Urei BL-40 Modulimiter Compressor Limiter

The UREI BL-40 Modulimiter is a professional analog limiter originally designed for AM broadcasting, offering a distinctive combination of optical compression and fast peak limiting. Built to maintain consistent signal levels while preventing unwanted overloads, the BL-40 delivers controlled dynamics with the smooth, musical character of classic UREI processing.

At the heart of the BL-40 are two independent limiting stages. The RMS section employs UREI’s patented electro-optical attenuator for smooth, unobtrusive level control, while the FET peak limiter responds to sudden transients with an exceptionally fast attack time of just 5 microseconds. Together, these circuits provide effective dynamic control while maintaining low distortion and preserving the character of the original signal.

A distinctive feature of the BL-40 is its proprietary Phase Optimizer, which automatically monitors signal polarity and reverses it when necessary to maintain favorable positive modulation. Originally developed to maximize AM transmitter efficiency, this circuit can be bypassed when not required.

Three dedicated analog meters provide simultaneous visual monitoring of RMS limiting, peak limiting, and output level. Independent adjustments allow precise control over the limiting characteristics, while transformer-isolated input and output connections reflect the professional broadcast engineering standards of its era.

Originally intended for AM radio transmission, the BL-40 was also designed for television, commercial sound systems, and other professional audio applications. Today, it represents an interesting piece of vintage UREI technology, offering an unusual combination of optical leveling, ultra-fast FET limiting, and specialized broadcast processing.

Main Features

• Vintage analog broadcast limiter manufactured by UREI
• Dual-stage limiting with optical RMS and FET peak processing
• Patented UREI electro-optical attenuator for smooth RMS limiting
• Ultra-fast FET peak limiter with 5 µs attack time
• Independent RMS and peak limiting adjustments
• Automatic Phase Optimizer with polarity reversal
• Switchable asymmetrical peak limiting
• Adjustable positive modulation up to 125%
• Three analog meters displaying RMS limiting, peak limiting, and output level
• Transformer-isolated input and output
• Adjustable input and output levels
• Peak limiting bypass switch
• Maximum output level: +27 dBm
• Frequency response: 30 Hz – 15 kHz (−0.8 dB)
• THD below 0.5% at +24 dBm output
• 2U rackmount chassis

PSU works on 100–120 V or 220–240V, EU power cord attached. 

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