Problem with adapter for using a Rev. B audio shiel with a T_4.1 (for MicroDexed)

[C0d3man]

Hi,

I made an adapter board for using a T_4.1 as a replacement for the T_3.6 on my TMA boards. This adapter maps the used pins to new destinations - especially the I2S pins.

Everything works (encoders, I2C display, MIDI-I/O) but the audio seems to have problems. I am getting much strange noise when starting up. When recording via USB-Audio everything sounds fine, only on audio out there is strange noise (with played notes in the background).

Pin assignment is double checked and with the T_3.6 everything works fine.

I am using a Rev B board. So my predefined answers are:

[ ] Your I2S signals may be garbled by your PCB routing and the adapter.
[ ] You really need to add a 100 Ohm resistor into the MCLK line for a Rev A or B audio board.
[ ] You idea, throw everything away and do something you know about.

TIA, Holger

[PaulStoffregen]

The 100 ohm resistor is absolutely required with Teensy 4.0 & 4.1, even if the wires are short.

[C0d3man]

The 100 ohm resistor is absolutely required with Teensy 4.0 & 4.1, even if the wires are short.

Thanks, Paul. So I will try to add one to my adapter board.

[C0d3man]

Thanks, it works fine with my patched Adapter:



More questions:
- Do I need this resistor also for Rev C boards? is it problematic if the resistor is also used for Rev C?
- Can/should I add the resistor also for Rev A/B boards when using a T_3.6?

My T_3.6 has some quiet noise in the background wchi the T_4.1 does not have...

Regards, Holger