なぜV 402プリアンプの背面にON/OFFスイッチがあるのですか?

理由は、この方法では、電源の背面に右のスイッチを持っているため、電源の前面と背面のスイッチに背面から主電源電圧を実行した場合に発生するであろうオーディオの干渉を避けることができます。

What is the purpose of the headphone amplifier of the V 402 Preamp?

For some users in special recording situations, a completely latency-free monitoring is very important. The internal headphone amplifier is useful e.g. for ensemble recordings. You can set up and finetune the main stereo pair or the position of spot microphones without the irritation caused by the latency of digital signal chains.

When recording a singer for a multitrack recording, latency free monitoring can be provided by using channel 1 for the vocal microphone and routing the DAW playback signal to the DI input of channel 2. Selecting the mono option, both signals appear in the headphone’s stereo center.

It could also be helpful to be able to listen to the pure microphone signal in order to check the influences of the subsequent signal chain.