The No.1 Website for Pro Audio
 Search This Thread  Search This Forum  Search Reviews  Search Gear Database  Search Gear for sale  Search Gearslutz Go Advanced
DIY – 12 to 2 – Passive Analog Summing Panel. Equalisers (HW)
Old 17th November 2009
  #1
Lives for gear
 
rhythminmind's Avatar
 

DIY – 12 to 2 – Passive Analog Summing Panel.

I wanted to make myself a nice little passive summing panel for my home rig out of parts laying around the shop. I wanted to simplify/improve my final summing stage. Pleased with the results, Sounds great. Gives me piece of mind bypassing the channel IC’s & master section on my Sony MXP desk.

I used a simple XLR panel, Neutrik XLR mounts, Neve super conductive cable, & OHMITE 1% metal film resistors. Took all of 2 hours to wire up.

10.7k resistors on the inputs & a 220 shunt on the outputs.

After level calibration my noise-floor is at -80 & crosstalk @ -88.

FYI – this is with a John Hardy M1 transformer pre for the make up gain. Nothing better IMHO.




Old 18th November 2009
  #2
Lives for gear
 

I don't see the cold hooked up to the output jacks. Is it hidden or what?

I'm thinking about one building of these myself.
Old 18th November 2009
  #3
Lives for gear
 
rhythminmind's Avatar
 

Quote:
Originally Posted by mixedupsteve View Post
I don't see the cold hooked up to the output jacks. Is it hidden or what?

I'm thinking about one building of these myself.
It's attached, just hard to see in the pic..
It's working out wonderfully.
All you have to do is figure out how many channels you need. Pick a input impedance value. I picked 21.4kohm, only because I had "military grade" resistors on hand that happened to be 10.7k.
Resistors between 5k-15k should work well for most applications. It's a balance between noise or crosstalk.

I recommend using a transformer based pre for the make up gain that accepts a wide range of impedance, like the hardy.
You should pick your shunt resistors on the outputs to spit out around 150ohm for most mic pres. Mine is 200 something. But the hardy can easily handle anything from 60-600ohm.
Old 19th November 2009
  #4
Lives for gear
 

OK Thanks,
I think I'll just go ahead and build one like yours using a prepunched panel. I have the NYDave schematic and he reccomends 5Ks on the inputs and no shunt for this simple version. I wanted to do the version with level and panning but this is so easy I think I'll go ahead. I'll be using Purple Audio 500 series pres at line in for make up so I'll just skip the shunts.
Nice job.
Old 19th November 2009
  #5
Lives for gear
 
rhythminmind's Avatar
 

I think you will be better off with them. Improves crosstalk & will set the impedance to what your pre will want to see. I used NYD's schematic for reference myself.

Checkout these posts as well
Yet another passive summing box! (Pics Included)

My DIY summer is done!

This is the NYdave PDF I used for a mic pre makeup gain setup.

http://www.twin-x.com/groupdiy/album...mixnetwork.pdf
Old 21st November 2009
  #6
Lives for gear
 

how does the shunt improve crosstalk, did you measure this? if anything it would seem it would just add noise.

nice job btw!!

was thinking of fabbing a pcb for this and make it available to diyers
Old 21st November 2009
  #7
Lives for gear
 
rhythminmind's Avatar
 

Quote:
Originally Posted by johnnyc View Post
how does the shunt improve crosstalk, did you measure this? if anything it would seem it would just add noise.

nice job btw!!

was thinking of fabbing a pcb for this and make it available to diyers
I don't have the answer to that. The main reason it is needed is to bring the output impedance down to mic level. But more experienced men then I have recommended it.

Quote:
Originally Posted by ulysses View Post
A shunt resistor on the output will increase the attenuation, reduce crosstalk, and set the output impedance wherever you want it.
Taken from here
Optimal resistor values for passive summing


...
Old 14th February 2010
  #8
Gear Addict
 
floydisbest's Avatar
 

Nice box/work!

I want to do this myself by just modifying an XLR patch bay I have lying around.

My question is a good resistance to choose, and I'll be running the stereo out to a pair of Great Rivers, so the shunt also? Maybe I'll just use the same values that you did.

Old 14th February 2010
  #9
Lives for gear
 

Hi
If all your sources are from seperate outputs from a DAW or other line out devices that are ONLY feeding the mix box then there will be NO crosstalk unless your wiring is spectacularly bad. This parameter comes from the time when this form of mixing was used in 'mixers' where the same signal would be feeding other channels (post a pan pot perhaps) or auxiliaries. Then signal could get back through the mix resistors to a possibly non xero impedance of the pan pot or amplifier stage thereby cross feeding other outputs.
Part of the reason for shunting the bus was to establish a low crosstalk figure with non zero source impedances and to reduce interaction when more or fewer sources were addded to the mix. In your case using XLRs which do not terminate unused sources the resulting output level from ONE source will vary depending how many other contributors there are to the mix.
You can do a pile of maths to work out what will happen in various scenarios but for example if you do not shunt the output and you have a high impedance input and only 1 source connected you will get a reduction in level of about 6dB (10 K mix resistance and 10K input impedance).
Adding a second input will drop the level by about 4dB (rough top of head calculation).
Adding a third source will drop it again but a bit less than another 4dB.
Having a 10k mix resistor but with a 600 Ohm 'shunt' will drop a considerable amount but adding another source will drop this by less than half a dB.
Since mic amps are usually optimised for minimum noise with around 200 Ohm source impedance it is quite sensible to aim for this as a combined bus impedance (mix resistors plus shunt) although a higher resistance may be beneficial as you would not need so much 'make up' gain. a mic amp noise figure is usually quoted at near maximum gain, where the design usually excels but you only need about 25 - 35 dB of gain and not all mic amps 'sparkle' so well at this low a gain setting (usually NOT quoted!).
Matt S
Old 14th February 2010
  #10
Lives for gear
 
rhythminmind's Avatar
 

Quote:
Originally Posted by floydisbest View Post
Nice box/work!

I want to do this myself by just modifying an XLR patch bay I have lying around.

My question is a good resistance to choose, and I'll be running the stereo out to a pair of Great Rivers, so the shunt also? Maybe I'll just use the same values that you did.


That box would work great. Good to know for future projects.
for 12 inputs I would use 1% 10k's on the inputs & something close to a 227ohms as a shunt.

shunt ohm resistor = (20000/n)*200/((20000/n)-200)
WHERE N = NUMBER OF INPUTS


Just copy that formula into google & replace "n" with the number of inputs you are using.


more info here

DIY – 12 to 2 – Passive Analog Summing Panel.
Old 14th February 2010
  #11
Lives for gear
 
rhythminmind's Avatar
 

Quote:
Originally Posted by Matt Syson View Post
Hi
If all your sources are from seperate outputs from a DAW or other line out devices that are ONLY feeding the mix box then there will be NO crosstalk unless your wiring is spectacularly bad. This parameter comes from the time when this form of mixing was used in 'mixers' where the same signal would be feeding other channels (post a pan pot perhaps) or auxiliaries. Then signal could get back through the mix resistors to a possibly non xero impedance of the pan pot or amplifier stage thereby cross feeding other outputs.
Part of the reason for shunting the bus was to establish a low crosstalk figure with non zero source impedances and to reduce interaction when more or fewer sources were addded to the mix. In your case using XLRs which do not terminate unused sources the resulting output level from ONE source will vary depending how many other contributors there are to the mix.
You can do a pile of maths to work out what will happen in various scenarios but for example if you do not shunt the output and you have a high impedance input and only 1 source connected you will get a reduction in level of about 6dB (10 K mix resistance and 10K input impedance).
Adding a second input will drop the level by about 4dB (rough top of head calculation).
Adding a third source will drop it again but a bit less than another 4dB.
Having a 10k mix resistor but with a 600 Ohm 'shunt' will drop a considerable amount but adding another source will drop this by less than half a dB.
Since mic amps are usually optimised for minimum noise with around 200 Ohm source impedance it is quite sensible to aim for this as a combined bus impedance (mix resistors plus shunt) although a higher resistance may be beneficial as you would not need so much 'make up' gain. a mic amp noise figure is usually quoted at near maximum gain, where the design usually excels but you only need about 25 - 35 dB of gain and not all mic amps 'sparkle' so well at this low a gain setting (usually NOT quoted!).
Matt S
Thanks for the info..
Old 14th February 2010
  #12
Gear Addict
 
floydisbest's Avatar
 

rythminmind, thanks for the help- I just ordered up all the resistors from mouser.

Where would you suggest going for super conductive wire?
Old 14th February 2010
  #13
Lives for gear
 
rhythminmind's Avatar
 

Quote:
Originally Posted by floydisbest View Post
rythminmind, thanks for the help- I just ordered up all the resistors from mouser.

Where would you suggest going for super conductive wire?
I would go for Belden 9451 or whatever the current gepco equivalent is. The neve cable I used isn't available to the public. There isn't anything special about it. Any decent shielded line audio cable will do.
Old 17th February 2010
  #14
Lives for gear
 
filthyrich's Avatar
 

hmm

OK, so normally when I do mic cables, I do 1 red 2 blue 3 ground.
So, do I just connect a 10k resistor to #1 and 2 of each and then chain all of the wires to the resistors?
If so, I do the same for the other side I guess.
What do I do with the #3 pin on all of them? Does that blue wire in the XLR summer have 3 wires in it? If so, they are all just simply chained together..all three wires right?


I then run a 200k resistor (shunt) across the 2 wires coming in to the outputs? If so, is the shunt going from pin 1 and 2 on each of the L and R?

Or is it going from the 1 to the 1 on the L and R?

Thanks.
Old 17th February 2010
  #15
Lives for gear
 
rhythminmind's Avatar
 

Quote:
Originally Posted by filthyrich View Post
OK, so normally when I do mic cables, I do 1 red 2 blue 3 ground.
So, do I just connect a 10k resistor to #1 and 2 of each and then chain all of the wires to the resistors?
If so, I do the same for the other side I guess.
What do I do with the #3 pin on all of them? Does that blue wire in the XLR summer have 3 wires in it? If so, they are all just simply chained together..all three wires right?


I then run a 200k resistor (shunt) across the 2 wires coming in to the outputs? If so, is the shunt going from pin 1 and 2 on each of the L and R?

Or is it going from the 1 to the 1 on the L and R?

Thanks.
1st off lets make sure you have the standard xlr pinout down.
Pin 1 = Shield (Ground)
Pin 2 = T/Red/+/Hot
Pin 3 = R/Black/-/Cold

Quote:

Pin Function
1 Chassis ground (cable shield)
2 positive polarity terminal ("hot")
3 return terminal[2] ("cold")
Old 17th February 2010
  #16
Lives for gear
 

Hi
The loading resistor should be 200 Ohms, NOT 200K Ohms.
Matt S
Old 17th February 2010
  #17
Lives for gear
 
filthyrich's Avatar
 

yeah.

I thought about it right after I posted, 1 ground 2 blue, 3 red is what I usually do for cables. Thanks for the help.
Old 17th February 2010
  #18
Lives for gear
 
filthyrich's Avatar
 

any reason

Any reason it couldn't be made out of wood?
Old 5th March 2010
  #19
Lives for gear
 
filthyrich's Avatar
 

3 wires in the wire?

OK, so all the 1's go to the next 1's and the 2's to the 2's and the 3's to the 3's right? The hot and cold have resistors going to the pins and then put a resistor across the hot and cold at the end...the "shunt"...right?

So, there are three wires inside that blue wire?
OR, are there 2 wires and the 3rd is the metal shield?

Thanks.
Old 5th March 2010
  #20
Lives for gear
 
rhythminmind's Avatar
 

Yes 3 wires.

The flow is as follows.

  • XLR input Pin 1 to shield wire - shield wire to pin 1 on the next xlr.
  • XLR input Pin 2 to resistor - resistor to RED wire - RED wire to next xlr resistor.
  • XLR input Pin 3 to resistor - resistor to BLK wire - BLK wire to next xlr resistor.
The shunt resistors get placed across pins 2&3 on the output xlr's


...
Old 5th March 2010
  #21
Lives for gear
 
rhythminmind's Avatar
 

How many inputs are you wiring up? & what resistor values are you using for the inputs & shunts?
Old 6th March 2010
  #22
Lives for gear
 
filthyrich's Avatar
 

haven't done it yet

I haven't done it yet. I don't know where I'd put it in my rack and my setup isn't ideal to make me come out of my DAW outs back into the front of my rack..so I'm trying to figure out a workaround. Maybe another snake coming to front.

I'll likely have 8 ins going into 2. I guess I could go up to 12 or 16 and get all crazy with it. I don't know about the resistor value. I've seen it all over the board in the DIY summers and over on a couple other websites. I'll figure that out when I finally get around to trying this.

EDIT. I think this might work. There are two extra holes. I'll come through with wire from the back for the inputs on front.

Last edited by filthyrich; 6th March 2010 at 07:48 PM.. Reason: thought of something else.
Old 8th March 2010
  #23
Lives for gear
 
filthyrich's Avatar
 

Inserts?

It seems like you would have to be able to do this or why bother, but...

Can you run some or all of the inputs into the summer through various compressors and/or eq's and bring the signal back into the summing unit without any problems volume wise or anything else?
Old 8th March 2010
  #24
Lives for gear
 
rhythminmind's Avatar
 

Yes, this is the main functionality. Allows for the easy use of analog outboard.
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Similar Threads
Thread
Thread Starter / Forum
Replies
d_pert / Bass traps, acoustic panels, foam etc
17
bbgallaway / Bass traps, acoustic panels, foam etc
10
recall / So much gear, so little time
10

Forum Jump
Forum Jump