[sdiy] Analog crossbars and backplanes

Tom Wiltshire tom at electricdruid.net
Sun Nov 10 22:58:07 CET 2013


My apologies, Damian. I thought "16 x 16 crosspoint switch" meant it gave you all the points in the matrix. Apparently not, at least for AD.

Still, I'm sure I've seen genuine analog switch arrays somewhere, where you can connect any of the X/Y points. I'll try and find it. 16x16 is only 256 switches, which is hardly beyond modern integrated circuit design. And if you need bigger X and bigger Y, you only need gang up a few ICs. Something more like this:

http://www.microsemi.com/products/switches/analog-cross-point-switches/mt8808

This is available as a 28-pin DIP and with four chips + a uP you could do a 16 x 16 programmable matrix. Obviously as the matrix gets larger, the number of chips goes up exponentially, so you still can't go crazy.

This MT8808 IC doesn't offer any figures for DC accuracy, but it's a basic analog switch with Ron between 40R and 80R, so I suppose we'd have to design something for which that range was negligible and gave a satisfactory result. That means a decently high impedance on the mixers for the output buses.

T.

  
On 10 Nov 2013, at 18:49, cheater00 . <cheater00 at gmail.com> wrote:
> > But there *are* good 16x16 and 32x32 crosspoint switches out there that are easily ganged together to build larger arrays. You could easily build something that would give you more options than the largest Ghielmetti patch pin panel you've ever seen, and has memories to boot. That's not bad, even if it isn't wish-fulfillment.
> 
> When I first received this email, I wasn't sure of the amount of patch cords on a complicated modular. I think I've spent 4 hours googling for modular systems with complicated patches. The plan was to try and roughly count the amount of patches on each and make a distribution, correcting for different sizes of modular systems... until I tried. I counted about 92 patch cords on the first image and decided to give up after that because that image took half an hour. I think the photos speak for themselves, and if you browse through them you will likely agree that only the smallest systems have less than 16 patch cords.
> 
> Yes, many needs are satisfied by 16 patch cords. Some needs, from exceptional musicians, researchers, and enthusiasts, are not.
> 
> If the future of synthesis does not include the likes of Tonto, Wendy Carlos, Joe Paradiso, Bob Moog, R. Feng, Klirrfaktor, Don Buchla, Dieter Döpfer, Mark Glinsky, Ken Braheny, Keith Emerson... then maybe that future isn't worth working for.
> 
> Cheers,
> D.




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