Q: I want to connect a line-level signal to a mic input. Will this work?
A: Mic levels are much lower than (typical) line-level signals. This means that any equipment designed to work only with a microphone as an input may be overloaded when you hit it with a line-level signal. The likelihood of this varies widely so it’s always best to try it first and see what your results are.
If you do find the input distorts, and there is no way to change the input level of the mic-level device, then your only alternative is to lower the output of the sending device. There are a couple of ways to accomplish this:
1. If possible, simply turn down the output of the sending device until the receiving device stops distorting. This has the advantage of being easy (and free), but can also compromise the signal-to-noise ratio of your signal.
2. You maybe able to assemble various level-matching devices to make the whole thing work — for example, a line-to-instrument level re-amp-type device feeding a direct box, feeding the mic input.
3. If neither of these does the trick, then plan C is to buy or build a pad to put in the signal path to lower the voltage of the signal coming in.