"소리가 크다" literally translates to "big sound", right?

Is the -ㄴ/는다 form not applied for adjective verbs in writing? A native speaker once explained to me that the ㄴ/은(past) 는(present) ㄹ/을(future) doesn't apply to adjective verbs which only ever use ㄴ/은

In written Korean, 은/는 is also used as a Topic Marker. You will notice that it is attached to nouns rather than adjectives.