AKG C12A Inspired Build

[Icantthinkofaname]

Im gonna chime in here, I built a C12 and liked but to me it didnt make a very real sound, a good sound but not very natural.

I wanted a mic or mics which i could mic up a room and it would sound like that room.

The C12a came up as a mic that would do this time and time again.

Many studios using it for overheads or room mics or on toms or vocals.

Its quite simple to build the body and headbasket of the mic out of brass, cut out the main body pieces and braise them together to form a box, put a bottom on it then drill a hole for the socket.
for the headbasket, shaping some mesh for each side and a strip of brass down the middle then braise them together.
For the capsule mount i just used a bit of copper bent in a U shape then mount the capsule to it and it just slotted in.
The headbasket i then drilled and screwed it securly, then just getting the pcb in there along with the nuvista and transformer.
It was all pretty tight but I did two of the mics and they work wonderfully.
Didnt cost a bomb and i will get round to taking them apart and nickel plating them, but im using them all the time so i dont know when that will be!!

Just thought i'd speak up, and hope this helps.

My original plan was to make a c414 EB but there ended up being a few things that just didnt work out, the DC-DC converter for one!!!
I love to make a few C414 EB and make a few more bodies but pretty busy with everything else now!!

Good luck.

Spence

What separates the C12 build and C12A build sonically? Different capsule, different transformer, different tube, or something else?

 

[Spencerleehorton]

take a look at the schematics, they are quite different, the capsules make the most difference along with the headbasket, transformer and valve.

 

[justinheronmusic]

Since I have been asked this twice now, I will go ahead and answer.

I am specifically building a C12A for a few reasons. I have access to a vintage C414, and five modern 414s if I need them. Though I like these microphones, I want something more unique in my colour palette.

The challenge to difficulty level ratio, this is a big reason. The PCB layout. I don't like to rely on people to do things for me, and I knew that going into this I would have to do a bulk of the work, which I am alright with. The layout of the pcb and amount of components seemed workable for my experience level. It's a simple circuit, it's unique, and it is otherwise unobtainable to me unless I DIY it, or rent it from Blackbird Studios.

It is truly a unique microphone. The Nuvistor tube is a cool part of history, just reading over the datasheets gives me chills; and they are affordable & available. Did I mention that the microphone sounds great on piano, guitar cabs, and cello in a mix?

The circuit is often overlooked as not being a large contributor to the sound, but I think it makes a huge difference. With a good capsule, a good transformer, and a real 7586 tube, and a wet tantalum output capacitor; you're pretty darn close. I don't see why the body is stressed more so than the circuit. Do I want the original body? Yes! I just don't have the tools in my tiny apartment to do it. If someone wants to make me a body, I will for sure design the PCB for it.

The only reason why I bring up alternatives to Tim's legendary capsule is because they might sound amazing, and passable. My Maiku K47 sounds incredible in my Poctop M49b, especially for the price. I wouldn't have considered Maiku if it wasn't for Piotr's raving review of their K47. If their K47 sounds so good, which it does, then why not their CK12?

It's ok to cork sniff capsules, and have a preference on bodies, and want to get as close to the original as possible, but I am not going to let that keep me from building the circuit; if the capsule is the heartbeat of the microphone, then the circuit is the brain.

EDIT: What separates the C12 build and C12A build sonically? Different capsule, different transformer, different tube, or something else?

- To me, the C12 is all about the airy highs and the powerful lows, which is why it compliments women's vocals so well. The C12A is more detailed in the midrange with a more relaxed high end and low end content - perfect for guitar cabs.

 

[user 37518]

Do not use electrolytic caps, you need good tantalum ones.

I know little about microphones, but why use tantalums, they distort much more than electros, is this to keep faithful reproduction of the original?

 

[RuudNL]

I doubt if it is a good idea to 3-D print a microphone body.
You need a 'Faraday shield', to screen the high impedance parts inside the microphone.
Unless you can find conductive material to print the body with, I wouldn't recommend this.
(Of course you could apply a conductive layer inside the microphone body, but I think that is making things even more complicated.)

 

[justinheronmusic]

I doubt if it is a good idea to 3-D print a microphone body.
You need a 'Faraday shield', to screen the high impedance parts inside the microphone.
Unless you can find conductive material to print the body with, I wouldn't recommend this.
(Of course you could apply a conductive layer inside the microphone body, but I think that is making things even more complicated.)

Plastic with conductive paint, is that not how they did the original?

I know little about microphones, but why use tantalums, they distort much more than electros, is this to keep faithful reproduction of the original?

I believe wet tantalum has a different sonic result than solid tantalum or electrolytic. From what I have gathered since Spencer's response to my initial question, electrolytics tend to bring a frequency "smearing" effect to the sound, which I surmise is due to the phase issues that is introduced by this style of capacitor. Tantalums may distort but they have more clarity without the effect on phase. The more phasey a mic, the weirder it is when EQ'ing it in the mix.

All of these vintage microphones distort in a special way when they are pushed, or when a vocalist opens up, and it's actually something that I tend to favour over a super clean microphone (The M49 is a great example of beautiful distortion). I would much rather watch a movie shot on 35mm than in digital film. I surmise that the distortion in this microphone is due in part to the tantalum output capacitor, making it integral to the relics that are needed to summon the spirit of the C12A.

 

[Icantthinkofaname]

I doubt if it is a good idea to 3-D print a microphone body.
You need a 'Faraday shield', to screen the high impedance parts inside the microphone.
Unless you can find conductive material to print the body with, I wouldn't recommend this.
(Of course you could apply a conductive layer inside the microphone body, but I think that is making things even more complicated.)

Perhaps wood would be a better idea, though it would still have similar problems, but at least it would probably be much stronger. I know there are people who have done electret mics in wooden bodies, as well as ribbons.

I've heard some people use aluminum foil in mic bodies if the body itself isn't conductive.

If they do plan to use conductive paint, I'd still probably go with a wooden body over plastic. Though I guess it also depends on the quality of plastic used. Maybe ABS (and acetone smoothing, though I guess you could sand or file it as well) is the way to go with a plastic body. Though it's worth noting (for the OP) that mics and other electronics using plastic casing are usually done with injection molding. Of course for the DIY crowd that's off the table because of the cost. A cheap 3D printer can be had for a few hundred bucks.

 

[Spencerleehorton]

Mumetal sheets are fairly cheap to line the inside but I would always go with making a body.
If your really serious about this buy some brass, solder and a gas bottle (torch) 3mm brass is good, i could always measure mine to give you rough measurements?
Tbh if i had time I'd probably make you a couple of bodies!!!

 

[justinheronmusic]

Mumetal sheets are fairly cheap to line the inside but I would always go with making a body.
If your really serious about this buy some brass, solder and a gas bottle (torch) 3mm brass is good, i could always measure mine to give you rough measurements?
Tbh if i had time I'd probably make you a couple of bodies!!!

- Measurements would be very helpful to have for reference purposes. Thank you!

- What was your reason for using a 10:1 ratio output transformer instead of the stock 1.84:1? Did you wire it parallel?

 

[Spencerleehorton]

I was going by memory it was a 10:1 but wired 5:1 yeah , it was an old akg one re wound.
I will check when I open them up as I need to nickel plate them, along with quite a few other bits!!!

 

[Spencerleehorton]

Btw the capsule socket I put on leads and heatshrinked it all and didnt mount on the pcb to save space, same as txf.

 

[justinheronmusic]

I've been working on the schematic the last few days. I have yet to build in the tube socket and the capsule footprints into Eagle.
The dotted line is just the "net" but with a different symbol, does this work ok?

Can anyone look this over for errors?

 

[shabtek]

if you are designing a pcb it may be possible to avoid the socket all together. Ian and others have used harwin pin sockets soldered into pcb to forego 9 pin tube sockets. you may need relief cuts routed for the shell to fit  if the sockets did not stand proud enough from the pcb.
otherwise this should not be difficult to avoid pcb and p2p wire it.

 

[Khron]

A slight observation - it's a bit of an "industry standard", more or less, for the "input" (in this case, the capsule) to be on the left, and the "output" to be on the right. Also, the higher the voltage, the higher on the schematic it "should" be (and since there's no negative rails, ground on the bottom).

I've been working on the schematic the last few days. I have yet to build in the tube socket and the capsule footprints into Eagle.
The dotted line is just the "net" but with a different symbol, does this work ok?

Can anyone look this over for errors?

 

[RuudNL]

To be honest, I can't find head or tail on this schematic...
A more 'standardized' way of drawing is recommended.

 

[justinheronmusic]

A slight observation - it's a bit of an "industry standard", more or less, for the "input" (in this case, the capsule) to be on the left, and the "output" to be on the right. Also, the higher the voltage, the higher on the schematic it "should" be (and since there's no negative rails, ground on the bottom).

Thank you for the heads up! I am still a beginner, and I did not go to school for electrical engineering, I'm sorry. When I googled the original C12A schematic, the attached schematic is all that came up. For some reason I thought that the original schematic orientation would work.

Btw the capsule socket I put on leads and heatshrinked it all and didnt mount on the pcb to save space, same as txf.

Do you mean the tube socket? I was going to include two solder pads on the PCB for the transformer, then solder the transformer output to the 7pin connector. It might be extra steps to build it into eagle to build the tube socket but I don't mind. Would it be better to use the Russian leaded 7586 tubes and just do turret pins?

 

[Spencerleehorton]

Yes sorry I meant the tube socket!!!
You can do either, up to you really.

With mine it kept things simple if I needed to change a tube and it tucked away nicely in the little bit of space I had left inside the body.

I ended up buying about 10 tubes and tested all of them and used the two best ones.

 

[Marcedona]

- Measurements would be very helpful to have for reference purposes. Thank you!

- What was your reason for using a 10:1 ratio output transformer instead of the stock 1.18:1? Did you wire it parallel?

Hello! Surely he would be thinking of another mic, the family's most famous relative: the "AKG C12".

The C12A actually has only three things in common with it: the name, the body, and the capsule (or should we say "one thing", the cápsule)

Being Cathode Follower is more "forgiving" with various things - the tube for example - and yes, the output impedance is lower: you don't need a high ratio transformer.

In general anyone would prefer a C12 over a C12A, but CF can be a more feasible challenge. The sound of this topology could also be described as flatter or less aggressive, perhaps less defined or less aggressive, so I suspect that this configuration can also alleviate the capsule's incidents.

In fact the Sony C37 someone mentioned before is a fantastic mic, second to none.

Good luck! Maybe I will copy your idea

 

[justinheronmusic]

Once I get the schematic & PCB layout done I was planning on making this open source, so anyone can download the files and print & modify as they please.

I talked to David from Cinemag about doing a 1.84:1 ratio transformer copied from the transformer data sheet from AKG, he said they don't have the laminate in stock for the transformer, though he could use something that would be close. I also reached out to AMI and am awaiting response.

The tube socket should be here on Saturday. I will be able to build it into Eagle by the following Monday.

 

[Spencerleehorton]

Just wondered where you got the info for the txf being 1.18:1 ratio?
I was told 4:1 or 5:1 ratio for CF mic?

My build
https://groupdiy.com/index.php?topic=59875.0