Official C12 Clone - Build and Support Thread

[Melodeath00]

Yeah, but we haven't forgotten you.
Good for us you ran into some trouble. 
Nah, just kidding. This sucks, of course.
But good to see you. 

Ha! Good to see some familiar people still here. I'm afraid my interest in DiY mics had to submit to my lack of time over the past couple years. In turn, I wasn't at the forum for awhile. I still have Max's kit for  a U47 that I never even opened, as well as an unused CT12 capsule.

Most likely moisture in the capsule .
Try sealing it in a bag with desiccant bags for a few days to absorb and excess moisture.

It could also be dirt in a switch or contamination from fingers or flux somewhere. Leave the mic turned on for a few hours and see if it disappears.

Thanks for the tips guys!

As a first step, I put the mic in its pouch with a couple of silica gel packets overnight. I just plugged it in to test again, and now I'm getting no sound at all. The PSU is turning on, and I can see the meters jump on my audio interface when I turn the PSU on (or when I power down and unplug the 7-pin cable), but I'm getting no signal at all from the mic. Again, the only thing I did was store it with silica gel packs overnight. I am thoroughly confused.

 

[vinylwall]

Ha! Good to see some familiar people still here. I'm afraid my interest in DiY mics had to submit to my lack of time over the past couple years. In turn, I wasn't at the forum for awhile. I still have Max's kit for  a U47 that I never even opened, as well as an unused CT12 capsule.

Is it Max's full kit with the body?  Any chance you'd want to sell it?

 

[Tim Campbell]

You may have a loose connection or a stray piece of solder floating around inside the mic.

 

[Melodeath00]

You may have a loose connection or a stray piece of solder floating around inside the mic.

That was it. Somehow a ground connection (on the 7-pin connector) became disconnected in the PSU. It must have been loose yesterday, causing the noise, and then fully disconnected overnight. Very weird. I re-soldered and everything is back to normal now. Thank you for the help!

Is it Max's full kit with the body?  Any chance you'd want to sell it?

Possibly. Yeah, it's the kit from a couple years ago with the Flea-made headbasket I believe. I literally never even opened the box Max shipped it in haha

 

[cariocaman85]

Hello,

What do you think about replacing polystyren capacitors (C10, C11, C13) with Silver Mica capacitors?
Thanks

 

[ln76d]

Bad idea.

 

[cariocaman85]

Thanks!
Why if I may ask?

 

[ln76d]

Because silver mica have tendency to microphonic more than polystyrene, because original unit used polystyrene (early versions ceramic caps) and MP at the output.  Polystyrene/styroflex aren't so hard to find, for 5nF can be anything between 4.7nF-6.8nF.
For the output definately MP (can be also PIO or MBM type) is the best choice.
Of course it's valid if you want get close to original unit as possible.

 

[cariocaman85]

I'm using styroflex and Vcap OIMP but I just wanted to know if Mica would be best as I saw them a few times in certain builds.
Thanks  for your reply, I'll stay with the polystyrenes then.

 

[Matador]

I used silver mica in a few builds without problems - but I may have been lucky.  I never noticed any sound differences however compared to other cap formulations.  I think for filter caps it really doesn't matter one way or the other.

I would suggest to anyone who thinks their soldering may not be up to snuff take a look at micas, or NP0 ceramics (my current favorite), because they can tolerate soldering/re-soldering much better than styrene's.  They can also be cleaned with IPA without issue.

 

[Carl Cress]

I have built 2 of these mics. Mic #1 PSU was calibrated and tested with all polar patterns seeming to be  working although the back sounded darker. Completed mic#2 PSU calibrated, tested for signal and polar patterns seem to not be working, noticeably more gain and crackling when changing pattern selector. I thought I would begin diagnosis by isolating the issue to either the mic or the power supply by connecting mic #1 to PS #2 and crackling was gone but no difference when selecting patterns. Now mic #1 and PS#1 no pattern (may have been that way at first). I have quickly checked the pattern selector switch, wiring to PCB, connections to 7pin XLR out and & 7pin IN to mic PCB and all seems correct. It would seem as though I have no signal from the back of the capsule (hence the perceived darkness) which correct me if I'm wrong would not allow any pattern changes if the rear capsule is not active?

Where to start? Ground issue?

-Tim Campbell CT12
-AMI T14
-GE 6072 5 Star

 

[Tim Campbell]

Carl if I had to guess I'd say you have some shorts or cold solder joints somewhere in your mics. Try reflowing all your solder and clean the pcbs of any flux to check for solder bridges.

 

[Carl Cress]

Carl if I had to guess I'd say you have some shorts or cold solder joints somewhere in your mics. Try reflowing all your solder and clean the pcbs of any flux to check for solder bridges.

Thanks for letting me bounce that off you Tim. I suspected a back capsule and I was half right. Your reply got me to go back and check continuity from the PCB to the back plate bride. Regardless of the appearance there was no continuity at the screw but there was at the solder point. A touch of solder and all fixed. I guess  that in my haste i was quickly switching the selector on the other mic and not waiting for the slowness of the patterns engagement (I guess it's a few seconds for the newly selected pattern to engage). Now it's time to enjoy!

 

[chunger]

I was gonna recommend checking the capsule connection tabs, but Tim Campbell's capsules come with the tabs pre-attached and I assume tested with the same tabs in place, so I didn't think that would be a likely failure point!  Glad it is sorted out 

 

[Matador]

Someone asked a question about how to use capacitors to test in lieu of a capsule.

Two small caps, each in the range of 47pF to 100pF should be used.  68pF is a common value you can find.  The formulation of the caps isn't terribly important, however stay away from styrene for testing as they tend to be highly microphonic.  My favorite caps for testing are NP0/C0G ceramic disc (MLCC) capacitors because they can be re-soldered many times without damage.

Solder the two caps in series:  the two 'outer' legs become the front and rear capsules (respectively), and the inner connection between the two becomes the backplate.

 

[wave]

Thanks Matador!

 

[cariocaman85]

Hello,

I recently built another C12, with the yellow PCB for psu, but point to point inside the mic.
It is working (audio passing) but I have a hum issue.

My grounding scheme is:
Electrical 0V and grounding separate, but can be linked via a lift switch on the PSU.
Grounding is connected to earth, power transformer shielding, Metal Box of the PSU, shielding of the cable between PSU and mike.
I soldered the shielding of this cable to the metal connectors (not the pins) so it is making contact through the cable and reach the external shielding of the metal microphone's body. In the cable, the seven pins are for B+, Bias, Pattern, Heater, Audio+, Audio- and 0V. Shielding is carrying the ground (separate).
There is only one connection between the grounding and 0V, which is at the lift switch.
When testing with a DMM, there is continuity from the headbasket to the earth pin of the PSU, but none to the 0V if the switch is lifted.
When testing with a DMM, there is continuity from the headbasket to the earth pin of the PSU and to the 0V in the mic and the PSU, if the switch is activated.

When the PSU is Off, the mic isn't plugged, mic cable isn't plugged, I can hear no hum wether the switch is lifted or not.
When the PSU is Off, the mic isn't plugged, mic cable is plugged to the PSU only, I can hear hum when the switch is lifted, but no hum when the switch is grounded.
When the PSU is Off, the mic is plugged, I can hear hum (more I think) when the switch is lifted, but no hum when the switch is grounded.
When the PSU is On, the mic is plugged, I can hear very very loud hum when the switch is lifted, and a tiny hum when the switch is grounded.
When the PSU is On with a 180K resistor between B+ and 0v, the mic isn't plugged, mic cable isn't plugged, I can hear hum when the switch is lifted, no hum when it is grounded.

I made these tests listening through a SoundDevices portable mixer on batteries, which works well otherwise.

What do you think my problem could be? I've been searching all day... :-[

Thanks for your input!

 

[cariocaman85]

By the way, all my readings are good:
B+ 120v
Bias-1V
Heater 6,3V

 

[cariocaman85]

No one?  :-[

 

[cariocaman85]

Here is my grounding scheme.
Please tell me if you see anything wrong...

Thanks!