A new home with ceiling-mounted speakers throughout the property is quite exciting, right until the point you see pricing for multi-zone amplifiers, or really any amp with more than just a few channels.
In the case of my patio there are just 4 speakers, wires terminating in a garage cabinet. Why buy a new amplifier when a spare car stereo has more than enough power to drive 4 ceiling speakers?
Power Supply Hassle
While 12V DC is readily available from many sources, what I had on hand was a scavenged Dell power supply. Pulled from a small form factor Optiplex desktop, it used a non-standard and undocumented power connector. Luckily some angry users on the Dell forum already did the legwork to identify the pins1:
The main thing to note is that the power switch circuit must remain closed; from what I recall this is not consistent with standard ATX PSUs that only require a momentary signal to power on.
With the pins identified, the connections can then be made between the power supply, switch, and head unit; 12V to the stereo, Power On to the switch, and ground to both.
Stereo wiring harnesses will usually include both a yellow and a red 12V input line; the red cable (ACC) is intended to be high only when the vehicle’s ignition is active so as not to run when the car is off. For this usage, because the power is switched manually, these can both go to the same 12V line from the power supply
Mounting the Unit
I’d originally planned on using corner braces or fabricating some other means to mount the head unit to the underside of the shelf, but in interest of keeping a clean look I decided to try this universal under-dash mount from Scosche.
The enclosure is very simple and required no modification outside of drilling a hole for the toggle switch.
Constrained by the connector position and length of the wiring harness, it was not feasible to mount the enclosure to the shelf without first connecting the stereo:
With everything mounted in place, cables can then be cleaned up and outputs labeled:
Finally, the shelf is returned to its home and each of the speakers connected: