Is this what everyone with separates is going through or building a timer circuit like you mentioned. I find it hard it hard to believe.
I’ve been using the vintage Adcom ACE-515 for decades, which accomplishes the on and off power sequencing. You can readily find them used on ebay pretty cheap.
The 515 has two power cords – one heavy-duty that plugs into the wall, and a second “sensing” line that plugs into the switched convenience outlet on the back of my receiver. When the sensing line gets power (when the receiver is turned on), it activates the power sequencing and delays the amp power-on for 10s. When the receiver is turned off, it delays the power-off to the amp for 30s.
Your Marantz doesn’t have convenience outlets, but you could use the 12-volt trigger to switch a power strip, like the one linked below. The Adcom’s sensing line would plug into that, and it would work as I described above.
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www.adafruit.com
Regards,
Wayne A. Pflughaupt