the mux chips intended to be doing? Looks like you only use 1 channel on each.

Thank you very much for your help, I'm afraid the problem was very simple.

I'm quite new to Arduino, as you may have guessed and am not used to using multiple power sources in general and what to do.

The problem was that the grounds weren't tied together on my guitar circuit and the Arduino. I think i must have thought being scared by the requirements of the Arduino that nothing of the two circuits should crossover.

Thanks for you help,