Brass CK12 in C12, C412, C414EB

[Khron]

I must admit, i'm quite intrigued (if not even confused) by the apparent variation (if not even disparity) between the different applications of what, at least in theory, is the same capsule.

I believe everyone agrees that in the original AKG C12, as well as the C412 and the first i-don't-know-how-many C414EB's, the original brass CK12 was used - correct?

Is it all down to the headbasket affecting the midrange / top-end response?

Case in point - an AKG catalog i've come across, while looking for some data on the C412 (strictly because it certainly(?) used ONLY the brass CK12) : http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/AKG%20Catalog%20%281%29.pdf. Be patient, it seems to be a slow download. No real idea on the year it's from, but i think we can be quite sure it's before the C414EB P48 (and the teflon / nylon CK12) was introduced. In fact, was there even a non-EB C414? Because then, this catalog would pre-date the EB...

Page 3 shows the frequency response for the C24 (stereo C12) - wee bit of a dip at 4-5k, and quite the hump at 8-10k. Cylindrical headbasket.

Page 5 shows the frequency response for the C412 and C414EB - damn near ruler-flat. Flat-sided headbasket.

For the ones interested, here's the service manual (including schematics) for the C412: elektrotanya.com/akg_c412.pdf/download.html

Thoughts???

 

[moamps]

You can find some more info  about CK12 here:
http://www.mixonline.com/news/profiles/vintage-microphones-part-3-akg-c-12-c-24-and-telefunken-250251/377062

 

[Khron]

My curiosity / confusion is more about the dramatic(ish) response differences between the C12 and C412/C414. Considering there's no real tone-shaping going on, is it really all down to the headbasket?

And yes, it turns out there WAS a plain C414 before the EB, with 3 patterns, -20dB pad and no low-cut.

 

[tonzauber]

For a good overview over the history of the C12/C414, I would reccomend this page:

http://www.saturn-sound.com/curio's/story%20of%20the%20akg%20c414.htm

 

[Khron]

I *HAD* already found both of those links in my searches before, but neither really answers my question

 

[ln76d]

There was a plenty versions of brass CK12, these which you can find in FET models are different than in C12  Someone on the forum count 11 versions, basing on web informations

 

[Matt Nolan]

Headgrille acoustic resonance differences (see also why the 251 doesn't quite sound like a C12) and, possibly, self-microphonics of the tubes, which you don't get with FETs.

 

[Khron]

Well, the 251 also has that 100pF rolloff cap at / before the transformer, but... I suppose

Still, you have to admit, it's a pretty damn dramatic difference.

 

[ln76d]

100pF doesn't rollof audible range of HF.
Differences are mostly in the circuit i believe.
That's why C24 doesn't sound like C12.
Do we know from which year are the frequency response charts?
I think not...
First C12 had CK12 with styroflex diaphragm and different transformer...
Smaller headbasket + capsule mount  which may affect the frequency response in some way.

 

[granger.frederic]

coupled with a haufe T14/1 , a 100pf reduces around 1 to 2db at 15Khz and also softens a bit the transients.

Differences in ck12 mics are due to the headgrilles variations  ,different voltage polarisations, different headamps : tube vs jfet,biasing and output transformer,negative or positive feedback ,different coupling capacitor ...etc...etc...etc

 

[ln76d]

coupled with a haufe T14/1 , a 100pf reduces around 1 to 2db at 15Khz and also softens a bit the transients.

Any calculation for this?

 

[Matt Nolan]

coupled with a haufe T14/1 , a 100pf reduces around 1 to 2db at 15Khz and also softens a bit the transients.

Differences in ck12 mics are due to the headgrilles variations  ,different voltage polarisations, different headamps : tube vs jfet,biasing and output transformer,negative or positive feedback ,different coupling capacitor ...etc...etc...etc

All true, but the OP is asking specifically about stuff in the upper mid frequency response. This is almost entirely down to headbasket. The amp circuits themselves should be flat here.

 

[granger.frederic]

coupled with a haufe T14/1 , a 100pf reduces around 1 to 2db at 15Khz and also softens a bit the transients.

Any calculation for this?

save some time and just measure before/after !

 

[granger.frederic]

coupled with a haufe T14/1 , a 100pf reduces around 1 to 2db at 15Khz and also softens a bit the transients.

Differences in ck12 mics are due to the headgrilles variations  ,different voltage polarisations, different headamps : tube vs jfet,biasing and output transformer,negative or positive feedback ,different coupling capacitor ...etc...etc...etc

All true, but the OP is asking specifically about stuff in the upper mid frequency response. This is almost entirely down to headbasket. The amp circuits themselves should be flat here.

unless there are some multiple passive or active feedback filters in the headamp .

 

[Khron]

Well, apart from that one 100pF cap in the ELA M251 circuit, i can't say i can see anything resembling any sort of signal filtering, in any of the "classic" designs that employ the brass CK12 (M251, C12, C12A).

I guess it *IS* down to the headbasket after all - compared to the C12, the C12A's looking pretty flat indeed, assuming the graphs in the manual are accurate.

http://www.coutant.org/akgc12a/akg_c12a.pdf