SB2 Summing Box Kit

Plugged in and ready to go!

These days the market seems flooded with software emulations claiming to add depth, analogue saturation and “colour”. Mostly they work on the principle that for a fraction of the cost of the hardware you can have multiple instances in your DAW, which *enter producer/mixers name here* say are almost indistinguishable from the real gear.

Of course, I do own some of this software but usually if a plug-in costs three times what my DAW does (I use Reaper so most plug-ins DO cost three times what my DAW does )I tend to look for another similarly priced solution. For example, I own both an RNC and RNLA compressor and would much rather use one of them than a plug-in compressor of similar value, even if the plug-in in question is emulating the sound of a compressor ten times it’s value.  And there are companies like Lindell Audio that make a much praised 500 series 1176 style compressor which you can grab for just over £200. Ok, so it might not sound like an original 1176 but to me it seems better than using a plug-in version of an original 1176 compressor for the same price.

I’m not arguing analogue vs digital here, I use and like both, but in my experience even a cheap hardware compressor used properly will always be worth putting in the chain somewhere for the extra dimension it can add to a mix. I also find it helps with fast decision making, If I get a compression sound I’m happy with, I print the track and move on, then I can use the compressor somewhere else, rather than constantly tweaking a plug-in.

So in my search for affordable hardware alternatives I was extremely happy to stumble across DIY Recording Equipment, a small company based in Philadelphia that offers cost effective analogue kits for building your own hardware.

Founded in 2009, the guiding principles of the company are to introduce audio enthusiasts to the word of building and designing their own gear and to offer an open platform for further development. They also encourage you to use their designs for free even if you don’t buy kits from them.

The company was started by Peterson Goodwyn at a time when he was struggling to pay for the equipment  he needed for his recordings, and instead took to designing and building his own.

I have a similar story, and a few years ago began researching as much as I could and looking for simple how-to guides online I could follow. After a few false starts I put together a sub kick mic, then I started making my own cables (I might be stating the obvious here but if you are prepared to spend the time on assembly you can have the best cables, with the best components, for a fraction of the price of the like-for-like pre-assembled off the shelf ones), next I built my mobile set-up including the repair and testing of a broken power conditioner, as well as microphones (see mini mic post for the £4 omni), which I have used on a lot of recordings.

I only wished I had discovered DIYRE sooner. They make the whole process very accessible to beginners and have guaranteed support on all of their kits too, of which there are many to choose from.



My first acquisition was the SB2 summing mixer. I had always wanted to try out a summing box but could never really justify the expense. Instead, like most, I opted to use a console emulating plug-in on my mixes so was very happy to discover that DIYRE added the SB2 to their line of products this year.

The SB2 is a passive summing box that can be used as an 8×2 or 16×2 channel summing mixer. The main physical difference between this and other “off the shelf” passive summing mixers is that the SB2 has no panning switches (meaning it can fit into a much smaller enclosure). 

The SB2 “outsources” 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. This keeps the cost of the unit low.

The passive resistor network inside the SB2 has essentially no “colour” of its own and the only sound it will impart is the thermal noise of the resistors, which is very low level white noise. This means that the sound is dependent on the the pre amps you feed the signal back into.

Each channel is fed to a bus via two 10k resistors (one for each half of the balanced signal) and a single 150 ohm resistor across the buss sets the output impedance to mic level. As the box has no separate power or gain of it’s own, once the signal is routed back to the pre-amps 45dB of gain is needed to bring it back up to line level.

After emailing Peterson for more info about the box, he told me that the design is nearly identical to the circuitry that many consoles (including Neve, etc.) use for summing the individual channels to the master buss and whichever pre-amp sound you would like to add to your mix, you can.

He explained that most active summing mixers are just a passive summing mixer followed by dedicated makeup gain amplifiers, something DIYRE offer some tasty options of their own for. The colour modules designed to fit the 500 series palette have a growing range and I already have my beady eye on a pair of TM79′s, designed by Eisen Audio.

A close comparison to the SB2 would be something like the RMS216 FOLCROM passive summing mixer available from Roll Music Systems. They both have similar features; passive circuitry, 150 ohm output impedance and DB25 input connectors, however, the small difference of panning switches and pre vs self assembly gives an overall price difference of almost $700, making the SB2 even more desirable.


I ordered the box as soon as it became available on the site but Royal Mail thought it was better to return it to the states when there was no answer. It took 4 days to arrive the first time and almost three weeks to return! Anyway, second attempt was successful and it came within 5 days.

 The kit includes; SB2 Case Foam Pad SB2 PCB Front and back panels Input D-sub connector Output XLR jacks (2x) 10k bus resistors (4x) 150 resistors (2x) Screws (15x)
The kit includes; SB2 Case, Foam Pad, SB2 PCB, Front and back panels, Input D-sub connector, Output XLR jacks (2x), 10k bus resistors (4x), 150 resistors (2x), Screws (15x). (Stanley knife not included).

There are quite a few connections to solder but it took me about 25 minutes all in all, so as the website states it is a good beginners kit. Take it from a very recent novice, soldering gets better with experience and if you are new to it the step by step guides on the website are easy to follow and include pictures and soldering tips. As for support, given how responsive they were with emails when my order disappeared I can personally vouch for their speed and attentiveness.

In terms of price this is great value, especially if you are new to building and want quick results. To put the price into perspective, the cable I bought to connect the SB2 to my interface cost more than the box itself (I draw the line at soldering my own DB25 cables as suggested in the FAQ..).

actually, the clippers I have to clip the excess from my solder joints also cost more than the SB2.
…I just remembered, the clippers I have to clip the excess from my solder joints also cost more than the SB2.

What does it sound like?

I suppose the quick answer is it sounds like the pre amps you run your mix through. In the examples below I’m using channels 1-8 on the SB2 and running the mix back through the ISA 110 pre amps I have in my home studio.

The outputs from the DAW are set as;

1/2 Drums
3/4 Guitars
5/6 Bass Guitar/SH101
7/8 Piano

As the ISA’s are transparent, the differences are subtle, so I’ll let you listen and make your own mind up. Even so, I know that it’ll be used in a lot of my mixes from now on, especially given the endless sonic possibilities with the addition of different and more “coloured” pre amps to sum through.

In a digital version such as VCC, the process is intended to be cumulative with the more tracks you mix into the plug-in the more you hear the effect of the processing. In the example above I run an almost finished section of a mix through the box, which is fine for an A/B comparison, but if I had mixed into the SB2 from the start and added channels to my stereo sums as I went, just like summing through the master buss section of a console, I feel it would have slightly changed my approach to the mix.

I have only good things to say of my short time with this box, it is easy to put together, and at a fraction of the price of a similar “off the shelf” model, perfect for those (like me) who have considered using an analogue summing box and previously thought the price to be unjustifiable.

I love what the company does and I look forward to buying more kits, especially from the colour range, and I hope to revisit this thread once I have invested in some TM79′s.

Check out DIYRE here and get your hands dirty!


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2 thoughts on “SB2 Summing Box Kit”

  1. Hey thanks so much for the post! I just bought this box and was having issues with the make-up gain.When I send a mix that still has 6db of headroom and I add 45db from my preamps, as suggested, the level never gets back to where it was before I summed. Have you had any issues with this? Thanks again.

    1. Hi Jose,

      Thanks for your comment. What DAW are you using? Whats your set up, interface for sending from the DAW and Pre-amp?


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