ldc mic (pics)

i´m planning to put a (plastik) akg ck12 inside, but not shure which tube/circuit.
i found the grilles(it´s actually two halfes) on the flew market.



update: decided to make a circuit with the ef94/6au6 - i had a nice one lying around. circuit is similar to the c800 http://img56.photobucket.com/albums/v172/rafafreddy/TechTalk/C800Gschemvolt_resized.gif

changed the polarity voltage circuit for switchable polarity pattern like in g7(different voltage divider because i´m running the mic on 200v. 680k and 470k for 81 volts for capsule)-some of the parts are still missing on the pic below.
output transformer is a 10:1 beyerdynamic (thanks kubi!)




the connector is taken from an old bruel&kjaer signal generator. the whole innards are mounted into an bulb socket which is screwed into the aluminium tube.



waiting impatiently for the capsule, but i still have to do some machine work for the grille-tube connection anyway.
working microphones is real fun!

update:see first post.

I can't wait to hear how it sounds, and how the finished metalwork turns out. :grin:

Good luck finding a low noise tube. Telefunken mullard etc mean nothing with a 6au6. I tried "good" NOS 6au6s all had to much noise.

There is an answer to this in the 800 thread.

thanks gus- i read the mentioned thread.in fact i read a lot of your posts regarding microphones and learnt a lot. dreaming of building a capsule one day...
i have three 6au6 (2x tfk, 1xsiemens) to choose from, hopefully i´ll get acceptable noise performance with one of them. i wonder if i have to be afraid of the heat from the tube, it´s a tight fit in that microfon...

I put a heat vent on my 6au6 mic just to be safe. The vent is a perforated tube which is inside of the microphone above the 6au6.

do you have pictures from that part of your mic? would be interesting to see.

look for the thermocam picture of a tube in the meta

mic is nearly finished. still have to wait for the capsule and, of course, for the gigaohm resistors...

pics:
http://groupdiy.twin-x.com/albums/userpics/10055/finished.jpg

http://groupdiy.twin-x.com/albums/userpics/10055/ge%F6ffnet.jpg

grille close up with fake capsule
http://groupdiy.twin-x.com/albums/userpics/10055/grille.jpg

grille design:
http://groupdiy.twin-x.com/albums/userpics/10055/grille%20design.jpg

i´ll wait for the capsule before making the shockmount.
the psu still needs an an enclosure...

gus: i´ve seen the pics. still my experience is too limited to judge if the amount of heat will be to much...any how i´ll see when i plug it in for a couple of hours.

Why not buy an ark of lapping paper and make that thing shiny? :thumb:

[quote author="ChrioN"]Why not buy an ark of lapping paper and make that thing shiny? :thumb:[/quote]

Ditto. That thing would look 700% better with a nice scuff polish and the top edge softened a little bit.

Emery cloth is about $1 for a sheet at your hardware store, so go nuts.

You can use the can spraypaint if you like colorful things. Just scuff and prime it first.

I like the build jsut as it is. Sometimes I build stuff with what I have. A cool guitar overdrive in a coffee can a soup can fuzz etc.

well, thanks, maybe the surface only reflects the condition of the room i life in or you might imagine the mic is vintage ... or handbuild ... whatever. maybe i just polish it one day...intrinsic values much more important

Great looking design!

But I'd probably try to smooth it out a bit as well. The main body of the pipe looks interesting, but that top edge could be softened. I've used a buffing wheel on a bench grinder to do that kind of thing - not for a mirror polish, but for smoothing out edges and corners. And countersink that screw for a really finished look.

powered up for the first time a couple of hours ago. b+ is at 222 volt, heater is pot regulated (no pun...), best results with 5.5 volt, after a burn-in procedure on 7 volt for two hours.the tube comes from some old test equipment, its marked with a red point, so likely it was selected from bruel&kjaer - noise is not an issue, though i have to do further tests in a more silent environment.
the capsule is a ck12 (akg part nr. 2072z0005, as used in vr12 and 414 b-uls), polarized at 70 volt ( backplate 0, 70 and 140 volt for pattern).

the shockmount is build from two rubber washers (??) mounted with clamps on the construction you can see an the picture.

soundwise: what a mic. i´ve got no sony, brauner or neumann to compare with, so its hard to say. i really like it, thats all i can say now. no problems in the low end either, i was worried because of the small beyer.
need to find a nice singer for samples, maybe get a chance to compare it to some other mics.