Pedal switching matrix with the AD75019

[R.G.]

Well, the thing that most interests me about this would be for the wet side of the wet/dry/wet rig ...  You can also have two or three series strings in parallel by skipping busses.  I'm pretty sure I'm explaining this badly, but I can see it clearly in my head!)

No, the explanation is clear enough. Ought to work if you can iron out how to control it.

This begs the question, though - from the data sheet, it does say you can assign any and all inputs to any and all outputs, which I take to mean you can assign multiple outputs to an input (GOOD!  You would need this for parallel operation), but that means you need to sum those inputs some how.  Can you just have a summing resistor on each input, and a buffer on each output?  or is there a problem trying to sum things inside the chip?

I don't know how well summing inside the chip would work. They're fairly low resistance analog switches, so there's likely not to be so much summing as fighting. Resistor summing into a mixer would make sense.

At any rate, here is kind of the idea I was having - make of it what you will.  I think input and output busses makes it a lot more versatile.

Looks reasonable.

...

• Older Mitel MT88XX chip (retired by Mitel, but still made by Microsemi) that only had discrete address lines, not serial interface (cheaper, though). Not really a big issue with GPIO port manipulation.
• Complexity of user interface. Was thinking of a novel preset recall system, but how do you remember onstage that "preset 12" is this specific, complex effects path?
• I thought it might have to be a drag-and-drop touch screen app, too. Or maybe an offline editor for presets stored in the pedal.
• I was looking at a lot fewer loops, but had a couple of other routing ideas. Still, the number of permutations was overwhelming. I think user research to determine what are the most usable configurations could help reign it in.

I did a similar thing with the MT88xx stuff way back when. It worked, but as you say, it was pestiferous to use.

I'm recently enamored of using an otherwise useless old laptop as a dedicated (and very capable!) peripheral. So drag and drop interfaces are probably OK to consider. So are the newly cheap touchscreens and controllers.

On the fewer loops-front, the straw design I have so far has boards to implement an in/out (which one of the 16 pairs) and three in/out loops with spaced phone jacks, and then an x4 board with four in/out phone jack loops. You could build it as an X3 (not all that fun, but maybe for some people), an X7, an X11 and an X15 loop setup by adding X4 boards to the basic in/out/X3. I put the connectors for ribbon cables on the X3 and X4 boards so you could simply widen it by plugging in a 12-position IDC cable - although soldering would be more reliable.      the X7 or X11 systems are probably where most of the systems would be used.

I noted that one of the side effects of a nonblocking crossbar with truly independent accesses is that you don't have to implement loops in any position particularly. The three optional X4 boards can all go to dedicated loops, and one pin on the connector can ground a pin on the interface to the controller so that the attached controller can sense how many and which loop boards are added and insert that into the programming interface without having to mess about with installing things in any particular order to any particular in/out set on the AD75019. Again - A Simple Matter Of Programming. 

[G. Hoffman]

No, the explanation is clear enough. Ought to work if you can iron out how to control it.

Control is actually not something I'm worried about.  The Liquid Foot+ I'm using (a 12+) can use one switch to sequentially send MIDI commands, and you can set up different CC# commands to be mutually exclusive.  It's expensive, but it actually makes this kind of thing pretty straight forward.  For the most part, I'll have a switch for each device, and you press once for buss pair 1, twice for buss pair 2, etc.  I can even give each position a different colored indicator.  It's a bit more complicated for devices which are MIDI controlled, since I'll also need to send patch changes, but again, I can just set up a page of buttons for a particular effect.  Also, the way I want to set it up, it is pretty hard to do anything disastrous. 

And after all, the idea with all this MIDI stuff is to set up your sounds in the rehearsal room, and by the time you get to the stage to be pretty well programmed.

I don't know how well summing inside the chip would work. They're fairly low resistance analog switches, so there's likely not to be so much summing as fighting. Resistor summing into a mixer would make sense.

Ah, yes, well, I had intended to put a mix resistor on the return jack.  I kind of figured, given the use I have in mind for it (the wet side of a wet/dry/wet rig), everything going into it will probably have a pretty solid output gain stage (a Timeline, a Boss DD-20, etc.), so I could probably skip the input buffer.  It wouldn't be too hard to put one in, of course.


Gabriel

[G. Hoffman]

OK, so I bought a couple of these chips (OUCH! expensive!), and as soon as I'm done with the project on my bench I'm going to start experimenting with this thing.  I found the data sheet's description of the data input confusing, so the first thing is to play around with that, but then I'm going to try building something up on the big bread board, and this is what I've got in mind.





The values are a bit hard to read, for which I apologize, but most of those values are not really set.  Oh, and a lot of thanks to R.G. for the starting point on a lot of the blocks, particularly the transformer isolated outputs!  But, if anyone has input, I'd sure appreciate it!  (For now, I'm just going to send serial data from my PC - I'll worry about the microcontroller stuff when I've got a better idea how everything else is working.)


Gabriel

[Thewoodguy]

I've been dreaming up something like this for awhile now. I was planning on have 4 parallel out puts from the chip. My main hang up was how to digitally controll the the mixer
side of things. Seems most people around here don't like digi pots. I'm confused on what the benefit is to have the busses routed back in the chip and not just mix down to the outputs?

[G. Hoffman]

I can route things either series OR parallel, by assigning them to different locations.  For instance, if I'm using to rhythmic delays (say, a quarter note and a dotted eighth), I don't really want them feeding each other, so put them both in the same "location," and it keeps the sound a bit tighter.  But if I'm doing ambient swells, I WANT the delays to clash, so I want them in series.  Just one example of the versatility I'm after.   

Digital pots are prone to digital noise, but you can isolate them with a opto-resistor.  Just create a voltage divider with another resistor (or, if you prefer, use two optos).   I've got a tested schematic on the PC - I'll try to post sometime when I'm not on my phone.

[Thewoodguy]

Ok anouther question, can you not route the main/dry input to multiple loops/pedals in the chip? Or would you have to have the same # of dry inputs as out puts? By out puts I mean parallel outs from chip to a mixer curcuit, then to the actual out put. I was just going to buy the new boss es8 till I realized it could only do 2 parallel chains. Witch means that if you have stereo pedals then there are none left over for a overdrive.

[G. Hoffman]

You could switch the dry signal in and out through the switch, but I'm trying to make it both versatile and simple to use, so while I am planning to make the dry signal switchable on the front panel when I actually make the thing, but the way I am thinking of setting up is with the dry signal switch off for the last pair of busses, so I can (for instance) put a pre-delay on a reverb by putting the delay in the seventh location, and the reverb in the last location.



Gabriel

[Thewoodguy]

Just to clarify, can the matrix split the dry signal(any input at that matter)? So if I have one dry input to the matrix, can I send it to multiple out puts?

[Hatredman]

Might be of interest:

http://www.dorkbotpdx.org/blog/paul/ad75019_crosspoint_analog_switch

http://www.synthdiy.com/files/2011/45-ciarcia.pdf

[G. Hoffman]

Just to clarify, can the matrix split the dry signal(any input at that matter)? So if I have one dry input to the matrix, can I send it to multiple out puts?

Well, I don't know that I would say anything "is", since this is very much an early stage project, but yeah.  You have eight locations, and each one has and input buss and an output buss.  You have eight loops, and each loop can be placed in a location.  If you place two loops in the same location, they are in parallel.  If you place two loops in consecutive locations, they are in series.  If you skip a location, then you're back to parallel, but you can make multiple (well, up to three) series strings which are in parallel with each other. 


Gabriel

[G. Hoffman]

Might be of interest:

http://www.dorkbotpdx.org/blog/paul/ad75019_crosspoint_analog_switch

http://www.synthdiy.com/files/2011/45-ciarcia.pdf

Cool - Thanks!


Gabriel

[Thewoodguy]

I just did a sketch of the signal flow I was think about. I'm wondering if I need buffers on all the loops? I'm hoping to just have one that I can place anywhere in the chain.
https://www.dropbox.com/s/hp2f9f5u6inzrtv/20151227_164615.jpg?dl=0

[Thewoodguy]

Might be of interest:

http://www.dorkbotpdx.org/blog/paul/ad75019_crosspoint_analog_switch

http://www.synthdiy.com/files/2011/45-ciarcia.pdf

I love that this article is over 20 years old

[G. Hoffman]

If you are going to run loops in parallel, you are going to need to mix those signals.  And switching a mix amp in and out is just one more thing to think about, one more complicating issue.  But for what I'm using it for, the buffers aren't a problem.


Gabriel

[Thewoodguy]

If you are going to run loops in parallel, you are going to need to mix those signals.  And switching a mix amp in and out is just one more thing to think about, one more complicating issue.  But for what I'm using it for, the buffers aren't a problem.


Gabriel

I'm not following you, the switching of the mixer is done in the chip is it not? If I have a parallel mixer like in my drawing, all I have to do is route a chain to a out put. So... on my drawing I have 4 outputs from the matrix. If I want all my loops in series it would look like this, Input/loop1/L2.....output 1. If I want parallel loops, input/loop1/L2/Output1 and input/loop3/Output2.  Then you would have a mixer to mix your 4 outputs. If there is nothing routed to a output then it is switched off.
Does that make sense, or I'm I thinking the matrix can do something it can't?

[amptramp]

I'm not following you, the switching of the mixer is done in the chip is it not? If I have a parallel mixer like in my drawing, all I have to do is route a chain to a out put. So... on my drawing I have 4 outputs from the matrix. If I want all my loops in series it would look like this, Input/loop1/L2.....output 1. If I want parallel loops, input/loop1/L2/Output1 and input/loop3/Output2.  Then you would have a mixer to mix your 4 outputs. If there is nothing routed to a output then it is switched off.
Does that make sense, or I'm I thinking the matrix can do something it can't?

Take the red pill, Neo.  The matrix is real.  And watch for the guy with the sunglasses - he can replicate.

[Thewoodguy]

I'm not following you, the switching of the mixer is done in the chip is it not? If I have a parallel mixer like in my drawing, all I have to do is route a chain to a out put. So... on my drawing I have 4 outputs from the matrix. If I want all my loops in series it would look like this, Input/loop1/L2.....output 1. If I want parallel loops, input/loop1/L2/Output1 and input/loop3/Output2.  Then you would have a mixer to mix your 4 outputs. If there is nothing routed to a output then it is switched off.
Does that make sense, or I'm I thinking the matrix can do something it can't?

Take the red pill, Neo.  The matrix is real.  And watch for the guy with the sunglasses - he can replicate.

I really wish I have watched those movies so I could know what you are saying. Haha. I can only assume you are telling me I don't have a clue? Probably true, just trying to learn

[stallik]

Take the red pill, Neo.  The matrix is real.  And watch for the guy with the sunglasses - he can replicate.

Not helpful.         They ALL wore sunglasses!

[G. Hoffman]

I'm not following you, the switching of the mixer is done in the chip is it not? If I have a parallel mixer like in my drawing, all I have to do is route a chain to a out put. So... on my drawing I have 4 outputs from the matrix. If I want all my loops in series it would look like this, Input/loop1/L2.....output 1. If I want parallel loops, input/loop1/L2/Output1 and input/loop3/Output2.  Then you would have a mixer to mix your 4 outputs. If there is nothing routed to a output then it is switched off.
Does that make sense, or I'm I thinking the matrix can do something it can't?

Ah, I think I get it.  I guess that would work (kind of blind leading the blind here - where did our adult supervision go??).  Seems complicated to me, in that you have to assign each loop both an input and an output, which is exactly what I'm trying to avoid, but hey, if it works for you, you can program it, and you've got a way to control it, go for it!


Gabriel

[Hatredman]

Oh, and a lot of thanks to R.G. for the starting point on a lot of the blocks, particularly the transformer isolated outputs!

Wait, WHAT?

I totally missed that one.

It certainly does not hurt, electronically speaking, to have all those transformers isolating the sends.

But it DEFINETLY will hurt your wallet. Do we really need all those?