Fishmed
Well-known member
Here is my first attempt at a passive summing mixer. It has 18 inputs total, 4 mono and 14 stereo. I figured that I would use the extra stereo input as a link from a sub mixer. The outputs are on the front since I will be racking this unit next to my mic/mic pre patchbays. I also installed a ground lift incase I needed it (you never know).
I painted the back of the rack to indicate the mono (blue) from the left (white) and from the right (red). Its got that flag look going for it. I was going to paint some design on the front, but the case (Middle Atlantic) has a vinal coating and paint did not stick well. I manage to get the paint to somewhat stay on the back, but it needs some touch up. That is why I did not show the backside as it does look like A$$, but once I clean it up I will add the photo. The case top has a serious lip on the front side, so I need to notch it for the XLR outputs before I can attach it.
The resitors I used are the standard 10K for the stereo, 14.3K for the mono, and 220 for the shunt. Each mono channel uses four resistors, two for the left and two for the right. I tested it last night and everything seems to be in order.
I changed my design midway through the build. I was going to use a PCB I had and install multiple resistors (10k and 4.3k) to branch and sum the MONO channels. I had also drilled the case for that PCB. The PCB became a mess and I realized I could do the same thing with 14.3k resistors. I used one of the PCB's drill holes for my mount and it was not perfectly in line with the mount on the other side (you can see the old holes in the bottom of the case). I also tried to solder each resistor sliding shring wrap between each resistor which made the buss wire pull even more out of line. Next time around I will get the mounts perfectly lined up and string the buss wire across before I do any solding.
I painted the back of the rack to indicate the mono (blue) from the left (white) and from the right (red). Its got that flag look going for it. I was going to paint some design on the front, but the case (Middle Atlantic) has a vinal coating and paint did not stick well. I manage to get the paint to somewhat stay on the back, but it needs some touch up. That is why I did not show the backside as it does look like A$$, but once I clean it up I will add the photo. The case top has a serious lip on the front side, so I need to notch it for the XLR outputs before I can attach it.
The resitors I used are the standard 10K for the stereo, 14.3K for the mono, and 220 for the shunt. Each mono channel uses four resistors, two for the left and two for the right. I tested it last night and everything seems to be in order.
I changed my design midway through the build. I was going to use a PCB I had and install multiple resistors (10k and 4.3k) to branch and sum the MONO channels. I had also drilled the case for that PCB. The PCB became a mess and I realized I could do the same thing with 14.3k resistors. I used one of the PCB's drill holes for my mount and it was not perfectly in line with the mount on the other side (you can see the old holes in the bottom of the case). I also tried to solder each resistor sliding shring wrap between each resistor which made the buss wire pull even more out of line. Next time around I will get the mounts perfectly lined up and string the buss wire across before I do any solding.