Ervox R58 - French ribbon mic

Today on the bench we have an unusual microphone from France. I have never heard of this brand!

Ervox R58 ribbon mic

The Ervox R58 is a high impedance ribbon microphone designed for public address or home taping to a reel-to-reel recorder. It is made from a two part cast body, perhaps inspired by the RCA Varacoustic, and is nicely finished in hammertone paint. Paint still covers two of the screws, so I can see that I am the first person to look inside this one, which is always a nice feeling, like unwrapping a present!

Ervox R58, rear

Inside the mic everything looks nice and clean. The motor is built around a sturdy block of clear plastic with a large horseshoe magnet to the rear, and the ribbon itself is a piston-style design similar to those found in B&O and Altec microphones.

Inside the Ervox R58

Unfortunately the transformer is not working properly - the inductance measures only 14 microhenries, which for an (estimated) 0.2 ohm ribbon would make a HPF filter at around 2KHz... I'm sure it can't have been designed like that, so one suspects either insulation breakdown and a short, or the laminations have deteriorated with age and lost some permeability.

Ervox ribbon motor assembly

I'm not sure if it is worth the effort of re-winding this one, particularly if the lams are below spec. Luckily we can make a new low impedance tranny for it and bring it back to life.

The previous owner kindly included this scan of a wiring diagram for the mic.