It looks like the t14 solved the issue. It works like a charm, and sounds huge now. Strange since the leads on the t14 and telefunken eab primaries and secondaries all measure close to the same resistance. Thanks for the help Spencer.
maarvold said:Where did you get the switch and what part number? Thanks in advance.
craigmorris74 said:No pics, but I.finished my mic a couple of months ago (Beesneez k7, AMI T49), and love it. Wasn't expecting to be blown away, but the first time I heard playback of a kick drum recorded with it, it was a desk-rattling experience!
shot said:I've built this mic around two years ago. Nothing fancy to post a photo since it looks like every other mic in this thread (except Spence's diy bodied units!). It's a GT-2B body by Chunger.
I allways felt that it sounds weird on some sources. Sometimes it would be great, but on some vocalists and instruments it would suck big time! Especially since I built some other mics so I had others to compare with.
Few days ago I wanted to check what is going on with it. I tried swapping FET, going with 1000pf on C1, swapping capsule with spare one I had... I was checking freq. curve in a primitive way - putting headphone on the grille in front of capsule and doing sweep and playing pink noise. What I noticed in every situation is that I had a deep notch around 800-900 Hz. And it was a bit bumpy around 2.4k. There was nothing I could do to fix it. At least nothing in terms of component replacement.
I've put dummy capacitor instead of capsule and injected pink noise into the circuit to see if it has anything to do with bad capsules or mic acoustics - and it was flat this time! So there's actually nothing wrong with components...
After a day of experimenting and countles assemble-dissasemble cycles, I found out that the problem is with GT-2B body! It is resonant inside. When you assemble and screw the mic there's a large gap from grille/capsule into pcb section. If you stuff that gap with sponge foam it will fix this nasty 900Hz notch! It was an easy fix!
You may seem that this mic sounds good already. But it's a one minute mod. Nothing to solder or desolder. Just some sponge foam on top of the pcb to fill area from pcb to the inner edge of the body. Try it and you can take it back if you don't like it.
Now I'm on a quest to find something better than this ugly sponge since I feel it will degrade in few years. I need something that will last longer.
just my observations...
zephyrmic said:In my DIY mic bodies, I always use bonded acetate fibre, which is long lasting and will not deteriorate. The same sort of thing is inside cushions or pillows. One other good thing is that is is a good insulator, so should not affect the circuit as it comes in contact with components or the underside of a circuit board. In a couple of BM800 bodies I used, I found that the grille was resonant, and used the fibre on top of the capsule to dampen that resonance. Worked well.