Teensy 3.6 + Audio Shield huge noise

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zioaxiom

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[SOLVED] Teensy 3.6 + Audio Shield huge noise

Hi guys,

I'm having an issue with Teensy 3.6 and Audio Board. I stacked them one on top of each other and loaded one of the example projects.
Teensy is USB powered (dedicated and powered dLink USB hub), audio from analog out.

Here's what I get...
https://www.dropbox.com/s/vx0ojei06qtaqu8/Teensy36AB_Noise.wav?dl=0

I'm totally new to this, so may I ask you an advice about that? I supposed this should work straight away.

Thanks!
Luca
 
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Hi guys,
yes sounds like a ground issue to me too, but that's new to me since I work with audio professionally every day and never got such issues.

Here are a couple of pics of my boards.

IMG_0457.JPGIMG_0458.JPG

Thanks,
Luca
 
Is the audio adapter plugged in all the way? Picture 2 sure looks like either the pins are really long or it is not pressed in...
 
Thanks Paul! The ground isolator totally fixed that. Since I'm planning to develop an external fx, it would be advisable to use those same kind of transformers on the board?

Thanks,
Luca
 
I have a similar issue with the Teensy 4 and the new audio shield. When I attach it via USB to my Mac the sound is horrible. I got myself a ground isolator like in the link. That improves the sound tremendously but it still is plain bad. Lot's of noise. Since I was planning on building a USB MIDI synthesizer around the Teensy I would be very glad to hear if there are any other proposals of what I could do. (The general audio quality and especially the horse power of the Teensy 4 is really great for such a project).
 
Hi Frank, thanks for your reply. But I wrote "I got myself a ground isolator like in the link." which means I read those and bought the isolator which helps only somewhat. The result is by far not good enough for a synth.
 
Yes, the shield is soldered. No cables except for the USB cable and now the ground isolator.
EDIT: When I use the USB only for power and connect to a USB wall wart then there is not noise at all.
 
Ah, OK... hm.. in this case, I can't help.. (Have you tried a USB Hub?)

@Paul?


edit: self-powered USB Hub?
 
Thanks a lot, Paul. I will try that as well. It would be a shame if I could not use the Teensy 4 for that project. With the audio shield t is such a nice and powerful board for that purpose!
 
So finally I got the USB isolator. It improves the situation a bit more. Still when connected to the computer over USB unfortunately the sound is far from the great sound I get when just connecting to a power supply.
 
Hello Paul . Just yesterday I realised that teensy 3.6 has no connection from shield of headphones output to any ground. That was making a lot of noise for me, when I was trying to listen from headphones while I was transferring audio using usb or line in. I tried to connect the shield from the headphones out to any ground pin to hear the result and fortunately I am so happy to tell that the ground noise disappeared when I attached the cable from headphones shield to GND pin (when I attached the cable from shield to Analoge GND creates an other kind of ground loop noise). I am so happy that I have crystal clear sound with absolutely no noise from 3.6 without buying any ground audio or usb isolator . I can not measure the SNR percentage, however I can tell that in my ears is not recognised any noise from this board . Thank you Paul ! I am in love with Teensy boards, they are so powerful .
 
Hi Antonis, that sounds interesting. Which pin are you talking about exactly? Are you talking about the VGND pin on the audio shield where it says "caution: do not connection VGND to GND". Or some other pin? Thanks!
 
Hi Antonis, that sounds interesting. Which pin are you talking about exactly? Are you talking about the VGND pin on the audio shield where it says "caution: do not connection VGND to GND". Or some other pin? Thanks!

Hello Stevie. Yes I took the risk to connect VGND to GND. You can see to this photo the black wire that does this connection https://imgur.com/a/jEoYzgd . This is the project that I am about to finish and I fill so proud. https://imgur.com/MSWCCxb This is the first time that I am building something so big. With Teensy boards I fill that I am living in since fiction movie.
 
Hello Stevie. Yes I took the risk to connect VGND to GND. You can see to this photo the black wire that does this connection https://imgur.com/a/jEoYzgd . This is the project that I am about to finish and I fill so proud. https://imgur.com/MSWCCxb This is the first time that I am building something so big. With Teensy boards I fill that I am living in since fiction movie.

I have to ask, considering that it says "caution: do not connection VGND to GND", did you experience any downside to making that connection, other than shame or defiance?

And can anyone explain a reason (other than simply citing the glaring caution warning or the attached datasheet pdf warning) why to not connect VGND to GND?no-vground.png

Also looking at the datasheet I'm noticing the Audio Adapter schematic corresponds to their "Capless headphone design" show in the datasheet's 1st application example:

capless-vground.png

While instead their 2nd example is "Cap-coupled" with 220uF on L & R, and with the audio jack using common ground instead of VGND:

cap-coupled-common-ground.png

So if I were use a separate audio jack connected to common ground, and solder 220 uF capacitors in series with both the L & R outputs, then should I expect less noise on the headphone output?
 
To answer my earlier question why there is this prohibition, a quick google search leads me to another product's application note which says the reason is because a high current between the grounds could damage the codec:

View attachment 22257

Did you experience any damage or degradation to your synth's headphone output sound quality after using your hack of connected VGND to GND?
 
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