Clones
This interface was popular for its simplicity, and Beta 128 Disk Interface was cloned all around USSR. First known USSR clones were ones produced by НПВО "Вариант" (Leningrad) in 1989. Beta 128 schematics are included in various Russian ZX Spectrum clones.
Some variants of schematics support only 2 drives. Phase correction of drive data signal is made different ways.
Read more about this topic: Beta Disk Interface