Audio board is making strange sounds!

[letNic]

Hi everyone,

I received my Teensy Audio Board yesterday and immediately solder the (optional) mic and volume knob.

This morning I start to work with it mounted on a Teensy 3.6. Strangely, on top of the music (from the MicroSD card), there’s a rapid note parasite, like a synth sound, the same note repeating forever. When I turn down the music’s volume at 0, the “parasite” is not affected and doesn’t stop.

It is related to the MicroSD card control. For example, when I load the Hardware_Test script (Tutorial Part_1_02), there’s no parasite. It’s just and only in scripts where MicroSD card is involved. I tried using different MicroSD card and also the Teensy’s onboard MicroSD connector (selected in the script) and it’s the same parasite again.

(If it can help, I can upload a recording of that “parasite”?)

I thought that maybe it’s the Teensy’s CPU speed, I don’t know. For now, it’s 180MHz.

Did you ever encounter that kind of issue?

Thanks for your help!

 

[PaulStoffregen]

Did you ever encounter that kind of issue?

Yes. In fact, there's a problem called "ground loop" that's so common we sell this part:

https://www.pjrc.com/store/audio_ground_isolator.html

The first thing to try is listening with headphones, and disconnect everything that has a ground connection other than the USB cable you're using for power. If the problem remains when there's only 1 ground connection, then it may be some other issue (and this ground isolator would do no good).

 

[letNic]

Ok! I think I found the culprit.

There’s a power loop between USB cables and the Audio Board’ 1/8” output.

My amp speaker is taking its power from USB. So when both are plugged in the same computer and an audio cable is plugged from the module to the speaker, it générale a high pitch tone (the “parasite”) ONLY when a Micro SD contrôler is involved in the script (that’s very funny !!!).

- using headphones takes me out from the circuit, so there’s no parasite.
- when the audio is plugged in the speaker, if I pull out its USB cable (there’s a battery in it), the parasite stops immediately and only the music can be ear.
- when they are both plugged in the same USB charger, the parasite appears.

It is effectively a loop.

Workaround solution: don’t plug the Teensy / Audio board AND your speaker in the same USB power source.

Electronically, I can’t say why this happening, but we can say the problem is solved here.

Thanks for your time