Tips for debuging

To check if any noisy is gettting into your amplifier board, just use any voice recorder program. You should hear the noise. If present you can try (for testing) shielding the circuit with aluminum foil. You may also try, at your discretion, a 0.1uF jumped (by hand) to ground at specific points of the circuit (i.e. power supply lines).

For more serious debuging you may use an osciloscope. If you do not have access to one, you can use the sound board as osciloscope (and audio genator) with this excelente program at https://www.zeitnitz.eu/ (MY CONGRATULATION TO THE AUTHOR for the excelent job).

With this scope if you make a jumper of the sondboard, input to output, the waveform should mach perfectly in fase at the most horizontal expasion. If not "Huston we do have a problem" (Apolo 13, for those of you too young).

Integrated circuit such as PC2902 made by Texas, do not have two separate DACs, as one would expect. It use a tecnique known as multiplex, read left and then right channel and so on, done twice of the specfied sampling rate does not cause any problem for the intend application (sound). However for ASA is a hell of a problem. The program has to be modified to acomodate this and works just fine, The source code for this IC is placed on the download area. IT SHOULD ONLY BE USED FOR THIS CASE.