A simple suggestion is to try reducing the volume on ALSAmixer to a lower level (in the white usually). Alsa has a funny way of causing issues with some speaker types if the audio level is set to 100%, although this usually only occurs on less-common devices such as outboard sound card or wireless headphones. Worth a try though!
The “digital noise” you heard was probably a dry joint on the I2S “Frame Sync” pin. I found this out the hard way yesterday, when I spent ages wiring every ground pin to my test rig (a pHAT BEAT) trying to eliminate a horrible noise issue, and then realised I’d forgot to hook up the “Frame Sync” pin at all. facepalm
@jcmjcm This “diminished” sound is different issue as far as I can guess. It could be a dry joint in the signal path between the AMP and the Speaker itself, or possibly sub-optimal soldering of the speaker to the pHAT.
I ordered a new Speaker Phat yesterday (together with some other toys that fell in my shopping cart!) Received this morning, so fantastic service.
I tried the speaker from the new kit with the old board and can confirm that the volume was back to the original level.
So it is the speaker that has failed.
How can I get the original replaced?