The variation in loudspeaker impedance is a consideration in audio amplifier design. Hypex Electronics is a Dutch electronics company, known for its Class D audio amplifier modules. The premier cover shows the assembly of a Heathkit A-7B audio amplifier. This situation is mostly encountered in the interface between an audio amplifier and a loudspeaker. After the detector, it goes to audio amplifier. In the plane radio transmitter S203 was swapped against the audio amplifier S207. The extracted signal is then amplified by the audio amplifier. One such application is the power supply for a hi-fi audio amplifier. In public address systems it is amplified by an audio amplifier. In addition, Monolithic Power Systems manufactures class D Audio Amplifier products. The practical amplifier circuit shown above could be the basis for a moderate-power audio amplifier. In 2015, Korg released the Nutube, an analogue audio amplifier component based on VFD technology. This signal was fed into an audio amplifier and played back by a loudspeaker. It was commonly used as an output audio amplifier in tube TVs and radios. Receivers, sharing a common audio amplifier, included a short-wave, long-wave and beacon.