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The DIY Ribbon Velocity Microphone, a home project

How I did it 2

A more "in-depth" look at the construction.  I used some diagrams from other sites, but I will credit them when applicable.

Here's the basic idea of what we're doing.  The construction of the element is extremely simple.  It is a very thin aluminum ribbon suspended in between the poles of a strong magnet.  The space at the top and bottom allows the soundwaves to reach the back of the ribbon without much delay, so the frequency response is improved.

fig1.gif

This (and the next) diagram is from Steve Spicer's site again, and I believe they do a good job of explaining the basic setup. You see the gradual tapering of the poles at the top.  I imagine that this design allows for better frequency reponse because of the reduced distance to the back of the ribbon.

fig3.gif

This shows the other major design (or a version of it).  The magnets are actaully on the top and bottom of the element, and the magnetic flux is taken down to the ribbon portion of the mic by soft iron bars.  The bars are thin (A lot thinner than the magnets are), so the effect on the frequency response is favorable.  More space around it means better frequency response!

ribbonev.jpg

 
 
 
 
Here's a real photo to show the magnet and ribbon structure.  I don't know where this photo came from, so I can't credit anyone.  I used a tighter tolerance on the sides of the ribbon to the magnet.  It's actually difficult to see any light unless you are at the right angle.  The only concern was that if the ribbon started to twist or went through a big excursion, it might rub the magnet.  I made sure that this didn't happen before I settled on the ribbon into the clamps permanently.

Here is a simple breakdown of the basic ribbon mic.  This is the one that I built, anyway.  That's about all there is to it.  Most of the older mics have horseshoe or circular magnets, but I decided to use simple bar magnets because I had some already, and also because I can get neodymium replacements in pretty much the same dimensions.
 
IMPORTANT!!!  The pin configuration is not the same as in the diagram.  The pins that are labeled are correct, but their location on the XLR diagram is not correct.  It is just there for illustration.

ribbondiagram.jpg

Sorry about the crude nature of the diagram.  At someone's request, I made this to use as a visual aid in understanding the construction.  When I get some more spare time, I will try to make it a little better.

 
 
 
Here is the schematic from the Jensen website for the transformer wiring.  I haven't asked them if I could use it yet...Here's the address for it:
 
 
 
 
 

http://www.comtran.com/as/as067.pdf

transformer2.jpg

 
     Believe it or not, this is just about all I had to go on to make my microphone.  Also, some real photos of other production microphones helped, as well as some literature in textbooks.  The idea and application of the images is what is important.
 
     I knew that I wanted mine to be a little different.  Seeing as how the quality of materials has improved in the past 50 years, I figured that making an acceptable element that was smaller, but still effective, would be easy.  I was right, to a degree.  The magnets I used are exceptionally strong ceramics, but I plan to switch to Neodymiums when I get the money.  This will double my output from what I have right now.  Check the next page for more about magnets.
 
    

Let's see.  Other considerations...
 
The tranformer wiring may be found at Jensen's site as a PDF.  This allows for balanced output, and optimum signal.  Trust me, balanced output is the best way to go, considering that the output is so low, and the microphone is succeptible to more EMI than other microphones. 
 
I imagine that this schematic would work for other transformers as well, but some parts might need to be substituted. 
 
I kept the leads to and from the transformer as short as possible. 
Also the wires from the element itself need to twisted tightly together on the way to the transformer.  This reduces the amount of EMI recieved by the wires.
 
Speaking of EMI, it is almost essential that shielding be employed in the manufacture of the casing and windscreen, all connected to the shield of the XLR output.  Make sure the windscreen is connected to the body shielding via direct connection, a wire, or something.
 
Updated:  You may also want to split the positive (top) wire into two wires, and run them seperately down both sides of the element.  Someone told me that this would create a "humbucking" effect and reduce noise even more.  I haven't tried it yet, but it kind of makes sense, if you are used to wiring guitars.   
 
 

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