I want to make a 2x2 matrix mixer for video.
This type of mixer is useful for feedback patching.
I might change it into a 3x3 matrix, as I was reading up about the Color Chords.
Then it would be possible to do color mixing. This makes it a bigger project though.
For now I’ve included gain controls for the 2 outputs. I’ll test how useful this is in the context of feedback mixing. I might normalise out1 to in2.
Progress so far: (the resistor values are not calculated yet …)
again a great project, i want to do something similar at the moment.
My plan is to use the schematics of akiras mhzxer with some changes and build a 4 to 3 mixer. So 3 normal and 1 inverted input mixed to r g b outputs. Hope it will usable for feedback patching
these are exactly the questions I ask myself too after reading your schematic. I’m also still a beginner when it comes to electronics
With your schematic i would save 3 LM6172’s at all…
Morning all!
We’ve been using a pair of 8x8 Knox video switchers to select specific video sources and send them to specific video effects. One matrix for selecting the input and which effect to send it to, and the second video matrix for selecting which video effect is going to which video mixer. This is great for creating a video feedback loops and running it through effects.
You can see the Knox video switchers in the rack at the back of the table in the pic. The sources are PTZ cameras (for streaming) or visualizers and the video effects are all in a row at the front of the table - KPE, video equalizer, etc.
We use 3 video mixers to create a base mix, a middle layer, and a top layer.
These aren’t modular solutions, but I figured I could chime in. LoL
I built a 3x3 matrix mixer based on the CGS design (but all on one board, not modular; just replace TL074 with 2xLM6172). It’s highly recommended! Ken’s design supports polar/bi-polar switching on each output, but I modified the circuit to be polar with an invert switch on each input (which is much much better than having to carefully center a pot if you don’t want any of that input in the output). I also made each channel 2x gain, and with linear pots that gives me unity at 12 o’clock. If there’s interest please let me know and I’ll see if I can find my poorly scrawled schematics.
You need to buffer your inputs before the attenuators. Otherwise you are going to potentially have a gain drop of half on your input signals (and worse, when multing). The 499R resistors to the inverting input node will look like resistance to ground from the perspective of the input.
ok, thanks for the clarification!
If I want inverted inputs or outputs , I would need to buffer those too, right?
I might skip those in/outputs, because it won’t fit on my current 8HP size (single pcb)
I might be able to add the gain pots. which I left out for now. … we’ll see
@VisibleSignals the 3x3 matrix mixer sounds like what i need… im still waiting for some components to arrive… it would be awesome if you can find the schematics
Looks good! However you don’t need a buffer for each pot, just a buffer for each input. So each input buffer can feed two pots.
OR… with resistor values all changed to 10K (instead of 499R) as shown, you can probably get away with omitting the input buffers. Your input impedance is 10K then (the pot’s resistance), so with 499R output resistors (LZX standard output impedance) you get a 5% decrease in gain (more when multing.) Better than 50%! You could add some make up gain though, just lower the values of R13 and R23 a tad. It can sometimes be handy to push gain past unity on a video mixer anyway. For example, higher gains give you a more soft key type behavior (like Vidiot’s colorizer, each RGB input goes to 3X gain at max.)
Oh. I thought , because it is a matrix mixer, those input signals should be separate.
but it makes sense to me. it was early in the morning
The 10k resistor method sounds good. I did wanted to try out the gain because of the softkey effects.
Now I have to decide if I want inverted inputs or outputs (or both).
Getting closer!
(1) R9, R10, R11, R12, R1 & R2 can all be omitted if you’re going with nonbuffered inputs. The inputs are going to see 5K to ground (2x 10K pots in parallel). That’s not ideal (10% gain drop.) But if you raise the value of the pots too much (like up to 100K) you will get some bandwidth loss/softening. So buffers are best but this will work if you’re trying to go lo-fi/low cost. Maybe a 20K pot is a good compromise.
(2) Your inverted output coming straight off a passive pot (VR5 & VR6) is not good practice. This will put more resistance in series with your output and create softening. You could have it come off the first summing buffer though (499R to jack). If you want non inverting and inverting outputs with a gain control for both, you’re going to want another buffer in there (after the pots VR5 & VR6) and before the inversion buffer and outputs.
