Asked — Edited

Speaker / Servo Noise Help

Hey guys reaching out to you to see if anyone can help me trouble shoot this problem. Alan has a set of blue tooth speakers installed. Running them Bluetooth works fine. I had to hard wire them for a video I'm shooting. I plugged in a 3.5mm plug into the jacks for incoming audio to the sound card from my computer then Audio out cable from the audio card to the audio input for the speakers. The speakers are now picking up all the electrical noise generated by the neck servos. Here is a video displaying the issue. Any ideas how to fix this issue?

Thanks in advance.

Link to video


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What type of wire have you used to connect the speakers to the audio jack?

Is the cable shielded? If not, try that, it should at least help reduce the static and interference.

Reduce cable lengths.

Segregate cables (if they run close to the servos, can they be routed away from them?)

Ensure all grounds are good. If possible take them all back to the exact same point.

Others (Josh and Tony both spring to mind here) may know other things to check/try.


Have you checked going through "mixer" setting in the audio section setup to make sure the Aux input level control isn't turned up high or even all the way? This can happen if the microphone input is turned up too much as well (especially if you are actually plugging your audio input to the microphone input instead of the Aux input. You could also try reversing the wires going into the input audio plug.


As well as the suggestions above, a ground loop isolator could help. I use one in my car between my iPod and my stereo amp to eliminate engine noise, but they can also be placed in line between source and speakers.

Do you have a Fryes in your area? (I normally would have recommended Radioshack, but alas, they are no more....).



Will, All good suggestions above and should be explored. However I had this problem with my sound system in my B9. It would pick up all the motor noise, noise from the light controller boards and buzz when the Neon would flash. I could't find any ground loops, close or unshielded wires or any other reason for this to be happening. I found no way to stop it. After a lot of research and talking to a few Electrical Engineers at work I found that electrical noise travels on the grounds and nutrias. My solution was to add a second power supply and I moved my sound system to that one along with other "quieter" devices. If you go this route make sure all the grounds are matched with their own power conductors and running to the proper power supply. Do not run any common grounds between the DC sides of the power supplies. Remember that the electrical noise runs on the grounds. If your using AC-DC converters it's ok to interconnect the grounds on the AC side.

As a side note; You would want to run AC-DC converters in a parallel circuit, not series. Some think if they run these converts in series it will give you more amp available. Not really so. One converter will supply all the amps to the load and only when that converter is topped out will the other converter start feeding the load. unless you build or buy a complicated load balancing device to feed through this should be avoided. You always want to try to balance loading in a power supply system.

Hope this helps.


Fantastic ideas guys, what a way to wake up this morning. I will trouble shoot this afternoon!

The 3.5mm jacks may not be shielded. I purchased these very flat thin cables to get them thru the already crowded neck. I need two in the neck so getting shielded round cables might be impossible.

I'll start with the seperate power supply and if it's still noisy then I'll swap out the cables with shielded ones. Then go from there.


Please keep us posted. I'm very interested in your success. :)


Ok not sure if I "found out anything", but the problem is resolved.

My onboard speakers are simply those double amplified speakers you can connect you iPhone or device to listen to music. It has 2 inch speakers which fit the holes on ALan. When they are powered off and back on they come on with a medium volume as default. I connected one digital port to the volume control so I can control the speaker volume with it. So when the internal speakers are turned all the way up, and the line in is increased with my computer volume control, the noise on the line is obvious.

So by leaving the amplified speakers at the medium default level when turned on and allowing the computer alone to control Volume no noise on the line could be heard. The little speakers are some how amplifying that noise when turned all the way up?!? So with out shielding etc, I've got it working.


That's good. So it almost sounds like the speakers are the problem and are picking up the electronic noise. Are you saying that by turning them down half way you cant hear the noise? Sounds like it still there but the problem child is being kept quit. Nice work around.


That makes sense. The amplifier built into the speaker assembly is closest to the source of electrical noise and electrical noise, like any other "signal" simply becomes an input to the amplifier and out the speaker. Not to mention running off the same power source as the servo motors. Lots of noise can come from that path. When you turn the amplifier in the robot all the way up you amplify the noise as well as what you want to amplify. This noise is not present in the signal coming from the computer. By keeping that level lower and only increasing the computer input, you have made the signal to noise ratio better. The noise (static) is still there when the motor runs, you simply can't hear it now and the signal you want to hear overwhelms it to boot. Even if there is nothing coming from the computer at any given moment, the static noise from the motors in the robot is further suppressed by the sheer presence of the computer hookup. Sort of like the extra static you hear when a radio is not on a station.

EDIT I forgot to mention that the reason you don't hear motor static when you use the Bluetooth connection is that the Bluetooth transmission is specifically designed to eliminate interference from most sources (It uses a combination of FM transmission, Spread Spectrum, and Digital packet data exchange). When enabled, it overwhelms most noise sources. When you plugged in a cable, you shut off the Bluetooth and introduced a way for the motor noise to become overwhelming since then all you had was a regular amplifier. There are ways to ameliorate the motor noise (some have been mentioned here) but what you did is apparently good enough. Good work!


@dave, No, if i turn down the internal speaker volume then I can't hear the noise. It only happens when i turn the volume up all the way. By keeping them midway and control the rest of the sound with the volume control on the computer.

@WB, makes since on the BT. I look forward to going back to that after the video gets shot.


I'm still waiting for Alan to go on sale... is every thing still ok?


Will has been away working for the past 5 or so months on his "day job". I think he gets back home in a couple of months.