How can you tell if the head unit output signal is to strong for the amp?

if the head unit can produce sound to your speakers without the amp you have high level output from head unit if your amp only accepts low level input (rca) plugs you must buy a high to low level converter which take speaker high output and reduces it to low ( rca) output and then go to your amp converter is under 20 bucks but most new amp accept hi and low level feed