The MXL R40
Ribbon microphones are a great addition to your palette of tones in the studio. They tend to have a warmer and darker tone than many other types of microphones, which can work well for the right source at the right time.
I snatched up an MXL R40 recently for a great price, figuring it was a good place to start learning how to use a ribbon microphone. Thanks to great sources on the internet, I found that it is very easy to modify and upgrade lower- end ribbon mics like mine and make them comparable to their much more expensive counterparts. It is also a great beginner DIY studio project.
The transformer I decided to upgrade with is a Lundahl LL 2912. I purchased it from K&K Audio. Parts and tools needed are listed at the end of the article.
Ribbon microphones are very delicate, so you have to be careful not to drop them, or let any small metal pieces near the magnets that could easily snap the ribbon. I learned this the hard way. Taking apart the R40 is relatively easy, the bottom section of the body unscrews, allowing the lower housing to slide off. This will reveal all the wiring and underside of the mesh cover. To remove the cover, unscrew the two small screws that are located on the solid metal underside of the cover. Then you can remove the cover.
Now you will be able to see the ribbon motor assembly. The magnets and ribbon are protected by pieces of fine wire mesh taped to either side. You may decide to remove these to improve the microphone sound, but wait till the end, so that you do not damage the ribbon during the transformer upgrade
The transformer is housed in the metal cap just above the xlr connector. To access it, remove the three screws on either side of the cap. This will free the cap and the xlr connector assembly from the microphone chassis.
In order to make the upgrade easier, you may want to unsolder the clear and red wires from the ribbon motor, as well as the clear, black and red wires that attach the xlr assembly from the pc board mounted on top of the transformer cap.
Lundahl LL2912 Upgrade
I am not proficient in electrical terminology, so this explanation will be fairly layman.
In order to disconnect the stock transformer, you need to unsolder the white, red, blue and green wires that attach to the transformer. NOTE: keep track of what sides of the pc board you are disconnecting things from, so that you do not get lost.
You can now pull the stock transformer out of the cap, give it a good yank, it is attached with a foam adhesive. Remove the piece of foam as well to make room for the new transformer.
The wires on the Lundahl LL2912 are a bit shorter, and two are much thicker than the stock transformer's. I decided to put all the wires through one hole, which required me to drill one hole a little larger on the side where the ribbon motor wires attach. Keeping track of which wires are from which side of the new transformer, push them all through the hole as far as you can to make an easy solder to the pc board.
(NOTE: The two positive wires are on opposite "sides" of the transformer, and the thicker input wires have no markings - refer to the Lundahl schematic)
As per the above schematics, attach the negative thicker (input) wire to the same connection as the clear motor wire (also includes the black xlr wire). Attach the other input wire to the connection with the red motor wire. The thin white (output) wire attaches to the same connection as the clear xlr wire and the thin black wire to the same connection as the red xlr wire.
These connections were really easy to make, the solder points are large, and even a novice solderer like myself can get it right.
You can now reassemble the microphone, you may also need to bend the new transformer into the cap to get it to fit.
I made the mistake up snapping my ribbon in the upgrade process, so I went ahead and replaced it as well. The information I found said that the stock ribbon in the R40 is 6 microns thick. I ordered a new 1.8 micron ribbon from Geistnote Music. I am told in will improve the sound and the output volume. I found their better ribbons and a corrugator on Ebay.
To access the ribbon, you will remove the tape and wire mesh that cover the area on both sides. I chose to leave them off ultimately, to improve the sound. The ribbon is held by two pieces of electrical board that are screwed into the motor assembly. You need to remove both sides in order remove and reinstall ribbons.
The ribbon foil I bought came in an uncut sheet, packaged in cardboard so as not to damage it. Handle this material very carefully, it is extremely easy to tear. To cut a ribbon, leave the foil inside the thin paper it came in, so that nothing catches or bunches up. Make sure to use a heavy straight edge, preferably metal, and a new razor blade.
According to the sources I read, you can cut ribbons as thin as you want. The thinner the ribbon, the higher your output will be, and thus a better signal to noise ratio. Keep in mind that the thinner the ribbon, the more difficult it will be to handle and install. I chose to cut mine to 4mm, which was suggested for a novice like myself.
Place the ribbon inside the provided extra paper and run it through a corrugator. There are many things you can use to do this, the one that came with my kit is called a "Tube Wringer". Its original purpose was to to squeeze dry toothpaste tubes, or anything like that. You only need to run it through once to get a nice ruffle.
Installing the ribbon is a bit more tricky. I decided to handle the ribbon with some fine tip electronic tweezers instead of my fingers. Mostly so I could see things better. Gently lay the ribbon over the bottom mounting point and reinstall the board that holds it in. Center in as much as possible. Make sure you reattach the clear wire which was connected around the left hand screw. Tighten down the screws.
Next lay the ribbon over the top mounting point, don't worry about tension yet. Then place the metal mount on top, without screwing it yet. This metal piece will snap into place due to the magnets, so now you can lift it up a bit with your tweezers in order to tighten and center the ribbon. DO NOT pull the ribbon completely tight, it should sag a little in the middle and keep its corrugation. Once centered, you can screw the top mount down, trim the ribbon at the top and you are finished!