Ok. I had a layout based on the LZX / L.Larsen design of the Summing mixer.
The basic design of the Summing mixer already has a place in my custom video synth, but
I want to add some features, and make it suitable for the Eurorack format
Maybe a simple filter . I don’t know yet. I was looking at an Allpass filter for phase shifting and possible interesting feedback effect… Suggestions are welcome!
current layout & schematic features:
4 channel mixer
3 normal inputs with attenuators
1 inverted input with attenuator
3 outputs
2x normal output
1x inverted output
Sandwiched panel & pcb. No wiring, though-hole design.
Current schematic:
(the inverted output need some work I think. )
One neat thing that the MHzxER has is two switchable inputs per channel. I kind of wish I had one of those, but your matrix mixer and the cadet fader have been fulfilling all my mixer needs these days, so I never ended up building a MHzxER.
Working on this again. I was playing with assymetrical shapes and patterns. this summing mixer is perfect for it. especially with more inputs and outputs (to do feedback routing)
It now has 3 normal inputs, 3 inverted inputs, 2 outputs
(6 pots, 8 jacks, 8HP)
The layout is pretty tight, with vertical resistors to get it to fit!
I think the main input i missed for the matrix mixer was a “thru” input (so it could be chained), but that seems less relevant here.
It’s going to be hard with the space constraints, but having the inverters go from positive to negative rather than 0-negative would allow you to use it as a 6-channel general mixer, and is also useful for modulation signals.
This of course sacrifices the ability to easily zero out the negative inputs.
now that you say this, I am wondering is x3 normal inputs and 3x inverted inputs would be better .
makes sense in my head.
But the 4 normal channels give good results for pattern making… mmmh… choices.
Anyway, I wanted this project to be fairly simple. so maybe I’ll try not to let the feature creep monster get too close.
Attenuverting mixers are awesome but having a wider effective resolution on a pot for precisely dialing in a mix is nice, too. That layout above looks good to me in 8HP.
I’d be interested in seeing something like the Matrix Mixer expanded to an attenuverting version (second a thru input!). More options for video rate mixer modules seems useful.
I think I can’t sum the input signals at the “IN1” net. so it must be after. (?)
So the input summing stages all must have 2 or 3 opamps to setup the signal, right?
Can I sum the inverted signal just after U1A?
I think i could get it down to ~one amp per input and two per output, but i’m not convinced i’d be happy with the result.
(Buffer all inputs, add all inputs in an inverting summer, feed that into another summer together with the matrix)
Alternately, you typically won’t need attenuversion in every matrix point and can get most of the benefit by having just one attenuverter per input and then have those feeding the matrix inputs?
