Back To The Drawing Board

Awhile back, I wrote a post about building a ribbon mic. I completed the first one, with a completely custom fabricated shell and everything. It sounded pretty good, if I do say so myself, and I was quite pleased.

But I use the past tense for a reason. When I went to place the mic in its case, I noticed that my design is fatally flawed. The glue holding the magnets to the plexiglas frame has failed, bringing the two magnets together and obliterating the carefully placed ribbon. (it took three tries before I finally got it right… what a pain in the butt!)

So it’s pretty clear that the whole thing should be redesigned. I’ve learned a few things that should improve the performance anyway. The first and most obvious it my method for holding the magnets. I’d actually considered this before, but I need to include a small spacer to set the magnet gap. This way it’s physically impossible for the magnets to come together. An added benefit is that controlling the gap dimensions can be more precise, since the spacer determines the gap width rather than the frame.

Another design change for this version will be a metal frame rather than a plastic one. Metal (ferrous) provides a magnetic return path that can increase the output a few dB, and I need all I can get. It’s a little more difficult to machine, but I have the tools to do it, so why not?

It’ll be awhile before I can get to this, though. Every time I think of the hours put into the current mic, it really drains my energy and I hesitate. But I’ll start doing doodles on the backs of junk mail shortly, and I’ll get going on another design soon.

3 responses to “Back To The Drawing Board

  1. I’ve been following your ribbon mic building for awhile. Very nice work. I just designed, machined, and am now assembling mine. I made a metal frame, using 440C stainless steel. Stainless circumvented the need to plate anything else for corrosion resistance, and the 440 grade is magnetic. I like your idea of notches for setting the gap between magnets. In my case, the frame is so precisely machined (+/- 0.001″) that I didn’t need to fret about independently setting the gap. So far Gorilla glue between magnets and frame is working great.

    How did you corrugate your ribbon? I started with 1.2 micron and can barely handle the stuff.

    • bgilbertsound

      I corrugate the ribbons with something called a Paplin Crimper. These are just two gears screwed to a block of wood, I found it on eBay for about $12.

      Ribbon material is a pain to handle, no way around it. You get better response if the edges are closer to the magnets, but they cannot touch them. Eventually I want to design a frame where you can adjust the magnets with screws after the ribbon is mounted, so I can get a REALLY tight gap. Good luck, BG

  2. I have that Paplin crimper, too. The play — “wiggling” — caused by loose tolerances between gear bore and the lame wood screws wreaked havoc on my crimping efforts; this results from the foil being sandwiched between two layers of craft paper during crimping, else the ‘naked’ foil is totally destroyed by the meshing gears.

    The gears have a perfect tooth count/inch, so I salvaged those to incorporate into a crimping jig that I’m now building from solid aluminum. Sad that I have to build a tool to build a microphone, but that’s how it goes in the DIY world.

    BTW, I liked your idea of a faux mu-metal can so much that I fabricated one for my own microphones. It’s machined from a solid plug of 440C SS (again, magnetic), bolts solidly to the frame/motor, and is just big enough to house my Lundahl transformer and wires. Very clean and neat. That whole subassembly ‘floats’ within the mic body by using foam weather stripping. Kind of ghetto, but no one will see it.

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