SB2 Passive Summing Mixer Kit
16 channels of passive, analog summing in one tiny box.
The SB2 is an 8/16x2 passive summing mixer in a ultra-compact format. Using minimal, completely passive circuitry, it sums 8 or 16 balanced line inputs down to a single set of stereo mic-level outputs. Pair the SB2 with your favorite pair of mic preamps to add glue and color to your mixes.
- Ultra-low cost and small footprint
- Accepts 8 or 16 balanced inputs
- DB-25 (D-SUB) input connectors
- Balanced, microphone-level outputs
- XLR output jacks
- Neoprene foam pad for desktop use
What the Pros are Saying
"As a mixer that works almost exclusively in the box, there are some tracks that need the warmth, glue, and spacing that only analog can offer. When I run my mix through the SB2 paired with CP5s loaded with Rogue-tec Airs, I get that great low-mid presence that I'm looking for along with airy highs and a great stereo image. Other analog summing always made me feel like something was changed in the balance of my mix, but the SB2 gives me the analog enhancements I'm looking for without sacrificing anything. I currently have this setup replacing summing units in my home room at Lounge Studios NYC worth over $10k combined."
-Mikaelin "Blue" BlueSpruce
Solange, Mariah Carey, Blood Orange
|Input Impedance||10k balanced|
|Output Impedance||150R balanced|
8 or 16
|Recommended Load Impedance||1.5k (standard mic preamp input)|
|Recommended Source Impedance||100R (standard line output)|
How is the SB2 so inexpensive? Most summing mixers cost at least 10x more.
The SB2's radical affordability is due to its radical simplicity. By stripping the passive summing concept down to its essentials and "outsourcing" the pan controls (see below), makeup gain (to mic preamps), and assembly (to you!), we're able to make the SB2 low-cost and pass the savings on to you.
Why are there no switches/knobs? How do I pan the inputs?
You may have noticed that typical summing boxes are rather expensive, despite containing limited circuitry. This is mostly because they feature panning knobs or switches. In addition to being expensive themselves, these controls necessitate a larger front panel, case, and circuit board.
The SB2 bypasses all of these costs by "outsourcing" the panning to your DAW. Each of the SB2's inputs is hard-wired to one of the output channels: odd-numbered inputs to the left, and even-numbered to the right. You simply send pre-panned stereo buses to your interface's hardware outputs and connect them to the SB2. For example:
For a single track you want panned center, simply send it to a pair of outputs.
Do I need to provide makeup gain after the SB2?
Yes, being completely passive, the SB2's outputs require 45dB of makeup gain to be returned to line level. The best way to do this is with a pair of mic preamps.
Does the SB2 have a "sound"?
Nope, a passive summing mixer has essentially no sound of its own. The sound of your summing setup will be determined completely by the mic preamps you use for makeup gain. Indeed, one of the unique benefits of passive summing is that you can tailor your makeup-gain preamp choice to each mix.
What is the circuit design based on?
The SB2's circuit is a classic passive summing network--the same as found in countless mixers and consoles. The only difference is that instead of dedicated makeup amplifiers, the SB2 has mic-level outputs which must be connected to mic preamps. The circuit is the same one shared by NYDave on GroupDIY and featured in How to Build a Passive Summing Mixer.
Do you sell an 8-channel version?
You can use the SB2 as an 8 or 16-channel mixer. Just use inputs 1-8 for 8-channel operation.
Can I daisy chain two SB2s for 24 or 32-channel summing?
No, there is no way to daisy chain two units. We made this design decision because the performance of this kind of passive summing circuit degrades after about 20 channels.
Does it come with D-sub breakout cables?
Nope, cabling is up to you. Want to feel like a real DIY ninja? Build your own D-sub cables!
Can I use the SB2 with unbalanced gear?
No, the SB2 only works with balanced inputs and outputs.
This kit is really high quality - the enclosure and components are great, straightforward to put together, and it makes analog summing really easy. I didn't realise how small the box would be but this is a major bonus - I dig having gear that's easy to travel with so I'm really stoked!
This was a fun build, I'd done a little LED practice board and a condenser mic capsule swap before this. I took about an hour but I was going slow. After I had everything routed & wired up with fingers crossed making sure everything worked I had a chance to listen. Well whadya know, the mix had a little more depth and secret sauce to it. I can't wait to build some more gear!
Bought 2 SB2 passive mixers. Fast delivery to France, very good components, easy to build and working as expected. Worth every penny.
The build was a breeze. My whole workflow will change by adding a few of these mixers on patchbays around my DAW I/O, mic preamps, and outboard gear. What a blast.
That was my first ever DIY project. I'm super happy with the result. It gives warmth and depth to my mixes. Would give 10 stars out of 5 if it was possible.