They can be connected directly to a mixing console or other low-level audio signal source without the need for an external amplifier.

However, external linear amplifiers are often used illegally.

It plays through two smal internal speakers or through an external amplifier.

These speakers include their own amplifier, making the customary external amplifier or receiver unnecessary.

A 3.5 mm stereo jack provides output to earphones or an external amplifier.

In this case, an external push-pull amplifier can be controlled by the current into and out of the operational amplifier.

Some of the others were apparently designed on the assumption that external amplifiers and speakers would be used in the home.

C series: Mainstream (external amplifier) (not available in the US)

However, this model can also be connected to external trunk-mounted amplifiers if higher wattage is wanted.

Passive subwoofers have a subwoofer driver and enclosure and they are powered by an external amplifier.