You have to buffer each input (3), each output (4), so you’re looking at 7 opamps minimum, or 4 LM6172’s. I guess you also need some for the luma mixer, too?
@joem is correct, the signals need gain in this case so they need to be amplified as well. I breadboarded a single channel similar circuit few years back and it would have used 6 LM6172’s (my memory’s hazy - no input buffer, inverting amp and inverting output buffer I think).
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More updates on this, PCB from factory came and I built it.
I’m noticing some bleed noise on channels when doing the “hard edge” test that Lars always recommend to detect bleed, otherwise the board is good to go. I wrote to Lars and Phil to see if anything can be done to remove/reduce this.
This means maybe two more weeks of delays so you all start ordering yours. I don’t want to ship you a board that has some noise (even if is small) and I’ll end up refunding paying stuff so just want to be super honest and clear with what you will be getting… I will record a clip explain this hard edge test, and showing the bleed so you all know a little bit more on how you should test your video equipment/modules.
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I feel a little stupid here, so please excuse the noob question!
Can anyone explain, simply, why I might want to do this with my Visual Cortex? I’ve read through the thread here, but I can’t get a grasp on what this upgrade might be used for, in practical terms?
this gives your visual cortex LZX standard 1/8 outputs of whatever is coming out at the composite/svid/component outs
RGB and LUMA
this could be used for feedback, further processing connecting to another system lots of fun stuff!
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So we’re not placing orders yet right? Don’t want to miss this when it’s time!
Im waiting for final PCBS with ground plane to reduce bleed noise, they have been manufactured and their are on their way to me so should be receiving them next week probably.
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One use case would be if you have another module with its own set of video outputs and you want to feed it a signal that’s mixing both of the Visual Cortex’s compositing channels together. Some LZX modules have RGB 1v outs (Color Chords, Marble Index, Mapper, Memory Palace), just as the Visual Cortex has two sets of RGB ins in its compositing section.
However, the only way you could get full RGB (or the functional equivalent, at least) out of a Visual Cortex without any sort of expansion attached is via the component outputs. BUT, in order to put this back into another part of the LZX system, it would need to be decoded again via another Visual Cortex input decoder section or a TBC module, as it is now a valid video signal instead of the LZX 1v standard. This expansion panel serves as a much less cluttered way to continue processing a fully patched Visual Cortex, or to take advantage of final output via another module (such as the DVI/HDMI output of the Memory Palace).
Did that help? 
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Thanks Tylerm, that’s very clear explanation.
I guess I’ll join the queue for this awesome upgrade!
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Finally got my expander installed and it’s working great! This thing kicks ass with memory palace
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Great to hear that enjoy it 
yeah no turning back
it really made the chromagnon make more sense
that was I think one of the last straws for me before pre ordering (getting this up and running)
It’s like have an entirely new flavor of feedback for memory palace. Wonderful!
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Thank you so much for this @luix it’s amazing!
I can’t believe that it’s taken me this long to get around to building it!
The only thing that I would advise is that if you use a shrouded, keyed header, then it will overhang the PCB a little bit. This makes it a little bit to fat to fit between Doepfer type rails. I desoldered it and put a pin header on, instead.
As you mentioned, the PCB ground plane makes desoldering difficult.
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Great news!!! so let me know if I can do anything for you or share any patch ideas
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every time i used this expander it makes me more excited for chromagnon
things are going to get wild
is it normal that all my knobs are at about ~75% turned to pass through the regular colors?
I guess my expectation was that it would be at 50% but I could just be misunderstanding something
this has always been the case since I got it from you but I never really mess with the knobs so I forgot until the other day when I was re setting up my system
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Following this because I’m a bit unsure on that too!
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Yessss I specifically designed the circuits so they have about 120% gain when full clockwise or counterclockwise (inverted), I found I wanted to have extra “saturation” on my output signals sometime and that extra 20% worked fine. The downside of this is you will have to dial in the unity gain which has not been a problem for me really but well doesnt have to work for everytone as it works for me
12:00 > zero gain
3:00 > 100%
4:30 > 120%
9:00 > -100% (inverted)
7:30 > -120% (inverted)
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Nice Expander, @luix! If one would forego the RGB pots, how hard would it be to just put the RGBY jacks right on a Visual Cortex, so as to save HP and keep my panels consistent looking?
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