Heritage Audio OST4 4Slot Rack with OS Tech: The OST-4 is a 500 Series enclosure in a "square box" format, able to accommodate up to 4 modules. As the rest of the new Heritage Audio line of 500 Series enclosures, it features "ON SLOT" Technology (OTS). "ON SLOT TECHNOLOGY" takes advantage of last generation power electronics to handle power supply on a "per slot" basis. Each slot has its own power supply linear regulation stages, therefore modules are isolated from the rest. They just share the metal enclosure. With literally hundreds of brands making 500 series modules, we at Heritage Audio think this is the professional way of handling this reliably, eliminating issues often associated with sharing power between different modules of different brands and natures. Each slot features test leds for checking correct power operation (red for +16v, green for -16v), located aside of the slot connector. Thanks to the use of OST, the power capability of the OST-10 is 400mA per rail per slot maximum, with an overall of 700mA per rail, whichever is reached first. Each slot has its own red (+16v) and green (-16v) leds for easy testing of the power status. Phantom power available is 80mA total. The RAF Blue Gray enclosure is made out of heavy gauge steel in the United Kingdom. Connections are by means of gold plated XLR Input and Outputs.