AKG C12 / Siemens SM204 help needed

[micaddict]

12AT7/6201 has lower output impedance ,  i would choose a transformer around 9 or 10:1

Thanks again. 

Edited to add:
I went to the Samar site and the 12AT7 gets mentioned there, too. Marik recommends 10:1, as well (there's no 9:1 Samar tranny available as standard).
And as low as 6.5:1 for the 5840 subminiature.

 

[ln76d]

Yes, i really like small transformers, never had problem with low end - comparing to the bigger one with same ratio.
If transformer is pretty linear from 20Hz-20kHz or even from 30Hz, why not
All depends on application - for vocal microphones mostly i would use smaller transformer, for instrumental microphone maybe bigger but in both situations there's to many factors to get desired sound, so there's no one way to choose proper transformer (except the ratio of course ) and make some general rules.
With small transformers, most which i used, overall sound is much more "airy", also usual these are more colorfull probably due to saturation. Those are very subtle differences but really usefull for vocal recording.
Anyway SM204 circuit is great option for new project, so when i will finish at least ten projects  which currently building, probably i will think about it
There's some Haufe replacement for V2148 which Andreas Grosser have in the offer.
The best application for 12AT7 in microphone which i found is CCDA type circuit.
In this application 6:1 ratio sits very well.

 

[granger.frederic]

we can go to 4:1 with CCDA , but this schematic is not my favorite : too clean and sharp sounding

in a SM204 i'd mount a 6072A plate follower , self bias with 47uF /6.3v , silmic II , 0,47uF PIO, and T14/1 haufe

 

[TLRT]

Ok, got the PSU and the pattern switch, however I'm not sure how this will work together, the N12 has a 5 pin XLR output, the S36 pattern switch has a 5 pin tuchel input, and a 3 pin output?, but the mic has a 8 pin connector (FLEA will prepare a new input connector for the mic) All suggestions are welcome!

 

[ln76d]

we can go to 4:1 with CCDA , but this schematic is not my favorite : too clean and sharp sounding

http://groupdiy.com/index.php?topic=62219.0

Here's my mod for t.bone with 6:1, if you would like to look what am talking about.
I tried 3:1 and it was really too low but 4:1 could be reasonable unfortunately i didn't have it  when i make this mike.
I will try on another.
With CCDA all depends how it's build and what components used. Definately am not using metal resistors in nefralgic parts of the circuit.

TLRT - how to paste multiple images in one post?

 

[granger.frederic]

we can go to 4:1 with CCDA , but this schematic is not my favorite : too clean and sharp sounding

http://groupdiy.com/index.php?topic=62219.0

Here's my mod for t.bone with 6:1, if you would like to look what am talking about.
I tried 3:1 and it was really too low but 4:1 could be reasonable unfortunately i didn't have it  when i make this mike.
I will try on another.
With CCDA all depends how it's build and what components used. Definately am not using metal resistors in nefralgic parts of the circuit.

TLRT - how to paste multiple images in one post?

that makes sense to me
i use a lot of CCDA topology
i like it a lot in my main RIAA preamp for ex.
however my preference , in a mic, still goes to plate follower with a matched tranny

 

[TLRT]

we can go to 4:1 with CCDA , but this schematic is not my favorite : too clean and sharp sounding

http://groupdiy.com/index.php?topic=62219.0

Here's my mod for t.bone with 6:1, if you would like to look what am talking about.
I tried 3:1 and it was really too low but 4:1 could be reasonable unfortunately i didn't have it  when i make this mike.
I will try on another.
With CCDA all depends how it's build and what components used. Definately am not using metal resistors in nefralgic parts of the circuit.

TLRT - how to paste multiple images in one post?

You can upload your pictures to a pic hosting server and you can insert the image links with "Insert Image" code (

)

 

[ln76d]

however my preference , in a mic, still goes to plate follower with a matched tranny

So as i, but sometimes is worth to make something else

You can upload your pictures to a pic hosting server and you can insert the image links with "Insert Image" code (

)

Great! Thanks!

 

[MS Vienna]

@ TLRT: the S36 pattern selector goes with the D36 switchable dynamic microphone (contains 2x DK12 - one facing the frontside, one the backside). It can be modified to work with the SM204, however the S36 - and D36 - are quite rare and potentially valuable on their own.

The time correct SM204 pattern selector box is simply called "U". It has a large multipin connector on the input side and a small 3-pin connector on the outputside (both AKG connectors not Tuchel).
It might be very hard to find this switchbox. AFAIK FLEA used to make a replica of the C12 switchbox. Just ask them if they still do.

@ all:
I have quite some pictures of SM204 guts - somewhere. If you´re interested I´ll search my archive and post them here.

 

[TLRT]

@ TLRT: the S36 pattern selector goes with the D36 switchable dynamic microphone (contains 2x DK12 - one facing the frontside, one the backside). It can be modified to work with the SM204, however the S36 - and D36 - are quite rare and potentially valuable on their own.

The time correct SM204 pattern selector box is simply called "U". It has a large multipin connector on the input side and a small 3-pin connector on the outputside (both AKG connectors not Tuchel).
It might be very hard to find this switchbox. AFAIK FLEA used to make a replica of the C12 switchbox. Just ask them if they still do.

@ all:
I have quite some pictures of SM204 guts - somewhere. If you´re interested I´ll search my archive and post them here.

Hello, thanks, I have never seen this S36 version. I will ask FLEA. I would be very happy if you can find those pictures of your  SM204!

 

[ln76d]

I have quite some pictures of SM204 guts - somewhere. If you´re interested I´ll search my archive and post them here.

I'm not OP, but i'll be really happy to see the guts - and probably not only me

 

[micaddict]

No, probably not ...



;D

 

[MS Vienna]

Ok, I´m still searchin and copy/pasting but for the start here´s one that was on ebay around Christmas 2014 (seller from Vienna but I didn´t know him)
Interesting: This one has a C12-style grillecap. Usually SM204s have diagonal mesh grilles in satin nickel finish.

 

[MS Vienna]

Here´s a friend´s mic. That´s an exceptional one! It doesn´t have it´s orignal capsule anymore but one from the very early 60´s (still completely original as such) - some people say "ELAM-capsule" because of the era.

It has a slight upper midrange rise. From comparisons I´d describe the frequency balance as somewhere in between a Schoeps MK4 and an U87. While not that impressive when soloed it´s an  incredible useful sound - very mix-ready with great dimension.


To be continued...

 

[micaddict]

To be continued...

 

[MS Vienna]

Hi-Resolution closeup of amplifier

Edit 11.8.2016: Inserted image link to make picture visible for guests too

 

[MS Vienna]

And for the very unlikely case someone´s interested in the capsule 

Edit 11.8.2016: Inserted image link to make picture visible for guests too

 

[MS Vienna]

Filthy thingy...but as long as it works and sounds great - never touch it!

So that´s it for now. I plan to post detailed pics of a third SM204 specimen tomorrow (to me that´s the most interesting one).

I have the impression that the number of remaining SM204 in Austria outweighs the C12 by far. I guess that´s because - to my knowledge - the ORF never had C12, and some lucky guys were able to buy those SM204 for dirt-cheap when they were sorted out.  Today you probably won´t get a complete all original set below 10.000 Euro.

Edit 11.8.2016: Inserted image link to make picture visible for guests too

 

[micaddict]

I must not look.

Must not look.

Must not look.

Must not look.

Must not.

Must not.

Must not.

Must.

 

[Rossi]

Looking at the SM204 schematic, I'm surprised nobody has commented on the cathode bypass  cap, which is only 25 nF, not 25 uF as you'd expect. At first I thought it might be a typo, but the cap symbol is for a nonpolar cap, not an electrolytic.

25 nF will produce a additional gain in the upper frequencies only, i.e. a shelving boost above about 5 kHz.

Speculation: Obviously a brighter sound was wanted. So perhaps the later, brighter CK-12 capules were the result of building that treble boost into the capsule rather than the amplifier.