Radial SpaceHeater User Guide
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Using The Space Heater™

The following page describes the basic functionality and some of the many applications that you will enjoy by adding the Space Heater to your setup. For complete details on how to use the Space Heater, we invite you to download the full manual by clicking on the icon at left.

Before making connections, always ensure your audio system is turned off or levels turned down to avoid plug-in or turn-on transients that could damage more sensitive components such as tweeters or headphones.


The Space Heater is an 8-channel device with stereo summing. The eight channels pass through four 12AX7 tubes, each of which is wired in stereo. All eight outputs are transformer coupled for isolation and analog character. While individual LEVEL and DRIVE controls can be found on each channel, other features are shared across both channels of the tube. It is important to understand these features before connecting your Space Heater for the first time.

  • ON
    Used to turn on and off each channel pair. When in the out position, the channel is bypassed completely. Audio is passed from input to output without being effected by the controls, tube, or output transformer.
    This switch is common to each channel pair and routes the channels to the stereo master bus. Individual channel outputs remain active.
  • HPF
    Engaging this switch will set a high-pass filter across both channels.
    This switch activates the 12AX7 tube circuit for each channel pair. When in the out position, the Drive control and tube section are bypassed. This is useful when a cleaner signal is desired, as audio will only pass through the output transformer.
  • HEAT
    This switch sets the 12AX7's B+ voltage for each channel pair. 3 different voltages are available, each affecting the way the tube distorts in a different way.
    No matter how you decide to use your Space Heater, everything revolves around the DRIVE and LEVEL controls. DRIVE controls the amount of signal going into each tube. The more you turn up the drive, the more the tube will distort. LEVEL acts like an output fader, controlling the output of the channel.

Master Section

Activating the BUS switch on each channel pair will route the audio to the Space Heater's master section. Odd channels (1, 3, 5 & 7) will be assigned to the left output, and even channels to the right output. Direct channel outputs remain active when using the master section, which allows for different parallel processing possibilities.

  • ON
    Activates the XLR stereo outputs.
    Sets the output level of the main stereo outputs.
    Controls the volume of the ¼" headphone output. This output is always on, allowing you to turn off the XLR outputs but still listen to the mix bus with headphones.

Using the Space Heater to mix tracks from your digital workstation

When mixing in a digital audio workstation (DAW) or even with some digital mixers, folks often complain that something is lost. There are lots of theories as to why or even if this actually occurs, but most agree that something magical happens when audio tracks are combined in the analog domain. The Space Heater handles this task with ease. Not only is it an extremely high quality, transformer coupled analog mixer; it also offers a tube circuit for endless personality!

A common method for using the Space Heater as an analog summing mixer alongside a DAW is to work with stereo stem mixes. This means that you mix similar instruments to separate stereo outputs. All panning is handled by the workstation, so the Space Heater is only performing the final stereo mix from these groups. When you engage the BUS switch on the front panel, odd channels are automatically routed to the LEFT bus and even channels routed to the RIGHT bus.

Because the tube drive section may be turned on and off for each channel pair, the Space Heater can be used when clean analog summing with slight vintage character is preferred. In this case, the signal will only pass through the level control and output transformer on each channel.

  1. Make sure all LEVEL and DRIVE controls are turned fully counter-clockwise to prevent accidental volume spikes.
  2. Connect your DAW outputs to the Space Heater's 8 individual channel inputs via ¼" TRS or DB25.
  3. Connect Left and Right XLR outputs of the Space Heater to your recorder. Try routing the final stereo mix back to new channels on your DAW for recording and monitoring or if you prefer, connect to a dedicated 2-channel tape machine.
  4. Turn each channel pair of the Space Heater ON and engage the BUS switch to assign outputs to the stereo mix.
  5. Turn the TUBE DRIVE ON for each channel pair where desired. Leave off if simple resistive analog summing through transformers is desired.
  6. Setup DAW or recorder to play back 4-stereo recordings assigned to the outputs connected in step 2.
  7. Turn MIX BUS ON and adjust level control. If sending the stereo mix back to your recorder, set the output level between 12 o'clock and 3'o'clock. If connected directly to studio monitors, set at a lower level until playback begins
  8. Begin playback. Slowly increase the LEVEL and DRIVE controls on any one channel (only LEVEL control is necessary if tube is not engaged).
  9. Adjust balance between LEVEL and DRIVE on all eight channels. Increasing the level will result in a cleaner sound while increasing the drive will introduce more distortion.
  10. Adjust the HEAT switch between the three different voltages. Lower voltages will starve the tube and result in a grittier distortion while higher voltages will produce a warmer overdrive.
  • A Typical Selection is as follows:
  • Drums Left...Ch-1
  • Drums Right...Ch-2
  • Bass Left...Ch-3
  • Bass Right..Ch-4
  • Guitars Left...Ch-5
  • Guitars Right...Ch-6
  • Vocals Left...Ch-7
  • Vocals Right...Ch-8

Using the Space Heater as an insert on individual tracks

One of our favorite ways to use the Space Heater is as an effect on individual channels. Whether applying heavy distortion on a single instrument to completely change its character, or simply adding subtle warmth to a sterile recording, the Space Heater will add all kinds of analog mojo to the music.

To use the Space Heater on individual tracks, it should be thought of as a compressor or EQ. It can be connected in the following ways:

Hardware Insert: Most hardware mixing boards are equipped with insert jacks on every channel. These allow the Space Heater to be inserted before the fader on an individual channel. Sometimes the option to be pre or post EQ on the consoles channel strip is also possible.

Using in-line: The Space Heater is a professional +4dBu line level device and can be used in line (connected in series) with other analog hardware. Try connecting the output of a microphone preamp directly to a Space Heater input when tracking, or as the last device in a recording chain (mic pre --> EQ --> compressor --> Space Heater)

Software Insert: Most audio recording software provides a method of setting up hardware inserts within the program. These utilize different inputs and outputs on your audio interface, and allow them to behave as a hardware insert within your software. This is the most popular method of connecting the Space Heater when using it as an effect.

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Hardware Insert Inline Software Insert

Sample Applications


The Space Heater is a fantastic piece to add some excitement and punch to a drum kit by inserting it on individual channels. As you slowly bring up the distortion by increasing the DRIVE control, the audio will compress and become more present in the mix. Adding subtle distortion to a kick or heavy distortion to a snare is particularly effective as it is often difficult to increase the presence of these instruments without drastically increasing their level. A slight amount of distortion on a stem mix of the entire kit can really make a drum mix pop!

TIP: Try assigning the output of the Space Heater to a different channel on your recorder. This will allow you to bring up the distorted track separately from the original clean track. Playing back the two channels in parallel will allow you to adjust the blend between the two, which will allow you to dial in your sound even more quickly!

In Ear Monitors

In-ear monitor systems often sound sterile and out of place. Close-mic'd instruments and direct box signals passing through a digital console and into a pair of ear buds will not create the same sound as what is coming out of the PA system, where the speakers are actually moving air. Some musicians can never get used to them while others simply put up with the sound. The Space Heater quickly brings back the natural feel and tone that has been missing. Applying distortion to individual instrument tracks or even the stereo bus slightly compresses the signal without a loss of dynamic range. Less EQ and compression is required overall, and the added grit makes you feel like you are standing in front of a speaker instead of listening to tiny little buds!


Bass guitar is an instrument that can definitely benefit from some grit. First, it can limit the amount of compression needed, as the distortion will add harmonics to the bass sound, allowing it to live in a different frequency space that is not competing so closely with other instruments. Distortion can also help define bass frequencies in small speakers or headphones. Try applying a small amount of distortion with the Space Heater while listening with headphones. Even if the change is inaudible in larger speakers, it can make all the difference when listening on small speakers.


It is always a challenge to maintain a lead vocals presence in a mix, particularly in rock music where they are competing for space with distorted guitars. The guitar distortion tends to live in the same frequency space as the vocal, so turning up one will quickly mask the other. Using the Space Heater to apply a small amount of distortion to the vocal can help the track move into a different frequency space, bringing clarity and definition without resorting to heavy-handed compression or drastic EQ.

Electronic Music

Keyboards, synths and various tone generators will all react differently when applying distortion. Experiment by running different signals and instruments through a channel on the Space Heater and listen to the results. Even simply running a fixed frequency tone through the Space Heater can transform the sound and enhance creativity.

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Recording drums With in-ear monitors Electronic Music