Guitar Input to Teensy Audio Shield

T

TonyAme

Well-known member
Thanks for reading. I am working on making a simple guitar buffer circuit that will connect to the Teensy Audio Board Rev D. Is it ok to connect RIN and LIN together for the buffers circuit output signal? The audio output GND of my buffer circuit connected to the RINGND and LINGND? Or is it better to keep these pins separated?
(I won't be using stereo).
*Also. is it OK to connect the GND to AGND?
Sincere Thanks for any advice/help



TeensyAudioInputCircuit.png
 
Those pin numbers don't agree with the Audio Adapter pinout? Also there is no LINGND or RINGND on the adapter (audio connections are LINEINL, LINEINR, LINEOUTL, LINEOUTR), and you've shorted the two headphone outputs together which will be bad news. The headphone output volume is controllable on chip so an external volume control doesn't make sense.
 
MarkT said:
Those pin numbers don't agree with the Audio Adapter pinout? Also there is no LINGND or RINGND on the adapter (audio connections are LINEINL, LINEINR, LINEOUTL, LINEOUTR), and you've shorted the two headphone outputs together which will be bad news. The headphone output volume is controllable on chip so an external volume control doesn't make sense.
Click to expand...
I'm using Teensy 4.0 with the Audio Board RevD. I am only using LIN, LINGND and LOUT, OUTGND now.
Thank you.
Tony
 
MarkT said:
LINGND isn't a thing - there's GND, LINEINL, LINEINR, LINEOUTL, LINEOUTR.
Click to expand...
Right. I was going by what was printed on the actual pcb, there are 2 gnd connections one the for Line in Right and the other for the Line In Left? Then there is only one gnd connection for both Left & Right outputs? (I call that one gnd connection for both audio outputs "Audio Out GND".
Am I missing something?
Thank you.
teensy4b_audio_back.jpg
 
All those grounds are the same. Not sure if any specific connectors were envisaged, a dual row header could be used. Doesn't seem very logical to provide only one ground with the outputs (which have dual pads per signal), but individual grounds for the inputs.

What's actually on the PCB is "LINE OUT" and "LINE IN", which is close to the schematic names of LINEOUTL, LINEINL etc.

Note that the headphone output can only be used for headphones as it has a different ground voltage to the line inputs and outputs - its also a lot noisier than the line outputs.
 
Thank you. I thought that the GND in between L & R on the "out" section of the PCB was an isolated GND specifically for audio output. I assumed it was isolated from the digital realm of the PCB as a way to prevent potential noise. Looking at the schematic I can see they're all connected?
What is AGND used for?

Sincere Thanks,
TonyA
 
Hi,
I would recommend to reserve the unused channels. They can be used for send/receive as they are totally independent.
Also some variable gain at the input instead of a pure buffer can be helpful to improve s/n ratio.
Cheers Christof
 
cebersp said:
Hi,
I would recommend to reserve the unused channels. They can be used for send/receive as they are totally independent.
Also some variable gain at the input instead of a pure buffer can be helpful to improve s/n ratio.
Cheers Christof
Click to expand...
Thank you.
 
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