low/zero feedback low damping factor SS/Hybrid amplifiers : Vitus Audio, Dartzeel, CH Precision, Lamm, Robert Koda, Ypsilon, Ayre, Hovland
low/zero feedback low damping factor tube amplifiers :Kondo, Audiopax , Audio Note UK , Border Patrol , Wavelength Audio , Leben , Lamm ML3 , PrimaLuna , Sophia Electric , Wavac , Antique Sound Lab
https://www.hifi.ir/2018/06/output-impedance-negative-feedback/