Why so classic?
The original hardware versions of all three processors have quite interesting design features. The Dimension D is valued for its subtle sound and stereo effect and its black box design has always created a real air of mystery. Under the hood are two BBD (Bucket Brigade Device)-based delay lines modulated by a triangle-shaped LFO. The LFO to one delay is inverted and careful cross mixing of the two signals coupled with pre and post filtering and the stereo in and stereo out signal all contribute to its sound.
Mu-Tron’s Bi-Phase, with its accompanying optical expression pedal, has remained a popular design with guitarists and studio users since its introduction in 1974. Its complex watery sound is created not just by the two independent sweep generators but also by the use of a photocell and lamp circuit and onboard feedback.
Finally, the Bel brand are probably best known for their ubiquitous 1980s digital delays, the BD80 and BD80S. However, it was Bel founder Mick Barnard’s desire to produce a decent rack-based flanger that got the ball rolling in the 1970s. The stereo design uses twin BBD delay lines and although original units are now quite rare, a hardware version was recently re-issued in 500 rack format.