Gustav, can you pls shed some light on the signal route / phase when Blend is engaged and M/S processing is fully OFF?
so far what i think : signal is "in phase" at the out of the debalancer stage, but then it flips at the CLEAN-L(/R), right? (after the buffer / inverting stage). then it flips back at "BLEND-L(R)" and stays the same at the balancing stage / output.
the "DIRTY" signal is "in phase" at LM-OUT, but then it flips at "BLEND-L(R)" and stays flipped?
thanks
Note that the buffer tapping the clean blend is non-inverted.
And sorry, I dont understand the observation you made on "dirty" tap. It just reroutes the signal to one pin of the blend circuit, same place is comes back. Make sure you see that the MS is switched in two locations as well (I am just taking a guess it might be relevant).
Honestly, I am not 100% sure I nailed the blend (Its actually #1 on my "check if you screwed this up" list. #2 is my implementation, using a doubler to provide 30V, so I could use a 2x15V trafo). I went through it quite a few times, sometimes thinking I had it, but then changing the phase on the buffer back again, and again. I had a unit in for service to compare some issues to, but I gave it back before I checked the blend phase/realised I am a bit lost understanding how the signal is inverted (or if its not) in the AB stage, and I actually had an opamp providing the 12dB of gain at some point as well in the schematic, which would've been easier to see for me.
Theres
always errors on a first rev board, so in the spirit of moving ahead, my plan ended up being - Measure the phase on the blend, hack and correct the board, make any needed changes to a second revision board. Factory is closed for the holidays ,so this way I have something to work with, make needed revisions, make a new board after the holidays.
If it weren't for the German postal workers, I would have had it fired up by now!
Gustav