Kerwax VM-124

Kerwax VM-124 is a mono tube compressor built around a vari-mu circuit topology that Kerwax explicitly ties to the classic Altec/EMI RS124 limiters, the same compression lineage behind the famous Fairchild. It's a fully balanced design running two 6N1P tubes plus a 6AL5 rectifier in the control path. It's the only purely dynamics-focused processor in the Kerwax range, alongside the brand's preamps and microphones.

Vari-mu gain reduction, not VCA or optical

Instead of the optical cell or VCA chip found in most modern compressors, the VM-124 controls gain by shifting the operating point of a control tube, which is what gives vari-mu designs their musical, harmonically rich compression character, the same behaviour prized in vintage broadcast and mastering limiters. UTM-series input and output transformers add further tonal shaping on the way in and out.

11-step attack and release instead of an unmarked knob

Attack switches across 11 steps from 3 to 138ms, and release across 11 steps from 127ms to 6 seconds, giving repeatable, describable settings instead of hunting on a smooth pot. A 6-step output attenuator (0/-5/-10/-15/-20dB) lets you match levels without losing the compression character, and a "Comp off" mode delivers pure tube coloration with no gain reduction when you want the tone without the dynamics control. The "Comp off" mode is especially useful on material that only needs a subtle tube tint with no audible gain reduction, lead vocals or drum overheads being typical candidates.

KEY FEATURES

• Mono vari-mu tube compressor
• Circuit inspired by the classic RS124 limiter (Altec/EMI lineage)
• Tubes: 2x 6N1P + 1x 6AL5
• UTM-series input and output transformers
• 11-step attack: 3-138ms
• 11-step release: 127ms - 6 seconds
• 6-step output attenuator: 0/-5/-10/-15/-20dB
• "Comp off" mode — tube saturation with no compression
• True bypass
• Designed and hand-built in France

TECHNICAL SPECIFICATIONS

• Type: mono vari-mu tube compressor
• Tubes: 6N1P (x2), 6AL5 (x1)
• Transformers: UTM, input and output
• Attack: 11 steps, 3-138ms
• Release: 11 steps, 127ms - 6 seconds
• Output attenuator: 6 steps, 0 to -20dB
• Format: 2U rack