The Roland Chorus DC-50 is a rare 1976 bucket-brigade device (BBD) delay and chorus effects unit.
Despite its name, 'digital', the Roland DC-50 is anything but digital. In fact, the delay lines are created using a bucket-brigade device or BBD.
A Bucket Brigade Device (or BBD) is an analog circuit contained within a small chip that delays an incoming audio signal. This “circuit-within-a-circuit” was the main reason why an analog delay could fit into stompbox form. The term “Bucket Brigade” is a reference to the technique used by firefighters to put out a fire by passing buckets of water, one by one, down a line. The water in this example is the incoming audio signal. The “buckets” in a BBD come in the form of a series of capacitors inside the chip. Capacitors “carry” the signal much like the buckets carry the water. Because the capacitors are continuously filling and emptying, this slows down or “delays” the signal as it takes more time to pass through the BBD. What's more, imagine a line of 1024 firefighters, each passing a bucket of water to each other… that’s a fair amount of spillage. This spillage also occurs in the BBD meaning more noise and distortion added to the signal. Add to that the “ticking” noise introduced by the CLOCK and you have a signal that needs some clever filtering to get rid of the unwanted noise. This filtering leads to a delay signal that is much “darker” than the input guitar signal.
This frequency difference between the clean and delayed signal is what gives analog delay its desired response. The dark repeats wash away in the background and don’t get “in the way” of your original audio signal. It is this specific carachteristic that makes BBD delays so desirable as an audio effect. The characteristic warm, smooth and organic sound of an analog delay is actually due to its limitations and not because of any mystical mojo in a chip. Effects with BBDs at its core are a great example of how an effect can inspire a whole generation of music and artists – even though it technically isn’t a “perfect design”.
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