Radial SpaceHeater User Guide
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Using The Space Heater™

The Space Heater 500™ is a studio-grade tube overdrive that is used to produce different levels of harmonic distortion on sources of all types. It is designed to be used with standard 500 series chassis including the Radial Workhorse™ frames. This quick reference guide assumes you are familiar with 500 series modules and racks. Complete details on using the Space Heater 500 and making connections to and from your 500 series rack can be found in the users guide (PDF download).

Making Connections

As with all audio equipment, always turn levels down and turn equipment off before making connections. This is particularly important with 500 series modules as the applied voltage on the back plane is quite high. This will help avoid turn-on or plug-in transients that could damage speakers or more sensitive audio equipment. Plug the Space Heater into the Workhorse or 500 series rack. There is no power switch on the Space Heater, so it will automatically turn on as soon as your rack is powered up.

Understanding the signal flow

To get the most out of the Space Heater 500, it is important to understand the signal flow and building blocks that work together to produce the sound.

    Sets the input level to the tube section. As you increase the drive, more signal is forced through the tube, driving the tube harder, producing more distortion.
  • HEAT
    The Heat switch selects the plate voltage that is applied to the tube. You can select between 35, 70 and 140 volts to change the type of distortion produced by the tube.
  • 12AX7 TUBE
    The heart and soul of the Space Heater 500! This is where the analog warmth and saturation is produced.
  • HI-CUT
    A variable low pass filter lets you focus the distortion in the lower registers or attenuate high frequencies that may be shrill or otherwise undesirable. Gives you complete control from 20kHz down to 500Hz.
  • LO-CUT
    A variable high-pass filter lets you reduce low frequency build-up and resonance to clean up tracks or focus the distortion to enhance upper harmonics. Can be applied from 5Hz up to 500Hz.
    Lets you filter the incoming signal before distortion or apply a filter after the track has been brutalized. Choice of low-pass (hi cut), high-pass (low cut), bandpass (used together) or bypass.
    The last step in the signal path. An oversized Jensen transformer was selected to produce fat bass tones and vintage vibe.

Quick Start

Connect the output from your workstation to your 500 series rack using the XLR input associated with the Space Heater 500. Connect the XLR output from the same channel back to your recording system. Select a source such as a bass track for testing purposes.

For optimal signal-to-noise, use the LEVEL control to match the wet output to the dry signal. This can be quickly accomplished using the IN button to compare. Press to activate, depress to bypass. You should now be able to hear a subtle, distorted change when audio passes through the Space Heater 500. Increase the plate voltage to 140V. This will increase the output slightly and clean up the signal. Now, reduce the plate voltage down to 35 to hear the effect of starving the tube.

For fun, try playing with the filters. The high-pass (lo-cut) filter can be extremely effective at reducing excessive low frequency build up. It also allows you to focus the distortion so that it will only be applied to the upper registers. Try the low-pass filter (hi-cut) to hear how you can remove top end sizzle. Applying the filters before or after the distortion will sound very different.

Omniport™ - Using the Space Heater 500 with instruments

When installed in a Radial Engineering Workhorse™ rack system, the Space Heater 500 utilizes the Omniport™ ¼" connector as a direct hi-Z instrument input. This allows the Space Heater 500 to be used as an instrument preamp, providing warmth and saturation to your direct recordings. Plugging into the Space Heater directly allows you to apply texture and distortion while tracking, making it especially useful on bass guitar and keyboards.

Sample Applications


The Space Heater is a fantastic piece to add excitement and punch to a drum kit. You can apply the effect to a stereo mix or 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!


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 effectively 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 by providing definition in higher frequency ranges. 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 500 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 sound and react differently when distortion is applied. Experiment by running different signals through a channel on the Space Heater 500 and listen to the results. Even simply running a fixed frequency tone through the Space Heater can transform the sound and enhance creativity.


Direct recorded electric guitars can often be too clean or shrill. Applying a slight distortion can make them sound more like they are coming out of a clean amp rather than a direct box. Turning up the distortion can make you quickly forget that the guitar was ever clean in the first place, and leave others thinking that you recorded a tube powered half-stack!

Distorted Delay or Reverb

A bit of distortion on an EFX return can make your delays or reverbs sound quite a bit different than the dry recording. This makes the effect much more present in the mix, and can add a vintage character to your digital delay or reverb. Light distortion can mimic famous vintage analog gear, while a heavy distortion can transform a delay into a completely different effect.