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SPL TwinTube Processor

Tube saturation & tube harmonics processor in a 19-inch rackmount
SPL TwinTube Processor
SPL TwinTube Processor SPL TwinTube Processor


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The SPL TwinTube is a tube saturation & tube harmonics processor that delivers the two single most important sound effects generated by tubes: Saturation and Harmonics.

The warmth, presence and suppleness analog tube and coil filtering provide can enrich any production, regardless of the music genre.

  • TwinTube's saturation effects are sonically comparable to the effects of tape saturation
  • Saturation for more warmth and loudness; subtle to clear effects
  • Harmonics for more presence and clarity without adding appreciable levels (as with EQs); moves signals to the front of a mix
  • Extremely versatile for all kinds of signals, such as vocals, acoustic guitars, drums, strings, brass ...

The TwinTube is the first ever combination of two essential tube effects into a single processor, that is, saturation effects along with harmonics processing. Both stages work separately from each other and are based on an individual tube circuit, therefore each module employs two tubes. The effects can therefore not only be applied both individually or separately, but also in common.

Saturation effects are generated through the tube being pushed to and beyond its normal operating limits. In contrast to semiconductors, a tube thus pushed to such levels does not clip from a certain level, approaching more gradually its level limits and thereby producing its typical tonal result, which in audio signal processing can have such often profitable aural effects­—on one hand (and depending on the amount applied), from subtle to extensive harmonic distortion and on the other hand, a compaction of the sonic event, that is, a limiting effect that exhibits a pleasant, rounded or soft sound.

Acoustically and also in its range of applications this can be compared very well with tape saturation effects. Harmonic distortion and limiting are the generally known, “classic” tube effects, which are today cornerstones of sound processing. But other less known and potentially important effects are a tube’s ability for improving presence and spacial qualities through its processing of specific regions of the overtone series.

A special circuit comes into play for overtone/harmonic processing that involves a combined coil/condenser system working in conjunction with the tube. The control reacts dynamically to the audio signal and thereby processes both overtones as well as a signal’s phase structure.

The processing of the phase structure influences the moments of acoustic perception and occurs in microsecond time divisions – it has to do nothing with the cancellations one associates with 180-degree signal shifts. A decisive factor in resultant tonal quality is the alignment of level relationships the overtone spectrum. Such overtone “enrichment” does not operate on the generator principle of exciters (wherein distortion is added to the original signal). In this case the TwinTube harmonics control effects a rather a more equalized overtone structure resulting in a sound which in effect appears much more in the foreground, but without doing so through extreme level changes. Thus, for example, a voice appears immediate apart from the overall mixture, “sitting” clearly outlined in the mix’s foreground.


Here we refer to only two significant examples, of course without suggesting completeness. SPL would like to simplify starting with the TwinTube by sharing some thoughts and experiences in these applications areas. The effects and results described here can be applied to many other instruments—nothing should keep you away from using the TwinTube without restriction.


Optimizing vocal tracks is a highlight among the processing applications of the TwinTube. Often further EQing is not necessary anymore in order to lift a voice from a mix and get it up front. A recommendation for female voices: Harmonics switch to 6, Harmonics control to about 2 o’clock, Saturation to about 12 o’clock.

With these settings the described effect should be clearly audible and from here individual tracks can be optimized. With female voices, try the Harmonics switch settings 6 and 10 while switching between 2, 3, and 6 with male voices.

Acoustic Guitars

The success in treating e-guitars depends on previous recording and processing gear and techniques—if tube amps and further effects were already applied, it is hard to foresee how much the TwinTube can contribute when optimizing or designing a sound.

In contrast to e-guitars, there is a huge potential in processing acoustical guitar tracks. Picking sounds can be intensified, in general tube saturation and limiting can improve loudness and condenses the sound. Presence is emphasized and the instrument cuts through a mix much better without raising levels too much. A well chosen amount of harmonic distortion always adds some roughness which may often be a nice touch in several playing styles.


  • XLR connector, electronically balanced, opt. transformer balanced
  • Input Impedance: 20kOhm
  • max. Eingangspegel Harmonics: +18dBu
  • max. Eingangspegel Saturation: +21dBu
  • Output Impedance: 150Ohm
  • max. Ausgangspegel: +21dBu


  • Frequency range Harmoncis: 10Hz-80kHz
  • Frequency range Saturation: 10Hz-77kHz
  • THD Harmoncis: 0,1%
  • THD Saturation: 0,02 - 15% (Sat. max)
  • S/N Harmonics: -87dBu (A-weighted)
  • S/N Saturation: -96dBu (A-weighted)
  • Dynamic range Harmonics: 103dB
  • Dynamic range Saturation: 114dB
  • CCMR: -74dBu

  • Signal-LED: -20dBu

  • Overload-LED: +18dBu (peak hold 1,5 seconds)


  • Toroidal transformer
  • Voltage Selector 115V/230V
  • Power Consumption:
  • bei 230V: 9,1W/10,8VA
  • bei 115V: 5,6W/7,1VA
  • Fuses:
  • 230 V AC, 50 Hz: 315 mA
  • 120 V AC, 60 Hz: 630 mA

Dimensions & Weight

  • BxHxT: 482 x 44 x 300mm; 19" x 1.73" x 11.81"
  • Weight: 4,8kg; 10.6lbs

Additional Information

Condition New
Channels Dual-Channel
Chassis 19-in Rackmount
Rack Spaces 1u
Input Connectors Analog XLR
Output Connectors Analog XLR
MIDI Connections N/A

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