Here's an early Electrovoice velocity ribbon mic, model V1. These are great looking microphones, but the early versions are rather crudely made and this one, like many others, suffered from low output due to weakened magnets.
Bob Crowley has a few things to say about these mics - not all of them nice!
The motor of this model is based on a single cylindrical permanent magnet, clamped to a pair of metal plates which make up the pole pieces of the assembly. Because of the positioning of the magnet, the magnetic field is uneven, with a significant difference in field between the top and bottom of the motor assembly. In our example we found that the field varied from around 700 gauss at the bottom to 1000 gauss at the strongest point. This is very low for a ribbon mic, and, along with the oxidised ribbon is responsible for a low, noisy output.
Fortunately, we have sourced some very powerful cylindrical N42 neodynium magnets of a suitable size and shape, which are a perfect replacement for the original weak magnet.
With the new magnet the field is increased by a factor of around four, to about 3000-3200 gauss, a much healthier figure which should lead to an increased output and much improved signal-to-noise performance.
Now it's time to cut a new ribbon, reassemble the microphone, and do some listening tests. In the meantime, we made a rather attractive bracelet from some of the spare magnets.
What did I say that wasn't "nice"?
ReplyDeleteHello Bob,
ReplyDeleteGood to see you here - we are still enjoying those custom Naked Eye Roswellites in out studio - I find them particularly handy for close snare drum.
Maybe 'not nice' wasn't quite the right way of putting it - I was agreeing with your comments that the transformers are not great, and that there are other weaknesses in the design.
http://microphonium.blogspot.com/2007/12/ev-1a-explosion.html
Those ribbon clamps are a pain to service too!
Stewart
Ha! Stewart, I caught your attention. Just kidding anyway. Hey they look really nice, nicer than a lot of mics from that era I think.
ReplyDeleteDid you notice if the midrange came up with your mod?
I was just checking visitors to the old microphonium blog which I hardly update any more, but maybe I will.
Since we sold the Crowley and Tripp mics to Shure, I've been working on new antennas - RFvenue - and new films for 4x5 cameras - The New55 Project.
Merry Christmas, Happy New Year and good to see you on the WWW.
Bob
Hi Bob,
ReplyDeleteI don't have any 'before' and 'after' comparisons for the EV mics - well, I just have the 'after'. Although I have worked on a few of these, I have never seen one with a good original ribbon to make a direct comparison.
I enjoyed the Microphonium blog, and over the years I have directed several people to your myth-busting articles in particular. Good stuff!
Happy Christmas!