sdc tube mic

i´m really happy and surprised with the sound of this one. i recommend this circuit for the ck1 /ck3 (cardioid) capsule for
everyone who feels that the sound of the c451 is not suitable for voice.
circuit is close to the g7 (thank you, jacob!)



*edit: missing 2.2µ cap (15k to ground)
*edit: missing 100n cap (trimmer´s whiper to ground)

some pics
http://groupdiy.twin-x.com/albums/userpics/10055/sdc_tube_mic_top.jpg
http://groupdiy.twin-x.com/albums/userpics/10055/sdc_tube_mic_inside.jpg
http://groupdiy.twin-x.com/albums/userpics/10055/firstmic%7E0.jpg

edit: never mind

standard circuit

You might want to make the trim pot into two resistors with a cap from the 1g and two voltage divider resistors node to ground.

Assume the wiper of a trim pot will lift with time or corroded

Use the trim to find the ratio or calculated it knowing the B+

I do like how you build stuff.

in fact there is a 100 n cap from the wiper to ground, i simply forgot to draw it...
when my supply is finished (i use my bench supply for now) and i have a fixed b+, i will change the trimmer to fixed value resistors.

thanks for your kind words!

psu (12x9x5cm):
http://groupdiy.twin-x.com/albums/userpics/10055/sdc_tube_psu.jpg

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

replaceable grille with build-in pop-filter:
http://groupdiy.twin-x.com/albums/userpics/10055/sdc_tube_mic_grille.jpg

Very funky mic!
I have three CK1 and two CK3 capsules, but only three C451 amplifiers, so two of those nice capsules are laying around unused. I would like to try your preamp-design on them.
My question is: where did you get the connector for the capsule? Directly from AKG as a spare part?
Do you have sound samples? I always felt that the CK*-capsules seem to be a little bit too bright (cool on rock-overheads, "to cool" for recording classical instruments, where my C480/CK61 are much better...). Any chance that the tube and the oep reduce this a bit?
Toff

thanks. at this time i dont have any soundsamples, but soon i´ll try recording voice for a project.
my connector is from a worn-out c451, maybe you can get it from akg (i´m not shure...) or you have to find a machining shop.

locating an ef12 is hard as well, try finding a ef12k (less noise&microphonics)
while testing i prefered the ef12 over the ef86, it seemed more melow to my ears-bringing down the "crisp" from the capsule a bit.

I see you are underheating it at 5,8v, instead of 6,3v...

Did you do listening tests and liked the underheated tube better?

yes, all the design is made by listening tests only. in fact its 5,6
volt heater in the heater supply. less noise.

here a short sample from a friend´s production.
http://groupdiy.twin-x.com/albums/userpics/10055/sdc_tube_sample.mp3