API 8 channel "BIG BOY" Summing mixer Design (Need help / advices)

[Sinkia]

Hi Folks !

After having build some great pres and comps, I'm throwing myself into the design of a summing mixer..

Nothing new I guess, but I want to make a 8 channel summing box after CAPI 4 Channel Inverting ACA and CAPI 2 Channel ACA & Booster. 

The general idea is to have a great summing box which add some MOJO to my mixes.


I attached the design I'm thinking about.


The power supply section will be Ing's one, APP STUDIO ING. PSU2
http://groupdiy.com/index.php?topic=33576.0


As you can see, I want to add a stereo  vu meter from JLM audio with maybe some nice hairball vu meter!

http://www.jlmaudio.com/shop/vu2-stereo-vu-buffer-kit.html


So the summing box will consist of 8 input into 2 card of CAPI 4 Channel Inverting ACA (1-3-5-7 on the left card, and 2-4-6-8 not the right card), hitting a 2 INV ACA BO

As you can see, there is some green round where I need some help to design it…

First round : before hitting the 4 Channel Inverting ACA board :

Here is what CAPI says :

"You can take the summed monitor section or any outboard mixer's unbalanced outputs through 47K bus resistors and simply "inject" them into your 2-mix ACA.

By removing each channel's 47K output bus resistor and adding any of our 2623 transformers, you will have 4 independent channels of classic, vintage style summing. 2623-1-CF's are a good versatile mount for use with that application."

I guess I'm a little bit confused…

what would be the best option for me?

the point is to go from output 1-8 of my audio interface to each channel on the board.

Is it better to Use a 47k resistor or a tranny?

this question attract an other one :

The output of my interface is balanced. The input of the board is unbalanced.

How can I make from Balanced to unbalanced? a reamp box? Small pcb with components..?

the second green circle is in between CAPI 4 Channel Inverting ACA pcb and CAPI 2 Channel ACA & Booster pcb :

Here is my question :

Can I go straight from one board to the other one?
Do I need a resistor/tranny? 47k? 2623 transformers again?

and then my last fog area : the trim pot

Here is what CAPI says :

"The returning signal needs to be routed to a user supplied stereo potentiometer, rotary or slide-fader type"

I'm thinking of using 2 Elma 04, 1x24-1k, Shorting Rotary Switch
http://capi-gear.com/catalog/product_info.php?cPath=51_133&products_id=399

Here is my question :

The output of the Right Side from the board is balanced. the input of the rotary switch is unbalanced, as well as the left side input.

Do I just link - and ground? or I need something more special?


I know, most of my questions are really basics ones, but I'm learning little bit after little bit.
I kind of newbie on design, and I want to learn !

What do you think of this project?

Is this summing mixer make any sense?

Thank you so much for your answers !

Cheers !

PS : "BIG BOY", why "BIG BOY"?
Because I'm thinking to use some really Big Boys Knobs \o/
https://www.don-audio.com/XXL-Monster-Daka-Ware-Knob

 

[gato]

How can I make from Balanced to unbalanced? a reamp box? Small pcb with components..?

Check out the input of the GSSL (go to gyraf.dk then to DIY-projects).


What are the white squares in your diagram? I assume on the input they are stand-ins for a de-balancing stage? Again, see the GSSL input as a reference. You can do this with a DOA if you want. What are the white squares between the two boards? I need to check out how Jeff's boards are intended to be used, but I don't think you need a buffer or anything between them.

 

[qmp audio]

I'm working on one of these.  Maybe you can get some ideas from here:
http://www.diy-racked.com/diy-talk/viewtopic.php?f=7&t=234

You should only need 1x 2 Channel ACA & Booster from CAPI.
The 4 Channel Inverting ACA cards are to sum groups down into smaller groups.  You don' t need this for an 8 channel summer.

 

[Sinkia]

Check out the input of the GSSL (go to gyraf.dk then to DIY-projects).

Yeah ! many thanks !

I will check that beginning of next week !
I guess I will find all the answer I need there !

At least I'll come back in here and double check with you !

Will work on my design and upload it here again !

 

[Sinkia]

I'm working on one of these.  Maybe you can get some ideas from here:
http://www.diy-racked.com/diy-talk/viewtopic.php?f=7&t=234

I have already checked, but there's not too much info of the schematic.. only boards pictures and wirering links..!

You should only need 1x 2 Channel ACA & Booster from CAPI.
The 4 Channel Inverting ACA cards are to sum groups down into smaller groups.  You don' t need this for an 8 channel summer.

OK !

So I would only need the 2 ACA BOOST card !

I was thinking to use the 4 ACA INV board to have the DOAs and add "flavor" to the sound..! Was I wrong?

 

[nielsk]

Using the simple "resistor" summing buss will deliver some of the advantages of analog mixing such as not loosing spacial definition, but is not going to get you any "mojo"... the only way to really get the sound of a great console is with the signal path:
Transformer to line input amplifier to summing buss.
It is more expensive, but even the difference between using  a good transformer and using an electronically balanced line input is well worth the expense...
When you consider the low channel count you are after, I think that is even more of a reason to build something that actually sounds great.