[sdiy] Matrix patch panels

Tue Jan 6 02:18:03 CET 2009

Yeah, I actually thought of that path and looked into various switch ICs. But after I figured in the cost of the leds, buttons, PCBs, etc, it turned out to be more complicated and more expensive than the jack matrix solution.

But I did come up with one idea while I was thinking along that route. Check this out: http://evilmadscience.com/tinykitlist/75-peggy2

So I was wondering exactly how hard it would be to outfit this with analog switches for a synth patch matrix.  The ICs, programmability, and leds are all there.  I figure all you'd really need is some transistors hooked up to the led contact and your signal path, and that would pretty much be it.  The kit is a thru-hole design, so you could probably mount the transistors on the other side; wiring for the signals would be a pain, though.

It's not only programmable, but v2.0 can do animation. This opens up the possibility of modulating your patches at audio rate (perhaps?), or doing other crazy programming stuff with it.  I decided against this path due to there not being enough connections (25x25 vs. 31x28), and the need for a separate interface to the Arduino connectivity. But I still think there's gotta be some good potential there.

Michael

----- Original Message ----
From: David G. Dixon <dixon at interchange.ubc.ca>
To: Michael Bechard <gothmagog at yahoo.com>; Synth DIY <synth-diy at dropmix.xs4all.nl>
Sent: Monday, January 5, 2009 11:55:01 AM
Subject: RE: [sdiy] Matrix patch panels

Hello Michael,

Very interesting project!  I wish you all the best.

Like you, I'm also pretty new to the synth DIY game.  Also, I'm thinking of
something similar, but I'd like to avoid jacks and cables altogether by
hardwiring every possible CV and signal in a switch matrix using LED-backlit
tactile MO pushbuttons, flip-flops and 4066 analog switches to keep down the
hardware cost and to avoid patch cables.  With a bit of extra work, one
should be able to arrange patch memory on such a beast as well.  One could
also program the patches simply by feeding binary words to each row of
flip-flops in the matrix, or randomize them by feeding digital noise to the
flip-flops, which could result in some cool effects (or garbage, who
knows?).  That still doesn't take care of attenuation issues, but it would
at least look cool and be fun and easy to use.  Perhaps each button could be
associated with a little tiny pot on a separate little pot matrix.  This
could even be added later.

Has anyone else on the list attempted anything similar?

David G. Dixon
Professor
Department of Materials Engineering
University of British Columbia
309-6350 Stores Road
Vancouver, B.C.  V6T 1Z4
Canada

Tel 1-604-822-3679
Fax 1-604-822-3619

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-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Michael Bechard
Sent: Monday, January 05, 2009 9:30 AM
To: Synth DIY
Subject: [sdiy] Matrix patch panels

Hi everybody, I'm trying to put together a semi-modular using a DIY matrix
patch panel, much like the one described here:
http://monopole.ph.qmw.ac.uk/~thomas/synthdiy/patchpanels.htm. There's not a
whole lot of info on the web about doing this, so I figured I'd ping you
guys.

Here's an overview of what I'm planning. My matrix will be a fairly large
(31x28) and combine both audio and control signals, with configurable
switching between unipolar and bipolar attenuation like this:
http://www.cgs.synth.net/modules/cgs33_matrix_mixer_euro.html. However,
instead of using pots for each connection (would be expensive!), I'm using
jacks for switches, much like professor Thomas' design. Each output and each
input will be separately attentuable (pre and post matrix processing) via
knobs setup along each of the matrix's axis. I'm also thinking of using RCA
jacks instead of 2.5mm, since I can get them fairly cheap @ $.25/per at
bulk. The PCB-mounted versions seem to be easiest to use, since the entire
jack housing is metal and forms one or the conductors. I figure I can solder
31 of them directly together to form one row, while using bare copper wire
to connect the other conductors vertically to each other. Here are the RCA
jacks I plan
to use:
http://mouser.com/Search/ProductDetail.aspx?R=161-0370-Evirtualkey11180000vi
rtualkey161-0370-E. My main concern here is the lack of grounding should I
use these jacks, but I really like the idea of being able to solder an
entire row directly together.

I should also mention I'm a complete newbie when it comes to building synths
(or most any kind of electronics), so please forgive any obvious blunders I
may include in this email and my plans. So far I've only put together a
couple of my modules.

Anyway, I would greatly appreciate any pointers and feedback you guys could
give me on my proposed design. I'm mostly concerned about crosstalk,
grounding, and wire capacitance/inductance at this point. I noticed
professor Thomas used bare copper wire to connect the leads of each jack.
Does anyone know if this works well? How much crosstalk/noise problems
should I expect? Should I plan instead on using grounded jacks, like 2.5mm
stereo? Lastly, do you guys think this design scales well to a matrix the
size of which I am planning?

I'm also wondering about buffering on the inputs and outputs. Since I will
be following Ken Stone's design on the outputs (to get switchable
uni/bipolar attentuation), I know they at least will be buffered. Do you
think I need to buffer the inputs as well, like Ken has designed in the
CGS33? Also, what effect do you guys think the extra current will have on
the signal crosstalk, if any?

Wow, this is a long email, so thanks for reading. I appreciate any and all
input.

Thanks,
Michael Bechard

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