Frac rack

Frac rack, FracRak or Frac, from Fractional Rack, is the modular synthesizer format designed by John Simonton of PAiA. It has a mainly USA following largely through the popularity of Blacet modules.

Panel 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 will take up three vertical units in a 19" equipment rack. Each vertical rack unit is $1 3⁄4$", so a 3U module is $5 3⁄4$" (133.35 mm) tall. The Frac format has a standard width unit of $1 1⁄2$". So 3" (76.2 mm) and $4 1⁄2$" (114.3) wide modules are common in this format.

Difference between Frac rack and Eurorack
Although both Frac and Euro modules are 3U, use V/octave and have similar signal levels the modules aren't interchangeable. Frac modules are deeper and have a different mounting system. The module power connectors are different and so are the voltages; Frac modules are powered with ±15V and Eurorack with ±12V. Check the specs of individual modules for CV compatibility. To patch between a banana Frac system and a Euro system a common ground connection will need to be made.

Patching
Frac format modules typically use 3.5 mm connectors and plugs for patching, although there are companies that offer modules with banana jacks e.g. BugBrand, Metalbox.

Power
Power requirements for Frac modules are typically ±15VDC. Current draw depends on the module. The power connectors are 4 way AMP MTA-156 headers. The control voltage is 1V/octave. PAiA P9700S modules are designed for an ±18V unregulated power with on module regulation where necessary, although ±15V regulated supplies can be used.

Frac brands

 * Ad Infinitum
 * Analog Metropolis
 * Bananalogue – Frac with banana jacks
 * Barton
 * Blacet Research
 * Bridechamber
 * BugBrand
 * CGS
 * Cyndustries
 * Encore Electronics
 * Flight of Harmony
 * j3rk
 * KissBox
 * Livewire Electronics
 * Magic Smoke Electronics
 * Metalbox
 * MFOS – not format specific and can be powered by +/-15V
 * Oakley Sound Systems – some support for Frac and some 5U PCBs can fit behind a Frac panel.
 * PAIA – pioneers of the Frac format
 * STG Soundlabs
 * Stroh Modular
 * Synthasonic
 * Synthesis Technology MOTM – never supported Frac but some 5U PCBs will fit behind a Frac panel.
 * Wiard
 * YUSynth