Official C12 Clone - Build and Support Thread

[gyraf]

Remember that the AKG CK12 capsule is/was notorious for being all-over the place sonically - I know of no other classic capsule that was manufactured with that much variation in response. I think the reason it's forgiven for this behavior is the fact that it takes EQ very well, quite a lot differently from nearly every other large-membrane design I've heard.

I have a friend that hand-makes these capsules, and he has carefully listened through literally hundreds of original AKG capsules to find the one that he likes the best, and this has become his fixed reference for tuning/adjusting every single new one he makes.

Just recently he stumbled on an original (a repair he did) that sounded slightly different, but subjectively just as good - which temporarily freaked him out in a chaos of doubts about where he should aim his adjustment.  Doing CK12-type capsules is not for the faint-hearted - every customer has a favorite among the originals, and it's not always easy to get the message through that there is no such thing as a "standard" CK12 capsule sound balance.

Jakob E.

 

[micaddict]

A C12 is typically a bright microphone; the brightest of the LDC classics, I'd say.
But yes, like Jakob says, the capsule is a tricky one and especially original ones can vary. (Does yours have an original capsule?)
All that said, a dark C12 does seem odd, particularly if it has a modern capsule.

 

[kidvybes]

Remember that the AKG CK12 capsule is/was notorious for being all-over the place sonically - I know of no other classic capsule that was manufactured with that much variation in response. I think the reason it's forgiven for this behavior is the fact that it takes EQ very well, quite a lot differently from nearly every other large-membrane design I've heard.

I have a friend that hand-makes these capsules, and he has carefully listened through literally hundreds of original AKG capsules to find the one that he likes the best, and this has become his fixed reference for tuning/adjusting every single new one he makes.

Just recently he stumbled on an original (a repair he did) that sounded slightly different, but subjectively just as good - which temporarily freaked him out in a chaos of doubts about where he should aim his adjustment.  Doing CK12-type capsules is not for the faint-hearted - every customer has a favorite among the originals, and it's not always easy to get the message through that there is no such thing as a "standard" CK12 capsule sound balance.

Jakob E.

...this is very relevant information, and IMHO, a good reason when building a C12 clone to chose a capsule that satisfies your particular goal in reference to the voicing of your mic, rather than stressing over a particular capsule-maker or "historically correct" construction...if the original reference mics vary to that degree, than it may be more prudent to opt for your particular preference/need within the "C12 range"...it would be most helpful if all the available capsule options could be graded by their "brightness" factor for reference purposes...

...just my .02c...

 

[dmnieto]

Ok, this is my last attempt. I am planning to build my C12 clone, but I want to burn-in the tubes. Something I have no experience at.

I was wondering if it will be safe for the tube 12ay7 (aka it will not overheat) to be burned in by placing it in a gyraf G9 preamp on the SRPP stage.

I have checked the graphs and It seems that the triodes will be biased on a safe zone without any modifications to the circuit (upper: plate ~120V Ia 1.3mA Va~-2V) But I am not very sure my calculations are correct.

Any comments?

 

[Melodeath00]

Thanks for the replies. I am aware the CK12 was all over the map, and that must be frustrating as a capsule-maker. That being said, most people think "bright" when they think of a C12. Perhaps that is an erroneous perception?

micaddict - No, mine does not have an original capsule. My C12 is not "dark," so much as it is "not bright." It is extremely smooth and very balanced; not dark, not bright. I expected it to be bright, so because it is more neutral, it is "darker" than I expected. Through a few months of use, I have realized it sounds surprisingly close to my DiY U47. In comparison, my C12 has a little bit more 12kHz, but less 15kHz and above, for example. Either way, it is almost difficult to tell them apart on my voice. Now, you might argue perhaps my U47 is brighter than expected, and it's all relative. But I also own a Manley Reference Cardioid, and judging by those compared, I'd say my U47 is in the right ballpark tonality-wise. I can easily tell the Manley from my C12 or U47.

PLEASE NOTE: I am not in any way bad-mouthing my current C12 capsule. It sounds fantastic as is. In fact, it has inspired a friend of mine to build his own C12, and another friend has heard the mic on guitar and said "that is the most realistic acoustic recording I've heard. It sounds like I'm playing the guitar itself." All I am saying is that it doesn't seem to be as bright as I expected. If I were to shoot for something brighter, I am not sure if I should consider a capsule adjustment, or if I should be looking somewhere else in the circuit; perhaps there is a problem somewhere that is sucking out high-end? Most people would probably leave the mic as is because it sounds great. But even though I am new to DiY, I feel like somewhat of a "tinkerer," and am curious if I can get the mic closer to how I had envisioned it. Perhaps I have just been too influenced by the most recent shootout I've heard, where a vintage C12 sounded much closer to a Manley Reference Cardioid in terms of balance than to a vintage U48. As I said, I own a Manley as well, and my DiY C12 is much, much closer to the DiY 47 than to the Manley.

I welcome your thoughts. Thanks!

dmnieto, if you are very concerned with burning in your tubes, why not burn them in within the mic itself? Build the C12 and burn your tube in the C12. That way you wont have to wonder if there will be damage to the tube, and you will be "burning in" the tube in its actual intended circuit.

 

[Category 5]

Thanks to k67 capsules in uncorrected circuits, as in this popular Chinese mics, I think our opinion of bright may have changed over the years.  Bright compared to a vintage u47 isn't really that bright at all.

 

[dmnieto]

dmnieto, if you are very concerned with burning in your tubes, why not burn them in within the mic itself? Build the C12 and burn your tube in the C12. That way you wont have to wonder if there will be damage to the tube, and you will be "burning in" the tube in its actual intended circuit.

Because during burning in the biasing can change on a new tube, or not being stable (in the build thread they actually mention not to bias with an untested tube). The body mic I have will make it very difficult to reopen/close multiple times over the burning in to re-bias. So why go over that when I could potentially burn-in in a much more accessible circuit?

With that I can troubleshoot much easily. So yeah, I would love to know what are the thoughts of other people, specially regarding if my calculations are correct.

 

[Patrick from Davis]

dmnieto, you can burn in the tube in the V1 spot of a small Fender Guitar amp, like a "Champ."  This is a self biased/cathode biased tube position in the amp so you should not have to worry about things going out of whack during the burn in.  If you have a device like a reAmp or a Line to Amp from DIYRE you can have the tube get a signal from just about any source, if you wish.  But, that is the easiest simple way to heat the thing up and have it settle in that I can think of.
Patrick

 

[granger.frederic]

Hi guys,
did someone try a historically accurate ck12 from beesneez?
it seems promising...
the K7 that i have is a nice capsule too

 

[dmnieto]

dmnieto, you can burn in the tube in the V1 spot of a small Fender Guitar amp, like a "Champ."  This is a self biased/cathode biased tube position in the amp so you should not have to worry about things going out of whack during the burn in.  If you have a device like a reAmp or a Line to Amp from DIYRE you can have the tube get a signal from just about any source, if you wish.  But, that is the easiest simple way to heat the thing up and have it settle in that I can think of.
Patrick

Not having any of those unfortunately... The only tubey thing I have is the preamp.

 

[Patrick from Davis]

Any friend with a tube guitar amp should work, or buy one off the list'o'craig for cheap.  Anyhow, it might not be a good/economical option, but it is something to think about.
Patrick

 

[dmnieto]

That precludes that either I have a friend with a tube guitar amp (which I dont) or that I should buy something I won't use other than for burning tubes.
I may indeed have to buy one of craiglist, but why should I do it if I could use the G9 pre? That is my question.

I checked the schematic, and if I understand it correctly It should be ok to drop the tube on the SRPP stage. And here is where I wonder... I am right or not?

 

[Gus]

I would not use a guitar amp to burn in a tube, vibration might hurt the tube and make it more microphonic.
Look for a post of mine, might have been 04 05 about how I burn in tubes

 

[gyraf]

why should I do it if I could use the G9 pre? That is my question.

Yes, you can burn in the 12AY7 or 6072 in the G9 output stages - the two tubes at the outputcaps/transformers to the right of the pcb, when seen from front

Jakob E.

 

[dmnieto]

Yes, you can burn in the 12AY7 or 6072 in the G9 output stages - the two tubes at the outputcaps/transformers to the right of the pcb, when seen from front
Jakob E.

Thanks Jakob, I really appreciate your confirmation. I though it would be ok, but I was not sure. Just for my own knowledge... were my calculations concerning the biasing correct?

 

[gyraf]

yes, I think it'll idle around 1.5mA - but you can always measure voltage across the cathode resistor to verify

Jakob E.

 

[mica]

I have a finished C12 build that im trying to calibrate. Heater is trimmed to 6.3v on mic, Bias is -1V, but i cant get B+ to hit 120V i have turned the trimpot all the way till it says *click* and the voltage stops at 109V. When i did the PSU it was at 120V, but now with the mic connected its maxed out at 109. What to do!?

/M

 

[Category 5]

I have a finished C12 build that im trying to calibrate. Heater is trimmed to 6.3v on mic, Bias is -1V, but i cant get B+ to hit 120V i have turned the trimpot all the way till it says *click* and the voltage stops at 109V. When i did the PSU it was at 120V, but now with the mic connected its maxed out at 109. What to do!?

/M

You probably got the lower output transformer like many of us did.  You will need to drop the value of r1 and r2 if that's the case.  Wasn't it 56K instead of the specified 91K?  Double check back in this thread for confirmation because that's off the top of my head.  If your transformer is labeled 175V on the secondary then that's your issue.

Chunger, maybe you should add this info to the build guide and pop a couple of 56K resistors in the kit because it seems like more than a few have the 175V transformer in their PSU's.

 

[mica]

Thanks man! Found your quote on page 45:

If anyone else has this problem (B+ Adjustable to about 110 maximum) double check the AC voltage at the output of the transformer.  The good one output 225VAC.  The bad one was only outputting 198VAC.  FWIW, the bad one was labeled 175V whereas the good one was labeled 200VAC.  56K for R1 and R2 instead of the specified 91K (as Matador kindly calculated for me) did the trick!

Mine does indeed read 175V on top. I'll try with some 56K's in there..

/Michael

 

[funkmaster3b]

Sorry if this is off the current topic ;D
firstly thanks for the great mic matador and great instructions Chunger!!
I've been trying to understand this Build a littler better but I'm a bit confused about the capacitor and resistor choices and values used as it's confusing my (tiny!) understanding of OHMS law for example on the heater we have 12.7V after rectifier into  5W  4.7ohm  resistor Ohms law calc shows  19.202 Watts  and 2.021 AMPS so why only a 5W resistor? Also the B+ supply shows 270 volts at the rectifier so why are we using 250v filter capacitors? Any help understanding this would be awesome!!
Thanks Again!