Erica Synths Black Spring Reverb is a different take on spring reverberation units. Firstly, it has a built in compact spring reverberation tank and vactrol-based audio compressor, secondly, it can operate an external tank and combination of both internal and external ones for effects unheard before. Thirdly, apart from feedback send-return loop, it has built-in feedback effects – delay, various filters, etc; feedback amount and effect parameters can be controlled manually and via CV, making the module an experimental instrument on its own.