Preventing Speaker Pop When Switching on Teensy 3.2 with Audio Adaptor

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lerxstrulz

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Hi All,

I have a Teensy 3.2 that is connected to the Audio Adaptor and have cut the Vin/VUSB pads and am powering it with the Trinket LiPoly backpack from Adafruit. There is a switch on the Trinket that lets me turn the Teensy on/off (when the USB is connected it will charge the battery, or with the switch on it will charge the battery while it powers the Teensy.) Whenever I turn the switch on, there is a pop sound on the speaker and was just wondering if there was a way to prevent that. I was thinking a small capacitor on the switch, but not sure that would do it. Any help appreciated! Thank you!
 

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A capacitor on the switch would make the Teensy’s supply voltage go up slower, too, and create other unwanted effects. The pop comes from loading the 2.2uF capacitors at the line outputs to 1.65V (3.3 / 2).
As good HiFi equipment does, you should think about using a relay to enable outputs only after all voltages have stabilized after powering the circuit.
 
A capacitor on the switch would make the Teensy’s supply voltage go up slower, too, and create other unwanted effects. The pop comes from loading the 2.2uF capacitors at the line outputs to 1.65V (3.3 / 2).
As good HiFi equipment does, you should think about using a relay to enable outputs only after all voltages have stabilized after powering the circuit.

I'm using the built-in speaker port, so I don't think I have the ability to add the relay? For the line-out I could do that. Thank you!
 
Maybe there's an amplifier between the audio board and your speaker? The audio board is really only able to drive headphones...

Many modern amp chips have a power down mode and a way to go in & out of power down mode without causing a pop. Those techniques usually require half a second or more, so they can't usually be done when a switch simply turns off the power. Usually the code needs to know you've changed the switch and do the procedure to shut down without a pop sound.

Of course, this is a lot of assumptions without knowing about how you're driving your speaker. Such details matter...
 
Sorry yes I am just connecting a 3.5mm cable from the headphone port to a powered speaker, so now am thinking it's on the powered speaker's side.
 
Here is a video where you can here the pop when it is turned on and off.

https://youtu.be/KPCN3QVxX-o

I have the Trinket LiPoly Backpack connected to the Teensy like so (Vin/VUSB connection is cut as specified):

Bat pin to VIN on Teensy
5V pin to VUSB on Teensy
GND to GND

The speaker is a 10watt powered speaker connected to the headphones jack. The battery is a 350mah LiPoly.


So I'm wondering if it may be that the speaker is powered? Or maybe I should wire up the Line-Out and use that? Is it because the headphones jack is powered? It's not really a show-stopper, though ;)

Thanks!
 
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