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Strother Bullins on Radial Engineering Space Heater Tube Overdrive and Summing Mixer


’s unique 

Space Heater

($1,699 street) is an eight-channel stereo summing mixer featuring a 12AX7 tube per input pair for saturation, packaged in a 1U rack-mount chassis. It uniquely creates aurally pleasing line-level saturation-generated tonalities while providing transformer-coupled outputs and a whole lot of useful flexibility, making it a cool tool for both studio and live sound applications. Its routing features makes it a great addition to a house-of-worship (HOW) FOH or auxiliary mixing system, dedicated audio systems at clubs and theaters, and much more. Applications for the Space Heater abound. Radial suggests using it for a range of things, from the last stage of a vocal recording chain to warming up in-ear monitor mixes, all of which are personally tantalizing after having heard its capabilities in both recording and sound reinforcement settings.

Eight channels of DB25 inputs—wired in parallel to the Space Heater’s eight quarter-inch TRS balanced inputs—and eight DB25 outputs provide multichannel I/O, while stereo sum outputs via XLR are offered, too. With the unit’s quarter-inch TRS link I/Os, additional Space Heaters can be linked together, allowing for 16×2, 24×2, or 32×2 configurations. This is a fully pro-grade unit; from the 5-pin locking XLR connection to its external power supply to its 14-gauge steel chassis, the Space Heater is ready for years of service.

The Space Heater’s front panel offers a quarter-inch stereo headphone output with level control, mix bus off/on switch with level control, and eight paired (1/2, 3/4, 5/6, and 7/8 feeding strictly to L/R as odd/even pairs) input channels, each featuring variable Drive (level to the tube drive circuit), Level (output level from the tube drive circuit), and three switchable Heat settings that change each stereo pair’s tube voltage between 35, 70, or 140V. Also available per stereo channel are switchable stereo mix bus send select, high-pass filter and tube drive.

In use, I discovered how useful the Space Heater could be to allow for analog processing and flavor on some rather “cold” sounding performances and/or key audio channels; this is rather common in our increasingly digitally-networked HOW and theater infrastructures. Varying between subdued analog flavor to downright gritty vibe, spreading the Space Heater’s deep, even-order harmonic distortion generously over squeaky-clean inputs meant that my vanilla tonalities became something more compelling, from an aural perspective, not to mention all the available headroom, per channel, that is gained. Further, the unit’s insert points allowed me to pop in more discrete channel compression, allowing for additional flavor and effect during the summing process, all outside of the digital domain. In all, it’s intuitive and a whole lot of fun to use.

Notably, the unit is always crystal clean when you need clarity, or as dirty as you want it when you need grit. As a tube-packed unit, it is weighty for its size (8.5 lbs.) and understandably runs warm to the touch. Most importantly, having used Radial Engineering DIs and other associated gear for a long time now, I can assure you that the Space Heater is built to last, serviceable if needed, and will retain its appeal and value in the future.

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