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Topic: Audio noise caused by a micro servo (Read 2 times) previous topic - next topic


I have built a wireless pedal board. I can now control my amp and my effects from switch panels taped on my guitars.
Effects are located in a box and connected to my amp by short patch cables (mono 1/4 jack).

So I tried to add a new function, kind of programmable volume control by using a micro servo. 
I have chosen this el-mechanical solution because I didn't want to modify my amplifier.
I was afraid that two sided tape wouldn't be strong enough to hold servo in position and worried about hundred other things.
See video clip: http://youtu.be/yxiDniBHDig
Both mechanical transmition and arduino sketch turned out to work perfectly but micro servo caused another problem:
Audio noise, a lot of audio noise, booming, buzzing and popping noise.
Not only from my amp but it affected PA and few other amps in the room.
(You can't hear the noise because I don't have a speaker cabinet at home so amp was off while I was recording video)

I wonder is there any way to prevent this noise... Maybe micro servo and audio equipment just don't work together.


I wonder is there any way to prevent this noise

Well if it electrical noise getting into the amplifier then good power decoupling will help suppress it.
Lots of different  techniques, you might have to employ them all.


And I'd say start with shielding the cable to the servo and keeping the Arduino and associated components in a metal box/enclosure and connect the case to ground.

There's likely to be RF pickup in the amplifiers from the logic speed and PWM signals flying around in unshielded cables.   Adding more
RF suppression on the audio amp inputs can help (100pF across audio input might help, though you really need to know the audio
input impedance to know what value capacitance is best.).
[ I won't respond to messages, use the forum please ]


Thank you guys,
I spent most of last two days reading about de-coupling. It makes sense but I never figured out how
to do it in my case.
If it was only my amplifier it would be clearer to me, but how to prevent noise in PA?
PA has nothing common with my amplifier and my pedal board. But it looks like the noise affects PA through main 240V AC power supply.
The building is old and probably bad electrical system but still...

I think I'll try to run my servo and arduino on battery and see what happens.
Then I'll try to experiment with metal box and shielded servo cable.

What do you guys think about battery as power supply for servo and arduino?

There are guitar tuning systems on the marked which run on the battery.
They're probably controlled by a microcontroller and driven by special servos. They don't affect amplifiers arround them.

Another critical question:
Let's say I run arduino on 9V DC buttery and my pedals are powered by 9V DC switch adaptor.
Can I still connect grounds together?



You apply the decoupling to the noise generating circuits, that is the arduino's power supply and the servo's supply, not the PA.
A battery powered solution will help but you will still need the decoupling components.

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