Standard Audio Level-Or Mk2 Limiter/Harmonic Processor 500-Series Module

The Standard Audio Level-Or Mk2 is a 500-series limiter and harmonic distortion processor with a core circuit inspired by the JFET-based Level-Loc PA Limiter of the 1960s. Two distinct operating modes give the module a split personality: Level mode engages a high-ratio, feedback-style JFET limiter with selectable release times, while Crunch mode replaces the limiter with multiple discrete Class-A transistor stages that generate harmonic distortion with an adjustable output low-pass filter for taming higher-order harmonics. A 1/4″ DI instrument input is auto-detected on connection, and true relay bypass is accessible from a dedicated position on the Mode switch. The Level-Or Mk2 brings aggressive, character-driven processing—lower noise floor and modern control features intact—to any API 500-series rack.

Key Features

• LEVEL mode — engages the JFET limiter circuit: high-ratio, feedback compression inspired by the original Level-Loc; MODE LED illuminates green with brightness indicating gain reduction
• CRUNCH mode — bypasses the limiter and routes signal through multiple discrete Class-A transistor stages for harmonic distortion generation; MODE LED illuminates red with brightness indicating distortion amount
• SPEED switch (mode-dependent) — in LEVEL mode, sets limiter release time: Fast / Med / Slow; in CRUNCH mode, sets output low-pass filter: Fast (disabled) / Med (15kHz LPF) / Slow (8kHz LPF) for shaping higher-order harmonics
• INPUT pot — controls signal level entering the JFET limiter or harmonic distortion transistor stages
• OUTPUT pot — controls output level in all modes; in Bypass mode with DI active, provides clean gain control over the DI signal
• 1/4″ DI instrument input — auto-detected on plug insertion; configurable for line-level input via PCB jumpers; passes clean, unaffected signal in Bypass mode with output level control
• True relay bypass — dedicated BYP position on the MODE switch; MODE LED off when engaged
• 500-series format — compatible with the API 500-series standard

Specifications

• Format: 500-series (API 500-series compatible)
• Operating Modes: Level (JFET limiter), Crunch (harmonic distortion), Bypass (true relay)
• Compression Type: High-ratio JFET feedback limiter (Level mode)
• Distortion Type: Discrete Class-A transistor harmonic distortion (Crunch mode)
• Release Time (Level mode): Fast / Med / Slow (SPEED switch)
• Output LPF (Crunch mode): Disabled / 15kHz / 8kHz (SPEED switch)
• DI Input: 1/4″ instrument level (auto-detect); PCB jumper-configurable for line level
• Bypass: True relay bypass
• Controls: Input, Output (pots); Mode, Speed (toggle switches)
• Indicators: MODE LED (green = gain reduction in Level mode; red = distortion in Crunch mode; off = Bypass)