Hi,
i have a question: i bought my k4003 amplifier and assembled it, but now, iwant to buy the K8084. In the description of the k8084, i see you can change resistors to weak or to amplify the input. I want to connect the k8084 to my k4003, what resistors do i need to use ( it says that you can change R2 and R4 and R21 to R24). I want to be sure i have a good sound quality before i buy it…
greetings
No need to change the resistors.
second problem:
i want to connect my k4003 and k8084 to one transformer. It’s a ring transformer with 2 grounds (from 2 wires to 4 wires). On the k4003, i can connect the 4 wires. But on the k8084, i can only connect 3 (there are 3 connection points). For the k8084, what do i have to do with the 2 ground wires that i have on the transformer?
greetings
The two points ‘GND’ on the K4003 are electrically connected, so they are only 1 point.
On the K8084 it is called ‘0’.
yes, i know that, but i want have two grounds on my transformer (velleman 5012). For the k8084, do i need to connect the two grounds (the two ground cables from my transformer) to eachother and conect it to the ‘0’ on the 8084?
Yes.
okay, thank you very much for the help 
i’m sorry i have a lot of questions that aren’t very difficult, but i’m a noob at those things and i want to make it work 
greetings
i have finished my amplifier, but i have one more question:
i have soldered the LED with 2 small wires to the PCB, but if i switch on the pre-amp, the LED doesn’t work… All the rest works fine. How is this possible? the wires have a good connection. Maybe, if you look to my video, you can tell me what’s the problem? In the video, you’ll see the 2 wires (red and black) from the LED. I soldered the red wire to the longest pin on the LED and the black to the shortest. I really don’t know why it doesn’t work…
Greetings
You connected your red wire on the PCB with the NEGATIVE point of the LED (flat side = cathode = negative) and the black to the positive. Switch the position of these wires on your PCB and your LED will work.