XP needed to level up at 20 medium encounters per level:
Level / XP to Level
1 +1000
2 +2000
3 +3000
4 +5000
5 +10000
6 +12000
7 +15000
8 +18000
9 +22000
10 +24000
11 +32000
12 +40000
13 +44000
14 +50000
15 +56000
16 +64000
17 +78000
18 +84000
19 +98000
20 N/A
This should give more of a Classic D&D type feel, with PCs levelling after 20 medium encounters, or about 20 hours of play if there's an encounter every hour.
Level / XP to Level
1 +1000
2 +2000
3 +3000
4 +5000
5 +10000
6 +12000
7 +15000
8 +18000
9 +22000
10 +24000
11 +32000
12 +40000
13 +44000
14 +50000
15 +56000
16 +64000
17 +78000
18 +84000
19 +98000
20 N/A
This should give more of a Classic D&D type feel, with PCs levelling after 20 medium encounters, or about 20 hours of play if there's an encounter every hour.