Analogue Systems RS-500N
The Analogue Systems RS-500N is a Eurorack filter module built around the diode low-pass filter from the EMS VCS3 and AKS. Per the listing on ModularGrid, it is the only officially licensed remake of that circuit. Former EMS engineer Steve Gay recreated it for Analogue Systems' RS Integrator line. He aimed to reproduce the VCS3/Synthi filter as exactly as possible.
The module carries a few practical modifications - the same ones that were commonly performed on vintage EMS instruments. A front-panel switch selects between the pre-1974 and post-1974 filter types and responses. The CV slew switch and the 18dB/24dB slope options were standard modifications in the EMS world. One feature goes beyond what the original synths offered from the factory: the filter response can be voltage controlled. That capability was designed into the VCS3's circuit board but never brought out to the matrix.
The RS-500N belongs to the era of the EMS VCS3 and Synthi, designed in England between the late 1960s and mid-1980s. Those instruments gained a reputation for behaving very differently from American and Japanese synthesizers. Detroit Modular calls the underlying filter "legendary." The surviving record is thin. No production years, original price, or detailed electrical specifications are documented for the RS-500N itself.
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