Direct Boxes (DI’s) with Stereo to Mono Summing


In my article, The Stereo to Mono Summing Cable that No One Makes, I described how to build (or buy) a cable that will take a stereo unbalanced signal and sum it to mono for connection to a PA system (mixer, power amp, etc.). You can connect the output end of such a mono-summing cable directly to a regular line 1/4″ line input. If, however, you need a balanced signal for connection to an XLR mic input on a mixer, you’ll need to use a mono-summing cable in conjunction with a DI box. Since writing that article, there have been several DI boxes that have hit the market that do something similar to what the mono-summing-cable-plus-DI-box combo do, so I thought it might be good to provide a quick overview of some of them. I’ve decided to list these in the order of the selling price from least to greatest.

First up is the Klark Teknik DI10P. It takes a stereo unbalanced input signal via RCA or inputs, sums it to mono, and outputs it to a single balanced XLR connector. This is perfect for connecting the audio output of a smartphone, MP3 player, laptop, tablet, or CD player to a mic input on your PA system. There’s even a separate volume control for the left and right inputs if you need to adjust the balance of the left and right signals against each other. This is the most affordable box of the ones that we’ll be discussing today.


DI10P Features:
– Passive design (no phantom power or batteries required)
– Choice of RCA (phono) and 3.5mm (1/8″) stereo inputs
– Left and right volume controls for level-matching and balancing the left and right sources
– Ground lift switch

Virtually identical to the DI10P in connections and functions, the Whirlwind POD DI accepts its inputs via RCA/phono jacks or a single 3.5mm (1/8″) TRS jack. Left and Right volume knobs are provided and the mono-summed output is on a single XLR jack. There’s also a Ground Lift switch provided.


POD DI Features:
– Passive design (no phantom power or batteries required)
– Choice of RCA (phono) and 3.5mm (1/8″) inputs
– Left and right volume controls for level-matching and balancing the left and right sources
– Ground lift switch
– Unused input can be used as a “loop thru”
– Made in the USA

The On Stage DB1100 is another box that offers two unbalanced inputs and mono summing. It’s equipped with a regular 1/4″ input and when the Merge switch is OFF, a Thru jack. However, when the Merge switch is flipped ON, the Thru jack becomes a second input. The signal from the two input jacks is summed to mono on the single XLR output jack. This box boasts a lot of features in a still relatively affordable box.


DB1100 features:
– Active design (requires 48-v phantom power)
– 1/4″ inputs
– Single XLR balanced output
– Merge switch combines the two input signals and sums them to mono
– 15 dB pad switch
– Ground lift switch
– Polarity switch
– Low cut switch

The Radial StageBug SB-5 accepts its input via an integrated 1/8″ stereo cable, so there are no extra cables required to connect your device to the box. Outputs can be kept separate on two 1/4″ balanced TRS jacks for stereo operation, or via a single XLR output for a mono-summed output. There are also 15 dB pad and ground lift switches provided.


StageBug SB-5 features:
– Passive design
– Integrated 3.5mm (1/8″) stereo cable for connection to device’s audio output
– Two separate 1/4″ balanced TRS outputs for stereo operation
– Mono-summed output on a single XLR output jack
– 15 dB pad switch
– Ground lift switch
– Radial quality and reliability

The Samson MCD2 accepts its inputs on two 1/4″ jacks, two RCA/phono jacks, or a single 3.5mm (1/8″) stereo TRS jack. The outputs can either be separate on the two XLR outputs jacks or mono-summed to single jack using the Stereo/Mono switch. Ground lift and 12 dB pad switches are also offered here.


MCD2 features:
– Passive design
– Choice of 1/4″, RCA/phono, and 3.5mm (1/8″) stereo inputs
– Stereo/Mono switch for separate stereo or mono summed output
– 12 dB pad switch
– Ground lift switch

Finally, the Klark Teknik DN200 will accept either an stereo unbalanced signal via the RCA inputs or two balanced signals via the XLR combo jack inputs. Using the Sum switch, the inputs can be summed to the Left output. This is one of very few devices on the market that I’ve identified that will take a stereo balanced signal and sum it to a mono balanced signal. This is a pricier alternative to a balanced stereo to mono summing cable or box like I’ve described in one of my previous blog posts. But it’s great if you need the extra features or want this functionality in a ready-made, off-the-self product.


DN200 features:
– Active design
– Stereo input via RCA (phono) jacks, XLR, or 1/4″ inputs via two XLR combo jacks
– Separate left & right XLR outputs for stereo applications
– Sum switch sums the left & right inputs to mono on the Left output jack
– Split function splits the left input to both outputs
– 20 dB pad switch
– Ground lift switch

Each of the boxes listed above offers a slightly different feature set, running the gamut from a no-frills design to lots of extra bells and whistles (switches). But each one of them has one thing in common: it allows you to take a stereo source, sum it to mono, and send that mono output on a balanced XLR jack. I would encourage you to fully explore the features of each box to decide which one will best suit your needs. And if you try one out, send me a message and let me know how it works for you!

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