to be clear, the wiring advice I gave you DID indeed "help" to at least enable the slave module again to produce audio? Because previously you had stated
My master/slave wiring advice was intended to address
that problem (
there's no audio) and I believe this WAS helpful as such.
So what you mean by "
didn't help" is that your
noise issue remains.
The exact purpose of master/slave is a bit unclear to me. I have read this document
https://www.ti.com/lit/an/slaa787/slaa787.pdf which says the following:
Class-D amplifiers use pulse-width modulation (PWM) switching (450 kHz – 600 kHz), which are discrete packets of energy, to deliver large amounts of output power at a very high efficiency. However, issues can arise if multiple Class-D amplifiers switch simultaneously, but are not synchronized and managed. Issues include:
• Power Supply Overloading resulting from all amplifiers switching on the same edge, causing the supply to droop or sag below the regulated voltage.
• Beat Interference or Beat Tones are audible tones that occur when slightly misaligned switching frequencies interact to create another frequency.
The oscillator sync pins allow multiple devices to share a common clock and draw power on different phases to improve performance. Different phases reduce power supply loading during the switch cycles. Sharing a clock improves performance by preventing beat tones.
It seems that YOUR noise is not the type of issue that master/slave was ever intended to solve.
Having seen your pictures, the soldering around opamps and resistors (especially on one of them) looks unclean, perhaps even the board itself (traces) may be burnt. Have you thoroughly cleaned the places where you soldered (say with alcohol and Q-tips)? Can you try various combinations of boards/channels being connected/not connected to isolate this noise to a single channel?