Continuing with where I left off in the prior thread, I will show the wiring for the DT-1990 Pro. What needs to be kept in mind is this may only apply to my set of headphones. Or it could be that Beyer has indeed wired the drivers of the 1770 Pro and 1990 Pro differently. It is up to the individual to figure this out because I can't say for certain. What I do know for certain is that the plugs for the PCB sockets must be in the correct spot or the driver polarity will be messed up.
Anyway, the figure below shows the the stock 3 pin wiring of my DT-1990 Pro.
As can be seen, the wiring for 1990 varies from that of the 1770. Instead of the jack being wired to the right socket of the left driver, it is wired to the left socket. Also, the right driver wiring is connected to the right socket of the left driver. The right driver PCB is wired the same.
Again, if you place the plugs into the other sockets, the signal and ground will be reversed.
The wiring for a 4 pin XLR jack ended up like shown in the figure below.
Actual 1990 stock 3 pin PCB wiring.
Anyway, hopefully this can help someone who desires to convert their 1770 or 1990 from a 3 pin XLR to 4 pin XLR jack. I'll leave the subjective part out, but I will say the either way gives excellent performance. I wanted only to take advantage of my 4 pin amplifier jacks.