Repair of a Shure KSM 32 after falling over while being used as a drum overhead.

Juice Sound & Light

Repair base


By John Silk at Juice Sound & Light


This is not a hard repair so long as you have a little bit of workshop know how and access to some work shop facilities. The Microphone is question has a problem in it’s construction because it uses a poor quality cast metal “wishbone” frame to hold the capsule mount in the tubular body. This whole construction is then held in place by a nut at the bottom of the microphone tensioning the wishbone and pulling the top and bottom together with the this central wishbone being under tension. When the microphone fell over it did one of those “dying swan” impressions as it moved slowly down held back by cables and drum framework. The microphone hit the deck square on to the top and when it was recovered there was no signs of damage but the body was loose. Once back in the warehouse a quick dissection showed that the wishbone had snapped at the base of the legs, where they meet the collar that takes the XLR plug. The wishbone, because it is under tension and has no way of flexing to absorb an impact such as this, the cross section of the wishbone is in a T shape and not flat bar, so it does not allow the wishbones to flex when receiving a shock on the end, sideways would be no problem but with this system so it is not surprising that this broke or indeed it won’t be the only one in the world to end up like this.


So after contacting Shure and finding out that the microphone would cost more to replace on their service exchange deal than it cost in the first place (You get a replacement for 50% of the purchase price, and the purchase price they state is astronomical and certainly not a price I would pay for this product) and did you know that parts are not supplied for it! Such an expensive microphone (Apparently) and you cannot buy the main supporting part of the microphone. So I went about a repair that would make this unit a fully serviceable item without the help of manufacturer and hope if you have the same problem that you can effect a similar repair with this little bit of help.


As you can see from the photographs this product is built with an awful lot of space inside the body that allows work to be done while not impinging on the the design or aesthetics of the microphone once re-assembled.


Parts.


For this repair you will need a short length of thin wall steel or copper tube at 3 mm ID (internal diameter), a 3 mm  tap, 4 off 3 mm  by 5 mm screws, two drills , one for the tapping size for 3 mm and one for the clearance size for 3 mm screws, a modellers or small drill (I used a PCB drill) screwdriver to suit, a metalworking file and a small vice to hold the product in.


Preparation.


Obviously the broken microphone in pieces. The nut at the bottom holds the assembly together so if you have a shattered wishbone then this will be loose or you may even have the bottom half coming out anyway. It is best to remove the, power and balancing circuit board, which by the way is the same as the b91/98 powering unit and capsule, the powering unit is easy and unscrews at the xlr end and unplugs from the main mother board, the head shell comes undone with screws and the mother board also is screwed in. The capsule itself is fragile so do this with care, there is one wire to unsolder, note the colour and the position, remove the rubber mount containing the capsule by removing a screw at the bottom and take out the rubber mount placing this on one side. Do not touch capsule and try to not let it get touched or dusty. The wish bone that is broken on one side or both is what we are after to repair, where the break occurs clean up the broken end and take the top off of the Tee so you are left with a flat end at around 8 to 10 mm in length (See picture). Once trimmed and prepared mark a point for drilling that should be central to the bar in width and at least 4 mm to 5 mm up the beam. Don’t forget that this is a casting, what we used to call “gun metal” and has no strength so our hole for taking the tension needs to be safely up the beam so as to not pull the end back off the cast metal when it is tightened.


At the threaded end of the microphone where the xlr is plugged into the “T”  ends of the wishbone join. It is in this area that the break would happen and so you should have one or two “ends” here. These need to be cleaned up or rather cleaned off and leave a nice flat surface but don’t take away too much of the metal as we need this to tap into. It is quite thick at this point but again the more metal you have the better the job will be. Mark these flat areas ready for drilling so that the hole will be 4 to 5 mm down from the top edge. (See Picture).


On both ends now drill out to tapping size and then tap the hole to the 3 mm thread size. Use cutting oil or any oil to stop the cast metal from binding and ripping the thread out. Just a small amount will suffice.


Once done we now have the microphone ready to re-assemble with our new bit to be made. Here we now take the tube and insert one end into a vice or hammer closed just about enough to lay on the flat that we have just made. If its too long we can file it down but we want to keep the tube as long as possible as tube is the structural part with the flats being the bolting together parts, there is a length to make these, but only you know what this is as it varies dependent on how far up the wishbone shattered. Mine was right at the end but I cut the wishbone back to give more metal and that is up to you. In fact I cannot see why you could not just put the pieces back together with the flats cut and bolt a small flat plate across the break in a similar method to what I have stated and pictured but I chose to rejoin by cutting out the lower part and by crimping flat a short piece of tube at either end and then marking and drilling a clearance hole for the 3 mm screws I was able to fit these with some filing and a little bit of “flexing” of the flats to allow the new metal tubes to meet and be screwed into the existing metal work with the screws flush so as to not touch the circuit board in the xlr end and as already stated there is so much space inside the the lower body the length of screw just had to be sensible


After this the microphone can be re-assembled, make sure you note that the front and back of the diaphragm are important but also there is an orientation peg for this.. Tighten the nut back up and voila! A saving of many hundreds of pounds for three hours work. The microphone has been back in service and no one is none the wiser, in fact out of all of our KSM32 you would not know which one it is…..!



















The photograph shows the remaining side arms that are T shaped with the top part of the T removed ready for drilling. The second photograph shows the xlr end with the remains of the arm removed and slightly flattened to allow for drilling and tapping.



















The 3rd photograph shows the pieces drilled and the 4th shows the tapping



















In the 5th photograph the tubes can be seen crimped flat and drilled one end. To get the length I had to use another KSM32 Microphone to get the total length correct. The 6th photograph shows the two side by side.



















The 7th Photograph shows the other end of the tubes crimped and in the 8th they are drilled and fitted



















Re-fitting the electronics and the final assembly



































Detail of the repair

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