I am always puzzled by quotations of tonearm effective mass. Let’s assume 14.5g is the effective mass of the tonearm plus its OEM headshell. To this value, one has to add the mass of the cartridge and mounting hardware. In the case cited, that would be the mass (weight) of a Denon 103, which is a rather heavy cartridge as cartridges go. Furthermore, many of the many mods available to the 103 will further increase its mass. So let’s say the 103 weighs at least 10g. That’s a low end estimate. Then let’s say the mounting hardware adds 2-3g. In this case, you only need to add 3-4g to the ensemble to achieve a 30g total effective mass. Probably you wouldn’t need to add any mass over and above that of the DL103 plus hardware, because probably the DL103 weighs more than 10g. Then there’s the counter-weight.
