8 channel virtual ground mixer equations

Hey guys long time listener first time caller. I am just in the process of making a mixer and was hoping for some help/feedback/critisism on a part of it. I have built a few before and have read the Meta on mixers and have found it of great use however I am still in need of another opinion.

The mixer will have 24 channels in total. 8 left, 8 right and 8 with pan and volume control. It uses a 24>4>2 mixing network using discrete mixamps as seen in this block diagram. http://imageshack.us/f/23/blockdiagram.png/ The inputs will mostly be fed from a soundcard.

In the picture below is what I have proposed for the 8 channels (only 3 shown) which will have volume and pan options. After these 8 channels have been summed into a stereo pair they will then be mixed with the sum of the 8 hard left and 8 hard right channels respectively in a second stage of mixing as shown in the block diagram. http://imageshack.us/f/692/mixere.png/

My questions are:

-Can anyone suggest values for RX, RY and the pots?
I have toyed with a few values but I'm still unsure how to split the pan feeding and exiting resistors. I think in the past I used to use 3K6 for both RY and RX with a 2K2 lin pan pot but am thinking that maybe I should be using a higher impedence? usually 10k for the volume pot too.

-would I better off to go with a design like this? (perhaps without the shunt resistors) http://sneak-thief.com/passivemixer/balanced_PassiveMixWithControls.pdf

-Any thoughts on the proposed grounding and shielding?

I'm very open to any other suggestions and comments too.

Thanks so much for your help! - Benjamin

This is from a post from NYD



http://www.groupdiy.com/index.php?topic=3816.0

I hope it helps you

There are numerous ways to skin this cat...

I would suggest that you start by looking for what value pots you can find and work backwards from that.

JR

I have spent quite a while in my thinking chair today sharpening my knife, salivating over how to skin this cat and the many others in this mixer. I've almost got the operation figured though, so thanks for the advice guys!

I guess I'll bite the bullet and go for that dual pot design that New York Dave suggests. By my calculations the volume pot before it should be about 4k7-5k? (what ever is cheaper I guess). I took another snapshot which is down the bottom for perusal.

Just a drawing mistake I guess, but 2k2 resistor should be connected to both sides of pan (both 4k7 resistor). With this it should work fine.

JS

Thanks Joaquins! A drawing mistake indeed.

I hope your own mixer project is going well! I have been following it with interest.