DIY – 16×2 – Passive Analog Summing Panel.

DIY – 16×2 – Passive Analog Summing Panel.

DSC_0317

Update : increased the channels from 12 to 16 (16×2)

Made myself a nice little passive summing panel for my home rig out of parts lying around the shop. I wanted to simplify/improve my final summing stage. Pleased with the results, Sounds great. Gives me piece of mind bypassing the channel IC’s & master section on my desk.

I used a simple XLR panel, Neutrik XLR mounts, Neve super conductive cable, & OHMITE 1% metal film resistors. Took all of 2 hours to wire up.

10.7k resistors on the inputs & a 220 shunt on the outputs.

After level calibration my noise-floor is at -80 & crosstalk @ -88 (via – John Hardy M1 & or API-A2D transformer pre for the make up gain. Nothing better IMHO.).

 

My design is based on the mixing network in NYD’s drawing.
http://www.twin-x.com/groupdiy/albums/userpics/balancedmixnetwork.pdf

All you have to do is figure out how many channels you need. Pick an input impedance value. Modern balanced gear has a high input impedance usually around 20k. I picked 21.4kohm, only because I had “military grade” resistors on hand that happened to be 10.7k.
Resistors between 5k-15k should work well for most applications. 10k input resistors work well.

Now for output impedance most mic pres want to see 150ohm signal.
I recommend using a transformer based pre for the make up gain that accepts a wide range of impedance, like the hardy.
You should pick your shunt resistors on the outputs to spit out around 150ohm. Mine is 200 something. But the hardy can easily handle anything from 60-600ohm

The formula to figure out the output shunt resistor value for a 200ohm output with an input impedance of 20k =

shunt ohm resistor = (20000/n)*200/((20000/n)-200) FYI – google is a great calculator

WHERE N = NUMBER OF INPUTS

12 Responses to DIY – 16×2 – Passive Analog Summing Panel.

  • Looks great – congrats! A question…. would the resistor values stay the same if you were to increase it to an 18×2 configuration? I’ve got a J. Hardy that I’d love to mate to a passive homebrew summer, too.

  • My design is based on the mixing network in NYD’s drawing.
    http://www.twin-x.com/groupdiy/albums/userpics/balancedmixnetwork.pdf

    All you have to do is figure out how many channels you need. Pick a input impedance value. Modern balanced gear has an high input impedance usually around 20k. I picked 21.4kohm, only because I had “military grade” resistors on hand that happened to be 10.7k.
    Resistors between 5k-15k should work well for most applications. 10k input resistors work well.

    Now for output impedance most mic pres want to see 150ohm signal.
    I recommend using a transformer based pre for the make up gain that accepts a wide range of impedance, like the hardy.
    You should pick your shunt resistors on the outputs to spit out around 150ohm. Mine is 200 something. But the hardy can easily handle anything from 60-600ohm

    The formula to figure out the output shunt resistor value for a 200ohm output with a input impedance of 20k =

    shunt ohm resistor = (20000/n)*200/((20000/n)-200) FYI – google is a great calculator

    WHERE N = NUMBER OF INPUTS

  • Thank you for interesting information!

    Best Regards,
    Andrey

  • so are you connecting your ground pins (pin 1) to anything on the inputs (doesn’t look like it)? what about the outputs?

  • I’d like a summing mixer to use more like a mixer/router for live and recording use to consolidate several instruments into stereo which will be sent to FOH, and when recording, the stereo output would be sent to the same two input tracks on the recorder. Possibly both at the same time, but I figure I can probably look for a stereo preamp that will have two outputs for each channel. This will save me a lot in terms of inputs and cabling too. So, I am not sure if there might be a better project to look at for this. Any advice is greatly appreciated. Thanks in advance.

  • Looks real cool! Just for fun, I’m going to built an 8 input summing mixer with two flavors. 1 flavor will be cheap carbon composite 5% tolerance resistors and the other will be metal film 1% tolerance resistors. A switch will be utilized to activate the difference signal paths (one going though the composite resistors and the other though the metal film resistors). Will be interesting to hear how each circuit sounds.

  • Where i can buy neve super conductive cable?

  • Nice one, respect. On another note me, too, doesn’t find Neve superconductive cable anywhere. Do you have apart number or something similar for the cable you used? Thank you!

  • Pingback: Summing experiment

Leave a Reply