Sebatron THORAX Manuale utente
~Sebatron~
Innovative Australian Audio
THORAX - operating manual
Copyright Sebatron 2020
Valve Microphone Preamplifier with EQ and Compressor
THORAX
1/Introduction
2/Features
3/Functions and Dials
4/Inputs and Outputs
5/Operation
6/General Maintenance
7/Specifications
Table of Contents:
In real life acoustic situations the human voice is cable of producing sounds
that cover a wide dynamic range - from a gentle whisper to an ear-piercing scream.
The same can be said about electric and acoustic instruments. If these dynamics are
recorded linearly there is a tendency for softer sounds to drop below the threshold of
perception, particularly if the sound playback systems (amps and speakers) are not
aligned to real life volume, but are instead, adjusted for listening pleasure.
This creates a need to reduce the dynamic range of a sound so that it can fit into the
limited range of a playback or recording system.
This is where valves and audio compression enter the picture. The Thorax uses
a transformer coupled valve preamp to subtly act on the signal and reduce dynamic
range. The Class A circuitry running on High Voltage rails means that internally,
the signals can have a wide voltage swing that permits all the goodness of the valve
and transformer to come to the fore, shaping the signals naturally.
This preamp also features a passive EQ designed to accentuate the positive
aspects of the textures and harmonics generated in the valve. The frequencies
chosen are the ones that resonate best within the architecture of the circuit.
The preamp/EQ is followed by the optical compressor, there the user can
further interact with the signal process and apply audio compression as needed. The
dynamic range of the output can then be adjusted so that vocals, for example, sit
consistently and clearly present in a mix. The quieter moments won’t drop out and the
louder moments won’t distort or overload. Naturally this also applies to all
instrumentation.
For recording signals direct from electric instruments such as synthesizer,
electric guitars, Bass etc. the Thorax is also well suited as a valve D.I with the Direct
Input on the front panel. This is a High Impedance direct feed to the grid of the valve
and when levels are optimised will yied an excellent signal to noise ratio that is
perfectly suited to digital recording.
The running of pre-recorded tracks is another process the Thorax has been
designed for, signals can be fed into the Thorax and organically sculptured to suit.
Signals can be injected in up to three different ways by using the preamp XLR input,
preamp direct input or external line input for the compressor.
For creative applications the Compressor section of the Thorax has been
designed with added features such as compression mix, as well as, two modes of
compression based on where detection takes place - feedforward or feedback.
All these features, coupled with a well thought out and streamlined circuit,
is what makes the Sebatron Thorax a highly desirable and practical
recording tool solidly built to last a lifetime.
1. Introduction
2. Features
• Transformer coupled XLR microphone input feeding valve triode
• Fully balanced XLR inputs and outputs
• High Impedance phono Direct Input for Guitar, Bass, Keyboards or
line level signals etc
• Six-way pad/gain control in 6db increments that sets the gain
and colour of the preamp
• Quality 12AT7/ecc81 Valve running on a High Voltage rail providing
steller musical signal amplification and enhancement
• Six-way High Shelf selector dealing High Frequency boost or cut
• Six-way Low Shelf selector dealing Low Frequency boost or cut
• 180 degree mic input phase reversal switch
• +48VDC Phantom power for condenser microphones
• Signal indication LED indicates signal is in correct operating range
• Output level control for transparent control of the final output signal
Thorax preamp
Thorax compressor
• Fully balanced XLR inputs and outputs
• Switchable from Thorax mic pre or external line input
• Compressor ‘mix’ control adjustable from 100% dry to 100% wet
• Fully variable Threshold, Ratio, Attack, Release controls
• ‘Pump’ switch for extended ratio range
• Tight/Normal/Smooth switch for selection of attack/release ranges
• Switchable feedforward or feedback compression styles
• Transperent Output Level/Gain Makeup
• External Control Voltage input to link two units in stereo
• External Side-chain insert for detection EQ or ‘Ducking’
• Switchable Preamp/Main Output/Gain Reduction metering
• Wide swing and internally calibrated accurate VU metering
• Wide Bandwidth and Low Noise quality Class A circuitry
running on High Voltage rails
• Quality switches, potentiometers and components throughout
2. Features
(top row)
-Phantom Power Switch: Switchable +48V power for condenser microphones
-Signal LED: Illuminates when signal is present and in optimum range
-Pre-amp output control: Adjusts final output level of preamp section
-Normal/Reversed Phase Switch: Selects the phase or polarity of the signal
-Passive EQ High Selector: Six position selector switch for
High Frequency cut or boost
(bottom row)
-Direct Input: 100k High Impedence Balanced/Unbalanced Phono input for
electric Bass, Guitars, Keyboards and line inputs
-Pad/Gain Selector: Acts as a pad and gain control by varying
negative feedback around first stage of triode/Valve - set in 6db steps
-Passive EQ Low Selector: Six position selector switch for
Low Frequency cut or boost
3. Functions and Dials
(top row)
-Compression indicator LEDs: Indicates when compression is active
-Threshold: Sets the point at which compression begins
-Ratio: Adjusts the amount of compression when compression begins
-Normal/Pump Switch: Selects between normal and pump modes-
Pump mode extends ratio range
-Attack: Adjusts attack constant of compression characteristics
-Release: Adjusts release constant of compression characteristics
-Normal/Tight/Swim: Switches between three attack/release ranges
(bottom row)
-Mic/Line input switch: Switches between mic pre (to the left)
or external line input (back xlr)
-Comp mix: Adjusts the degree of balance between comp and dry signals
-Comp bypass switch: Selects between complete bypass or compressor
-Feedforward/Feedback switch: Selects where detection of compression
takes place - More apparent at higher ratios
-Main Output Control: Adjusts final output level of signal when compressor
circuit is switched in (not bypass)
3. Functions and Dials
Ext. CV input Side-Chain Insert
Preamp Output
Main Audio Ouput
Preamp Input/Output
Compressor Input/Output
Balanced TRS Balanced TRS
Balanced XLR Balanced XLR
All XLR inputs and outputs are pin 2 hot.
All TRS outputs are Tip=hot, Ring=cold, Sleeve=Ground.
Ext. CV input is 0 to 12 VDC max.
*This is not an audio input/output.
Only direct current control voltages must be fed into this in/output.
External side-chain input insert is TRS but can be used with unbalanced
phono cable for external trigger to detector.
4. Inputs and Outputs
Mains Power Input
Voltage Selector Switch
The Thorax can be switched between different voltages via the voltage mains
selector on the back of the unit.
This switch is usually set in the factory for the appropriate voltage that the
unit is destined for, however, in cases of re-sale etc. it is always recommended to
check this switch before initial power up.
If Voltage Selector Switch is set to the wrong position the fuse should blow
before any damage occurs.
Fuse rating is 0.8 amp @ 240/250 volts (or 1.6 amp @ 110/120 volts).
4. Inputs and Outputs
General Tracking with Mic or Direct Input:
1./ Turn output level control fully left, phase switch to normal, both EQ set to flat
Set Pad/Gain six way selector to default 0db setting, set VU meter to pre-out.
2./ Plug chosen vocal microphone into XLR mic input socket on back.
If the microphone is of the condenser type then activate the phantom power switch
and observe phantom LED to confirm power.
3./Observe signal indication LED lit when speaking or singing into the microphone
to confirm microphone signal.
4./Slowly adjust pre output level control so that signal range is around optimum on
the VU meter when meter is switched to pre output level.
5./If more gain or colour is required then adjust six way pad/gain selector to suit.
6./Adjust output level to maintain optimum signal level.
Adding compression:
1./Set comp mix dial to 100% or fully right, set to feedforward, threshold fully right,
ratio to mid-way or 4:1, attack and release mid-way and range selector to tight.
Select which input source you are feeding the compressor - Thorax mic pre
or external line input on back.
With comp switch set to bypass confirm signal is in the right level range by
switching meter switch to output and observing signal range. Adjust if necessary.
2./ Activate compressor by switching toggle to comp active.
Slowly turn threshold control to the left and confirm compression by active LED.
Notice how compressor pushes down the louder moments.
Adjust ratio, attack and release to suit material and tastes.
3./Switch to GR metering and observe how compressive action is taking place.
Adjust main output level control to suit destination level requirements.
For more dynamics turn mix control to the left slightly.
4./ Choice of feedforward or feedback compression depends on taste and
requirements.
For Acoustic instruments in a classical setting we would recommend feedforward.
For Vocals and Rock instrumentaion we would recommend feedback.
5. Operation
Altri manuali per THORAX
1
Altri manuali Sebatron Amplificatore
