aha, the 12mm pot.
I’ll check if the hight matches the thonkiconn jacks
I decided to keep it like this (no inverted inputs)
I have normalled the inputs together for easy 1 input coloring.
now for the routing…
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fantastic! looking forward to a unit if prebuilt definitely!
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Routing puzzle:
what would make more sense? (pot layout wise)
option 1 (current layout)
R R R (red)
G G G (blue)
B B B (green)
Zr Zg Zb (gain)
inR, inG, inB - outR, outG, outB -> jacks
or
option 2:
R G B
R G B
R G B
Zr Zg Zb (gain)
inR, inG, inB - outR, outG, outB -> jacks
To me current layout makes more sense.
The inputs could be connected? In the sense of copying from inR to inG to inG until I plug something into either? ala passage…
yes. the inputs are normalled.
but then the gain pots are shifted in position.
I try to visualize the paths in my head, but it is hard
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I keep it to option 1. we’ll see how that works out.
next is the panel.
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looks great! 
I have finished my 4x3 mixer yesterday, 3 normal inputs and 1 inverted input to 3 outputs.
For me the inverted input is really really usefull, some kind of soft keying is possible, i prefer it over the gain pot per output.
mmhhh… yeah, I might make something. or a mod option or so
I added the gain pot to do keying as well, with 3x amplification - as Lars hinted at.
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maybe you make take a test and decide what you like more… with the inverted input i can make the keying with an cv signal, with the gain it would just be manual or am i wrong? 
Or add cv control over the output-gain? 
how does that work with the inv input and CV?
you put CV in the inv to subtract that amount from the rest of the signal ?
By the way, How did you order the pots?
(see my post above)
if you put for example a triangle wave signal into the invert input it subtracts with a soft border from the mix of the 3 normal inputs. The inv signal goes between the last two lm6172 where your gain pots are located in your schematic. But the signal you put in needs already some softness to softly blend to black. So no control over the keying in the module itself like with a gain pot
My order with in/outs:
in1 R G B
in2 R G B
in3 R G B
INinv Rinv Ginv Binv
outR outG outB
I like this arrangement. Makes sense to me. I think I’m favoring the inverted input over the gain pots, too. I’m going to have to breadboard up one of these matrix mixers to try it out myself…
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If I do the inverted option, the panel will be 16HP.
I have the jacks at the bottom now. If I place them at the left side next to the pots, the panel must be even wider.
note: I can add gain pot pads mod points. as for an expander .
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sure sure, my panel is 20 hp i dont have any space problems in my rack atm
A passive expander sounds like a fantastic idea. I could even mount it in a 1U panel
did you also use 6 LM6172’s ?
current schematic:
mod pins for gain pots, inv input + inv pots added
I think it still fits in 14HP
and layout
panel
puuh great, still 14 hp! also like the solution with the expander!
yep also 6 lm‘s
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