17a Pass surrounded by mixture of clay and chalk (7)
?a?????
20a Briefly putdown detective falling short in both cases (4)
I think it's starts with Jo(t)
21d fancy harp on nearly outdated machine (6)
O?p?a?
Only word I can think of is orphan. Dosent make sense
17 and 20 are thematic ones. 17, you need a three letter word for (mountain) pass inside a word for clay and chalk mixture.
20 is Joey....easier just to tell you.