Frac rack

Frac Rack or simply Frac is a modular synthesizer format.

Like the Eurorack format, Frac is considered a 3U format. The height of most modern modular synthesizer modules is measured by the number of vertical units it consumes in a standard 19" equipment rack. Modules conforming to the 3U format, for example, will take up three vertical units in a 19" equipment rack. Each vertical rack unit is 1.75", so a 3U module is 5.25" tall.

The Frac format has a standard width unit of 1½". So 3" and 4½" wide modules are common in this format. Frac-Rac is an American format designed by John Simonton of PAiA, which has found a wide following largely through the popularity of Blacet modules. Note that even though the height of both Frac and Euro modules are 3U, differences exist in the mounting rails and screws. Thus, each format requires its own mounting system (screws, rails, etc).

Frac format modules typically use 1/8" or 3.5mm connectors and plugs for patching, although there are several companies that offer modules with banana jacks (BugBrand, Metalbox).

Power requirements for Frac modules are typically +/-15VDC. Current draw depends on the module.