classic tube mic

featuring telefunken ef83 tube and beyerdynamic 10:1 transformer. circuit is close to g7. capsule will be a new ck12, if i cant find any alternative (m7 or lomo or whatever - if you apperar to have a nice one lying around pls pm me)

Very cool! :thumb:

How does it sound?

What mic does the body originally come from?


Roddy

I like the build

A guess a PS filter cap built up from 4 caps

4.7uf MKT

The electro cap top and body kind of look like an older panasonic can't tell from the picture

Build with what you got.

Is it planned to have multipattern control?

thanks for your kind words!
[quote author="rodabod"]
How does it sound?
What mic does the body originally come from?
Roddy[/quote]

i dont know how it sounds yet, waiting for the capsule. i´ve just tested it with the ck703, it works.
the body is made from different parts i collected on the flea market.

[quote author="kubi"]It's that one of the trafos from the groupbuy?[/quote]
yes, i still got a couple i succesfully build several things with them:
first ldc mic
micpre #7

gus, everything you guessed is right!
choosing caps was more a matter of size, i will play around wit them when i got the capsule. no multipattern planned, maybe omni/cardioid inside the mic.

In the big red book all I could find about G3 connections for triode operation was it is a try and see for noise.

Some have G3 to cathode some have G3 to plate, some have G3 to cathode connected inside. With tube microphones I would GUESS most of the electrons are collected by G2. The u47 has g2,3 and plate u67 g2 to plate and g3 to cathode some GTs have the plate lead cut off and G2 is the plate.

I don't have the curve for the triode operation of an ef83 but I would guesss you have about 1.6V at the cathode and about 58V to 60V at the plate.

i made a mic using a very similar simple circuit like yours.
this is the final version after all my experiments with noise etc.
its an ef86 (similar to 83 except 83 is remote cutoff) tube.
the mic sounds fantastic and is very very quiet.
i mostly plug it into pultec MB1 style preamp.

funky mic°!
whats that output transformer?
capsule looks like plastic ck12.
for a well documented tube mic with the ef86 see the g7 www.gyraf.dk


gus,
i did some prelimary tests with a sdc today, trying to hear differences regarding g3 to plate or cathode. a little more gain was the first thing i recogniced while connecting g3 to ground. trying the same experiment with another brand ef83(valvo) i had the opposite result: little more gain with g3 to plate. next i started replacing the mkt plate to transformer cap. the 1µ wima sounded good to me, but only with g3 to cathode. i´ll go on fiddling around, so much fun to see that in such a simple circuit every small part does some difference...

yes. i think the capsule is an akg c12 plastik but the backside doesnt go.
the output transformer is a senhiezer 200k/200ohm.
the MB1 i plug the mic into has the same txf 200ohm/200k (lucky I had a pair) the power supply is from some other c12 set and i chose to put the hpf on the mic body. the mic grill is an outdoor candle wind cover and its top is a baby food can.

man, that mic looks funny! :razz:

200:200k input transformer? WOW!

yep, looks to be ghetto rigged to maximum.. but I bet it sounds awesome.

i hope that i helped ioaudio. must admit that ive never tried altering which screen grids connect to where. yes there must be effects and the tube must perform quite differently.
what kind of audio do you play to your mike when youre testing it?
whats a sdc?

Screen connnected to plate for less gain, better for close micing.
Output transformer on cathode = lower output impedance = easier to design transformer and possibly better response.

thanks cj & ekadek,

i was curious about the screen connection, so i repeated the experiment with both tubes and they both gave higher gain with g3 connected to plate. i must have mixed something up in my first try.

i test with playback from a studiomonitor for level and my voice for frequency and response. i am not too much into that scientistic approach :wink:
sdc means small diaphragm capsule, ldc large...
i presume that your mic must have lower output than most circuits i´ve seen: you didnt bypass the cathode resistor and the transformer is big step down.
whats the rectangle part near the xlr?

i first had a cathode follower circuit in that mic (and a lower z trafo)and it was all too toonoisey. needed so much gain. and still wasnt loud enough.
i liked the voltage amp circuit for its gain and simplicity. the transformer is there cos its the best qualty one i had at the time ... and i thort that the matching into the mic pre would make one of those rare "ideal" situations.
i did try a decoupling cathode cap and it sounded too hard. like it was just "trying too hard". ive been doing that lately with alot of my really old gear.
taking gain boosting components out and relaxing the whole circuit. sounds to me like the circuits have more headroom and less gainey noise. you can turn the interstage levels higher.

the steel box is the high pass filter inductor. a tidy akg thing that is torn out of the akg power supply. i took it out cos ... i did. i like the mic with the bass cut on the mic.

whats your B+ ?

[quote author="EKADEK"]i like the mic with the bass cut on the mic.[/quote]
you could have taken a smaller transformer for the same purpose :green: just kidding...
most circuits in the famous old mics use voltage amp instead of cathode follower, something to think about...

got the capsule :grin:



now some final tweaking, good thing about the housing is that you can open it with just 2 screws... i think this is gonna be a real nice mic.


:sam: :sam: :sam:

b+ on that one was 120V.

b+ on that one was 120V.
thats one beaut mike mate.
i like the suspension method. is it(kind of) "laced" from inside outer ring to the outside ring around the capsule with a rubber banding type material?
my mike has terrible isolation. the stand clanks and bangs.
the capsule has a flat stand at base so it should be easy to shock/isolate mount. your capsule looks to be entirely round.
oo oo just remembered ive got another capsule. a b&k testing one.
i'll dig it out over weekend and post the sucker. that one's a sdc.

That looks like a NEW AKG414 capsule. How does it work? it makes sense to me because the capsule has a known mass and the plastic/rubber can be adjusted for that mass when it is made.