True to the Music
Radial Engineering Ltd.
Space Heater™ User Guide
5
FEATURES AND CONTROLS
DRIVE AND LEVEL
No matter how you decide to use your Space Heater, everything revolves around the DRIVE and
LEVEL controls. The DRIVE sets the amount of signal going into the tube. The more you turn up
the drive, the more the tube will distort. The LEVEL acts like an output fader, controlling the output
of the channel.
BE CAREFUL! Turn down the DRIVE control before turning the tube drive on. As you turn up the
DRIVE, you will need to compensate by turning down the LEVEL control. Engaging the tube drive
with both controls turned up could get loud… quickly!
-10
20
50
100
200
500
-5
+0
+5
Hz
High Pass Filter Response
DRIVE
LEVEL
UNDERSTANDING THE CONTROLS
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
fi
rst time.
TUBE SECTION
The tube drive circuit can be turned on or off on each channel pair. When the tube section is
switched ON, the signal will pass through the 12AX7 based on the level of the DRIVE control. When
the tube section is switched OFF, it is effectively bypassed and the signal will only pass through the
LEVEL control and output transformer.
HEAT SWITCH
The HEAT switch allows the user to adjust the plate voltage of each tube. There are three selectable
voltages: 35V, 70V and 140V. At 35 volts, the tube is starved for voltage. This will cause it to break
up at very low levels, which makes it ideal when heavy, crushing distortion is desirable. 70 volts
allows for more headroom before the tube starts to distort and provides moderate distortion as you
apply more drive. At 140 volts, the tube will accept a lot more signal before breaking up. This allows
you to warm things up slightly at low drive settings, or ramp it up to drive the tube with plenty of
voltage, reminiscent of your favorite high-gain guitar ampli
fi
er.
HIGH-PASS FILTER
Each channel pair on the Space Heater is equipped with a high-pass
fi
lter. This
fi
lter starts at 40Hz
and has a very gentle 6dB/octave roll-off. It is intended to subtly reduce low frequency rumble and
resonance. This gradual slope makes it very useful on kick drums and bass guitar when retaining
most of the low frequency content is desirable.
TRANSFORMER COUPLED OUTPUT
The Space Heater is equipped with output transformers on each of the eight channels. These
oversized transformers were selected to deliver deep bass and add a vintage character reminiscent
of a classic analog mixing console. They also help eliminate buzz, hum and other DC noise issues
that can occur when connecting equipment in a studio. Because the tube drive can be bypassed on
each channel pair, the transformers can be used to add character all on their own. Simply run your
signal through the channel and adjust the level accordingly.
