If I have to, I can link a pic of my convoluted setup, but I think my description of the circuit should suffice.
Edit - as a new user, I am only allowed to post a maximum of two links, so please go to the Parts Express website and query 120-040 for the AC adapter, and then query 320-612 for the amplifier modules. I’m using the power supply to power both amp modules.
I cut the tip off the power adapter and split the output with a 2 to 4 lever splicer.
I just noticed that the speaker buzz goes away as soon I power on the Bluetooth receiver, even if it isn’t paired. It does, however, have to be in receiver mode. If it is in transmitter mode, the buzz remains.
The source is either a Taotronics TT-BA07 Bluetooth receiver/transmitter in receive mode, paired to the same device in transmitter mode, or the same Bluetooth receiver paired to my iPhone, or the same Bluetooth receiver powered on and in pairing mode, or the same Bluetooth receiver powered on, just before it enters pairing mode.
https://fccid.io/2AFDGBAXX/User-Manual/15-TT-BA07-UserMan-pdf-2956728
The Bluetooth receiver then connects to a 3.5 mm audio cable, then to a coupler, then to a splitter. Each splitter goes to a 3.5 mm cable, which then connects to a terminal block panel mount connector. I wired one connector only to left and ground, the other to right and ground, and each connector goes into one of the two amp modules. I wired the two speakers accordingly.
Not high-fidelity system, but it was a fun proof of concept project to create a stereo system from two mono amps. It’s also an emergency power loss system, as I can easily and quickly swap out the power supply with two 9-volt batteries.
My audio cables are all shielded, so I’m assuming the multiple paths to ground are what is causing the speaker buzz.
Thanks