In the case of the Fountek (and some other ribbons as well) the cap protects the ribbons from DC and also provides a better load to the amp. The transformer is almost a dead short below 200hz so this makes a cap mandatory.I will say that I've not had any ribbons damaged in the arrays including the older JP2 version. The CD2.0 has a different termination which is more robust so if my guidelines are followed everything will be fine.