This is follow up on my prevoius thread on the restoration of my EKO Tiger P61 organ. I gave up on fixing the original sound generation board as more components were failing and couldn't find replacements. Now i am generating the sound with an stm32h723 mcu and a max98357 i2s amplifier, powerd by a LM317.

I can't figure out how to connect the differential signal output of max98357 to the power amplifier i have rescued from the organ. All the ground paths in the attached schematics are common.

What i have tried so far:
1. Left the input of the power amplifier floating results in loud noise like wind blowing.
2. Connected the input of power amplifier (66) to ground results in silence.
3. Connected the input of power amplifier (66) to my phone's output results in clean and nice sound.
4. Connected the output of max98357 directly to headphones results in clean and nice sound.
5. Connected the input of power amplifier (66) to the positive outout (91) of max98357 results in loud noise like wind blowing and low volume of wanted signal.

What am i doing wrong at 5. and how should i debug this and connect it correctly?
I assume i should shift the positive output of max98357 to negative in order for the power amplifier to function properly. It that's so and if would fix my problem how could i do it?

 

Gave up the idea, no longer an issue.

Please delete this thread