[FEELER] C12 Clone Project

UPDATE:  Project is nearing final release.



I've been collaborating with Matador to develop a series of microphone projects designed for the Alctron HT-11A / Apex 460 donor body.  The first of these projects is a reasonable clone of the C12 circuit.  99.99% of the credit for this design is Matador's and I am only contributing a few physical configuration and general project parameter opinions.

As we are now entering the prototype phase of the project, I thought I should start a feeler thread to gauge interest if there is any.  PCB production is not too much of an issue, but donor bodies require some lead time and slightly more complex logistics to procure.  I am also in the process of getting a nicer-than-stock headbasket manufactured to support this project.

A change in the physical arrangement of internal components in this design will allow the HT-11A body to accommodate larger components than currently possible with mods on the stock PCB's.  The psu board for this project is designed to fit the stock donor enclosure and utilize the stock power transformer.  It will also supply the required voltage for fixed bias like the original C12.

Our test capsule will be Tim Campbell's CT12 and we will optimize to this configuration.  We hope to make a project of uncompromising quality at a reasonable price-point.

Thanks Chunger!

Here is a silkscreen of the first prototype panel:



The mike PCB's are the long one at the top and the small tube socket half-round at the bottom.  Power supply is in the middle.  Ignore the two DOA projects I tacked on as riders. 

The idea is to bring some of the point-to-point turret construction ideas of the original.  This mike is a tight fit for things, so I've tried to clump devices along the centerline where clearance to the shell is at maximum.  There is no easy way to reuse the stock rubber mount tube socket so I recreated a new 90 degree mounting that is similar to poctop's U67 design (and many others like the MK47, etc).

As Chunger indicated, the power supply bias is tweakable by adjusting a 2K bias pot.  The heater supply has a CRCRC filter in front of a heats inked LM317T:  a very standard design.  The heater is tweaked for 6.3V as measured at the tube sockets.  The power supply PCB is the exact same size as the Alctron/Apex460 PCB and it will bolt right in to the same chassis.  The stock transformer, fuse, and all XLR connectors are reused.  The stock polar pattern switch is also reused.

The PCB contains all of the necessary wiring to make the C12 circuit with the exception of three connections to the tube that must be done with regular wire.  The large circles are for Keystone turrets which are tin plated and the same as what are used on many point-to-point turret projects.  They are cheap at about 30 cents each as well.

I will post a preliminary schematic one I can get it cleaned up a bit.

EDIT: schematics posted below.

http://www.musicalsparks.com/images/c12/c12_clone_schematic.pdf
http://www.musicalsparks.com/images/c12/c12_psu_schematic.pdf

Hey Chunger and Matador, I would love to be a part of this in some way. I just ordered all of the components to start my own pcb for a C12 build in the Apex 460. I think that any of the options you gave would be pretty great for the community.

+1 ,  Sign me up,    Awesome work matador and Chung.

Good looking! Does this project follow on the original C12 schematic? I might be interested in replacing the PCB I etched for my C12 clone with one of these.

Kris

I would love to have a more exacting circuit, count me in

+1 for me

Looks great, in for two.

I'm assuming if you're fitting for TC CK12 that an original will work as well.

It would be nice to allow for a T14 transformer in place of the stock transformer.

Mark

When at the top of the page, it says stock transformer, I assumed that this meant the transformer in the PSU.  The implication is that the Apey transformer is used for the audio output of the mic.

David

Biasrocks said:

Looks great, in for two.

I'm assuming if you're fitting for TC CK12 that an original will work as well.

It would be nice to allow for a T14 transformer in place of the stock transformer.

Mark

Click to expand...

+1, Tim's capsules are great.  Make it fit a T14 as well! 

It's the year of the MIC.

Im already on this list for two donor mics, so definitely count me in for some sort of kit.

...looking good Chunger!...very interested in your progress with the more accurate headbasket design...

Biasrocks said:

Looks great, in for two.

I'm assuming if you're fitting for TC CK12 that an original will work as well.

It would be nice to allow for a T14 transformer in place of the stock transformer.

Mark

Click to expand...

The stock audio transformer in the microphone will not work with the C12 circuit.  We are re-using the stock power transformer in the psu.  Cinemag, AMI T14, and perhaps Marik's transformers should be viable options for the audio transformer.

Enchilada said:

Good looking! Does this project follow on the original C12 schematic? I might be interested in replacing the PCB I etched for my C12 clone with one of these.

Kris

Click to expand...

It's shamelessly a direct copy of the original AKG C12 schematic.  The reference designators for the mike are even the same. 

david-p said:

When at the top of the page, it says stock transformer, I assumed that this meant the transformer in the PSU.  The implication is that the Apey transformer is used for the audio output of the mic.

David

Click to expand...

Sorry yes, it is meaning the PSU transformer only.  The stock output transformer will not work in the C12 design.

I will take one!

Make it fit a T14 as well!

Click to expand...

+1
Big Hiller momma.

Cool.

If you make a T-14 fit, I'll take a pcb set as well.

Well I'd be in for two of everything, I already have various parts to build but would be happy to support the project (and it would probably make my life easier anyway).

Good work chaps!

I'm interested also to fit a T14

Thanks
Neil

Le Roux said:

I'm interested also to fit a T14

Thanks
Neil

Click to expand...

Unless I missed something obvious, the AMI T14 looks to be about the same size as the Cinemag CM-2480 (roughly an inch long and half an inch wide/deep). 

This Alctron/Apex460 body design features a separate bell housing at the bottom that contains space for the output transformer.  I used a Cinemag in my first ELAM 251 build and it had gobs of space in this transformer housing:  so much so that I added a piece of foam in there to keep it from rattling around.