Built in the early 70s, the Carlsbro Mantis was probably one of the early, but less common, commercial BBD echo/delay units.
As with many BBD echo/delays, it has a warm and distinctive dark sound.

BBD-based delays were a good alternative to the bulky and fragile tape echoes, although with several limitations.

The Mantis had the delay time fixed, but it was possible to adjust it by opening and tuning each BBD trimmer. It was also quite noisy, especially when using all the taps and swells.

The BBD (bucket-brigade device) technology was developed by F. Sangster and K. Teer of the Philips Research Labs in 1969.

BBDs are essentially a series of capacitors that pass an analog signal down a chain in discrete steps, like a bucket brigade passing buckets of water.

The clock rate (base delay) determines the rate at which the signal is passed down the chain of capacitors. Capacitors are not perfect and can experience some leakage. This results in a gradual loss of information as each new capacitor in the chain receives slightly less signal than the previous one. As a result, longer delay times on these devices can cause the signal to become distorted and darker with each repetition.