Official C12 Clone - Build and Support Thread

Finished my C12 last week.
Tim Campbell capsule, Haufe T14/1 and GE 5 star 6072 tube.
Sound incredible! Thanks to everyone who made this happen.

BTW, I have some extra Haufe T14/1 transformers left...

Hank Dussen said:

Finished my C12 last week.
Tim Campbell capsule, Haufe T14/1 and GE 5 star 6072 tube.
Sound incredible! Thanks to everyone who made this happen.

BTW, I have some extra Haufe T14/1 transformers left...

Click to expand...

Hi Hank,

Congrats on your new build! What would you like for one of your Haufe T14/1 transformers?

Thanks,
Steve

sl said:

Congrats on your new build! What would you like for one of your Haufe T14/1 transformers?

Click to expand...

They're €55 a piece.
I've send you a PM.

RPC360 said:

Hmm, why not do it with a relay powered by the filament supply? That way the HV would automatically bleed off when the AC was removed.

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That would work, however the point of the standby switch is to allow the heater voltage through while preventing the B+ voltage from rising.  Since the B+ rises quickly, it takes the tube some time once the heater voltage is applied to start conducting and drag the B+ back down.

Hi,

This thread should have the OP or the reserved post updated with the latest version of the boards, and with the test resistor values for both 6072 and 12AT7 tubes. It's sort of silly to have to search through the entire thread for that info.

Thanks,
Josh

hi sorry for my english ) i work on 2 matador mic C12 and elam , the first C12 work well some week with a french CEK 12 but a morning no response , i can't find the bug , after some manipulation i test bias B plus and heater and ? B plus 120 V  heater 6,33 V but bias - 100 V woauah , i turn the trim but never under 35V ? and the trimmer make sound and  flash . i replace it and now never under 95 V , do you know this disturb ? the second psu is the same bias - 100V , have you meet this problem ?  . when the C12 work it is fantastic  , i have the C12 blue circuit board and elam 251 white circuit board there are not as good as the matador , but their PSU work well )  thanks and regards ps: i think my GE 6072 A  vintage don't resist to this bug , may be i can use the other side )

snaredrum said:

hi sorry for my english ) i work on 2 matador mic C12 and elam , the first C12 work well some week with a french CEK 12 but a morning no response , i can't find the bug , after some manipulation i test bias B plus and heater and ? B plus 120 V  heater 6,33 V but bias - 100 V woauah , i turn the trim but never under 35V ? and the trimmer make sound and  flash . i replace it and now never under 95 V , do you know this disturb ? the second psu is the same bias - 100V , have you meet this problem ?  . when the C12 work it is fantastic  , i have the C12 blue circuit board and elam 251 white circuit board there are not as good as the matador , but their PSU work well )  thanks and regards ps: i think my GE 6072 A  vintage don't resist to this bug , may be i can use the other side )

Click to expand...

First; look If the fuse in the psu is not broken.

I have been comparing Matador's schematic to the original and I noticed two things that seem to be different. I was wondering why they are different?

1st thing - R17 on the original looks like 400k.  Meanwhile, R17 on Matador's schematic is 100k.

2nd thing - pin 3 of the triode connects directly to the ground bus on Matador's schematic.  On the original schematic pins 3 & 4 connect to capacitor C10, then both go to the ground bus. Im not sure if this makes a difference or not.

Here is a pic of both schematics side by side.

Pin 3 and C10 are the same on both schematics, just drawn differently.

Yes, C10 is grounded, and so is pin 3.  It's just drawn in a slightly unusual way.

It's doubtful that R17 is 400K.  Look at the other resistors that start with a 1, they are drawn similarly.

Also, it's common practice to design the plate load resistance to be twice Rp, which running at these currents is about 40k, so 100k is pretty close to an ideal balance between signal swing and gain.  Most other medium-mu design run at similar points as well.

Thanks Matador!

Just wanted to make sure before I started building this thing. 

Congrates on having the best diy C12 project on the web.  Very impressive.

Hello guys!
I’m having some issues with my of MataChung C12 pair. I built them about 3 years ago, but havent used them since. Started using them this year and now some issues have risen. Since I don’t have the proper knowledge, I am hoping someone can lead me in the right direction for troubleshooting.

Firstly; when the volume  into the mic gets at a certain level, the mics distort. This is in cardioid setting. I was recording finger cymbals (yeah..), and at lower volume everything seemed fine. When hitting a little hard, the mics distort the sound completely.

Secondly; setting the mics to omni causes this problem to be exagggerated a lot and sounds distort very quickly. And like someone else mentioned here; when turning the pattern knob, there is white noise that goes away after a couple of seconds. For this issue I will try to tighten capsule lead screws.

Thirdly, when tapping the microphone body lightly, is it normal to hear loud noises?

On of the mics experienced some rough play during a recording session when the stand fell over, but I am having the distortion issue in both mics.

The mics are built with the Eric Heisserman capsules and the 6072 tubes.

Any ideas on what I should be checking in what order?

All help is appreciated!

Thanks

Did they always do that, or is this new since they were built?

Do you have any test equipment, like a DVM or scope?

Hi Matador! Long time!
This is something that suddenly happened. I previously used them as overheads without any issues. That was a while ago. When using them now, they suddenly distort. At first i suspected the high frequencies of the finger cymbals, but blowing ever so gently into the mics resulted in the same distortion. But as I mentioned, below a certain volemume level they seem to work ok.

I do have a DMM i can use for troubleshooting.

It seems odd that two different mikes would develop the exact same distortion.

Is anything else in your signal chain different?  Can you post a clip of the distortion?

Hey Matador.
Here is link to where you can find clips of the distortion:
https://www.dropbox.com/sh/2x5g3hi086jef2u/AABqSkw00FuOJOAWRocn55lJa?dl=0

Could it be caused by the preamp?
I am running the mics through a pair of BAE 1073MP into a Apogee Symphony I/O.

Thanks for taking the time to help me out!

Those distortions sound like they are only happening on the hardest hits (every third it sounds like).

Does your DAW show the recorded clips exceeding 0 DBFS?  If not, can you check your bias voltage?  Is it still at -1V? 

They´re nowhere near 0dbfs.
I´ll check the bias when I get a chance!

Also, today while recording soft acoustic guitar with the mics I noticed that they have an inherent noise. I didn´t notice it before when I was recording loud sources, but the noise was quite easy to hear when recording soft instruments.
Is that to be expected from these mics because of the tube design, or is it caused by something in the mic?

Tube condensers are noisier than other designs, but noises can come from many places.

Can you describe it?  Or post another clip?

Hi all,

quick question here: Is it possible to use a cheap Chinese k67-type capsule in a 251E build for testing purposes before attaching an expensive CT12 capsule? I don't see any reason why not.

Cheers,
Waldemar