Sure, I've seen all of that. And every time the two words "preamp output" or "preamp out" have been used to mean what you meant, they have either been capitalized or written as "the preamp output." Try substituting those tiny changes to what you wrote and see that the meaning is more clear.

You seem to be stuck on thinking that what you wrote could not have been misinterpreted, but it could. It's not enough for us to look at what we write and judge that we, who know what we mean, can understand it. Communication requires that we look skeptically at what we write, after having written it, to see if perhaps a person might not get what we're talking about. Omitting capitalization of terms usually capitalized is a way not to get the meaning across.

For that matter, did you read it after you wrote it, to see if it was clear?