Beta Disk Interface

Beta Disk Interface is a disk interface for ZX Spectrum computers. It was developed by Technology Research Ltd. (United Kingdom), in 1984 and released in 1985 with price £109.25 (or £249.75 with one disk drive). Beta 128 Disk Interface is a 1987 version supporting ZX Spectrum 128 machines (difference is in access points addresses). Beta disk interfaces were distributed with TR-DOS operating system in ROM, also attributed to Technology Research Ltd. Latest firmware version is 5.03 (1986).
The interface was based on the WD1793 chip.
The interface handles single and double sided, 40 and 80 track double density floppy disks, up to 4 drives.
Clones.
This interface was popular for its simplicity, and the Beta 128 Disk Interface was cloned all around the USSR. The first known USSR clones were ones produced by НПВО "Вариант" ("NPVO "Variant"", 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 the drive data signal is made in different ways.
Since 2018, a clone called Beta Disk 128C has been produced in the Czech Republic. The electronics are realized on two PCBs horizontally above each other, connected by the connectors.
The bottom PCB includes a completely through bus with a connector on the opposite side, and the drivers of all the signals that Beta Disk uses.
These exciters are powered directly from the computer for a negligible power take-off.
On top of the board is the whole controller and DOS system, implemented by TTL-LS logic, as in the original. Several minor bugs have been corrected in the wiring,
TTL chip optimization has been optimized, and a DOS activity LED is added. The top plate is powered by an external power supply, the 5V regulator on the board for the logic branch is included, and the 12V converter for the FD1793 controller. Czech Beta Disk can be purchased on Sellmyretro or on eBay.