Line mixer (active)

[enthalpystudios]

yeah, i think having a separate module for aux masters and another for aux returns is the best way to go as well.....

i'm still interested in keeping it simple... it all looks nice and pretty in your head and on paper until you go and try and integrate multiple features and options and intense routing... there are inevitable problems, and keeping it basic will reduce those problems.

working within an acceptance of murphy's law i guess.

but also, this whole deal, as far as i can guess, has a definitive air of right angle pcb mount controls, and right angle 2p5t (or 2p6t, or 2p12t for that matter) switches are def. not cheap...... pretty much need a 20+ dollar grayhill to right angle any rotary's.

LCR would be a whole different story.

still, I'd go for Dave's pan pot, as he not only has obviously done some thinking about it's law, but has put in some good time thinking about its integration into the summing bus and designed around it....

dont get me wrong, i'm all for doing things so that they suit personal needs, but this i feel should be basic, but very solid, project for accomplishing standard mixing tasks with outboard....

no need to personally, i need to try something out, see how experienced people would design and layout the circuit, and get a better feel for whats possible....

if i had the experience and the knowledge (i have way too much time on my hands), i would just go ahead and build my custom desk

 

[the scum]

I'm making some slow progress here.

I've ordered a handful of pots and switches from Mouser, so I can evaluate the robustness of some of the smaller pots, verify that my component footprints are right, and build up a prototype channel or two. I'll be doing the prototype channels with some DOAs that have significant DC offset, to guarantee that it's handled correctly.

I've flopped back to the E-switch pushbuttons, as Mouser doesn't stock the ITT/Cannon ones. I'm trying for a single source for parts in N America. Don't order any parts until you've seen a parts list and at least a board mockup from me!

The dual-opamp footprint is loke Fabios. Overlaying the DOA/MOA parts isn't all that hard by itself...but doing it so the component in my Eagle library isn't unweildly or error prone has taken some more tweaking. I was hoping that I could lay a single opamp in the schematic, and the double footprint would show up on the board. But there's no easy way to do that, so I'm putting 2 actual opamps on the schem, and renaming nets so they're connected. It's the cleanest option I've found so far.

Eagle gives us some great tools to not screw boards up, if we can figure out how to navigate them properly.

I don't mind sharing this stuff, what's the best way to share the files?

I've also got the summer section schem captured, with a rough mockup of the board layout.

The input board is 4.75" by 3.5," and the summer board is 4.75" by 4". The summer board has Dave's master scheme (main summer plus 2 aux returns, and MOA for the meter driver), which is repeated as one of the aux masters (minus the aux returns), on the same card as well. I'm keeping Dave's return scheme here. If you want to build another couple input channels to return FX to, go right ahead.

As you surmise, it's using the pots to mount the cards behind the panel. For the I/O connections, I've been using the symbol for a 2-screw Phoenix connector, but you can solder leads to the same footprint, if you want.

So a mixer would be N input channel cards, a pair of summer cards, and maybe some perfboard lashup work with a relay for the solo/control room output stuff (or, if there's demand, one more card there, too).

If you can abandon the DOAs, and move to dual-package MOAs, these boards can be tiny...like stick-of gum sized...

Are you able to etch double-sided boards, or should I be trying to keep them single-sided? I'll see if I can get a quote from my usual PCB house, as well, if people are interested.

Does anyone know of the clearance between the rails on a Frackrack is less than 4.75"?

 

[enthalpystudios]

not sure about frackrack.... i haven't really ever looked hard at its specs, but I'll take a look, because that will indeed be a great format for this. looking at the pictures, it's hard to tell, but I do know that a par-metal 3U has a useable verticle front clearance of 4.4 inches. might be able to squeeze a little bit more, but probably not. Honestly the frack rack looks similar, rails slightly less than 5.25 edge to edge, and the rails themselves taking up a bit of extra room, like the lips on the top and bottom par-metal panels.

if it'll squeeze, just under 4.4 might be a good idea, just to keep it from being the big squeeze when it comes time to mount.

i can host some space if you'd like, but my damn domain expired and i couldnt renew, as my domain company was bought out by a bigger domain company and they lost all record of 'me'

i still have ftp space on my host, and it is accessible without any problem.... besides, maybe i can go ahead and get a domain today. need to get an appropriate one

 

[falken]

that *might* be enough room to fit a fader but I'm not sure. plus, are you guys actually going to drill and file close to 100 holes?? 50 even? I still say we should get some panels made. I will be very impressed if you can fit everything into 4.5", including bus switches. Most of us will need busses....plus what's the point of building a fully modular console with no busses? one last thing....should there not be a gain stage at the front end of the input? any signals coming onto the board that are slightly weak will necessitate lowering the faders on every channel, the way I read this schemo..unless I am missing something?

 

[NewYorkDave]

unless I am missing something

Yes: the original point of this whole exercise, which was to mix a few line-level signals into a stereo buss with a couple of effects sends and minimal amplifiers and other junk cluttering up the signal path.

I don't want to discourage you guys, but you keep piling stuff on and it's probably never gonna get built... Or if it does, you'll end up with something that's about equivalent to a small console from Soundcraft, A&H, etc. but at a significantly higher cost in parts and labor.

I'm glad my sketch inspired you all, but at this point I must bow out. I have too many irons in the fire as it is.

 

[lofi]

please dont bow, re-direct!

 

[enthalpystudios]

yeah, see i still say simple

 

[enthalpystudios]

no reason to get panels made without a working board.

3U vertical is SMALL, but it can be done

without bus switching of course

if you need more than 2 sends, bus switching, trim, extra gain, you probably need separate modules for different purposes and etc etc.

this is just simple stuff.

it is indeed possible to fit aux 1, aux 2, 2x pre/post switches, pfl, mute, pan, and level, all on a 4.4 inch board

it's tight, but possible, wihout a fader.

4U would be better. Much better.....

it relieves some space to eliminate pre post switching, and just have it jumperable, or 1 fixed pre, 1 fixed post.

whatever happens, i'm going to go for 1 pre, 1 post.

so my panel would look more or less like this:

http://i110.photobucket.com/albums/n91/enthalpystudios/untitled.jpg

in fact, I may even lose the pfl and mute switches. this has a bit of gain, but it's not for mic and line signals. just feed it a nice healthy signal.

 

[NewYorkDave]

I like that panel. "Cue" and "Echo"... nice old-school touch!

If it were mine, I would try to scoot things upward a little bit to leave more room around the Level pot--maybe put the PFL and Mute side-by-side. My personal preference would be to have the pushbuttons above the level pot and below the Pan control.

Whoops... I said I was out, didn't I? OK, I'm leaving now. :wink:

 

[enthalpystudios]

yeah and you could use a slightly bigger knob ;]

actually, if i left off the pfl and mute, which may end up not being that necessary for my purposes, like i said, i could use these cool looking daka-ware knobs, 4 would safely fit on one 1.5 x 5.25 panel with a 4.4 or so inch board.

and it would look *sweet*

going side to side is what i wanted to do until i remembered that the 'plan' seems to be to make a pcb, which does indeed make things kind of handy, although to be honest, this thing could probably be wired off board and fit 8x2 all on a single eurocardish sized pcb. or pad per hole, its so low parts count it wouldnt be too bad at all.... just gotta be tidy with some'n like this ;]

in fact, there may just never possibly be enough people to agree on enough to even warrant a pcb being fabbed as a group project kind of thing.

i think its impossible to please everyone.....

although i would like to see how you're coming with the layout you've been working on scum... i'd like to get a feel for what a very simple mixer looks like on a board now that i have a good idea of what it looks like on a schematic.

i've been working on a langevin console channel strip, has a very 610A type of feel, but discrete, trafo in and out, and a few more bus/frequency options, but essentially its the same thing.... level, echo, solo, hi cut/boost, low cut/boost

just thinking about this stuff gets me reading stuff, and looking at other circuits, and I've learned a ton since this thread started....

but the thing is, the basic pcb for the basic design CAN have other things done along side it

if you want more gain, put a mic pre above it. if you want bus switching and faders, make bus modules and fader modules. aux return modules. send modules. control room headphone amp super 2 track return logic modules.

but the basic idea can get laid out. after that, its all how you use it.

i mean if you want bus switching, make a bus switching module. the output from the pan pot goes to there.

fader module, hook the fader module up to the pads on the main board.

the point is, nothing is going to happen if we dont keep it as simple as pie.

so is eagle free? maybe i'll start learning how to use it, possibly give you a hand scum.

billy

 

[the scum]

Enthaply,

Eagle starts as freeware, but with board size limitations. The freebie version will let you layout a 3x4 board. But it'll also open the files from the commercial versions, so you can see what's in 'em...you just can't drag anything on the layout page outside the 3x4 area.

I really dig Eagle...like I said, once you get to know it, it makes it very hard to make an incorrect board. Most of the perplexing stuff is actually in the definition of parts used in the libraries...defining the parts in the first place is the most labor intensive portion.

So point me at some FTP space.

As a teaser (and assuming my hosting is actually working), here's the rough layout of the input channel card:

The pushbuttons are the ITT/Cannon ones, and the pots are a stab in the dark. The sideways pot on the right is for the fader...just 3 pads to fly a wire to whatever device actually gets used. The outer border is a eurocard. The two white lines on the right are at guideposts at 4.75" and 5.25". The traces are all in yellow "rubber band line" because I don't want to have to rip anything up when the coupling caps start moving in.

I'll work on tweaking the schems so they'll fit in a single screen easily. They're unweildly right now.

And my PCB quote came back: for 50 channel PCBs, it'd run about $7 each. I don't know if there's enough interest to hit that threshold. If this has that much momentum, then getting some metalwork done isn't that tough, either.

As for drilling holes, I've got a drillpress and an XY table. It'd be tedious but doable.

And as for more advanced features, this card is just a springboard. With some resistors and a pot, the follower in Dave's original could become a variable gain stage. If you want a totally different gain structure(40 dB over unity in the fader? Sure, why not?), that's some more resistor changes...buss switching would indeed hang off the panpot, but for every buss added, you'll need another summing amp & line driver for it as well.

 

[NewYorkDave]

Hey Billy, here's a space-saving idea. Label the two aux sends as "Echo 1" and "Echo 2/Cue." Use a pull-pot for the latter to switch pre/post.

I don't know about you, but there are times when I definitely want two post-fader sends for effects--to feed a dual-channel reverb, for example

 

[Guest]

Could somebody just take 5 minutes to explain the way that those DSubs or whatever connectors they are work from a mechanical point of view
Do you attch them with ribbon cable
How do you run grounds - one ground or alternate?
What are the part numbers needs... etc.. examples from digikey
Are they cheap?
How do they connect - I want to use them rather than 7 pin XLRs but I am flying in the dark - I see IDC etc,...
Sorry to hijack

 

[therecordingart]

At $7 per PCB....I'll take 16.

 

[enthalpystudios]

pushpull is perfect... absolutely perfect for this.

i wonder if alpha makes a pc mount 12 or 24mm with a switch?

 

[enthalpystudios]

10K log with switch, pc mount:

CTS part no: (digikey)
270X232A103B2B1

10Klin with switch pcmoutn:

270X232A103B1B1

prices arent the absolute worst.

and it could really help things out with space, because 5.25 is really really tiny for 4 switches and 4 pots.

only i cant tell from the datasheet if those are rotary or push pull?

oh wait... maybe those are spst, click at one end of the rotation....

cant tell.... the datasheet is running me for a loop

billy

 

[the scum]

Enthalpy,

That looks like a SPST mounted into the CCW end of the pot. The giveaway is the part footprint: 3 pins for the pot, and only 2 for the switch.

Mouser have Alphas with a DPDT-push-pull on em for similar prices.

But the CTS and Alpha parts are all linear...

I got my handful of parts in today. The Eswitch pushbuttons are a lot smaller than the ITT ones in the picture above. I'll update my libraries and report back.

If there were an easy way to mount two pushbuttons on top of each other, so they're side-by-side on the strip, that could save some room, as well. But for something that people are talking about building 16 of, minimizing how much lies offboard results in some serious time savings.

uk03878,

The connector on the bottom of the above diagram is a Harting ribbon connector. They also come from several other makers, 3M and Amp among them.

IDC means insulation displacement connector...the connectors have V-shaped notches with sharp edges. You wedge the unstripped wire into the V, and it cuts through the insluation to make contact. They come in a variety of shapes and sizes.

The ones we've been discussing here are used on ribbon cable, and the connectors have pins arranged on a 2-row, .1" grid.

The advantages:
-they're inexpensive, and so is the cable...you can get fancy ones with lots of pins for a couple of bucks.
-They're easy to work with...you can put the connectors on the cable with a regular bench vise.
-they're great for something like this, where we need to run busses to many modules. With one stretch of ribbon and a fistfull of connectors, you could wire up the "backbone" for this project in 10 minutes. No stripping, no soldering, no buss wire.
-they're available from many vendors, all around the world.

The disadvantages:
-The cable isn't super-mega-audio-hifi quality...line to line capacitance on a long one can be problematic, and lead to crosstalk. I've addressed that by leaving a "quiet" line between each active mix buss line...in this design, the ground sense lines. And they're small and cheap enough that it wouldn't take much to leave a grounded line between each active line, or pair of lines.
-the wire itself is 28-AWG...not a lot of current carrying capacity. But again, they're cheap and they can be run in parallel.
-it's not sheilded.
-(as discussed above) cheap ribbon hardware will crap out on you.

And homework for someone: what's the recommended max current to run on a 28 AWG wire? And what reference did you look it up in?

 

[the scum]

Just a quick update for those of you following this:

I'm headed to AES, so there's not going to be much progress in the next week.

I've got a pile of parts on the workbench, slowly breadboarding a proof-of-concept for a couple channels and a couple of summing amps. With AES-prep work, my bench time has been limited.

Look for a real project update in a week or so!

 

[strangeandbouncy]

Hi guys,

forgive my ignorance, but I wonder if it would be possible to drive say 4 auxes instead of 2? I would definately be using a DOA, say a 2520 rather than a 5534 or whatever. This could be exactly what I wanted for xmas . . . .

Thank you, Santa, I'll be good!


AndyP

 

[therecordingart]

Anymore updates on this one?