A Direct Box or DI box converts an unbalanced, high impedance signal to a balanced, low impedance signal that can be run long distances with relative immunity to noise. DI boxes are an essential part of any sound reinforcement system and can be either active or passive. Active DI boxes employ electronics to balance the signal and require some sort of power source, either an internal battery or external phantom power provided by the mixing console. Passive DIs use a transformer and require no external power to function.
More information on what a DI box does and why you need one: https://youtu.be/2SBGSDKgKHo
More information on the difference between passive and active DIs: https://youtu.be/gBCEBS2F5dw
More information on the difference between stereo and mono DI boxes: https://youtu.be/eSsCPuARRFU
At time of writing I have pretty much settled on DI boxes from Canadian company Radial. They have become the de facto standard for professional DI boxes across the live sound industry, used by engineers in every genre of music and at every level, from local club acts to international touring productions. Their build quality and sonic integrity are second to none. I am not sponsored in any way by Radial, but own and use every single one of the DIs listed on this page.
Passive Direct Boxes:
Radial Engineering JDI
Widely regarded as the current industry standard for passive direct boxes. Unparalleled fidelity through the use of a Jensen transformer. Built like the proverbial brick **** house. Useful pad, merge to mono and speaker level input functions. Not cheap, but the best in my opinion.
Featured in this video: https://www.youtube.com/watch?v=-wVcIsh_XN4
Buy on Amazon: http://amzn.to/2CXuScf
Radial Engineering JDI Stereo
A stereo version of the JDI, without the bulk and cost of the duplex. Outstanding on keyboards, stereo guitar rigs, active bass guitars etc. Also an excellent replacement for two mono DIs eg a player who doubles on acoustic and electric guitar, or somebody who plays bass but also operates a drum sequencer.
Buy on Amazon: https://amzn.to/2FAfdU5
Radial Engineering PRO DI
Half the price of the JDI at time of writing, mainly due to to the use of a less expensive transformer and fewer bells and whistles. Still a great DI box, especially for live use where ultimate frequency response is less of an issue.
Buy on Amazon: http://amzn.to/2zgzg44
Whirlwind IMP 2
If you need an inexpensive yet decent-sounding DI this is the one to get. Absolute bare minimum of features, aluminium housing instead of steel but will still get the job done night after night.
Buy on Amazon: http://amzn.to/2BkBCk1
Whirlwind pcDI
The original multimedia DI, and still one of the few passive DIs capable of either mono or stereo operation. Not quite as well built as the Radial units (aluminium housing instead of steel, input connectors are not secured to the front panel) but still an excellent professional tool. RCA, minijack and 1/4″ inputs. Unused inputs can be used as thru connectors.
Featured in this video: https://www.youtube.com/watch?v=ge4Iynh4rcc
Buy on Amazon: https://amzn.to/2Cg3fA8
Radial Engineering PRO AV1
A specialised stereo to mono multi-media DI with quarter-inch, RCA and 3.5mm inputs AND outputs. Connect the output of laptops, media players, ipads etc to the mixing console noise-free and with correct matching of levels. I always carry one of these to every gig as a problem-solver. Even has an XLR INPUT so can be used as a line isolator when connecting two mixing consoles together.
Review video: https://www.youtube.com/watch?v=iDtSSRefIak
Buy on Amazon: http://amzn.to/2BQB9qZ
Radial Engineering PRO AV2
A true stereo multimedia DI with two completely separate audio paths and two individually shielded transformers. Intended for computers, media players etc but I often use this on keyboard, digital pianos, stereo effects rigs etc. Has the same transformers as used in the PRO DI. Has no option to merge signals to mono.
Review video: https://www.youtube.com/watch?v=iDtSSRefIak
Buy on Amazon: http://amzn.to/2BQB9qZ
Radial Engineering SB-5
An alternative to the ProAV1 and 2: much smaller footprint and a permanently attached minijack cable that is impossible to lose. Features mono output on XLR and stereo output on quarter-inch TRS connectors. Small enough to fit in the front pocket of a laptop bag.
Buy on Amazon: https://amzn.to/3aTUp8c
Active Direct Boxes:
Radial Engineering J48
The current state of the art in workhorse, no-nonsense active DI boxes. Massive 9-volt headroom to handle the output of the active basses and acoustic guitars, built in merge-to-mono and high pass filter. Phantom power ONLY – cannot be battery powered. Also note that the input impedance is only 220-kohms so is not suitable for unbuffered piezo pickups.
Featured in this video: https://www.youtube.com/watch?v=-wVcIsh_XN4
Buy on Amazon: http://amzn.to/2Dv1kE1
BSS AR-133
Regarded as the industry standard for active DI boxes before the J48 came along. Still a useful piece of gear with interesting design features – has both quarter inch and XLR inputs, allowing use as a line isolator. Features an active front end with a transformer balanced output – effectively a hybrid active/passive design. 1 MOhm input impedance and -40dB pad allows it to handle almost any source. Has the option for battery powering making it viable in situations where phantom power is not available. One of the few non-Radial boxes that I still carry to gigs.
Review video: https://www.youtube.com/watch?v=4XXfn6_XFL8
Buy on Amazon: http://amzn.to/2DvZdQx
LA Audio DI2
In production for over two decades now, this DI box is firmly in the category of ‘an oldie but a goodie’. Features both phantom power and 9V battery operation as well as pad, ground lift and signal boost switches. Unusually for an active DI, it features both link as well as unbalanced outputs, the latter being a lower-impedance buffered output tapped after the DI’s active circuitry. In addition, the PAD switch drops the input impedance to 10k ohms and allows the DI box to be connected to the speaker level output of an instrument amplifier, another unusual and valuable feature.
My overview video: https://www.youtube.com/watch?v=wM5imzfVk30
Company’s website: http://www.laaudio.co.uk/?c=msg&id=249
This product does not appear to be available on Amazon, so no affiliate link here. According to the LA Audio website, it is still in production as of February 2021, and available via certain pro audio retailers.