HLabs Audio CL089 500 Series PWM Compressor

HLabs Audio CL089 is a 500 series compressor/limiter that brings back the rare PWM topology of the Studer 089 console. Studer's first fully transistorised mixing desk appeared in 1968 with a dual compressor/limiter module, the 1.091.070. HLabs kept the original fully analogue PWM circuit, built 99% with through-hole parts, and added what it lacked for a modern studio.

Fast control without losing transients or top end

PWM compression controls gain by switching the audio at a very high frequency and varying the width of the pulses; after filtering, the waveform is rebuilt at the new level. The result is very fast, precise gain reduction that keeps attack and high-frequency detail, without the pumping and grit of many compressors of that era. The original attack is 0.6 ms, and Slow Attack mode stretches it to 10 ms when you want the hit of a snare or kick to pass through. You get four ratios, 1.5:1, 2:1, 5:1 and LIMIT above 20:1, five release times from 0.1 to 2 s plus AUTO, and a 120 Hz sidechain high-pass filter that stops the low end from driving compression on a bus or group.

Character you hear even without compression

The output stage is a Lundahl LL1588 transformer driven by the HLabs H101 op-amp, a redesigned Studer A101 in the 2520 format. It sounds open and powerful even with little gain reduction, so the CL089 also works as a colour stage. The H101 is socketed and can be swapped for other 2520-compatible op-amps. Three output transformer configurations, extended input attenuation and output make-up gain complete the set. Two modules linked in TANDEM mode run as stereo or dual mono, and a classic bulb shows how hard the unit is working.

KEY FEATURES

• Analogue PWM circuit based on the Studer 089 console compressor module
• Ratios 1.5:1, 2:1, 5:1 and LIMIT
• Attack 0.6 ms, or 10 ms in Slow Attack mode
• Five release times including AUTO
• 120 Hz sidechain high-pass filter
• TANDEM mode to link two modules
• Lundahl LL1588 output transformer and swappable H101 op-amp (2520)
• Bulb gain reduction indicator, relay bypass

TECHNICAL SPECIFICATIONS

• Format: 500 series module
• Ratio: 1:1.5, 1:2, 1:5, LIMITER (above 1:20)
• Attack: 0.6 ms (original), 10 ms (Slow Attack)
• Release: 0.1 s, 0.3 s, 0.75 s, 2.0 s, Auto
• Sidechain HPF: 120 Hz
• Max input and output level: +28 dBu
• Input impedance: 48 kOhm
• Output impedance: 60 Ohm or 240 Ohm (depending on transformer setting)
• Frequency response (1 kOhm load, light compression): +/-0.3 dB from 6 Hz to 20 kHz
• S/N: above 108 dB (0.2% THD)
• THD: 0.005% at 0 dBu
• Power consumption: below 120 mA
• Designed and assembled in France