System Standards

All modules follow the Frac Rack size standard of 5.25” height (3U) and multiples of 1.5” width (FW – Frac Width). The front panels are made of PCB material (3.2mm thickness) which provides clear, eye-catching appearance combined with durability.

The Frac(tional) Rack system was invented by John Simonton of PAiA and is also used by Blacet. Personally I have always preferred the standard & wider size of the Frac approach compared with the more common Euro rack.

Modules are held in custom aluminium enclosures known as Frames. While small cases exist for Standalone/Reds (3 & 5FW), the standard Frames hold 11FW of modules, mounted with M3 bolts and with power supplied via internal powered bus-boards.

Frames are designed for free-standing desktop use, 19″ rack mounting, or can be combined into larger systems via End Cheeks. See the Cases & Cables section for examples.

The system Power is based on an external 12V DC brick connected to the rear DC socket, while inside the frame this is converted to the bipolar (twin rail) +/-15V system power via a DCDC converter. This supply is then distributed internally on a PCB distribution bus to individual MTA100 power headers to which the module power cables are connected.


Power connections are polarized so cannot be plugged in back-to-front but care should always be taken to ensure that connections are correct (eg. Not ‘offset’) and power should be disconnected when adding or removing modules. Note, the pin arrangement for power is the same as for standard Frac, but with MTA100 rather than MTA156 headers.

External Supply Voltage: +12V DC, 1.5A (per Frame), 2.1mm, centre-positive, polarity and over-current protected
Internal System Voltage: Bipolar +/-15V, 500mA per rail per frame
Power Bus Connections: 4 Way MTA100, 5” power cables

Waveform Voltages: 10V peak-to-peak (unipolar 0-10V or bipolar +/-5V)
Gate Input Threshold: approx. +1V

Main Path Input Impedance: 30K Ohm Typical
Control Input Impedance: 100K Ohm Typical
Output Impedance: 470 Ohm Typical

Signal Connections: 4mm Banana Socket, Impedance Balanced 1/4” socket

Module Size: Frac Rack Standard
Modules are measured in multiples of FracWidth (FW) with 1FW being 1.5” width.
Modules are 5.25” tall (3 rack unit) and a maximum of 1.65” deep.

Module Fixing: M3 x 10mm Bolt.
The Frame Chassis and PCB Panels are all connected to Chassis 0V which joins the System 0V by the DCDC converter.
Frame End Cheek Fixing: M4 Bolt x 3 each end
10mm Panhead for PCB cheeks, 10mm Countersunk for 19″ cheeks
Custom wood cheeks typically need c.20mm bolts