Page 1 of 1 1
Topic Options
#1000675 - 09/21/10 07:07 PM Anyone made a passive summing device?
Randyman... Offline
Planeteer


Registered: 03/30/02
Posts: 8670
Loc: Houston, TX
I'm interested in analog summing - and knowing me - I'd prefer to DIY something simple than spend thousands on a brand name box with bells and whistles I don't need and can't afford. I realize an active gain stage will be needed for make-up gain - and I have plenty of nice Preamps that will easily fit the bill.

I'm looking to make a simple DB25-to-L/R XLR passive (resistive) summing cable that will take the 8 Outputs from a DA converter (RME ADI-8 or SSL AlphaLink) and sum them to the stereo pair of XLR's - the XLR's will then feed a high-quality Mic Preamp for make-up gain and return to the AD Converter to be re-recorded as the Main Mix. I won't need any Mono/Stereo switches or expensive trim-pot controls - just a fixed level summing network for 1+3+5+7 to Left XLR, and 2+4+6+8 to Right XLR.

I'd also like to see how much more difficult it would be to expand to 16 channels (2x DB25's). I'm assuming the resistor values would change, but that's probably all that would be different aside from more soldering.

So - what is a good starting point (and ballpark resistor values for a professional Line Level DAC)? Is it as simple as Line Level Inputs > Resistors in series > tie resistor outputs together and done? Or would this involve something a bit more involved than that (like multiple H-Pads summed together)?

I'm betting this can be crammed into an adapter cable opposed to building something in a project box / rack chassis to save space. I don't see why this would sound any different from any of the $,$$$ summing boxes that have nice gain-stages built in?

Any bright ideas on where to start? Thanks!

_________________________
Audio + PC is the place to be
Randy V.
Audio-Dude/Musician/Crazy Guy
Other Crap The Radio Devils
My PC Components My Mics My Gear


Top
#1000818 - 09/22/10 02:09 PM Re: Anyone made a passive summing device? [Re: Randyman...]
Randyman... Offline
Planeteer


Registered: 03/30/02
Posts: 8670
Loc: Houston, TX
Anyone?



_________________________
Audio + PC is the place to be
Randy V.
Audio-Dude/Musician/Crazy Guy
Other Crap The Radio Devils
My PC Components My Mics My Gear


Top
#1000831 - 09/22/10 03:19 PM Re: Anyone made a passive summing device? [Re: Randyman...]
LakeStone Karl Offline
Planeteer


Registered: 06/26/02
Posts: 15816
Loc: Eastern PA, USA
I'd start with a fistfull of 2K 1% resistors and see what happens.
_________________________



-karl

LakeStone On The Web

Top
#1000840 - 09/22/10 03:39 PM Re: Anyone made a passive summing device? [Re: LakeStone Karl]
Randyman... Offline
Planeteer


Registered: 03/30/02
Posts: 8670
Loc: Houston, TX
Fistful - Nice!

Is the general concept to simply wire the resistors "in series" with each input (one for each leg of the balanced signal) and then tie (parallel) the outputs of the resistors together (keeping the 2 legs seperate, of course)? Or is an "H-Pad" type network needed where you'd add a shunting resistor across the series resistors? What kind of dB loss are we talking per input?

I obviously need to do some research - but I'd love to get pointed in the right direction - and you seem like the one to help \:p

I plan on using descent resistors (1% 1/4 or 1/2 watt - I'll try to find "Low Noise" resistors suitable for high-end gear)

Thanks for the reply, LS Karl!

_________________________
Audio + PC is the place to be
Randy V.
Audio-Dude/Musician/Crazy Guy
Other Crap The Radio Devils
My PC Components My Mics My Gear


Top
#1000846 - 09/22/10 04:11 PM Re: Anyone made a passive summing device? [Re: Randyman...]
bear Offline
Planeteer


Registered: 10/25/99
Posts: 6223
Loc: abq,nm,usa
http://www.twin-x.com/groupdiy/albums/userpics/balancedmixnetwork.pdf

http://www.rhythminmind.net/presetblog/2009/11/diy-12-to-2-passive-analog-summing-panel/

http://www.gearslutz.com/board/geekslutz-forum/440806-diy-12-2-passive-analog-summing-panel.html


Edited by bear (09/22/10 04:17 PM)

Top
#1000847 - 09/22/10 04:25 PM Re: Anyone made a passive summing device? [Re: bear]
Randyman... Offline
Planeteer


Registered: 03/30/02
Posts: 8670
Loc: Houston, TX
Peeking now - Thanks bear! I've got 40 channels of DA outputs and I'd like to use more of them (Only using 20 as of now) \:\)
_________________________
Audio + PC is the place to be
Randy V.
Audio-Dude/Musician/Crazy Guy
Other Crap The Radio Devils
My PC Components My Mics My Gear


Top
#1000852 - 09/22/10 04:42 PM Re: Anyone made a passive summing device? [Re: Randyman...]
Randyman... Offline
Planeteer


Registered: 03/30/02
Posts: 8670
Loc: Houston, TX
Looks like my loose assumptions were correct! It appears that simply using ~10K resistors (still researching the exact values I'll use) in series with each input's leg and then using a single shunt resistor on the output is the ticket (basically an H-Pad with summing between the leg resistors and the shunt resistor). The Shunt might not even be required since I'm feeding from discrete DAC outputs and not from a Mixer's "busses" that can feedback through each other per se.

I think I'll be able to wire the resistors into large-bodied DB25 shells (two DB25's for 16 channels) and then marry the 2 connectors sums together and shunt at the XLR connector - so this should be able to take on the "Cable" form factor I was hoping for (I'd prefer not to use a project box and XLR inputs as all of my converters have DB25's and I'm short on rack space).

Thanks for the excellent links - bear. Much appreciated

I'll wrap up my resistor value research and order the parts ASAP. Who needs a $4,000 Tube Tech summing box when you have a "Fistfull" of nice resistors and a good Mic Pre (I'll likely use an ADL600 or my SCA Neve clones for gain) \:p

Any suggestions on the largest bodied DB-25 Solder type connectors that are available (so I have ample room to cram everythnig in there)? I'll only need a single mic cable exiting the connector - but will need enough room for 16 resistors and some short wiring inside the shell. I've got XLR's coming out my ears, but no DB25's on hand...

_________________________
Audio + PC is the place to be
Randy V.
Audio-Dude/Musician/Crazy Guy
Other Crap The Radio Devils
My PC Components My Mics My Gear


Top
Page 1 of 1 1


Hop to:
Shout Box

Who's Online
8 registered (rpk, wjgypsy, What does this button do?, C Jo Go*Crystal Studios*, motown59, Infinitymobile, 2 invisible) and 52 anonymous users online.
Top Posters
45933
Jazzooo
42442
Al
40000
Silversmith
36747
Timster
32942
Tom Mix
28594
NOK
26303
Ismellelephant
25995
gonzo
24577
Doughboy
24293
Popmann
23691
paulb
22784
RGR
22035
moontan
21692
flatcat
21586
Mooseboy
21125
fonts
20392
Marty Gilman
19598
vvvm
19160
String Jammer
18871
Vanillagrits
18791
Jammer
18741
T57Strat
18714
glennsimonds
18245
Gretsch 6120
18232
GAMBLE
17600
GAWZDigitalUnderground
17522
Geo
17203
SteveW
17047
Hano
16203
C Jo Go*Crystal Studios*
16161
Delso
15816
LakeStone Karl
15499
fabulousthunderbird
14958
virtualan
14908
kid-surf
14698
JazAddict
14626
Dave Morris
14492
Dan Barnes
14405
Stuart
Forum Stats
20248 Members
32 Forums
125537 Topics
1439542 Posts

Max Online: 226 @ 03/21/16 07:30 AM
Newest Members
rpk, RJWashburn, REX, aybz2413, FireSailing
20248 Registered Users

Generated in 0.009 seconds in which 0.003 seconds were spent on a total of 13 queries. Zlib compression disabled.