More bad magnets

These rather disturbing photographs are of bad magnets inside a T-Bone RB500 ribbon microphone.
Failed magnets in a T-Bone microphone

The coating around the magnets had peeled away, allowing the rare earth magnets to oxidise and expand. This process of course destroys the ribbon too. The magnets can be replaced, but may not be worth the expense.

I have seen a few microphones that look like this, and the worrying aspect is that it seems to happen spontaneously, possibly because the coating on the magnets was not of high quality, or perhaps they were scratched or cracked on installation.

Nearly all manufacturers now use neodynium magnets for their microphones, and I fear a epidemic in the future.

Many thanks to Andrea Cappellato for sharing the photos of his microphone.

T-bone RB500 reribbon & upgrade

Ronnie at Diesel Studios in Italy sent in a pair of T-bone RB500 ribbon mics for service and upgrade. Ronnie asked for some photos of the process, and I thought they would make a nice photo-blog.

Here is one of the mics on arrival…

Inside the body, there is further screening to protect the ribbon, and the transformer sits in a metal can.

One of the old ribbons.

This one is not so great!

New 1.8 micrometer ribbons….

The old transformer has primary DC resistance of 90 milliohms, and 30 ohms for the secondary. Those laminations are not very well packed.

Winding new transformers for the mics.

Potting the transformers in the wax bath keeps the coils and laminations from vibrating….

The finished transformers. We may as well re-use the metal can for some extra screening.

Back together again