Interface/Summing mixer wiring

[Buffalo Tom]

Hi. I wanna build a interface with the capability to run Mono, Stereo, W/D, W/D/W without unplug any cables on the fx pedals. Im thinking this can be done with four 3PDT mini toggle switches and some resistors. I have read the Rane article about passive mixing and found the Stereo-to-Mono Summing Box schematic that I wanna use.


http://www.rane.com/note109.html

I have three questions before I start messing up!

#1 Does my grounding look correct? All ground lugs tied together and grounded to the box through DRY IN jack.

#2 How about the summing part, two 475 ohm resistors tied together and from there 20k resistor to ground lug on respectively output. Have I got that right? Will the 20k resistors placement be a ”problem” in Stereo and W/D/W mode.. There is no summing in those modes but the 20k resistor is still there.

#3. If I wanna put a isolation transformer with ground lift on the output side. On which output should I put the transformer?

[slacker]

The grounding is fine how you've said you're going to do it, on your drawing not all the ground lugs are tied together though, the out side needs tying to the in side.

The 20k resistors will be fine where they are even when you aren't summing. I think you can simplify your design though and reduce the number of switches and resistors. In your drawing the "wet/dry/wet" switch doesn't seem to do anything useful, when the switch is in the position where the middle row is connected to the top row, it just does the same thing as the "stereo" switch and sends the left and right inputs to the left and right outputs. In the other position it sends the left and right ins to the "wet/dry" switch, so it looks like you can remove it.

I think this will do what you want and saves a few resistors and a switch.



EDIT: just noticed the broken connection from right in to the stereo switch, that should be the same as your drawing.

[Buffalo Tom]

Thanks for your help! Very nice! Im working on a version with only 3 switches now... 

The grounding is fine how you've said you're going to do it, on your drawing not all the ground lugs are tied together though, the out side needs tying to the in side.

The 20k resistors will be fine where they are even when you aren't summing. I think you can simplify your design though and reduce the number of switches and resistors. In your drawing the "wet/dry/wet" switch doesn't seem to do anything useful, when the switch is in the position where the middle row is connected to the top row, it just does the same thing as the "stereo" switch and sends the left and right inputs to the left and right outputs. In the other position it sends the left and right ins to the "wet/dry" switch, so it looks like you can remove it.

I think this will do what you want and saves a few resistors and a switch.



EDIT: just noticed the broken connection from right in to the stereo switch, that should be the same as your drawing.

[bool]

If you want to use this in the "guitar-fx" world, you will most likely have to "up" the resistors by the value of 10. IOW, two 4,75k resistors and a 200k one (215k or 221k will be just fine).