Music Intrusment Reviews

Warm Audio Direct Boxes Review

Warm Audio Direct Boxes Review







Feature Reviews

Recording Reviews: Warm Audio Direct Boxes Review



Passive or active, the choice is yours


D irect boxes are one of those things that many people don’t give a lot of thought to, but if you’re a musician, recording engineer, or live sound technician, they’re something that you should not only know about, but they are also something that sooner or later, you’re going to need. Direct boxes have a fairly limited yet important set of tasks that they need to fulfill. The first is to convert a high impedance, unbalanced source (such as the output from an electric guitar or bass) into a low impedance balanced output. This allows the signal to be sent over much longer distances with less chance of interference or signal loss. The second is to convert an instrument level signal to mic level, so that the signal can be fed into a mixing console or outboard mic preamp.  

There are two common types of direct boxes; ones that use either active, or passive electronics. Passive models use a transformer to accomplish their tasks and need no power supply. They are commonly used with instruments such as acoustic-electric guitars or basses with onboard preamps, while active direct boxes use active electronics and require a power source, but also have a preamp circuit to provide a hotter output signal, and usually have a higher input impedance too, so they’re less likely to load down passive pickups. Warm Audio has recently released two new direct boxes, including an active and a passive model, and we’ll be looking at both of them in the course of this review. Unlike some of their other releases, these were not inspired by any particular vintage units, but represent all-new, original designs. 




What You Need To Know

  • Both the Warm Audio WA-DI-A Active Direct Box and the WA-DI-P Passive Direct Box are housed in identically-sized and very similar looking extruded aluminum boxes that measure roughly 4 7/8” W x 5 3/8” D x 1 7/8” H, including the knob and switches, which do extend slightly beyond the edges of the boxes themselves. 


  • The aluminum keeps the weight down, but the boxes still feel rugged and sturdy. The bottom of both the WA-DI-A and WA-DI-P are lined with a dense sponge rubber material to help keep the box from sliding around on the stage or studio floor, or to help keep it in place when you sit it on top of a table, amp head or speaker cabinet. 


  • The top and bottom of both units are black, with a large silver WA logo on the top of both direct boxes. 


  • One of the “sides” is also black (the top and bottom are formed in a single piece that “wraps around” the box on one side, while the other three sides are silver-gray and slightly recessed to help protect the various jacks and switches. 


  • The “sides” (or ends, depending on how you want to look at it) of the direct box is where you’ll find all of the input and output jacks, as well as the various switches and so forth. The Input ends of the two direct boxes are basically identical. 




  • First up is an Amp Out / Instrument switch. When the Amp setting is selected, you can feed the speaker output of your amplifier into the direct box input, which allows you to send the amplified sound direct to the board. For normal instrument applications, you’ll want to select the Instrument setting.  


  • The 1/4” Input jack has a built-in switch so that power (for the active unit only) is turned off when the input is unplugged. 


  • A handy Phase switch is also included, so you can reverse polarity to get the phase of the direct box signal and, for example, your miked-up bass amp to match. 


  • You also get a Thru jack. When using the Instrument input setting and plugging your instrument directly into the DI’s input jack, the Thru can be routed to your amp’s input so you can feed the DI and your amp simultaneously.. When using the amp’s speaker output to connect to the direct box input and using the Amp Out setting on the direct box, you’ll usually need to use the Thru jack to send the signal back to the amp’s speakers - failure to do so can create a “no load” condition that can destroy many amps. 


  • Finally a ground lift switch helps to deal with pesky hum issues that can result from having two paths to ground. One nice thing here is that even the WA-DI-A Active Direct Box can utilize this feature without disabling the ability of the box to be phantom powered - this isn’t the case with some other active direct boxes on the market.  


  • The Output end of the two direct boxes is where the external differences become visible; the names of the boxes are silkscreened on this side, and the WA-DI-A has some additional features that the WA-DI-P Passive Direct Box lacks.  




  • Both models have a low impedance XLR output jack for sending the signal to your mixing console, computer audio interface, or mic preamp of choice, either with an XLR mic cable, or by way of the PA’s snake. 




  • On the Active DI Box, an Active / Passive switch allows you to switch between those two modes of operation. The WA-DI-A Active Direct Box also has auto switching built-in. Whenever 48V phantom power is detected at the XLR jack the unit switches to active mode, even if the Active / Passive switch is in the passive position. While this may be a bit confusing, and could override your preferences if you really want to run the DI passively, it does help to preserve battery life. Two LEDs, located next to the XLR jack on the back panel, indicate which of the two power sources the unit is currently running on. 


  • Both units include a Variable Pad that allows you to fine-tune their levels. This consists of a switch to turn the pad on or off, as well as a knob that lets you adjust the level anywhere from -30 dB to -3 dB. This is an uncommon feature, especially on passive units like the WA-DI-P Passive Direct Box, but one that can be extremely useful for dealing with distortion from high-output sources. Being able to optimize the gain staging of your signal path is a great feature, and one of my favorite aspects of the new Warm Audio direct boxes. 


  • Inside, both units feature a high-quality, custom-wound, USA-made Cinemag CM-17106 transformer. 


  • A dual 9V battery compartment is located within the WA-DI-A for powering the direct box in those situations where phantom power is unavailable. The internal battery compartment is accessed by removing two screws from the top, and four screws from the bottom of the WA-DI-A. Battery life is rated at “well over 1,600 hours” if high-quality alkaline batteries are used. Two 9V batteries came pre-installed in the WA-DI-A review unit. 


Warm Audio WA-DI-A gutshot.png


  • The WA-DI-P lacks the active electronics of the WA-DI-A, as well as the battery compartment, but features similar high-quality construction inside. 


Warm Audio WA-DI-P gutshot.png


  • Both units come with a one-year limited warranty when you register your purchase with Warm Audio. Registration can be done on their website.




  • While the design of the case and the way that the black part of it overhangs the controls and connections largely protects the side mounted knob and switches, it doesn’t completely shield them from possible impact since they extend a bit further than the case extensions do. Then again, if anything smacks the front or back, or if the unit is accidentally dropped, the cables that are plugged into it would probably take the hit before the controls on the Warm Audio Direct Boxes would. 


  • It’s a minor complaint, but it would be nice if there was a more immediately obvious visual difference in the appearance of the two boxes. If both are sitting on a shelf in your mic locker, you’ll need to look carefully at the output side of the two boxes in order to tell which is the active DI, and which is the passive model. You could mark one with a strip of tape or something, but it would be cool to see the Warm Audio logo on the top surface silkscreened in a different color for one or the other. 


  • If you want to run the WA-DI-A in passive mode, not only do you need to turn the Active / Passive switch to the passive position, but you also need to make sure that phantom power is turned off for that channel of your mixing board, audio interface, or mic preamp; the presence of phantom power at the XLR jack will automatically put the unit into active mode, regardless of the switch position.  




Warm Audio’s new line of direct boxes may serve utilitarian purposes, but they do so very well. They feature solid construction, transparent audio quality, and come equipped with first-class transformers from Cinemag. Furthermore, they’re offered in your choice of active or passive versions - both of which offer the onboard variable pad, which is a really useful feature for dealing with distortion and getting levels set “just right.” I do wish that the active and passive versions were more readily visually distinguishable, but that’s a relatively minor complaint that won’t impact the majority of users (other than studios and live sound companies) who will probably only get one type or the other. 

For someone who is trying to decide between the two, I would tend to recommend the active model since it can also be used passively if needed or preferred, which makes it not only the more versatile unit, but in this reviewer’s opinion, the better value too. However, if you’re only going to be using it for a specific job (such as to pair it with your active-electronic equipped bass) where passive electronics are preferred or all you really need, you can save a few bucks by getting the passive model. For acoustic-electric guitarists, bassists, keyboardists, electric guitarists who want to run direct, live sound rigs, and recording studios, direct boxes are a necessity. No matter which one you decide to get, you should be able to expect years of reliable and great sounding service from these very nice new direct boxes from Warm Audio.    -HC-


Want to discuss the Warm Audio Direct Boxes or have questions or comments about this review? Then head over to this thread in the Studio Trenches forum right here on Harmony Central and join the discussion!



Warm Audio WA-DI-A Active Direct Box ($199.00 "street")

Warm Audio WA-DI-P Passive Direct Box ($149.00 "street")       

Warm Audio’s product web page 


You can purchase the Warm Audio WA-DI-A Active Direct Box from:


Guitar Center 

B&H Photo Video /BI/20252/KBID/14645  

Musician's Friend 

Full Compass 


You can purchase the Warm Audio WA-DI-P Passive Direct Box from: 


Guitar Center 

B&H Photo Video /BI/20252/KBID/14645  

Musician's Friend 

Full Compass 




• Custom-wound CineMag USA transformer.

• Converts instruments to mic-level signals without signal degradation.

• Ideal solution for plugging your instrument direct into any mic pre, mixer or recording device.

• Top-quality discrete components with gold-plated traces on circuit board. 

• Rugged aluminum chassis construction.

• Pad: Variable from -3dB to -30dB.

• Balanced Output: 600 ohms, mic level.

• Input Impedance: 1 Meg Ohms.

• THD: .01% from 20Hz to 50Hz. Less than .003% from 50Hz to 20kHz.

• Frequency Response: 10Hz to 90kHz +/- 0.5dB.

• Linear Performance: +/- 0.05dB 20Hz to 50kHz.

• Power: 48V Phantom or two 9V batteries. Can also be used passively.



• Custom-wound CineMag USA transformer.

• Converts instruments to mic-level signals without signal degradation.

• Ideal solution for plugging your instrument direct into any mic pre, mixer or recording device.

• Top-quality discrete components with gold-plated traces on circuit board. 

• Rugged aluminum chassis construction.  

• Pad: Variable from -3 to -30dB.

• Balanced Output: 600 ohms, mic level.

• Input Impedance: 1 Meg Ohms.

• THD: .01% from 20Hz to 100Hz. Less than .004% from 100Hz to 20kHz.

• Frequency Response: 20Hz to 70kHz +/- 0.5dB.












Phil O'Keefe  is a multi-instrumentalist, recording engineer / producer and the Senior Editor of Harmony Central. He has engineered, produced and performed on countless recording sessions in a diverse range of styles, with artists such as Alien Ant Farm, Jules Day, Voodoo Glow Skulls, John McGill, Michael Knott and Alexa's Wish. He is a former featured monthly columnist for EQ magazine, and his articles and product reviews have also appeared in Keyboard, Electronic Musician and Guitar Player magazines.  




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