Official C12 Clone - Build and Support Thread

[JessJackson]

I edited your schematic to what I understand is the 251 modification. let me know if this is correct.

 

[JessJackson]

Moved my Elam conversation to its own thread

http://www.groupdiy.com/index.php?topic=52712.0

 

[Pip]

Can someone confirm if the Carvin has a compatible psu?  I direct people to the Apex 460 because I know almost for certain that it comes from the same factory, but the Carvin unit has the tell-tale sign of being supplied by a different factory than Alctron (the dark red plastic pieces holding the tube as opposed to orange).  I am nearly certain I know who makes this mic and the psu should be just fine, but I'd really like to see a photo verification before directing customers who are needing to build immediately to the Carvin product as a suitable donor.

Matador built a prototype on an Apex 460, so we know for sure that one is good to go as a donor.

I built mine with this donor mic and PSU. Granted I had it for a few years so mine is older than the one they sell now but it doesn't mean different. Here are the differences between my build and Chungers:

- No difference in microphone at all. All differences relegated to PSU.
- Transformer in PSU mounted to PC board so had to drill and mount it to case.
- Power Transformer output lines reversed of those in Chungers build. No big deal just had to cross them over each other.
- I did have trouble as others did with my bias adjustment but it was an easy fix and I don't think tied to donor in any way.

More on this here: http://www.groupdiy.com/index.php?topic=51377.msg666445#msg666445

 

[JessJackson]

Moved my Elam conversation to its own thread

http://www.groupdiy.com/index.php?topic=52712.0

 

[jrmintz]

Just did a three-way test recording a 1965 Gibson Hummingbird with my C-12 clone, a KM-84, and a KM-56. Used a Daking preamp and LA-2A. They sound remarkably similar, but I think I preferred my C-12. Thanks, guys!

 

[Matador]

I edited your schematic to what I understand is the 251 modification. let me know if this is correct.

That's all correct.

 

[Biasrocks]

Just did a three-way test recording a 1965 Gibson Hummingbird with my C-12 clone, a KM-84, and a KM-56. Used a Daking preamp and LA-2A. They sound remarkably similar, but I think I preferred my C-12. Thanks, guys!

Something must be broken, I find those mics to have very little in common, especially on a source like AGtr.

The difference between a KM-84 and even a 414EB is miles and miles IME.

What is the configuration of your C12?

Regards,
Mark

 

[jrmintz]

Nothing is broken. When I said remarkably similar I think I was really trying to say I was surprised at how good the C-12 clone sounds. They don't sound exactly alike, but rather in the same league.

It's a Peluso capsule I had lying around that I'll replace with one of Tim's, a GE 12AY7, and otherwise the stock kit.

Edit: Since it was working well, I decided to fix it. I put in a 1uF Auricap output cap and did the 251 mods with a 330pF polypropylene cap. I'll give it a try tomorrow and see how it sounds.

 

[jrmintz]

When I first built the kit I did the 251 mods. The mic hissed and spit. I undid the mods and put it stock and it was fine. So I redid the mods and it was hissing and spitting again, so undid the mods again and now it's dead. Could the hissing and spitting have trashed the tube? Everything seems to be working okay, voltages are all right on, just no sound. It's possible I screwed up the capsule, I suppose, though I don't think so.

I had disconnected one backplate by accident. It's working now, though why it was unhappy with the 251 mods I don't know. There's also something weird going on between pro tools and my patch bay. I think it's time to take a nap....

 

[JessJackson]

When I first built the kit I did the 251 mods. The mic hissed and spit. I undid the mods and put it stock and it was fine. So I redid the mods and it was hissing and spitting again, so undid the mods again and now it's dead. Could the hissing and spitting have trashed the tube? Everything seems to be working okay, voltages are all right on, just no sound. It's possible I screwed up the capsule, I suppose, though I don't think so.

I had disconnected one backplate by accident. It's working now, though why it was unhappy with the 251 mods I don't know. There's also something weird going on between pro tools and my patch bay. I think it's time to take a nap....

lol, what exactly were your 251 mods? what values etc..

 

[sr1200]

Mr. Warshaw writes:

The Telefunken ELA M 250/251 was made for Telefunken by AKG after Neumann discontinued its OEM production of the Telefunken U 47. Of course Neumann still made the U 47 for many years. Telefunken needed a quality condenser, and AKG stepped in.

The differences between the C 12 and the ELA M 250 are small but important. The C 12 is remotely controlled for pattern by polarizing the rear diaphragm with a separate variable voltage from the power supply, while the ELA M 250/251 has switches in the capsule assembly that change its polarization pattern. The 250 has two patterns, Omni and Cardioid. The 251 included these patterns and also the figure eight.

The second difference is in the circuit. The C 12 and ELA M 250 circuits are similar but not identical. They both use the CK 12 capsule, T/14 transformer and either the 6072A tube (US version) or the AC701 (Europe), but the grid coupling, cathode bias and capsule polarization are different.

Third, the body style of the C 12 and ELA M 250 are not the same. Most important, the head grilles are different, so acoustics are also different.

Found this floating around on the net.  Not sure if the suggested mod was correct based on this description.

Edit: got this too:
http://www.coutant.org/akgc12/elam250_2.jpg 250-251 schematic

 

[Matador]

When I first built the kit I did the 251 mods. The mic hissed and spit. I undid the mods and put it stock and it was fine. So I redid the mods and it was hissing and spitting again, so undid the mods again and now it's dead. Could the hissing and spitting have trashed the tube? Everything seems to be working okay, voltages are all right on, just no sound. It's possible I screwed up the capsule, I suppose, though I don't think so.

I had disconnected one backplate by accident. It's working now, though why it was unhappy with the 251 mods I don't know. There's also something weird going on between pro tools and my patch bay. I think it's time to take a nap....

How did you guarantee that the tube boas voltage (sent through the cable and attaches to the "P4" node at the base of the mike) was forced to be ground?  Did you ground it in the mike?  At the PSU?

 

[jrmintz]

lol, what exactly were your 251 mods? what values etc..

I used a 1k82 1/4 watt metal film resistor in parallel with a 25uF 25VDC electrolytic cap for the cathode bypass with the positive end of the cap/resistor at TK1 and the negative end at the ground terminal just below it where the styrene cap is attached, and a 330pF 200V polypropylene cap bypassing the output cap just as in your picture.

How did you guarantee that the tube boas voltage (sent through the cable and attaches to the "P4" node at the base of the mike) was forced to be ground?  Did you ground it in the mike?  At the PSU?

I turned the bias pot in the psu all the way to the right and measured 0V. That's what I understood to be the 'recommended' way. Did I get that wrong? I checked for 0 V to ground, I didn't actually check for 0 ohms to ground.

 

[Matador]

Hard ground the tube grid right at the tube socket and see if the crackling goes away.

 

[jrmintz]

I'm kind of liking the mic the way it is - I think I might wait for the dedicated 251 kit.

 

[tonycamp]

I'm kind of liking the mic the way it is - I think I might wait for the dedicated 251 kit.

Hey!!! did i miss something??? Is there a ELA M251 kit in the works?

I'm with you mintz, I modded up my head basket acoustics a bit, it may not sound exactly like a C12(i wouldn't know, cause i've never worked with the real deal in person), but it sounds as nice as any mic i've ever worked with!!!

 

[JessJackson]

I'm kind of liking the mic the way it is - I think I might wait for the dedicated 251 kit.

Hey!!! did i miss something??? Is there a ELA M251 kit in the works?

I'm working on the pcb now.

 

[chunger]

we've always anticipated doing the ELA version of this build.  It is possible to do so on the existing pcb and I may be wrong, but there are provisions for pattern switching at the mic a-la original ELA if you are handy and able to cleanly hack a physical switch into your donor body.  Unfortunately for our prototyping efforts, I am out of donor bodies right now.  I do have a spare Tim Campbell CT12 capsule designated for the build though.  So, I'll be getting back on the horse when those arrive hopefully next month.  Note: if you are going with the original polarizing scheme, you should make sure your capsule has the required isolated backplates.  Tim's CT12 does.  I am not sure if the Beesneez and Microphone-parts.com capsules have this.

As I am getting near the end of this run of mic pcb's, we may make some topology optimizations on the rev. 2 pcb and make the ELA build a bit more straight forward.  Of course, that would necessitate re-doing the instructional photo set for the C12 configuration also, but that's how the cookie crumbles.

So, yes, we plan to make an ELA-specific version available at some point, but the changes can be easily made to the existing pcb set without much fuss and the necessary alterations have been discussed verbally here and should be clear for the seasoned DIY'er.  We have not, however, had the time to build out prototypes and photo-document the process in detail.

After a few discussions with MAtador on the subject, we determined that the changes to go for the M251 build were trivial enough that an entirely new pcb set was not necessary.  Better to use the existing pcb or make minor modifications to it in the next batch of boards to better accomodate both build versions.

I'm kind of liking the mic the way it is - I think I might wait for the dedicated 251 kit.

Hey!!! did i miss something??? Is there a ELA M251 kit in the works?

I'm with you mintz, I modded up my head basket acoustics a bit, it may not sound exactly like a C12(i wouldn't know, cause i've never worked with the real deal in person), but it sounds as nice as any mic i've ever worked with!!!

 

[Matador]

Here's an updated conversion schematic:

It's only 3 more components, with 3 removed (C13, C10, and R11 removed).  This particular version makes use of the PSU-based polarization mechanism (if you want to keep cardioid, figure-8, and omni selections) so no need for new holes in the mike housing.

This retains what I think are the essential aspects of the 25x design:  no gate coupling cap, a bypassed cathode resistor, and a plate cap to ground (100pF was the original value, but I think 470pF sounds a bit smoother).

And even better yet:  no new PCB is needed!  ;D

If you only want cardioid, you can remove even more parts:  remove R16 and C11, and just let the RC connection float (just like cardioid in a U47).

 

[pmcorbett]

Chunger/Matador....a hearty "Thank You" to you guys. After a little tinkering and some minor trouble shooting ( my first "real" DIY build)... got my mic up and running. This was a very satisfying build. This will most likely be the last bit of major modding for my poor old Apex 460. I'm really looking forward to hearing this mic evolve during it's breakin' in process. Thanks again. You guys do great work. ;D