The D.MODE switch on the KA15 is the switch for the desktop mode. When toggled to ON, the desktop mode is turned on. The KA15 will have more power, more gain. It is suitable for high impedance headphones and headphones which is not easy to drive.
When it is toggled OFF, the desktop mode is turned off. It is suitable for normal listening and low impedance headphones that are easy to drive.
Why setting desktop mode?
Traditional USB dongle will have a limitation on the output power in order to be adpated with the mobile phone. Especially for Apple phones, if the output power of the USB dongle is designed to be too large, which exceeds the power supply capacity of the LT port, it will lead to abnormal situations such as stutter and other abnormalities.
In fact, the TC port output current of most Android mobile phones is large enough. The desktop mode designed by KA15 is to give you one more option. When the desktop mode is turned on, the output power can be higher. When the desktop mode is off, it can be adapted to some mobile phones with small output current, such as Apple phones.
Therefore, the desktop mode is for users to balance the conflict between adaptability and output power.