HLabs CL089 500 series Compressor

The  HLABS CL089 is a fully analogue 500 Series PWM compressor/limiter inspired by the legendary Studer 089 mixing console, combining vintage Swiss compression circuitry with selectable ratios, flexible attack and release settings, stereo linking, a discrete H101 op-amp and a Lundahl LL1588 output transformer.

Classic Studer PWM Compression for Modern Studios

The HLABS CL089 brings the distinctive compression topology of the 1968 Studer 089 mixing console into the modern 500 Series format. Drawing inspiration from the original Studer 1.091.070 dual compressor/limiter module, the CL089 captures the transparent yet characterful dynamics that helped establish Studer's reputation for exceptional audio quality.

Originally developed for professional broadcasting and classical recording, the Studer 089 delivered controlled, musical compression while preserving the integrity of the source material. Its PWM-based gain reduction offered an alternative to the VCA, FET, optical and diode-bridge designs that dominated professional audio.

The CL089 retains the sonic character of this rare Swiss design while introducing practical enhancements for contemporary recording, mixing and mastering workflows.

Analogue PWM Compression with Exceptional Transient Response

Unlike conventional compressor designs, the HLABS CL089 uses Pulse Width Modulation (PWM) to control gain. This technique switches the audio signal at a frequency well above the audible range and adjusts pulse width to determine the amount of gain reduction. Filtering then reconstructs the audio waveform at the required level.

This approach provides fast, accurate dynamics control while maintaining transient definition, high-frequency detail and tonal clarity. The result combines the transparency associated with classic Studer equipment with a rich, solid and controlled sonic character.

The CL089 suits applications requiring subtle dynamic control, punchy compression or more assertive limiting without unnecessarily compromising the original signal.

Flexible Compression Ratios and Timing Controls

The HLABS CL089 preserves four compression ratios from the original Studer design: 1.5:1, 2:1, 5:1 and LIMIT.

The 1.5:1 and 2:1 settings provide gentle dynamic control for vocals, acoustic instruments and stereo programme material. The 5:1 ratio delivers firmer compression for sources requiring greater consistency, while LIMIT provides more decisive peak control.

Five release settings, including AUTO, allow the compressor to respond to different musical material. The automatic release mode adapts the recovery behaviour to the programme, helping maintain natural dynamics.

An additional Slow Attack mode extends the original design's capabilities, allowing more of the initial transient to pass before compression takes effect. This provides greater flexibility when shaping drums, percussion and other transient-rich sources.

Enhanced Gain Control and Sidechain Filtering

The CL089 introduces extended input attenuation and output make-up gain, providing greater control over signal level and compression intensity.

Input attenuation helps manage the level entering the compressor, while output make-up gain compensates for level reduction and supports consistent gain staging throughout the signal chain.

A switchable 120 Hz sidechain high-pass filter reduces the influence of low-frequency energy on the compressor's detection circuit. This helps prevent bass-heavy signals from triggering excessive gain reduction, making the CL089 particularly useful for full mixes, drum buses and other sources with substantial low-frequency content.

H101 Discrete Op-Amp and Lundahl Transformer Output

The HLABS CL089 features the H101 discrete operational amplifier, which takes inspiration from the original Studer A101 design.

HLABS developed the H101 to recreate the character of the classic Studer output stage while adopting the industry-standard 2520 footprint. A Lundahl LL1588 output transformer complements the discrete amplifier, delivering a powerful, open and harmonically characterful output.

This combination contributes to the CL089's sonic identity even when the compressor applies minimal or no gain reduction.

The socketed H101 also supports compatible 2520-format op-amp replacements, allowing engineers to experiment with alternative output-stage characteristics. HLABS also offers the H101 separately for other compatible equipment.

Stereo TANDEM Operation and Vintage-Inspired Construction

The CL089 retains the original Studer TANDEM functionality, allowing two compatible units to operate together for stereo compression.

This makes the compressor suitable for stereo buses, paired instruments and other applications requiring coordinated gain reduction across left and right channels.

The fully analogue signal path and 99% through-hole construction maintain a close relationship with the original Studer circuit architecture while supporting traditional component-level servicing.

A miniature incandescent lamp provides visual gain reduction indication. Rather than relying on a conventional LED display, the lamp changes brightness in response to compression activity, adding a distinctive vintage-inspired visual element.

Why Choose the HLABS CL089?

• Capture classic Swiss console character: Bring the distinctive sound of Studer-inspired PWM compression to a modern 500 Series recording setup.

• Preserve detail and punch: Control dynamics while maintaining transient definition, high-frequency clarity and natural musical expression.

• Shape compression to suit the source: Move from gentle levelling to more assertive limiting with flexible ratios, release settings and Slow Attack mode.

• Keep low frequencies under control: Prevent bass-heavy material from dominating compression behaviour with the 120 Hz sidechain high-pass filter.

• Add character without heavy compression: Benefit from the H101 discrete op-amp and Lundahl transformer output stage even with minimal gain reduction.

• Expand stereo processing options: Link two units using TANDEM operation for coordinated stereo dynamics control.

• Explore alternative sonic characteristics: Experiment with compatible 2520-format op-amps through the socketed amplifier design.

• Enjoy authentic vintage-inspired engineering: Combine classic analogue circuitry, through-hole construction and incandescent gain reduction indication in a compact 500 Series module.

This item, like everything we supply, comes with the complete support of our expert team. Our excellent technicians have been specifying, building and supporting studios for over twenty years. If you have any problems with installation, setup or everyday use, they’re never more than a click away, and always happy to help.

You can contact them here.