As Jerry has advised, reducing the capacitor reduces some of the deep bass. In some of my adaptors I've made that capacitance switchable so that I can drop some bass when it's excessive or unnecessary.
But it's a gentle rolloff, not sharp. If you're looking for a sharper cutoff to eliminate your hum issue, you'd need to design a sharper filter, or use the HP filters built into your recorder or interface. Or tackle problem frequencies after, with a parametric EQ in your audio editor.
