I want to build a mixer with the option to switch each channel through a delay circuit to a final mixed output with the unswitched (clean, no delay) channels. This way any channel of the 12 total can be either clean or with delay. This is what I’ve come up with so far:
In your first diagram I don’t see the point of having separate input buffers for the two signal paths, and you also don’t need a mixer for the delayed and un-delayed signals before the final mixing stage. Especially since you’re not really mixing delayed and un-delayed signals because only one is active.
(OK, if the delay circuit otherwise has very low input impedance you might need separate input buffers.)
As I understand it the whole “true bypass” thing isn’t really relevant for synth signals. A simple DPST switch works.
So I would think you could just:
I would also advise using 10k resistors rather than 100k for any amplifier stages not directly connected to an input. You need 100k on input stages because you need that input impedance, but for stages downstream 10k is fine and will result in a lower noise floor.
I’m having a hard time visualizing this. I just don’t understand enough of the engineering terminology. I’d like to use any of your suggestions, though, because they are always helpful. I’d like to have the best design I personally can build for myself. If you have time and feel inclined to help with a schematic it will definitely be appreciated and studied and (hopefully) built with your name burned into the frame… 
So I’d need a separate buffer for each input?
12 inputs, 12 buffers.
(I guess if there’s a non inverting buffer at the input to the delay section, there doesn’t need to be another buffer. The un-delayed input could go directly to the switch; but in that case the 10k resistors in the final mixer would need to be 100k, and you’d want a second inverting stage after the mixer.)
I think that is the line of thinking I was using in the first diagram I posted. The simple mixer
In this case, what you really need is to design a mixer that has a FX send/return for each channel. No need to incorporate the delay circuit in the mixer. This way you can keep it open and patch any effect(s) in the FX loop.
Send and return fx loops are useful in a mixer but so is the insert loop. Inserts in mixers allow you to use a Y cable (2 mono jacks wired to one single stereo jack) The input signal is interrupted and sent out through one ‘leg’ of the Y cable, through an effect and then back in to the mixers input. Having the “option” to patch in an additional insert to a mixer or patchbay is useful. (plus 20 character obvious reasons why)
In this case, a simple matrix mixer would be most appropriate.
I don’t see send/receive as a useful way to solve the problem. What they asked for was 12 channels each with its own switchable delay. That would allow each channel to have its own delay parameters. It’s unlikely they already have 12 external delay channels, so they’d need to build them, and building them into the mixer would make sense, if it’s unlikely they’d be using them independently of the mixer.
If they actually wanted the same delay parameters for all delayed channels, they’d need only one external delay. But they’d need a way to take the, say, 7 channels they’ve selected and mix them into the delay before mixing the delay into the 5 undelayed channels. Pretty much they would need two 12-channel mixers.
Or one 13-channel mixer with two outputs and switches to send each channel to one or the other (or both?). Then 7 channels could be switched to one output, it could go into a delay, and then the delay output could be mixed with the other 5 channels.
Two 12 channel mixers is what it will most likely be. That is essentially the idea I have on paper, anyway. One 12 channel mix going into the delay, one 12 channel mix clean, and both mixed for the final output.
See that unused pin on the mute switch? Instead of a mute or open circuit the signal is sent through an identical mixer circuit to the delay. I will move the attenuator pots to the other side of the switches. I just need to put it on breadboard and figure out how to make it work. When I get my 100 switches from China ($25 
) I will give it a trial run. This will be one of the main features for my next project which will be a base for my big rack. Another feature will be a Baby16 of Moritz Klein design with 2 gate outs as well as cv.
Be careful not to heat then up too much when soldering, I have destroyed a few cheap switches from China this way.
Two 12 input mixers is essentially a 12 input mono mixer with an effects bus, as would be found in professional mixers. Pro mixers often have multiple effects buses plus EQ and such for each input channel, but that could turn into a monumentally epic project, it has been done though. 
I’m aquatinted with these cheap switches. I’ve definitely melted a couple in the past. Yeah, I’m definitely not going monumental with this one. Ive already considered how out of hand this effect thing could get if I don’t stop with the delay. I’m just looking for ways to use 100 switches now. 
I am gonna put a patchable distortion effect on the panel, though. I don’t currently have any fuzz or distortion effects anywhere on my rack.
I have finally made this idea into a reality.[quote=“Dogstar13, post:13, topic:6691”]
Two 12 channel mixers is what it will most likely be. That is essentially the idea I have on paper, anyway. One 12 channel mix going into the delay, one 12 channel mix clean, and both mixed for the final output.
See that unused pin on the mute switch? Instead of a mute or open circuit the signal is sent through an identical mixer circuit to the delay. I will move the attenuator pots to the other side of the switches. I just need to put it on breadboard and figure out how to make it work.
[/quote]
I ended up doing just as the quote says, and I added a trim pot on the delay circuit board to attenuate the delay mix volume to about the same as the clean mix vol out. It is in a plastic shoebox and only six channels, but this prototype is 100% functional and I’m ready to start building my mixer sequencer base rack!
