Some of the advantages of Class D amplifiers are their reduction in size, weight and power consumption, reduced power dissipation (heat), removal of a small heat sink because of high efficiency ratings of >90%, and a smaller power supply due to reduced power consumption. Disadvantages include: high EMI levels; frequency hopping or switching for AM reception; wiring to a loudspeaker can act as aerial (high order filtering); and the required PCB space. In addition, Class D circuits require careful PCB layout techniques.