That makes sense. I keep forgetting about vassals. Should stop doing that...

Technically, most vassals would be using conscription to build their own armies, which they would then send to the king, unless they have the rights to a mine or other enriching ressource that would allow them to pay for their own little army and the upkeep of infantry and yeomen, but there are numerous methods of getting professional troops, and they could all be using whichever best suits their fancy unless the monarch decreed a universal method or there was some law passed concerning peasantry and citizenship and conscription during active war time.