Hello,
I'm about to calibrate my third U87 clone build, but this time its the older Dany v1.2 model (green PCB). The other two were D87M (blue pcb) and i had no trouble calibrating, both sounding great.
Without calibrating the third mic it works fine, but with less volume than the other two.
So, i was ready to do the adjustments. But then I got very weird reading. I am probably doing something wrong or the circuits between models are a little different.
What am I doing:
- no capsules connected.
- scope on drain of the FET (pin 1 of 2N3819)
- injecting 1khz 200mV sine on the C1 pin (same trail and easier than using reversed R6 as the usual instructions)
- putting variable resistor on max
When doing this i only get a flat DC voltage from scope.
- measuring input again with same scope calibration as the output = nice 200mV sine wave on input (with DC offset).
- measure pin 3 of FET on this calibration = DC voltage on output.
So i though, it is so hot that is clipping both ends of the sine. Than i
- change variable resistor to lower values = barely noticeble wave starts to appear. appears to be lower amplitude than input.
- i had to go up to 1khz 6v input on my sine generator to get a visible adjustable sine wave
- than i proceed to change resistor and going up the amplitude until no flat top/bottom appear
Am I doing something wrong or is my fet damaged somehow? I have the impression the output is lower than the input.
edit: my sine wave is amost a triangle/sawtooth in the output.
Thanks,
have a good day