Vintage Digital & Analogue Studio Effects

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Al.So Hellax

Al.So Hellax Mono Compressor/Limiter

The Al.So Hellax is a mono optical compressor/limiter offering a very low distortion rate with side-chain filters and blend feature, and is 100% made in France.


The AL.SO Hellax is a mono optical Compressor / Limiter. The Hellax is not the mono version of our Dynax 2 but a separate design with dedicated features. The Hellax has been designed to perform as your go-to compressor for voice as well as various sensitive instruments such as strings, brass, woodwinds, guitar and bass…etc.

It does so without producing any audible compression artefacts so commonly heard with most competitors. Nevertheless if used with more extreme settings the Hellax can live up to the task of producing impressive and creative compression effects.

Like all Al.So products the Hellax’ construction is extraordinairy robust and is built to last a lifetime no matter if used in a studio environment or on tour . It’s entirely hand made in France and comes with an all metal chassis as well as highest quality controls and components only.

The front panel controls are very intuitive and quickly taken in hand.

The functions are:

  • POWER switch: turns the unit On / Off
  • VU meter: back-lighted in red it reflects precisely the reaction of the compressor according to the Attack and Release settings. It continuously displays the current gain reduction.
  • RATIO: Offers three different ratios.
    • LOW, about 3:1
    • MEDIUM, about 10:1
    • HIGH, infinite:1
  • Set to the latter, the Hellax performs as a Brickwall limiter and wont allow the signal to go beyond the level of the threshold setting.
  • BASS DRIVE (stepped): Adds a high pass filter into the detection chain of the Hellax. Three selectable frequencies are available: 100Hz, 200Hz and 300Hz. By activating this feature too much compression triggered by lower frequencies can be avoided. This can be particularly useful for instruments like bass or Cello and the like, more so if the user intends to apply a lot of compression. With the filter disabled (set to “Full“) the full input signal is sent to the compressor sidechain.
  • ATTACK: Sets the attack time of the compressor
  • RELEASE (stepped): Sets the release time of the compressor
  • COMPRESSION: Sets the compression treshold in a clockwise manner. Fully turned right is the max position. So it’s operating in an opposite way than a standard threshold function: Left is less, right is more compression.
  • MAKE UP: Sets the output level of the signal after processing.
  • BYPASS: Lets you compare the original input signal with the processed one. When active processing is bypassed by relay.
  • BLEND: Allows for parallel compression, i.e. to mix the original signal (DRY) with the processed signal (WET) from 0-100%. The control is unstepped.

Front panel
The front panel controls are very intuitive and quickly taken in hand. The inscriptions are protected high quality serigraphs. The front panel pots of Hellax are very high quality components like Sfernice, ELMA and Apem potentiometers and switches.

The electronics of Hellax have three main stages:

  • The input Stage is based on a DC servo technology that eliminates the capacitors in the signal path offering a very low distortion and high fidelity signal.
  • Then there is an Intermediate stage for the optical gain reduction. This is a technology that offers again a very low distortion rate of the signal. It allows to apply huge gain reduction rates without changing the signal tone or color.
  • The output stage uses a Swoster transformer (UK) offering high signal fidelity along with very subtle colouration.

The rear panel of Hellax hosts the IEC connector for the power cord, the 2 XLR input / output signal connectors and a 1/4″ TRS connector for the sidechain input or link or 2 units for stereo operation.



  • Mono Opto Compressor
  • 3 Compression ratios: 3:1,  10:1 and Infinite:1
  • Soft Knee
  • Extremely large time constant ranges
  • Bass Drive or compression Sidechain filters at 100Hz, 200Hz & 300Hz
  • Control through an external input signal for De-essing or De-popping
  • External sidechain input
  • Blend function or parallel compression for blending the original signal with the processed one
  • 100% hand made from high-end and selected components only
  • Designed by Olivier Bolling
  • Compatible with 110 / 230 Volts 50 / 60Hz

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