Passive Summing Box - To PCB or not to PCB

[jtoole]

[quote author="radiance"]I'm in if we make this an active 6 buss design (2 subgroupds and 1 master), 2 aux send per channel and maybe a simple passive EQ on the busses (or maybe per channel..).
Summing might be done by these Neumann/Lawo cards or so....
So far I think Í'll only need a pcb to mount the relays for group switching.[/quote]

I appreciate the interest, but I think I'd prefer to keep this project (or my part at least) to a fully passive design. Maybe someone else can startup another project in parallel to create a standardized PCB for active designs...

jt

 

[jtoole]

[quote author="kruz"]IMHO the joy of having a pcb here is to use a pcb mount DB25 connector.. avoiding the mess to solder those tiny tips one by one...
just a tought.[/quote]

Does anyone have a link that describes the wiring of the standard DB25 for audio i/o - I'm looking at the footprints of some DB25 pcb mounts to see if we could do a layout that can accept a DB25 or be wired directly at the builders option...

I don't personally need db25 as I don't have anything PT that will accept db25 directly, and a commercial db25->XLR cable is more expensive than this whole project...

Thanks -
Josh

 

[matta]

Hey Josh,

Here you go: http://www.tascam.com/Products/MX-2424/TECH_DB25_Pinout.pdf

Cheers

Matt

 

[Matt Syson]

Hi
It will be almost impossible to create a universal board where switches are wired via headers with onlt a DB25 and the mix resistors, it is almost pointless. If you don't like soldering a DB25, how about using a ribbon crimp connector and hard wire the other ends of the ribbon.
You could use 'veroboard' (stripboard) to mount the resistors on if you wish. I know it sounds a bit 'killjoy' but there is so little in it really and everyone wants something different.
If you want aux sends and EQ then either buy a cheap mixer or if it is for the intelectual excercise buy a broken modular mixer and design replacement boards as the metalwork would be done, which is often the hard bit.
Matt Syson

 

[jtoole]

Thanks Matt!

I'm looking at the footprint of right angle PCB db25 connectors - based on the digikey catalog I'm using, it looks like .109" between pins, in staggered rows.

Might be able to use .1" headers here (for non-db25 users), but unfortunately the db25 is wired so that each input requires 2pins from 1 row (+, g), and 1 pin from staggered row (-). Probably if we go this direction the best bet will be to solder wires directly to the board (or use db25) since I can't think of an obvious way to approach the headers that isn't awkward.

How many people are seriously going to need/use db25 directly on the PCB? I'm not opposed, I just want to make sure thats the best bet for the majority... I don't personally need them so I'm a bit biased :wink:

If we DON'T use db25 footprints, I was going to do .1" headers in one or two even rows, so people can wire directly to pads or use .1" connectors (could be multple 3pin or larger)...

Any other ideas?

Thanks!! :thumb:
jt

 

[jtoole]

[quote author="Matt Syson"]It will be almost impossible to create a universal board where switches are wired via headers with onlt a DB25 and the mix resistors, it is almost pointless. If you don't like soldering a DB25, how about using a ribbon crimp connector and hard wire the other ends of the ribbon.
You could use 'veroboard' (stripboard) to mount the resistors on if you wish. I know it sounds a bit 'killjoy' but there is so little in it really and everyone wants something different.
[/quote]

Well, thats certainly a valid point - As I stated in the original post, I've gone back and forth on the desire/need to create a PCB for this...

I like the fact that a PCB would seem to provide a more robust unit. A PCB would also speed up the build time for future builders. I was hoping that since it is such a simple design, that we could make something broadly useful to more people. I will admit that the responses do indicate that there is more variety of need than I expected...

On one hand I think I could put together a PCB pretty easily, and the cost isn't prohibitive - on the other hand, I could have probably already finished it point to point in the time I've taken trying to work out "swiss-army" PCB approaches that will be useful to all... :wink:

Care to clarify why its "almost impossible to create a universal board where switches are wired via headers"? Maybe I'm missing something here (very possible) that makes it particularly problematic... Thanks for the input. :thumb:

I'm still willing to abandon the PCB idea (I was originally going to go the veloboard route, directly attach shielded cables/connectors, and put in a small plastic enclosure - more of a 'summing snake') - Frankly I've continued to work on this because there was SOME interest from other users here for the PCB...

jt

 

[kruz]

Hey jt, you work is much appreciated here..
so.. speaking of that db25.. again, imho, it's a nice and tidy connector.. rme converter use them too i.e.
The "summing pcb" of my dreams would be a 4x db25 connectors (32ch), no controls: odd# channles wired to the L, the other to the R... and the summ directly hooked to a zero-ohm summing card like the neumann or lawo ones
This is what i was thinking lately.. but i'm working on another project now and moved this one in the back.

 

[Matt Syson]

Hi
Since the outputs of the DAW are all configurable in software I would like to suggest making a 'mixer' in a DB25 plug.
Wire 8 pairs of resistors from the plug pins at one end and link the 2 rows of 8 resistor wires together. Add a 'load' resistor (if wanted) then take a songle twin screened wire out to be one 'side' of the stereo. Do the same on another connector. Routle all your left channels to channels 1 - 8 and right to channels 9 - 16. If you want to make a 16 + 16 mix (or more) then you can simply parallel another 'plug mixer' onto it but in this case leave the terminating resistor out. If you were really careful you might be able to get some connector to fit into the cable hole in the D shell!!
When working, fill it with epoxy resin to make it robust if you like.
If still considering a pcb then you can track the input for a DB25 and a ribbon IDC either as a header or as a 'transition' connector, both are 0.1 inch pitch in 2 rows (26 pins total).
Matt Syson

 

[enthalpystudios]

I've been reading the thread here and there, and I've been thinking about it some....

I was thinking a pcb would be great, strictly for the ease of soldering db25 headers (to interface to a patchbay terminating in db25 in my situation.)

i think, however, that the fact may be that clearance from panel to pin on xlr connectors is a good deal greater than that of a db25. It may or may not actually work, but I have a feeling that it may be possible to have traces come to the back of the pcb arranged for pcb mount 3pin, and then for them to branch to their db25 arrangements.

just a feeling, but I think that both arrangements may be possible. Also of note is the number of xlr connectors that fit within 17 or so inches (width of a parmetal enclosure, 16.5 if you don't like dealing with the flap from the side panels)

I'll take a look at some sheets about it myself, because i'm pretty interested.

may be a good time, as someone noted in the blackmarket or the brewery that 4pcb.com is doing their 500.00 off promo again. My local rep apparently didn't like the fact that I'm not a "company," but shouldn't be a big deal for most. I think I was the exception that didn't get offered the promo code.

anyway.

thanks for the work on this!

billy

 

[Matt Syson]

Hi Billy
I think I understand what you were proposing. You could always use right angle versions of both XLR and D types or, if the board is flat then use either a transition conector and a little ribbon or even more cunning, perhaps a 'socket saver' like used on laptops as extra 'padding' with the advantage that if the D type gets broken you can replace it easily.
There are of course many ways of 'skinning a cat'!
I made up a board for 2 Male and 2 female XLR and discovered (on assembly) that the centre line of the female XLR (combo jack) was about 2mm different to the male XLRs. Grrrrrrrrr.
Matt Syson

 

[enthalpystudios]

hmm... transition connector could work.... it's just a shame that they can't be laid out side by side, tracks paralleling each connection, because xlr takes up the entire span of a parmetal enclosure. what really stinks, now that I *just* realize it, is that pcb mount xlr connectors for 16x2 require a 16.38 inch board. thats big, and could get expensive to fab. maybe a 2u project, with a transition connector from bottom pcb to top, 8 xlrs on bottom, 8 on top, d sub off to the side on the bottom? That would make a bottom board of about 14 inches, top board (with outputs) of 9 to 10 inches.

anyway, I just wrote all this, maybe its of some use:


if anyone has corel draw, i mocked up some things, with dsub holes being done up to scale from Amp model 788751-1 on mouser. Neutrik holes are according to their DXF files from model number NC3FAH1, and panel is indicated with yellow lines. bear in mind this takes out one or two of the neutrik supporting holes to accomplish both on the same.

the trace version got hurried at the end. lines are 1 pt, which i suppose means nothing. I have no clue what kind of track spacing is possible/optimal/acceptable. I have no clue about pcb's, just had a hunch that these could both fit on one board. anyway,, they're at:

http://www.enthalpystudios.com/diy/passive8chanwithtraces.cdr

and

http://www.enthalpystudios.com/diy/passive8chanjustholes.cdr

Hopefully it helps somehow.

Anyway, I'm very interested in a pcb with dsub holes, 16, 24, whatever.

Also, this is layed out with just a tiny bit extra spacing than neutrik recommends as minimum for these connectors. they say .906, i did .91 inches. That definitely fits 18 xlrs on the back (not much else, however)

Only two options I'd care to see, IMHO, are LCR switch (or mono/stereo per pair of inputs, like a d4ng3rous box), and a mute switch. Or maybe instead of the mute switch, at least a switch that routes inputs 1+2 direct to the outputs.

LCR probably needs rotary or a stupidly expensive (for pcb mount) toggle. Maybe just pads for user choice, or with some clever track routing (i think) a mono/stereo switch per input pair could be done.

i dunno.

billy

 

[Matt Syson]

Hi Billy
You are keen!
In terms of metalwork have you reviewed what is available as pre punched panels? In the UK we have several sources. Penn fabrication sell via several outlets, CPC.co.uk among them, then there is Canford Audio and Studiospares (again a variety of panels and pitches so you would have to pick one and design around it.
Switches, the ALPS or equivalent press switches rather than toggle as to do it balanced in stereo you will be wanting at least 4 pole.
It will end up a bit like a Folcrum I suspect if a passive mix you are making but a Dsub to XLR breakout would be handy. Of course you may be needing ins and outs and of course XLR pins get reversed male compared to female!!!
Where is this going now?
Matt Syson

 

[Guest]

Switches
I am partial to EAO series 31 (18mm I think) - or EAO series 19 (8mm)
Buy them in 1NO Maintained (locking) - and then use relays as switch extenders
In that sense you get lovely illuminated pushbuttons and the ability to ptrint of legends onto clear transfer film and put those inside the switches

 

[enthalpystudios]

[quote author="Matt Syson"]
Where is this going now?
Matt Syson[/quote]

ummm... yeah i know dude

lol

xlr's i suppose help appease.... if this had nothing to do with anyone else, I'd say go dsub all the way. It just makes everything so damned easy. Theres no way two breakout cables are as expensive as 16 xlr cables. well, i dunno, apples to oranges in a way. besides, i'm gonna hook all this up to a patchbay terminating in dsub, so its super convenient.

what i'm having a hard time with (and also as it pertains to a monitor control box i'd like to do at somepoint), is for example when one splits a signal, like one would slit an input in a passive box like this, you split it to both L and R busses, and have a switch somewhere in between to select where you would like it to go. What are the consequences of one split being unterminated? does one need to short that? or does it float?

anyway, i have issues with that stuff atm, basic wiring I suppose, but still, I don't want things f'ing up, or humming, or loading when they need buffer, etc..

but as far as this summing box, I think those switches uk03978 mentioned sound slick. To do mono/stereo, in one switch state, input 1 goes straight to Lbus and input 2 straight to Rbus. In the mono state, both inputs would split, get mono (4.3k or so?) resistors and go to both busses. 4 pole seems right for the "stereo state," but for the mono state... oh I guess inputs go to the 4 poles in the 'middle' of the switch, then one set of poles goes discretely to 10k summing resistors and to the busses, and the mono set of 4 poles goes to mono and 10k resistors and then to both busses. or 10 k resistors before the switch?


ok, i think it just clicked, at least i hope. someone burst my happy little bubble if i'm totally wrong.. 4pdt it would need to be then. still, the prospect using twice as many 4p3t rotarys for LCR switches makes 4pdt illuminated pushbuttons probably worth the cost. and the super slick look ;]

maybe somebody can let me know if that rant about switches even makes sense. I guess what I'm wondering is if the input can go to the switch, and if both outs from the switch can be hooked to the busses at the same time, with one set floating when off. If it needs to be terminated when off, i can't figure out how that would be done. maybe a different switch? or clever trickery as yet not known to this n00b?

billy

 

[enthalpystudios]

yeah uk, looked at eao's website, those switches are pretty hot... a

anyway, off to buy some damn solder

 

[Guest]

BTW -
4 Pole - Series 31 switches cost something like £30-40 each

1 Pole - Series 31 switch costs £5-7 - A 4PCO relay costs another £4-5 (or cheaper)
And this schematic from PRR makes links everything together

 

[Matt Syson]

Hi
Passive summing needs terminating for non selected sources so life gets more fun!!
EAO and relays, not cheap (!!) but nice.
Is this still passive (yes the audio is).
Who said a microprocessor to control it all and give a MIDI interface???
Routing and mutes automated?
I think we have loads of projects on here.
Matt Syson

 

[Matt Syson]

Hi
Your post arrived while I was doing mine. You want a fifth pole to operate the LED........
Matt Syson

 

[Guest]

it should be already in the circuit as a push on, push off
Matt - I am only a little newbie but the EAOs I have are ..
1NO - has four connections
in/out
led (or little lamp thing) on in/led out
So the LED comes on and the circuit is engaged when the switch is depressed without any other relays

 

[kruz]

[quote author="enthalpystudios"]
http://www.enthalpystudios.com/diy/passive8chanwithtraces.cdr

and

http://www.enthalpystudios.com/diy/passive8chanjustholes.cdr[/quote]

Hi Billy,
I can't open your files with my corel 12.. what version have you used?