DiY AKG C12

They're in the mail. Waiting for Poctop's 251 boards with floating Hi-Z section with the 3 switching relays.
I already  have all the new Mouser parts for mic and power supply.
I'm going to convert over one of my DIY C-12s with the Tim Campbell capsule.
Might sell Matador's C12 finished and tested Mic and power supply boards. If interested let me know.

Here's a rough mix of a band I'm recording using my C12 copy for vocals.  EQ was a cut around 1.8k for a nasal note, cut around 300hz for clarity (both pre compressor).  Post compressor EQ was wide boost around 7k for clarity, narrow cut around 200hz for a boomy note.  Compressors were 1176, medium attack, fast release and an LA2A, around 4db reduction.  Preamp was 1272.

www.theopiumdenproductions.com/spacely/parkinglots.wav

It is!  

It's just rewired to match the C12 circuit with an old 12AT7 I pulled out of a vintage Fender amp when I re-tubed it.  The capsule is a C12 edge-terminated clone.  I bought 2 capsules for cheap and selected which one I liked better, and then selected which side I liked better to use as the primary side.  I used the other capsule to play around with tensioning.  The bulk decoupling caps in the mic were paralleled for increased decoupling.  The audio path caps were changed to 'styrene or polypro depending on the location and value, and the RFI caps were removed to get rid of that LC peaking of the transformer.  I also cut apart the cheesy rubber capsule mount and fashioned an epoxy-putty mount that is conical in shape, just like my Gefell's have.  This is supposed to reduce the reflections inside the headbasket, but who knows if it really does..

I also shortened the 7pin cable to 10ft.

This artist I was recording came in right after I made the mic and he was always complaining that none of the studios he had been to could capture his voice quite right.  He did have a very strange harmonic in his voice which would cause mics to "warble" at high levels.  I still don't quite know what it was, but maybe some kind of sympathetic vibration of the capsule or something..  Anyway, we tried the C12 clone and he LOVED it, although it still "warbled" just a little bit.  He loved it so much that he begged me to sell this mic to him.  Instead, I offered to show him how to make his own.  So he bought a 460 on ebay for 150$, and I did the same mods and installed my second capsule in his mic.  To our amazement, the different tension on the second capsule didn't "warble" at all with his voice and the lower tension kind of lessened the upper harmonics in his voice too.

Unfortunately he moved away and I don't get to record him, but to this day he still carries that mic to every studio he goes to to record and he's told me that none of them can find a mic to beat it on his voice.  

svart, can u show a pic of the guts of ur modded 460? I'd love to see what u did, also, how did u mess with capsule tensioning? That seems like quite a trick!

Thanx

Looks great, Jim! I'd love to hear more about that Seimen's MP. Might be the perfect fit for a C12 or U47.

Awesome! Does MP in this context stand for Metal Paper, or something German? I have always wondered if the original AKG C12 output cap was metal paper or PIO Siemens. I think all of those would be too big for my U47 and C12, unfortunately

Here's the pics.  not much to see.  There is a styrene cap on the back of the board.  One of the coupling caps was changed with a polypro (large reddish cap), a couple of the resistors were changed to different values, the RF caps removed, etc.  All these parts I put in because I had them already and needed to change them to make it more C12 like, not really due to tone or anything like that.  I figure that if the circuit is functioning correctly, the difference in how the singer sings into the mic from take to take is greater than the difference a cap could ever possibly make.

Yes, or in german: Metallpapierkondensator.

MP "Metallpapier" capacitors have paper as dielectric. Therefore Paper-In-Oil caps are MP capacitors as well. The paper is soaked or impregnated with oil or wax. Pre 1980 PIO caps can be highly toxic in case of fire, because they release PCB polychloric biphenyle.
I do not know of any caps that use paper as dielectric, that were not using oil or wax. All of them are called "MP".

They are picked for their exceptional hysteresis properties due to paper as a dielectric and in this regard they shine. Followed by polystyrene and poöypropylene as dielectrics (KS and PP).
Obviously the physical dimensions limit the use of MP caps.
You want to take them for output cap, where they shine.
The cap connected to the capsule, you definitely want to be styroflex (polystyrene?)...
I don't have the schem or BOM of the C12 at hand so i don't know what they used for other caps in the C12, but the above can be taken as critical choices that have proven to sound good in these positions(generally). Also in other mics.

Best regards,
Martin

EDIT:
PS: I do not know if i am right calling styroflex polystyrene caps, the material in the styroflex caps is called "Polystyrol" in german. Both are trivial product names, not chemical names, which is in fact "Styrol-Butadien-Block-Copolymer" (SBC), a synthetic resin.

Another thing i forgot about MP and Styroflex capacitors that are good to know when experimenting with them for audio use, that is not regarded as much as it should...
Capacitors are susceptible to microphonics to different degrees. E.g. Styroflex are quite microphonic, therefore you have to watch out where and how you pick and mount them. Sometimes it is better to mount them off the PCB, point to point.
The huge MP caps on the other hand are very insensitive in this regard.

250v is fine. The voltage is usually around 120v-150v unless it's stated otherwise somewhere. I believe the voltage across that Cap is halved as well, but I suppose it would depend on which circuit you're using, in mine I have 70vdc on the plate.

Do the polystyrene caps have to be polystyrene? What's the sonic benefit? As far as voltage, I assume that anything from 120v on up would be ok on a 120v circuit? (Maybe a bit more for good measure).