Official C12 Clone - Build and Support Thread

[JessJackson]

I know I've posted it here before, but it bears repeating.

You can get a 'poor mans' de-emphasis by using the ELA M251 plate cap, just picking one of higher value.  If you place a small ceramic cap right where the transformer coupling cap connects to the tube plate (the other end grounded), you can make a simple low-pass filter.  Standard ELA M251 value is 100pF (about 19kHz rolloff), but 470pF will give a 10-12kHz roll-off, and a 1nF will give a 7-8K rolloff.

Picture of where cap goes is here:

So if you find the K67 type a bit too shrill, try this cap as a very cheap alternative/remedy.  I put a 470pF on a switch in one of my prototypes and it was useful on certain sources.

This works well but i would use polystyrene (styroflex) over ceramic. sounds better.

 

[micaddict]

Yes, I'm looking forward to your thoughts on this...I too have been considering trying an M7 or K47 in the C12 build...why not think outside the box...

OK Dennis, but only if you do a CK12 in a U47 or M49, too..

Fair is fair.

 

[Tim Campbell]

Feedback Studio had for many years a real Telefunken U47 w/VF14  tube that had a CK12 capsule in it. For certain singers it sounded magical. Many people using the studio never noticed much difference between it and the other U47's.

 

[kidvybes]

Yes, I'm looking forward to your thoughts on this...I too have been considering trying an M7 or K47 in the C12 build...why not think outside the box...

OK Dennis, but only if you do a CK12 in a U47 or M49, too..

Fair is fair.

...well Henk, I currently have 3 of the MataChung C12 builds, so there's nuff room for experimentation, but only one MK-47 (currently waiting on Eric Heiserman's HK47) and my Poctop  D-49b/c sounds too sweet to touch...but yes, if the opportunity arises to acquire another MK-47, I would love to try that combo...

...so do we refer to these hybrids as "C47" and "U12"?...

 

[icemanaman]

This doesn't sound like a tube problem. Try cleaning everything and check for solder bridges.
If it's easy enough to swap capsules do so. The you'll know. As has been said here many times, capsules can easily sound dissimilar.

I have tried to keep the builds very clean, but just in case I cleaned once again today.
That did not make the difference. So I tried switching capsules, and indeed the tone follows the capsule.
Here are further observations:

I have two mics. One is RED and the other GREEN.
I think the RED has a faulty front capsule.
I swapped capsules between mics and the fault follows the capsule.

Here are my observations:
The GREEN mic is the one I think is OK.
RED clearly has some sort of fault.

When I switch the polar pattern on the RED mic, there is a loud noise.
Kind of like when you blow into a mic.. the sound of air hitting the capsule almost..
Could this be caused by the PSU? I forgot to change PSU to check...
It goes away after the polar pattern "settles" and the mic goes back to its normal noiselevel.

Talking about noise, the RED mic has noticable more noise than the GREEN.

The GREEN mic seems to be working normally in all patterns.
The only difference is that in Figure8 the rear capsule seems to have a little less body and little bit more high end.
I am not sure, but I seem to recall that this is quite normal for figure 8???

I think that the FRONT capsule on the RED mic must be faulty, because:
When in Cardiod it has less volume (about 3 db) and less high end than GREEN.
In Omni the front still has less volume and high end, but the BACK has equal-ish volume as GREEN back (high end on RED still being lower).
In Figure 8 the RED front capsule still has less volume and less high end, but the BACK is again same as GREEN in volume, but still has high end loss.
But also: when singing in the back of the mics, the RED actually has MORE body than the GREEN.

So bear in mind here that I was having the same kind of results with the same capsule in the GREEN mic yesterday. Today i swapped capsules and the tone follows the capsule... I have attached a picture of the recordings for illustration.
I tried getting a freaking wave sound file made.. But my new setup really wasn´t working with me today...

Any thoughts?


Aman

 

[Tim Campbell]

Switching noise, as I've mentioned before usually comes from contamination on or within the capsule. It seems the problems you mention are the capsules.

 

[icemanaman]

Switching noise, as I've mentioned before usually comes from contamination on or within the capsule. It seems the problems you mention are the capsules.

Thanks for you help and time Tim!

On the mic that works:
Regarding the Figure8 pattern having a little less body and little more high (basicly sounding a little bit thinner) at the back compared to the front, is this normal?

 

[saxmonster]

I'm not sure if its normal and I can't remember if its fig 8 or omni but one of them has the opposite phase of the other when in that mode.  Try flip the phase on your preamp and see if both sides sound the same as you flip the capsule.  Front has the phase one way but when to go to the rear capsule flip the phase switch and the should sound the same.

 

[flatresponse]

Hi,
sorry for the delay, but I want to switch in with you again,

I have nearly the same problems like you, icemanaman,
I have one mic A, that is working properly with the polar patterns, and has very good sound.
The next one, mic B, has (nearly ?) proper sound in omni - when no polar voltage is needed (0 Volt),
when it comes to cardiod, it´s getting "thinner", "narrower" - lacking bass, a bit queaky,
figure 8 even worse than cardiod "out of phase", "one leg connected".
I attach mp3s I recorded, to make things clear:
mic A:
https://www.dropbox.com/s/xniv9xb2p23ai8s/TEST%20C12%20I%20-%20A%20only.mp3?dl=0
mic B:
https://www.dropbox.com/s/wri2k2sgsfwyceu/TEST%20C12%20I%20-%20B%20only.mp3?dl=0

I have the same switching noise one mic B, but not n mic A.
@ icemanaman: have you tried to desolder front casule, just to see, whether it´s functioning at all ?
And, @ saxmonster: I´m not sure, you remove a "phasey" sound from a mono signal by just switching the phase.

Next I will do tomorrow, just to be sure, is switching capsules between body A and B.
If it stays with the body, it´s my fault.
So , wait and see
Best
Manfred

 

[saxmonster]

no the capsules are out of phase with each other, there is a slight difference between the front and rear until you flip the phase switch.  See if you can test it on your good mic.

 

[tskguy]

Hi all,

Please contact me via email if you find any capsule issue!  I stand behind my capsules and will be happy to fix any issues. Sorry for any trouble,,

Eric

 

[flatresponse]

no the capsules are out of phase with each other, there is a slight difference between the front and rear until you flip the phase switch.  See if you can test it on your good mic.

Are you talking about the diaphragms of the "wrong" mic?
Did I get you right with:
When speaking to the rear end of both mics in fig 8, flip phase switch in of the mics channels.
It sounds "in phase" then. Without phase switch it´s "out of phase"

I contacted Eric via email and he will help.

Manfred.

 

[stelin]

Hi,
I have built two MataChunger C12s. They have worked perfectly, but now my C12 #1 has developed a problem: It is losing steam! And worse, it does so in a random way.

I can’t find any pattern, but often when I fire up C12 #1 it has 4-5 dB lower output than my C12 #2. Sometimes they both work and have the same output. But more and more often they do not.

I have switched the PSUs, but the problem stays with the mic.
I have switched the tubes, and the problem stays with the mic.
I have switched the cables, and the problem stays with the mic.

When C12 #1 has a lower output, I think I can also hear that the low end is even lower (even when compensating for the volume difference).
There is no additional hiss or hum, so I don’t think it’s a current leak.

Have anyone else had this problem? Does anyone have any suggestions about what I should do to hunt down the problem? Any help would be appreciated!

I should mention that I’m using a RME Fireface UC with digitally controlled gain. I have even switched the inputs to the Fireface, but the problem still follows the microphones.

- Stefan

 

[Tim Campbell]

Does the sound of the mic  change with the lower output?
I would guess you have a bad connection somewhere, a short or you are collapsing the capsule.
Check all your connections and clean your pcb.

 

[stelin]

Thanks, Tim,

Dirt (current leaks) often results in hiss that comes and goes (I’ve been there). One suspect is in fact a cotton fiber somewhere that acts as a half-short (a resistor).  That can sadly be a result of an attempt to clean the board.

And yes, the sound changes when the output drops. I wrote that I heard that the bottom end was weaker, but one time it was the opposite: the treble was lowered.

All the voltages are spot on in both mics, and the problem remains when I switch the PSUs.
My next step will be to inspect and clean the board of C12 #1 again. If that does not help, I will switch the capsules, but I don’t think the capsules are to blame.

- Stefan

 

[Category 5]

You didn't mention whether tubes are related to the issue?  Do the mics use opposite triodes?

Is the problem independent of the psu?  Checked the pattern switch?

 

[Tim Campbell]

Stefan, there's probably no need to switch the capsules. Make sure that the connections to the capsule are good( The screws are snug and are making good contact) and inspect the membrane with headbasket removed when it's powered on to see if it collapses.
The sound of a collapsed membrane is very midrange-y with less top and bottom.
Check for cold solder joints and shorts to the body or headbasket.

 

[MicDaddy]

I had experienced a similar issue, and my diaphragms were collapsing.

Tim can I get a capsule??

 

[stelin]

Thanks, Category 5, Tim and MicDaddy,

Category 5: I did not think about that, but the mics use opposite triodes. Have to figure out the logic of that. I have another tube I can try.
Tim: A collapsed membrane could be the problem since I've heard both loss of treble and lows (and volume). Will inspect the capsule without the head basket.
MicDaddy: How did you fix the problem with the collapsed membrane?

What can I say? This forum is so full of helpful people! Feel like I have a lot of new friends, even if I have never met anyone of you in person. This is really the best side of the internet!

- Stefan

 

[Tim Campbell]

Stefan, first find out if that is the problem. If it is make sure you are not getting spikes in the polarization voltage because of something else. If your polarization voltage is 55-60v and the membrane is collapsing then you would have to send the capsule back to me ( I assume it is a CT12).
I will warn people that hot plugging (plugging in the cable while the power supply is on) CK12 type capsules while in fig8 repeatedly can sometimes damage a membrane.