I've found that Denon 103 is too light for SPU headshell. RMG 309 has a ocunter weight that can add up to 6g. The tonearm will balance at 32g headshell/cartridge. So, if the tracking force is 2g, the headshell/cartridge combined weight has to be at least 28g.
Even with heavy headshells like Orsonic av101 (16g), it would be very hard to find cartridges at 12g or more.
So, a 32g (28~33g) SPU cartridge would be a must for Ortofon RMG 309 arm for cartridges less than 12g. The only other choice would be to add a metal block (5~10g) on the headshell.
A quarter coin (5.67g) would be a good choice if the headshell has a big flat top.
Even with heavy headshells like Orsonic av101 (16g), it would be very hard to find cartridges at 12g or more.
So, a 32g (28~33g) SPU cartridge would be a must for Ortofon RMG 309 arm for cartridges less than 12g. The only other choice would be to add a metal block (5~10g) on the headshell.
A quarter coin (5.67g) would be a good choice if the headshell has a big flat top.