For some time, I have been using a small audio amp with my MP3 player in the truck, but I have been using alkaline cells for power. Now, I would like to power the amp from the auto power supply. The amp circuit is rated for up to 18V. Do I need to take some precautions to protect the amp from noise and load dumps, and if so, what? Thanks.

 

If we had the instruction booklet or datasheet for the AMP it would be a great help.
Do you have a Model Number?

 

The amp that I have been using is based on the LM386 and is homebuilt. The schematic is attached.

However, I am thinking about upgrading to a version of the TDA7297 amp in the second schematic.

 

I had a look at the datasheet and there are no specific recommendations.
I see there are different versions most with an absolute max voltage of 15V and the LM386N-4 with 22V

If it were my amp I would simply drop the input voltage on the 12V+ side 0.7 V through a 3A diode (3A to future proof for higher loads) or better still 1.4V with two in series. This will keep you well clear of the 15Volt limit
Then a simple lowpass filter made from a suitable 100μH series inductor and a 0.22μF capacitor should filter out any line-born noise.

If you still get noise you could try increasing the capacitor value

 

Do I need to take some precautions to protect the amp from noise and load dumps, and if so, what? Thanks.

A lot of folks use a 7812 regulator to smooth things out. That just leaves the big stuff to worry about, spikes and whatnot. A 15v zener on the input maybe?

If you want to use valuable electronics, I might look more into the problem but in my limited experience, things seem to survive just fine without extraordinary measures.