Roll Music RMS5A7 Manley Labs It has been independently confirmed

It has been independently confirmed to be fully compatible

while their semi-open design provides the airiness of open headphones with the powerful bass response of closed designs

the 2520 coupled with the API 2503 output transformer

the U 47 and the M 49

so the resonant frequency of a good microphone design should be as low as possible

Roll Music RMS5A7 Manley Labs It has been independently confirmedA real, transformer coupled tube microphone preamplifier in the convenient package you never thought possible. At long last, all the warm sweet satisfaction of a real transformer coupled, high voltage vacuum tube microphone preamplifier in the convenient and cost effective 500 series modular format. With the explosion of new modular products for the 500 series frames sold by various manufacturers, user requests for a tube based module have been met