Gefell UM70 -- semi-circular metal ring loose inside headbasket?

T-Dogg · Nov 21, 2016

Hey folks... recently took a leap of faith and purchased a pair of older, RFT-branded UM70's (with the plastic pattern selectors) and MV692 mic bodies...

Seems one may have been damaged in shipping... I can hear -- and see when holding it up to the light -- a semi-circular metal ring floating around behind the grill... I've reached out to MG but have yet to hear back. In the interim, I'm wondering if anyone can wager a guess as to what it may be (I'm assuming some portion of the capsule mount) and what implications it may have in terms of repair viability\cost, potential damage to the capsule, etc... In the worst case, I imagine it may have scratched or damaged the capsule whilst banging around in transit.

I haven't been able to audition either mic yet, but plan to do so tonight after modding one of the MV692 bodies for use with standard XLR/48V connections...

Any insight is appreciated...

-tim

Gus · Nov 21, 2016

Tim
Good to see your post. I have the same microphone. If you want to open the grill. Look at the side of the UM70 you should see two push in caps. Remove the caps and there should be screws under the caps.
How are you going to mod the body small zener transistor circuit?
Check you PM

Gus

T-Dogg · Nov 21, 2016

Gus!!! Awesome, been a long time!!!

I'll be heading home in a few and will check this out (and my PM!)

T-Dogg · Nov 22, 2016

Thanks to Gus for his expertise in disassembling this thing! Figured I'd post some pics, should this ever prove useful to other folks...

As Gus mentioned, the biggest challenge in removing the grill is to get the pins on the pattern selector ring out. Tapping it and threading a small diameter screw seems the best bet, but in my case it appeared someone may have already attempted to do so -- and unfortunately the pins had been drilled out so aggressively low, and at such a large diameter, that there was simply no "meat" left on the pin face left to tap into... Required a different approach, so I drilled a tiny bit deeper with a super small bit and got the sharpest tweezers I could find, jamming them in at an angle into the side of the new, smaller hole. With some patience, I was able to work them out... Not sure I'd reuse them though...:

With these out, the plastic pattern selector ring slides right off the bottom of the head assembly, exposing three screws to detach the pattern selector assembly from the headbasket/capsule/grill assembly. This can be tricky, thanks to a warning from Gus I knew what to expect! There is a spring and ball bearing which could come flying out once the pattern selector assembly is removed -- do it over a controlled area so you don't lose anything! This mic FWIW did not have the ball bearing, so not sure exactly how it may have been used -- I suspect this had gone missing during someone's previous attempt to open the mic.:

Another shot of pattern selector assembly:

Back to that grill.... Looking at the bottom of the capsule mounting plate, you'll see one screw (already removed from the top hole in the below pic) and two metal pegs which help to align it to the pattern selector assembly. The pegs are threaded into the grill head and must come out in order to expose the capsule. There are holes drilled through the pegs, allowing you to feed some sort of small diameter tool through and twist them off... With the screw and two pegs removed, the grill slides right off

And the moment of truth... Here's what greeted me inside. I don't know enough about mic construction to comment, but some sort of little plastic support piece seems to have come dislodged, in addition to the black plastic rings which look to have been press-fitted and glued onto the capsule... One is off completely, the other is clearly loose and pulling away near the bottom. I don't see any obvious scratches on the capsule, which is good news, though it does appear to have some deposits and dirt... FWIW I tried it out prior to disassembly, and the mic did work.. even sounded pretty good, considering!

Still waiting to hear back from Gefell... I figured either way I'd have to get that grill off and secure whatever was going on inside the capsule to avoid further damage in shipping. I guess the big question is... what next? It's sort of a rhetorical question, cause you can damn be sure I'm going to pester Gus about it later ;D

Here's some capsule pics:

T-Dogg · Nov 22, 2016

...realized the black rings get pinched between the capsule and the plastic tower mount -- these can be tightened together via a screw on the bottom. I loosened the screw a bit, press-fitted them back on, tightened it up and it seems to hold pretty well! I'm sure that glue broke down long ago, and it's probably been happily supported this way for a long time, until jostling around in shipping...

I buttoned the darn thing up, and barring a better solution for the little plastic pattern selector pins... it sounds great hung over a drum kit, lol. I'm tempted to leave well enough alone for now? I'll probably use it in cardioid primarily anyway, given the acoustics of my home studio... at any rate, it's not a total loss and I can mull it over in calmness whilst enjoying a pretty darn good tone

Wonder if that capsule really needs some cleaning though... and how I'd better secure those plastic rings for shipping if so...