Hi!
I am driving electromagnets with an amplifier board as this one.
alt text

What should I do to protect the audio out at the bela board?
I use an external power source(18V) to drive the amplifier board.

Cheers!
Joel

If the diagram is the one at page 11 of this document, that is:

alt text

then there should be no need for protection. However, that circuit is bogged in that there is a resistor missing from pin 1 of IC1 to ground. Make it 100k or something, but you have to polarize the + input of IC1. If you don't, then it MAY still work, if the loss current of C4 is large enough, but it's bad design, and very dependent on the characteristics of C4 (and also on temperature and humidity)

Actually scrap my observation on the lack of a resistor from pin1 to GND. Apparently the TDA2003 is supposed to be used like that.