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Metasonix TS-21 Hellfire Modulator

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The TS-21 Hellfire Modulator is the most unique analog signal processor to be introduced in many, many years. [And it's 100% tube.]

Hellfire contains three processing blocks: a pentode preamp (that can be used as a VCA in an analog synthesizer studio), a metastable pulse-width modulator, and a waveshaper/switcher based on a unique TV tube. The latter two circuits have NEVER been used for audio signal processing before. Their characteristics are unique, giving a vast array of tonal variations usually unobtainable with existing circuits.

Waveshaper: based on "Sheet-Beam Modulator" vacuum tube. Processes mono input signal from 10 mV up to more than 10v peak-to-peak. Performs a variety of waveform "folding" and wave doubling effects, similar to the "Serge Waveshaper" but with considerable tube distortion and assorted nonlinearities added. Output is mono or stereo--waveforms on the two output channels differ slightly. Built-in LFO switches output between the two outputs at rates from <1 Hz to ~5 Hz, adjustable for rate and stereo beam width using the L1, L2 and SPEED controls.

The TS-21 Hellfire Modulator contains two independent effects circuits. The first one is the PWM circuit. This circuit was taken directly from a 1960 textbook on pulse and switching circuits using vacuum tubes. Its behavior is so peculiar that we just HAD to make an audio waveform processor out of it!

The PWM is actually a very crude "monostable multivibrator". Because it uses positive feedback, it belongs to a class of designs known as "metastable" circuits. Varying the PWM MANUAL control causes the switch point of the PWM circuit to change. It only responds well to sharply-defined waveforms, such as square waves or sawtooth waves. The output pulses tend to be short and rich in harmonics--but also might have noise or bursts of oscillation riding on them. There are some settings which will cause the PWM to burst into oscillation, whether a signal is going into it or not. It can produce something resembling "VCO sync" effects with certain settings and input waveforms.

The second circuit is the beam modulator. This is based on an obscure tube, which (so far as we know) has NEVER been used in audio equipment. The 6AR8/JH8/ME8 was originally intended as a balanced modulator for use in TV sets, as the chroma detector! It is a very, VERY crude form of balanced modulator--it literally uses electrostatic deflection to switch the input signal between two anodes, while also providing some signal gain. It's not a perfect balanced modulator, as it does pass some of the input signal to the output (in other words, it doesn't completely suppress the carrier signal). However, its electrical behavior is so strange and un-solid-state-like that it can be used as a sound effect.

The beam modulator in the TS-21 is wired to a built-in LFO. This LFO can be disabled if the modulation effect is not wanted, by turning down both the L1 and L2 controls.

It causes the beam to switch back and forth between two anodes, which then go to the output. That's right--this is a STEREO modulator. You can insert either a mono 1/4" plug into the AUDIO OUTPUT jack, and get a mono signal. Or you can insert a stereo plug, and get a STEREO effect. The beam tube switches the signal back and forth between the two outputs. Plus, the beam tube has something solid-state lacks--a screen grid. By adjusting its voltage, we get both gain control, and we get variable distortion--of a very unusual nature! You have to hear its effect to understand. The beam tube is very non-linear in most settings, so it can be used as a distortion effect. At some positions, the beam screen control causes waveform "folding" roughly similar to that seen in the Serge Waveshaper modules--but with tube-style nonlinearities.

Technical Specifications
Type: Analog
Synthesis: Oscillator(s), Wave Folding, Wave Shaping
Oscillators: 1
Waveforms: Pulse Variable
Osc Modulation: Input, Knob, LFO
LFO: 1
LFO Parameters: Sine
Polyphony & Tuning
Polyphony: 1
Timbrality: 1
Tuning: Atonal
Modes: Mono
Case: Rack
Rack Size: 19", 2U
Controls: Knobs, Switches, Modulation 1/8" Jacks, Pedal - Filter
Display Type: LED
Dimensions (WxDxH): 484mm (19.0") wide, 88mm (3.5") high, 320mm (12.5") deep (incl. front-panel handles), depth behind panel: 255mm (10")
Weight: 8 kg
Audio Output Connections: 1/4" Phone Jack, Mono Out, Stereo Main
Audio Output Count: 3
CV Ports: CV IN
Power: 120v or 240v via internal wiring, 50/60 Hz, power consumption less than 20 watts
Year Released: 2000
Year Discontinued: 2002
Manuals & Documents
MSRP List Price: $750 - convert
References & Sources

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