stickjam

Other than making the cables shorter, I'm not sure it can get any smaller. ;D

Interfaces 16 channels of a Mackie SDR24/96 to a couple mic pres.  Works great!








tv

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #1 on: May 05, 2009, 05:21:27 PM »
carbon resistors for mojo?
If you sprinkle when you tinkle, please be neat and wipe the seat.

stickjam

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #2 on: May 05, 2009, 05:40:20 PM »
carbon resistors for mojo?

Yeah. (heh heh)  ;D   It's what I could lay hands on at that moment.

What the heck, my DAC's a retro Mackie recorder.  It sounds better than mixing in the box at least.

I'll rebuild 'em with the good stuff when Santa Clause brings me that pair of Apogee AD/DA-16Xs on my list.   8)

 

EmRR

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #3 on: May 05, 2009, 07:01:23 PM »
Well done!
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #4 on: May 05, 2009, 07:15:22 PM »
Wow, how long did that take and did you use a magnifying glass?

 ;D


mich

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #5 on: May 05, 2009, 07:51:44 PM »

:)    Thinking outside the box..

"Tubes gone - darkness,darkness,darkness no colour ,no contrast." - Joni Mitchell

signalflow

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #6 on: May 05, 2009, 09:19:19 PM »
Courious,  It looks like a db-25 connector....which only send 8 channels balanced.  I can see 16 if you were to send un-bal but doesn't the db-25 outout of the SDR only send 8 channels balanced? Also how are you mixing the audio coming out before the summing unit?

Not trying to devalue in any way, truly is a work of art with the solder job, I could not get it right the 1st try much less the 9th and 10th.

-Casey
The shortest distance between two places is a nap.

Tubemooley

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #7 on: May 06, 2009, 04:56:09 AM »
Correct. But he's got two of them. I think each cable sums eight channels into one. So you would have to choose your stems in the software app and port them appropriately (and pan them too) to get the stereo mix yer looking for. DW.

stickjam

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #8 on: May 06, 2009, 10:25:02 AM »
Wow, how long did that take and did you use a magnifying glass?

 ;D



A litte over two hours.  First DB25 took a hour and a half to wire up.  The second one probably only 20 minutes.  I got a rhythm down, the helpful part being leaving one end of the resistors attached to the reel tape to hold them straight as a group to solder to the connector.  Then sheared all but a couple mm of lead to solder to one of four buss wires slipping in bits of color-coded heatshrink, staggering the joints to prevent shorts.  It might have been faster had I used the crimp-on style DB25 pins, although even those I usually solder for security.  No magnifying glass--I actually had to take off my glasses to see better.  :)
 

Correct. But he's got two of them. I think each cable sums eight channels into one. So you would have to choose your stems in the software app and port them appropriately (and pan them too) to get the stereo mix yer looking for. DW.

Exactly.   The odd numbered channels on the DB25's sum to the Left XLR and the even channels to Right.

stickjam

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #9 on: May 06, 2009, 10:44:27 AM »
Courious,  It looks like a db-25 connector....which only send 8 channels balanced.  I can see 16 if you were to send un-bal but doesn't the db-25 outout of the SDR only send 8 channels balanced? Also how are you mixing the audio coming out before the summing unit?

Not trying to devalue in any way, truly is a work of art with the solder job, I could not get it right the 1st try much less the 9th and 10th.

-Casey

Actually, what took the longest on the first DB25 is fixing pinout screwups.  It's a connect two, skip one pattern.  I got the 13-pin half soldered right (from pin 1: R-skip-R-R-skip-R-R-skip-R-R-skip-R), but I started from the wrong end on the other half (from same end: R-R-skip-R-R-skip-R-R-skip-R-R.)  Those eight resistors. cut to nubs, had to be resoldered with forceps.  :P  I then soldered bare wires (the cutoff ends of the resistor leads still attached to the reel tape) to  all the skipped pins and connected them with a wrap-around bus with green heatshrink and connected that to the cable shields.  I left the shields unconnected at the XLR to avoid ground issues.


Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #10 on: May 06, 2009, 10:47:20 AM »
Seriously you should sell these.

People would dig the hell out of them.

Peace
Illumination
Langston Masingale, Sales and Customer Support @ JJ Audio Mics.

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #11 on: May 06, 2009, 10:48:39 AM »
can you explain what role the resistors play and how they are arranged including values used ?

Is the summing cable balanced or unbalanced ? "disconnected shields" , sounds like its unbalanced.

I'm interested in buliding a simple 4 bal in and 2 bal out summing box , but I think I'll still need
some resistors to impedance match the two signals into one output for proper operation. I think the same
principal applies to more inputs ( like your x16) which would go to one output Left/right.

your innovative summing cable looks very useful
« Last Edit: May 06, 2009, 12:18:15 PM by electrochronic »
curiousaudioparts at  gmail  dot  com
https://sites.google.com/site/diypartsstore/

stickjam

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #12 on: May 06, 2009, 11:18:46 AM »
can you explain what role the resistors play and how they are arranged including values used ?

Is the summing cable balanced or unbalanced ?

I'm interested in buliding a simple 2 in and 1 out summing box , but I think I'll still need
some resistors to impedance match the two signals into one output for proper operation. I think the same
principal applies to more inputs ( like your x16) which would go to one output Left/right.

your innovative summing cable looks very useful

Balanced.  Two 10k resistors on each balanced input channel (32 resistors total).   One 220 ohm shunt across pins 2 and 3 of the XLR.  The effect is that each channel is attenuated 20dB, which is made up by plugging the XLRs into mic preamplifiers.


The standard (Tascam) 8-channel DB25 pinout actually works in favor of producing this.  On the 13 pins on the Pin-1 (long) half, all the +signals are for even (right) channels and all the -signals are for the odd (left) channels.  The other 12 pins (short side) give the +signal for odd channels and -signal for even channels.

Essentially, the technique is to put 10K resistors on each of the + and - signal lines (16 in each connector)  Buss the free ends of the four resistors on the short side; that goes to XLR pin-2 Left.  Buss the four resistors on the - signals on the long side and connect to pin 3 Left.  Do the same for the right channel, except + comes from the long side and - comes from the short side.
 



« Last Edit: May 06, 2009, 11:21:45 AM by stickjam »

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #13 on: May 06, 2009, 12:17:11 PM »
Stickjam,

thanks for the explanation, but I'm lost in translation.

if its not too much trouble, any chance of putting up a simplistic diagram
I can follow. Or Linking the idea to a wwweb page that already has this info ?

4 bal input to 2 bal output

thanks
curiousaudioparts at  gmail  dot  com
https://sites.google.com/site/diypartsstore/

stickjam

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #14 on: May 06, 2009, 03:21:26 PM »
Stickjam,

thanks for the explanation, but I'm lost in translation.

if its not too much trouble, any chance of putting up a simplistic diagram
I can follow. Or Linking the idea to a wwweb page that already has this info ?

4 bal input to 2 bal output

thanks


I'd be happy to do that, but it'll take a while to make happen - in the middle of some heavy time-commitment gigs.  You could google for "Tascam Pinout" for a diagram of the DB25 connections.  That might help my explanation make more sense. 

There's a thread here (http://www.groupdiy.com/index.php?topic=16731.0) that's an 8-channel single rack unit version that's electrically identical to mine.


Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #15 on: May 06, 2009, 05:00:10 PM »
             Stickjam,

             Here is what I understand this to be,  putting 2 & 2 together, diagram below
             sounds noobish but it puts everyone on the same page. Same concept I believe.

             this diagram is assuming input impedance is line level 10-15K , If it were 600 ohm impedance
             would the 10K resistors be swapped to 600 ohm resistors ? and would the 220 ohm resistors change
             to a new value as well, or remain the same  ?
 
             I'm sure there is a mathmatical formula or web calculator for all this , just don't know what it is ....

« Last Edit: May 06, 2009, 05:33:50 PM by electrochronic »
curiousaudioparts at  gmail  dot  com
https://sites.google.com/site/diypartsstore/

kato

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #16 on: May 06, 2009, 08:55:41 PM »
Genius, Stickjam!

Potato Cakes

Re: Completed: World's Smallest 16 Channel to Stereo Summing Box?
« Reply #17 on: February 12, 2015, 11:29:36 AM »
What preamps have you used with this? Preferences?


 

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