Teensy audio board schematic and simplified audio “board”

Dr Flywheel (aka Ron N7FTZ) has provided some details of the Teensy audio add-on board.  This is used in the upcoming JackAl add-on board expected to be available shortly, but can almost certainly be home-brewed by savvy constructors using the Teensy 3.6 and audio add-on board.

Here is the circuit diagram for the PJRC audio module:

The CODEC part is very much the reference design provided by the part manufacturer. The support for the EEPROM and the SD card is optional.

The libraries will be compatible with any SGTL5000 or for that matter a long list of other I2S compatible CODECs (look at the source code). If you are homebrewing an audio processor on the Teensy you should consider integration of the CODEC. The libraries will support the internal A/D-D/A of the Freescale ASIC with very few components (resistors, capacitors) added.

Sample resolution of 12-bits is sufficient for the type of audio DSP that we need, though the higher bit-rate CODECs are much better. It is a matter of cost effectiveness and board space.

An alternative simpler approach

 

Below shows mono circuits for a lower grade Teensy, however the circuit is the same for the Teensy V3.6 with the corresponding pins.

The input circuit (mono):

Here is the output circuit (mono):

Reference

Another audio pop mod

Joe VE1BWV provides another audio pop mod:

You probably will want to install a pop click fix to eliminate a loud pop whenever TX is turned on and off.   This circuit uses a 1N4148 diode, a 470k  or 300k resistor, a .22 or .44uF cap and a 2n7000 MOSFET.  Joe says this works amazingly well and mounts on the rear of the volume pot as indicated below (ignore the 0.1 uF capacitor).
Reference

Removing the audio pop on T/R

A mod developed by Gary N3GO (and required for Full QSK) also mitigates the Tx and Rx pop/thump noises in SSB mode.   This mod should work fine with the existing relays and with or without other mods, but has yet to be verified by others.