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Summing Mixer Questions
Old 27th December 2010
  #1
Lives for gear
 

Summing Mixer Questions

Hello all,

Never posted in this particular forum, so I don't know if this is the right place for this....

First of all, I wish someone made a 32 channel passive summing mixer with 8 busses with inserts (I understand those would have to be active) but no one does....so I'm considering building something like this.

So...what I'm thinking of is a passive device that can do the Folcrom thing of L/R/L+R swtichable panning....and then (Maybe a concentric switch) that could assign to 8 busses in L/R pairs. Then, use a JLM audio circuit board that does buss summing with inserts....one that uses the JLM99V opamp for gain.

Then, since I'll have preamps sitting there that can do gain....that wouldn't otherwise be used during mixing....use the pres as summing makeup gain.

So my overall question is: With the senario mentioned above, how do you set up the gain between the L/R (passive) mixbuss and the 8 (active) busses? Is this possible? Isn't this kind of how a regular console works? Is this a workable idea? Enough questions.......THANKS!

Kirt Shearer
Old 27th December 2010
  #2
Lives for gear
 
Geoff_T's Avatar
 

Quote:
Originally Posted by kbshearer View Post
Hello all,

Never posted in this particular forum, so I don't know if this is the right place for this....

First of all, I wish someone made a 32 channel passive summing mixer with 8 busses with inserts (I understand those would have to be active) but no one does....so I'm considering building something like this.

So...what I'm thinking of is a passive device that can do the Folcrom thing of L/R/L+R swtichable panning....and then (Maybe a concentric switch) that could assign to 8 busses in L/R pairs. Then, use a JLM audio circuit board that does buss summing with inserts....one that uses the JLM99V opamp for gain.

Then, since I'll have preamps sitting there that can do gain....that wouldn't otherwise be used during mixing....use the pres as summing makeup gain.

So my overall question is: With the senario mentioned above, how do you set up the gain between the L/R (passive) mixbuss and the 8 (active) busses? Is this possible? Isn't this kind of how a regular console works? Is this a workable idea? Enough questions.......THANKS!

Kirt Shearer
Paradise Studios
Hi

You asked at the end... isn't this how a regular console works?

Well no, most regular consoles are not/were not passive and, although passive sounds simpler and cheaper, I think the more bells and whistles you add, the more pitfalls you may fall into.

I assume that you expect this proposed mixer to have balanced inputs? Now imagine your switching for the panning you describe. You will have to do some fancy wiring to keep the input impedance the same for all the options you offer.

My advise? Go to that That Inc web site and download the application notes for their balanced in and balanced out devices like the 1250 and the 1646.

You could make a nice active console out of parts like that.

Old 28th December 2010
  #3
Lives for gear
 

Quote:
Originally Posted by Geoff_T View Post
My advise? Go to that That Inc web site and download the application notes for their balanced in and balanced out devices like the 1250 and the 1646.
geoff, a bit off topic but do you prefer these to the burr brown line drivers and receivers?

back to on topic, what you are proposing is possible but not all that practical, there would be lots of signal loading issues to account for (although there might be creative ways around this). at first thought it would seem you are much better off as geoff mentioned with active devices in sort of a "mini-console" configuration. are you imagining basically a console that only does routing and no pres, faders, eqs, etc? this is doable and perhaps a manufacturer will make one if there is enough demand. but you would lose the cost savings of using existing mic pres for makeup gain.
Old 29th December 2010
  #4
Lives for gear
 
Geoff_T's Avatar
 

Summing Mixer Questions

Hi

No particular preference to the IC's but That Inc have nice application notes ideal for the DIY'er.

I would always advise folk thinking of passive summing to keep the options simple. If you want balanced summing it gets "interesting" when you want pan pots and aux sends.... All without a nice buffer amp to help resolve levels and impedance matching.
Old 31st December 2010
  #5
Lives for gear
 

Hi
To do what you are proposing is nigh on impossible using 'passive' circuits and retain balance and avoid signal level changes as auxes or routing are selected.
A classic case of use of 'buzzwords' without understanding what is actually involved with such a project.
Try researching constant impedance attenuators and to get your head around the necessary 'back loading' of all the switch permutations.
Matt S
Old 31st December 2010
  #6
Lives for gear
 
Geoff_T's Avatar
 

Summing Mixer Questions

Hi Matt

Well put and what I was tip toeing around saying out straight!

I have never built in the 14+ years I was at Neve a passive summing box and would not like to try, even now, if it needed bells and whistles rather than a straight sum into a resistive mix.
Old 31st December 2010
  #7
Lives for gear
 

Hi
If you happen to have a shedload of 600 Ohm constant impedance balanced attenuators to hand and some suitable multipole switches (the only easy part!) and then are happy to have a load of amplifiers to recover the various losses you can then do most of it, although insert sends would require dedicated amplifiers and you may need transformers to ensure insert returns remain balanced.
Certainly an interesting 'intellectual' excercise but then with all the necessary losses the chances are it will be relatively noisy when finished.
Matt S
Old 3rd January 2011
  #8
Lives for gear
 

Well, my original post was not totally complete or accurate. I meant that most analog summing has some sort of buss with signal loss, and therefore a summing amp with gain. I've had good luck with passive summing and a mic pre as make up gain, but it doesn't have to be that. My main point is that I would love to buy or build a product that has at least 32 inputs....I don't need or want faders....but again, I would like the ability to have 8 or so busses with inserts. I have no problem with using transformers where needed. Also, I have really liked the sound of the Sonic Farm tube mic pre, that uses no negative feedback. I wouldn't mind using something like that for the final summing amp. So my general statement is, I haven't seen any summing product with any sort of bussing....and it's something I think many people are interested in.


Kirt Shearer
Old 3rd January 2011
  #9
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Geoff_T's Avatar
 

Quote:
Originally Posted by kbshearer View Post
Well, my original post was not totally complete or accurate. I meant that most analog summing has some sort of buss with signal loss, and therefore a summing amp with gain. I've had good luck with passive summing and a mic pre as make up gain, but it doesn't have to be that. My main point is that I would love to buy or build a product that has at least 32 inputs....I don't need or want faders....but again, I would like the ability to have 8 or so busses with inserts. I have no problem with using transformers where needed. Also, I have really liked the sound of the Sonic Farm tube mic pre, that uses no negative feedback. I wouldn't mind using something like that for the final summing amp. So my general statement is, I haven't seen any summing product with any sort of bussing....and it's something I think many people are interested in.


Kirt Shearer
Paradise Studios
Hi

It's a little more complicated to get the insertions but you can use your summing amplifier as the pre fade send amp and then a transformer or subsequent amp as the insertion return. If you want a fader you would put it in that amplifier.

32 inputs with no fader or panning seems rather basic but if that's what you want, it's simple to achieve.

Whether all the work, both wiring and metalwork, justifies the means to the end, rather than buying a new or used 32 channel console, is also up to you.

Don't forget that unused inputs will work like an antenna unless you terminated them somehow. These DIY projects are fraught with issues that you haven't even dreamed of at the start!

heh
Old 3rd January 2011
  #10
Quote:
Originally Posted by kbshearer View Post
....and it's something I think many people are interested in.
I've build a active summing mixer with 20 inputs 4 busses and a master bus.
All busses +master have 2 switch able inserts for a total of 6 insert points.

I wanted to make this a public project so I asked around if there was interest.
Interest there was...however, EVERYONE wanted another bell or whistle.
There was no consensus... therefore I just left it.

PM me if you want more info...
Old 3rd January 2011
  #11
Lives for gear
 

Hi
It is a matter of 'lateral thinking' to get what you might need.
Since for example a Folcrum has 25 pin D connectors as inputs you can easilt stack several with 'commoned' inputs to give you more busses that you could then consider to be 'groups' or what I would suggest is to buy a patchfield and a large bag of resistors and make several passive mixe busses where you can then 'contribute' to them with the patch cords.
You could of course do it all with switches (the Folcrum is a premade example).
So my 'immediate' solution would be 6 or 8 Folcrums with inputs and outputs all available on a patchstrip.
Matt S
Old 3rd January 2011
  #12
Quote:
Originally Posted by Geoff_T View Post
These DIY projects are fraught with issues that you haven't even dreamed of at the start!

heh
Tell me about it...took me more than a year...lots and lots of tech reading.
I guess I was lucky cause the prototype worked ok and was very quiet.

I still have the PCB layout ...
Old 3rd January 2011
  #13
here a pic...
Old 3rd January 2011
  #14
another

Old 4th January 2011
  #15
Gear Maniac
 
digibiu's Avatar
 

Quote:
Originally Posted by Radiance View Post
another

Man, that looks SWEET!!
Old 16th January 2011
  #16
Lives for gear
 
once a roadie's Avatar
This would be cool.

Quote:
Originally Posted by kbshearer View Post
Well, my original post was not totally complete or accurate. I meant that most analog summing has some sort of buss with signal loss, and therefore a summing amp with gain. I've had good luck with passive summing and a mic pre as make up gain, but it doesn't have to be that. My main point is that I would love to buy or build a product that has at least 32 inputs....I don't need or want faders....but again, I would like the ability to have 8 or so busses with inserts. I have no problem with using transformers where needed. Also, I have really liked the sound of the Sonic Farm tube mic pre, that uses no negative feedback. I wouldn't mind using something like that for the final summing amp. So my general statement is, I haven't seen any summing product with any sort of bussing....and it's something I think many people are interested in.


Kirt Shearer
Paradise Studios
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