I'm building a unit which incorporates a small mono amplifier (TPA3116 D2 8-25V dc 100W) and various neopixel rings with a total of 77 LEDs.
I'm thinking of using a 12V power supply and a step-down converter to 5V to power the leds.
The leds at full power should use just under 5A at 5V.
What ampage should the 12V power supply be? Also 5A?
Thanks
Your sizing indicates you need about 25 watts of power for the LEDS (5V * 5A). A Buck converter is not 100% efficient; I generally use 80% as a rule of thumb, If they are greater fine. 25 watts *1.2 (efficiency of converter) = 30 watts so with the converter you will need 30 Watts. 30 watts / 12 Volts = 2.5 Amps. This tells us that any supply used must be able to supply 2.5 Amps or more at 12VDC, so your 5A device would be AOK!
If it works with the same supply, don't forget to add power consumed from your amp (well, your speakers)...
Thanks for the information guys. Much appreciated.
If you can split the 5V power for the LEDs into several sections of lower amperage, you'll be able to
use a few low-cost LM2596 buck converter modules. A buck-converter rated at 5A or more output
is likely to be more costly
Hi,
Make sure the power amplifier is connected DIRECTLY to the power supply with its own wires and does not share any gnd wiring with anything else.
This will help ensure that you will not be inducing noise from ground currents from the converter and LEDs into the amplifier.
Tom.... 
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