I thought the fourth pin on the photos is a loudness tap but the pin is just a part of the casing. Left/right channel measured with multimeter and there is a difference between two channels.
Seller F***ing m0r0n!!! on page 8 type of resistor - PAGE without selection - DISCRIPTION without selection - winthou any question send RANDOM resistor i need 1k, he send random 4.7k.