Sebatron THORAX User manual

Table of Contents
Page
1. INTRODUCTION
Introduction 1
2. FEATURES
Front Panel
Preamplier 2
Compressor 4
Meter 6
Rear Panel 8
3. USING THORAX
Setup and Use 10
Recommended Settings 14
Thankyou for purchasing a Sebatron unit. We are sure
it will give you many years of solid use and take your music
to another sonic dimension. We produce original, innovative
audio equipment that is serious value for money. To get the best
performance, we recommend you switch on the unit and let the
valves warm up while you read this manual.
Power Source - Your unit is factory preset to your local voltage on
shipping and this voltage is marked on the rear of the unit.
Please check this carefully before powering up the unit!
We are not responsible for any damage caused by
incorrect voltage settings.
Servicing - Please do not open the case unless instructed to do
so by Sebatron. There are no user serviceable parts inside, apart
from the valves. If your unit is not performing as expected please
contact your dealer to nd the nearest authorised service agent.
Ventilation - Like all other Class A equipment, this unit will
produce heat during normal operation . Please consider this when
mounting, do not block the ventilation holes, do not place directly
above or below hot equipment (e.g. ampliers, power supplies,
heaters - preampliers are also best kept away from this kind of
equipment due to electrical noise)

Thorax is a complete recording channel in one box. It consists of a valve
microphone preamplier based on the Sebatron VMP Series, switchable high
and low EQ and an optically controlled valve compressor. It is of course free of
integrated circuits, being fully discrete Class A with valves run from proper high
tension rails.
But Thorax is more than just another channel strip with nice specs. It
has some unique Sebatron circuitry and features that will enable you to create
new tonal possibilities. The preamplier section is an expansion of the VMP
Series circuit with more possibilities in the switchable passive EQ and more
valve warmth available via the Colour control. It can be driven ultra clean for
transparency or pushed through warm valve tones and into distortion. The EQ
can boost or cut the extreme high and low frequencies to enhance or clean up
your signal and is fully bypassable.
Thorax’s compressor stage uses a unique Sebatron-designed optically
driven gain reduction circuit that gives fast, tight control over the dynamics of
a signal with a minimum of colouration. It has controls for Threshold, Ratio,
Attack and Release, with the attack/release factor switchable over three ranges.
Makeup gain is provided by a valve stage with a three position Drive control.
This audio path is complemented by a large, easy to read VU meter that
can be switched to indicate preamp or main output level or compressor gain
reduction.
THORAX
Introduction
1

THORAX
Transformer
Balanced XLR
Microphone
Input
DI Input
EQ
Bypass
48V
Phantom
Power
Phase
Reverse
Pre-amp
Output Level
Input
Pad
Air
- High
Shelf
EQ
Deep
- Low
Shelf
EQ
Colour
The preamplier stage of Thorax has several input options. A balanced
microphone can be connected to either the front or rear XLR input or an
unbalanced instrument or line level signal can be connected via the DI Input.
The Phantom Off/On switch can be used to provide phantom power to
the XLR inputs when required.
The Input Pad will attenuate the signal before it reaches the valve, which
enables hot line level signals to be amplied cleanly. The Pad is also interactive
with the Air high shelf EQ. More Pad creates a stronger EQ curve, with the
ranges overlapping for a huge spectrum of EQ possibilities.
Phase Reverse can be used to allow for phase differences between
microphones when using multi mic techniques. If the combination of microphones
(e.g. top and bottom of snare) is sounding thin or weak, try reversing the phase.
Colour controls the gain from the valve, and as a result, the amount of
valve warmth. Low settings will give a clean and transparent sound, while driving
the valve harder will result in warm or even distorted sounds.
The Air High Shelf EQ and Deep Low Shelf EQ consist of a range of
musically useful cut and boost curves. They can be switched to a at frequency
response with the EQ Bypass.
The preamp Output Level controls the signal level being sent to the
preamplier outputs. On the rear of the unit there is a balanced XLR output
which operates at a nominal +4dBU for recording, a lower level TRS balanced/
unbalanced output intended for direct monitoring and the internal send to the
Compressor, accessible through the compressor input/insert.
Pre-amplier
2 3

Threshold
attack /
release factor
Ratio
Attack Release
comp drive comp bypass
output level
THORAX
Compressor
The Thorax Compressor is optical based, but thanks to some unique
Sebatron circuitry is faster and has a wider dynamic range than traditional optical
compressors. The Compressor Input Insert is a TRS jack on the rear of the
unit. The signal path between Preamplier and Compressor can be interrupted
here to use each section independently, or to insert another processor such as a
parametric equaliser between them.
Threshold, Ratio, Attack and Release are all standard compressor
controls. If you are unsure what they do, we recommend you read some of the
many excellent explanations of compression available on the internet before using
it while tracking.
Compression Drive is related to Colour in the preamp. It controls the
amount of valve gain in the compressor stage and can be used to provide gain
make-up or simply for more warmth.
The Compressor Bypass switch nulls the compression control voltage,
which stops any attenuation of the signal passing through the valve. This can be
used to compare the compressed signal to the dry or to use the compressor stage
as a pure valve line amplier.
The range of the Attack and Release controls can be Fast, Medium or
Slow by using the Attack/Release Factor switch. There is some overlap between
the ranges, enabling very ne detail setting of the attack and release times.
The Output Level controls the signal level being sent from the
compressor to the two main outputs on the rear of the unit. There is a balanced
XLR output which operates at a nominal +4dBU for recording and a lower level
TRS balanced/unbalanced output intended for direct monitoring.
Also at the rear of the unit is a Sidechain Insert. This TRS jack interrupts
the audio signal on it’s way to the level detection circuitry. You can insert your own
audio signal here to control the compression from another source.
4 5

Output Meter
Options
Power Switch
Meter Source
THORAX
Meter
The metering section allows you to gain an insight into the internal
operations of Thorax. The amount of gain reduction occurring in the compressor
can be indicated by switching the Meter Source to GR. The meter should then sit
at 0dB and the meter markings will indicate the amount (in dB) of gain reduction.
With the Meter Source set to O/P the O/P meter options become active.
These controls give you the choice of preamp or main output levels over 3
possible ranges.
The medium range is calibrated to 0dBu at the XLR balanced outputs.
The other settings enable you to monitor both the upper ranges of modern high
headroom equipment and the lower signal levels possible with 24 bit recording.
Always remember that the VU specication was developed with tape in
mind, and as a result only represents a fraction of the dynamic range possible
with todays digital recordings. All Sebatron products are designed with this wide
dynamic range in mind and the limitations of the meter in no way represent the
limitations of the unit. Because we use no integrated circuits, there is no hard
clip point, only a gradual increase in valve warmth and then distortion that can
be musically useful. What this means is that if the meter is slamming against the
stops but the sound is just what you want, switch the meter to a lower level or to
GR and follow your ears. The input meters of your recording device show the only
truly important levels.
6 7

Voltage
Selector
Switch
Fuse
1.25A
Slow
Mains
Input
Main XLR
and TRS
Outputs
Transformer
Balanced XLR
Microphone
Preamp Input
Preamp XLR and
TRS Outputs
Sidechain
Input
Compressor
Insert/Input
120v240v
Tip = Compressor Line
In/Receive
Ring = Preamp-Out/Send
Tip = Comp Key Receive
Ring = Comp Key Send
The rear panel of Thorax contains most of the input and outputs and the
IEC mains connector. The input voltage range is switchable between 110-120V
and 220-240V. Make sure it is set correctly before you switch the unit on!
Sebatron units are built tough and usually survive abuse, but we don’t guarantee
it.
The sidechain input interrupts the audio signal being sent to the level
detection circuitry which controls the compressor. This is normally the audio that
is being compressed, but through the use of the sidechain you can either process
the signal and then send it back or introduce an entirely different signal. See
Usage for more details.
The Main and Preamp XLR and TRS outputs are fully balanced by
discrete Class A driver circuits. They follow the industry standard Pin 2 Hot pinout.
The Compressor Insert/Input is a TRS jack that normally sends the
preamp output to the compressor input. You can
use an insert splitter cable to further process the signal between the preamp and
compressor, e.g. with further EQ.
This insert also allows you to use the pre and compressor sections
individually. Use a standard unbalanced patch cable or guitar lead to inject a
signal into the compressor. There is quite a bit of gain available through use of the
Compression Drive switch, making it possible to run a vocal microphone through
the pre and a guitar or bass through the comp.
THORAX
Rear Panel
8 9

Connect the Main output to your recording device. A balanced cable will
give the best signal to noise ratio but make sure that you are connecting to a line
level input, not a microphone input. Many modern computer recording interfaces
have 2 or more XLR microphone inputs and several TRS line inputs. In this case,
use a balanced XLR to TRS cable or if unavailable a balanced TRS to TRS cable
from Thorax’s TRS output.
DON’T connect a balanced line level output directly to an XLR Mic input,
the signal levels will not be matched, resulting in increased noise and possible
distortion, and there is a chance of damage ocurring to the line level unit if
phantom power is switched on. If you require a separate monitoring signal, you
should connect a balanced or unbalanced cable from the TRS output to your
mixer.
Connect a microphone to either the front or rear XLR inputs. Apply
phantom power if required. Alternatively, a line level signal or instrument can
be used via the DI input. The meter should indicate a signal now. If it is too low,
increase the preamp level and possibly the colour control. If it is too high, engage
the Pad switch. You can now increase the main Output Level and you should hear
your signal.
Preamplier
The preamplier stage is based on the Sebatron VMP Series and
shares many of the same characteristics. The Colour control is an extension
of the Pad switch on the VMP and can be used to change the amount of gain
available from the valve, which means more second order harmonics and soft
clipping compression when driven hard. Keeping the Colour low will give you a
clean, transparent signal, while increasing it will make your sound warmer and
eventually distorted, with each of the settings having a slightly different curve. A
whole myriad of possibilities that can’t be obtained from chip based units exist
within the circuitry. Similar overall gain settings ( e.g. 0db pad, 6 db colour OR -
10db pad, 12 db colour) will have totally different sonic textures.
Thorax is a complex device with many possibilities, but don’t be intimidated.
It is like a quality musical instrument, you can use it in a basic manner while you’re
learning and it will do the job well, but with time you will start to really understand the
subtleties and how to bring them out. There are many organic anomalies that allow
the circuitry to naturally stabilize any signal without sounding at and lifeless. On the
contrary, the unit will react musically.
Tracking should be a breeze with an array of tracks ‘stacking up’ perfectly.
Subtle compression on the way in means presence and width. The default setting
revolves around ‘ cool ‘ compression drive, 0db to 6 db colour with no pad. For
higher gain applications it is advisable to switch to the ‘warm ‘ or ‘hot ‘compression
drive settings where gain makeup in the second half is much higher.
For higher level D.I inputs or loud condenser mics it may be desirable to use
the pad settings...
Follow this guide for initial SETUP of thorax
Control Initial
Setting
Notes
Power > 10mins warm up time for valves
Output Level 0 increase after signal is present
Meter options pre-amp set to indicate preamp output level
Threshold fully right no compression
Compression
Drive
cool low compressor gain makeup
Colour 0 for a clean signal
Phase in
Pad 0dB
Deep + Air 0 Flat EQ
EQ out Bypass EQ
Preamp Level 5
THORAX
Using
10 11

The Thorax EQ consists of high and low shelves, and can also be
thought of inversely as a broad mid-range bandpass lter. For example, a high
and low boost is the same as a mid cut. Use the Eq in/out switch to do A/B
comparisons with the at signal.
The Air shelf enables you to boost the high frequencies before any gain
stages or other noise sources, which means the cleanest possible signal. There
are two cut and three boost settings, which move the high shelf to progressively
higher frequencies.
The Deep switch changes the low frequency response of Thorax, with
two cut and three boost settings of increasing intensity. Ultra low frequencies can
be difcult to control, with slow rise and fall times and a lot of power contained
within the signal. Careful attention has been paid to these frequencies, with plenty
of headroom allowed, which means fatter bass for you!
Use the Pad switch to attenuate high signal levels for a cleaner sound.
This control also affects the Air EQ curve, increasing the Pad increases the depth
of the Air setting. The Air factor is most prominent with a -20dB Pad setting. Allow
your self time to know the E.Q settings and how they are ‘factored ‘ with the pad
control.
The Preamp Level controls the signal level from the preamplier direct
outputs, which are on the rear of the unit adjacent to the microphone input.
This also controls the amount of signal being sent from the preamplier to the
compressor, so you can drive the preamp heavily using the colour and pad
controls and then reduce the output level to prevent overloading the compressor.
Compressor
Compression is occurring when the Active LED is lit, and the amount of
gain reduction can be indicated by switching the meter source switch to GR. Best
compression settings usually occur when the active led is ickering and the louder
peaks are registered by the ‘gain reduction‘ meter.
The compressor action can be completely bypassed by switching the ‘
compressor ‘ switch to ‘out’. This switches off the level detection circuitry while
still running the signal through the valve gain stage, and can be used for A/B
comparison or for obtaining more pure valve gain, similar to daisy chaining two
channels of a VMP Series preamp.
Default mode for the Compression is ‘ cool ‘ and ‘ fast ‘, with most
exibility attainable in these modes. To properly exploit the full compression
dynamics of the THORAX it is highly advised not to run the threshold parameter
fully counter clockwise as an overload of compression activity may result in subtle
audible distortion.
An EQ can be used as an insert across the compressor sidechain for
limiting the frequency response of the compressor so that only certain frequencies
are detected, for example in de-essing. To do this, use an insert cable that splits a
‘stereo’ jack into two mono jacks. The ‘ring’ connection will send the audio signal
to your EQ, the ‘tip’ connection will send the processed signal back to Thorax.
A different signal can be used to ‘duck’ the audio, for example reducing a
background track during a voice over. To do this, simply use a normal unbalanced
patch lead to inject the ‘master’ audio signal into the sidechain.
For stereo linking of two Thoraxes, connect the Sidechain Send of
one channel to the Return of the second channel. This can be done with an
unbalanced patch lead inserted halfway into the ‘master’ Thorax’s sidechain to
obtain the ‘send’ without interrupting the signal ow. The other end is fully inserted
into the ‘slave’ Thorax sidechain. The compressor controls are still independent,
so make sure they are closely matched for stereo operation.
12 13

Recommended Settings
To get you started we have included some basic settings. All of the settings,
especially compression, are very dependent on the signal source, including the
transient and harmonic content. Basically, you should always listen carefully, don’t
assume the obvious and be open to the unexpected. This applies to any audio
control device. We have also included some blank sheets for you to photocopy and
record your own settings.
Driven
For a rich and warm sound
Control Setting Notes
Pad 0dB Let lots of signal in to drive the valve
Preamp
Level
low Control the output level so you don’t
overdrive the next section
Colour high Lots of gain and valve colour
Preamplier
Ultra Clean
For a transparent sound
Control Setting Notes
Pad -10dB -
-20dB
Use 0dB or -15dB if more gain is needed
Preamp
Level
high Open up the output
Colour low Less valve drive = purer, atter tones
Fat Bass
Control Setting Notes
Pad 0dB Let lots of signal in to drive the valve
Colour high Lots of gain and valve colour
Deep Deep2 Back off here if it’s too much
Kick Drum
Control Setting Notes
Pad -10dB Leave headroom for transients
Colour Low-
Medium
As required
Deep Add to taste
Snare Drum
Control Setting Notes
Pad -10dB Leave headroom for transients
Colour Low-
Medium
As required
Deep Add to taste
Air Add to taste
Acoustic Guitar
Control Setting Notes
Pad -10dB Leave headroom for transients
Colour Low Keep it clean
Deep Gaunt Cut off some boominess
14 15

Compressor
Vocal Tracking
Control Setting Notes
Ratio ~10:1 Set threshold for gentle control of peaks
A/R Factor Medium Tune Attack and Release controls for
best results
Tight Bass
Control Setting Notes
Ratio High Set threshold to taste
A/R Factor Fast Set attack to fast, release as required
Acoustic Guitar
Control Setting Notes
Ratio ~10:1 Control peaks, leave the rest alone
A/R Factor Fast Set attack to fast, release as required
Snare Drum
Control Setting Notes
Ratio ~Innity:1 Set very high
A/R Factor Fast Set Attack as fast as possible, release as
required
Kick Drum
Control Setting Notes
Ratio ~Innity:1 Set very high
A/R Factor Fast Set A and R as fast as possible
~Sebatron~ Thorax User Settings
Date
Source
Notes
Control Setting Notes
Input Used
Pad
Phase
EQ Bypass
Preamp Level
Colour
Deep
Air
Threshold
Ratio
Attack
Release
A/R Factor
Compression
Drive
Output Level
GR amount
Pre Signal
Level
Output Signal
Level
Sidechain
16

~Sebatron~ Thorax User Settings
Date
Source
Notes
Control Setting Notes
Input Used
Pad
Phase
EQ Bypass
Preamp Level
Colour
Deep
Air
Threshold
Ratio
Attack
Release
A/R Factor
Compression
Drive
Output Level
GR amount
Pre Signal
Level
Output Signal
Level
Sidechain
~Sebatron~ Thorax User Settings
Date
Source
Notes
Control Setting Notes
Input Used
Pad
Phase
EQ Bypass
Preamp Level
Colour
Deep
Air
Threshold
Ratio
Attack
Release
A/R Factor
Compression
Drive
Output Level
GR amount
Pre Signal
Level
Output Signal
Level
Sidechain

input
transformer
direct
injection
pad
air colour deep
preamp
output
level
output
buffers
preamp
outputs
compressor
input
compression
drive
dynamics
detection
opto
attenuator
circuit
main
output
level
output
buffers
compressor
outputs
12AT7
valve
12AT7
valve
thorax preamp stage
thorax compressor stage
sidechain
input
+60V supply
+60V supply
+300 V high tension supply
+300 V high tension supply