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"Universal Channel Strip"


Tom Visser

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Digital mixers have (potentially) higher fidelity, are smaller, cheaper (absolutely and also relative to functionality), lighter, use less power, can be software configurable, especially when matched with something like an iPad... why do I still love analog mixers?

 

There's nothing as dependable as working with a traditional mixer.  Even when they fail, it's usually something you can work out, like a sore muscle... a little scratch on a pot, exercise it a bit, little bit of Deoxit, through time, you even get to know your mixer's weaknesses and make a point to do a little stretching / exercise routing before putting it to serious work, just like your own human body.

 

I have just received the capacitors I need to recap my Studer / Revox MR8 power supply, which is where I suspect an intermittent hum / buzz is coming from.  I look at this older German engineered mixer and see classic high end design.  Per channel PCB channel strips with easy to maintaing through hole DIP electronics.  High end preamps, as good sounding as boutique rack mounted ones.  Limited, but good sounding EQ for making broad stroke adjustments.  Strong chassis, with good feeling, sturdy faders, masculine switches, and tasteful spacing of all controls.  The back side has a large complement of I/O, including separate XLRs for mic and line inputs, stereo unbalanced I/O, and both pre-fade and post-fade outputs.  It is nearly the perfect mixer, except it is sort of big and heavy for an 8-channel desk, sometimes having a 6 channel would make more sense, or don't have access to AC, or sometimes you need more than 8 channels and what do you do then?

 

There are so many reasons to move to a digital mixer or control surface that it is logical that most of us should or already have.  That begs the question, is there still room for an analog product?  Ron and Pascal's Solice Mini is a great example of a purpose built mixer, for the working class cart'ish production sound mixer, if you need 8 channels.  What if your need 4? or 12? or 96?  What if you need to be able to switch between prefade and / or postface dynamically, or need an extra aux send?  Do you think that there is room for sort of an "open source" analog design concept, that would allow the end-user to...

build the mixer up with any number of channel strips

have a basic master channel with mix outputs and headphone level, or maybe a duplicate of an SSL 4K

or maybe no master section at all and just use to return into a digital routing device / interface

desired number of mix busses and aux sends

mic input, line input, both, neither (controller only)

 

If such a beast makes sense, here are some of my ideas for how one might go about making the basic undercarriage / chassis - after all, all open source projects need at least some common jumping off point to make a community, otherwise it is just a bunch of independent forks.

 

P.S. sorry for the flurry of posts, this is what happens when I get a holiday and some spare time to sit down in front of my computer.

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The channel strip control surface, room for a 100mm Alps fader.

Why Alps?  Pennies on the dollar compared to P&G.  They offer a motorized version that fits in the same bolt holes as the regular 100mm.

 

There are 10 spots for NKK B series toggle switches.  NKK also offers an illuminated version, so with a 10 LED LM3916 driver, they could serve double duty as a per channel input VU meter.

 

This control panel would fit into two aluminum extrusions and the whole thing would be 32mm wide and 11" long.  A 500 series rack is 1.5" so if you spaced these out in front of such a rack, you'd have a tidy 6mm between strips, or jam them together if you want 10+1 units that fit in the same footprint as a 15" MacBook Pro.

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post-1336-0-43756900-1420062313_thumb.pn

 

not a thrilling panel detail, but a necessary one.  shown are two D-style Neutrik cutouts, sideways.  You could not make the mixer even 0.1mm smaller than this while retaining the ability to have these two connections.  Minimizing size has always been an obsession of mine.  It could be configured as an XLR mic input + XLR line input, XLR mic input + XLR direct output, stereo XLR line input, XLR line input + CAT-5 for ? ? ?

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post-1336-0-63833000-1420062569_thumb.pn

 

Here's what makes it all work.  The bottom PCB is just a bunch of plated groups of pads, sort of like a prototype breadboard, but of higher quality.  There are 80 groups of 3 pads.

 

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Each pad could have a wire soldered to it, or a Mil-Max receptacle pressed in.  22 gauge wire (CAT-5 for example) could be inserted or use a specific mating pin.  The mating pin could be soldered onto a 22 gauge hookup wire for semi-permanent patching, but then if future changes were needed, you could solderlessly make them.  Resistor leads could just be placed, such as summing resistors, and in minutes, you could change the values if you needed.

 

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These same pads are on the other boards, like the switch boards, or boards that third parties would make on their own, so that easy board to board interconnection could be made.

 

Interconnecting channels could be done via bussing bars with male pins interfacing with the strips or a complete baseplate assembly that electrically and mechanically locks everything into place.

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Could make sense at some point.  The press-in receptacles for instance, are $0.58 each for a single one or $0.29 if you buy 1000.  At some point it would be wise to leverage some sort of investment capital in order to make a reasonable production run.  Right now I'm just throwing it out there as an intellectual exercise, see what other people think is missing or more important, and then gradually grow some interest to see if it is worth pursuing.  My goal is to build myself a small channel count proof of concept this year.

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