The problem with L-DOPA is that most if not all of it is normally broken down in the gut, outside the brain, and therefore unless you take truly massive doses it won't effect brain dopamine levels.
When it's used in Parkinsons therapy a second medication like carbidopa is also given, because it blocks the metabolism of L-DOPA outside of the brain, so that instead of 1-5% becoming dopamine in the brain and the remainder going to waste, now 80% or more does.
So basically, if you are taking L-DOPA and not taking a DOPA decarboxylase inhibitor too, I think you're gonna need to take doses of 50-100g a day to see major changes in dopamine levels inside the blood brain barrier.
5-HTP actually has the same problem: most is metabolised outside the brain.... amino acids are a little more complex than people give them credit for