MIDIBox MIXER / Switching Ideas

[gavgomad]

Hey All,

As I'm slowly amassing the parts for my SID, since I am in full blown parts amassing mode :P, I am also thinking about a nice submixer project based on the MIDIBox Mixer. I thought it might be interesting to revive some discussion on the MB Mixer project by lylehaze and pilo, give some of my ideas on what I'd like to do, and get some feedback from others (including the creators themselves!)....

This project is ideal for a keyboard submixer - for mixing your individual stereo SID channels, MBFM, filters, other keys etc.

The basic design is there for the mixer (level, pan etc. depending on the number of ICs), however there are a couple features which would be excellent for live purposes....

I think TK already alluded to possible storage of "scenes" as patches, and I think that this would be a critical option for live.

Additionally, and similar to the implementation of analog switches in the new SID software, I was thinking about implementing a switching system for routing to external effects (or, if you prefer, VCFs etc.), perhaps two switches (two destinations) per channel, and depending on some hardware configuration, the switches could route the signal either in series or parallel....

To give some idea, here is what I'm thinking of doing for each channel....

Once processed with the PGA chip, each signal is fed to the two (or more, if you wish!) switches. In my two switch scenario, the first switch would be parallel, out to a delay line - dry continues down the chain, and the return from the delay line is mixed in at the final summing amp. The second switch (which would not have an impact on the first send) would redirect the signal completely from the dry channel input to the final summer, redirecting the signal to a stereo-modified chorus unit (Boss Dimension Clone), which would have its own input to the final summer.

Theoretically, if one needs fewer than 16 stereo inputs, additional PGA chips could be placed in a different location in the chain to handle fx return duties, with storable results.

There's lots of panel space given the low requirements for the MB Mixer, so each channel could have its own tact switch and led for each send (or, alternately, if more sends are desired, maybe someone could do a button/LED matrix for each?). Ideally, these switches would connect to DINs, and the LEDs to DOUTs, all ready for storage, and easily viewed on the panel.

Concept I'm good at, hardware I'm not bad at, but coding is pretty rough....  ::)

To keep things modular, I think I could put together a design for each set of four stereo channels using four quad SPDT switches (DG333As or similar) for two sends (or, reconfigure it as four stereo switches for two channels). As the system is dependent on summing amps, where you pull the signal for the switches will determine if it is a parallel or series send. Maybe set up some jumpers on the board so that the signal from the previous switch is either sent down the line to the next, or a separate input is fed in through the jumper pin when a cable is connected. LOTS of possibilities!

Also, as each switch can be wired independently, you could, for example, have the logic signal for send 1 switch the output of the PGAs  to your VCFs - Channel 1 to its own pair of VCFs, Channel 2 to another etc.... Just wire the output back in to the chain prior to the other sends at the jumper points!

This board could also conceivably be used to directly control signal routing in other projects (SID etc., which already has slots in the patch for switches).

So what are people's thoughts? Does this sound excessive or worthwhile? Any ideas? I'm still in idea stage myself (busy fall at work!), but I'm starting to ponder the possibilities....  ;)

Gavin

[DrBunsen]

Yah thread necro strikes again:

Consider a matrix switching IC