Hey y’all, I’m working on a simple schematic for a “splittable” mixer. Basically, it can function as two independent mixers with 3 in each, and 1 out each, or a switch can be flipped to turn it into a single mixer with 6 inputs and 2 identical outputs. My hope is to cram a little more functionality into a compact modular. This is my schematic so far:
I don’t have the input attenuators shown in this diagram since I plan on doing that wiring off-board.
I’m just looking for a quick sanity check here - does this look sensible to y’all, or is there a far better way of doing this that I’m not thinking of?
Have you breadboarded this to make sure it works? I think the inverted inputs of the opamps being connected together might cause some issues because their feedbacks are affecting eachother.
Edit: with perfectly ideal opamps, linking the mixers would half the gain of each input. With real world opamps that have input offset, imperfectly matched gains etc you might get other issues too, like the levels being different on the different outputs.
Thanks for weighing in Sandelinos. After doing a bit more researching I think you are correct that my schematic would not work. I’m not entirely sure if halving the gain would be the issue, but it seems like the two op amps would fight each other to maintain 0v at the summing node and this makes them freak out and, according to some, saturate to the power rails.
Thanks for providing a link to that simulation - I’ve never seen that before, but it seems to work a treat based on what I can see. No idea how you arrived at that big brain solution but I’ll try to reason it out after I’ve had a good sleep.
Sadly my prototype isn’t working. I’m currently diagnosing whether my physical build is off, or if it is accurate to the schematic but there is an issue with the circuit. Currently both sides are always grouped regardless of the switch, and for whatever reason the circuit is randomly emitting high amplitude pops and pulses at the outputs. I’m officially too tired for any further troubleshooting tonight. I can’t see any reason why it would be doing this unless I did something wrong on my solder job.
HAhah wow I shouldn’t be building modules at 2 AM. I figured out the problem. The ground from my friggin circuit board was not connected to the ground for all the offboard components (pots, jacks, etc). No wonder. I fixed that obvious blunder and it works a treat. The switching is a bit noisy but I’m not terribly surprised by that. Could also patch it behind a VCA to deal with that. Anyway this is a neat little module, I’m stoked to see how it fits into my patches.
