dudu-lai
I have not measured the exact delay with a multimeter yet, but based on behavior it does look like the AMP control line is enabled a few seconds after startup (approximately 5 seconds), as described for this MCU version.
Also, after cold boot, there is usually no pop at startup, so the delayed AMP enable seems to be working in that scenario.
However, the popping still occurs in two other cases:
When turning ignition off / powering down the head unit
When dialing a Bluetooth phone call
Important additional observation:
Sometimes after switching ignition OFF, the head unit stays powered ON for a few seconds and then shuts down.
In those cases, there is no pop at all.
But when the head unit powers off immediately after ignition OFF, a pop usually occurs.
This strongly suggests that the popping depends on the shutdown sequence timing, i.e. whether the audio path / DSP is muted before the AMP control line goes LOW.
Regarding the audio signal type:
I am using the analog RCA line-out from the Dudu7 directly into an external amplifier (Pioneer GM-6500).
No optical or digital audio output is used.
So my impression is that:
on startup the AMP delay works as intended
but on shutdown and during call initiation, the amplifier may still be powered ON while the audio output or DSP state is muting / resetting, which produces the pop.
