Official C12 Clone - Build and Support Thread

[Matador]

Keep in mind that running 12.6VAC means 16.4VDC after diodes, which means you are dropping 10V @ 350mA which is ~3.5W dissipation in the regulator.  If you used my recommended heat sink in the BOM it should keep it tolerable even with no airflow in the case, but you might want to check it out after it's been running for a while and see how hot it's getting.

 

[bavabasra]

I used the recommended heat sink. It should handle 3.5W nicely in well ventilated setting.
Thanks again

 

[Studiogearlover]

Hey Guys!

Hope all of you are well. Finally, I am finishing this project and the last bit I am stuck with is the output transformer pins...I have a vintage UTC which will fit here nicely, however, it has 5 wires on it.

According to the description TOP side of the transformer has:

Red is the B+, Blue right next to it is the Collector. There is also a brown lead next to it and I do not know what it is?

The BOTTOM of the transformer has a green "base" and a black "GND" lead....

could any of you please advise me which lead goes where on the mic PCB? and which one should I leave out?

I'd really appreciate it. 

THANK YOU !

 

[Matador]

There is probably a center tap, likely on the secondary.  No data sheets online anywhere?

 

[Studiogearlover]

Thanks Matador,

I only have these on the paper came with it

Red>  B+
Blue> Collector
Brown ? (could be another collector?)

The above are on the top of transformer.

Green> Base
Black> Ground

This is on the bottom side.

I have attached some pic's of this....maybe I should leave out the brown...but not sure which other lead goes where exactly...

Thanks a lot!

 

[Matador]

Is there a part number on it?

Having two collector wires and a B+ implies that this is a push-pull output transformer.  Can you measure the DC resistance of the primary between the blue and brown wires?  Also the secondary (green and black)?  You might send a PM to CJ, as he might know about it off the top of his head.

 

[Studiogearlover]

Thanks Matador,

Primary

135.6 Ohm Red (B+) and Brown,

290 Ohm Blue (Collector) and Brown

160 Ohm  Red ( B+) Blue (Collector)



Secondary

2.5 Ohm Black (Ground) and Green (Base)

Not much info on this, its labelled SO10, found this on the catalog from 1964

Primary Imp.              4000/ 2000 CT
Secondary Imp.          8/16
Primary Res. Ohms    290
Secondary Res. Ohms  2

Imp. Ratio is fixed 1250: 1, Any impedance between the values shown may be employed.

maybe that is not usable at all..?

 

[Matador]

There may not be enough winds to give enough primary inductance to pass a reasonable amount of low frequency content, especially from a high source impedance in combination with a low secondary impedance (e.g. a 600 ohm input to a mike preamp).  You can give it a try though.

You want to connect the primary between brown and blue, and take your output from black and green.  Leave the B+ line unconnected.

 

[Studiogearlover]

Thanks so much Matador!

I have just soldered in. Microphone sounds really good BUT, a HUGE amount of buzz and hum coming with it. When I unplug the PSU, the buzz is fading away slowly.

This means something is short right? hmmm...i will poke around and see if i can find it...maybe the

I have followed this Category 5's schematic...cathode resistor and bypass - 1.8K and 20uF/6V (radial) - connect between TK1 (or 2) and any ground point on PCB bottom.

If i connect this to ANY ground point on the PCB, will this not short something else? hmmm.....nearly there!

 

[micaddict]

Is the headbasket (properly) on?

 

[Studiogearlover]

yepp, re checked everything.

A HUGE amount of electrical hum is coming. I have measured 276V AC between the B+ and the mic chassis (ground)...is this a normal thing? or this AC voltage is creating the hum?

......interesting thing:

I have put ob the mic body too fully. Weird thing is that the hum disappear if I connect the mic chassis to the ground point on the pcb BUT the audio signal has gone too with the hum...

what the heck?

Could you please guys confirm that I have done this right:

Pin1 on the tube  -----> 100uF cap goes to the same ground point as the Pin 3 cathode resistor and cap?

all these goes to the ground point right?

Tube pins 3,4,5,6,7,8,9 to ground getting continuity on my DMM.....ouch...this should not be OK at all...

DAMMMMNNNN Please...HEEEEELLLPPP!!!

 

[alkfalf]

Hi,
I'm new in this forum and I also have buz problems with 2 C12 I built. It's 2 micandmod kits with Tim campbell's capsules. I read some similar problems in this thread but I don't find a solution for this issue.
Mic1 PSU1 or Mic2 PSU1 make a hum noise like 50hz but it's not a great problem.
Mic1 PSU2 or Mic2 PSU2 make the same kind of noise + a higher buzz (cf audio). This adding buzz is a problem.
It seems the problem is with the PSU2.
PSU2 is the same as PSU1 but not the same transformer (cf photo).

"headbasket - PSU ground" impedance : 0,4 ohm. with both PSU

Thanks a lot to help me!

Audio is there :
https://www.dropbox.com/sh/4r3q8jky36rse4h/AADdWIrRz58uypailex26vY1a?dl=0

 

[rmburrow]

Going from the V1.3 schematic:  if you want cardioid only:

PSU: eliminate R11, C11, and the switch
In the microphone: eliminate C11 and R16.  You can leave the rear diaphragm floating (if your capsule has one)

If you get random noise when floating the rear diaphragm, try tying the unused diaphragm to the center  plate...the charge on both elements is equal and tying it off may cut down random noise from a floating element....

 

[alkfalf]

I don't know if it's a random noise problem. I think it's a constant noise in both cases but the higher noise with PSU 2 doesn't allow to make a clean record. More over, this solution is for a cardioid only microphone? I mainly use my mics in omni or wide cardio.
My question is : what could be the reasons why the PSU2 adds (with both microphones) this noise in the higher range (above 200hz)?

 

[alkfalf]

Hi,
I've tried to take the transformer of the PSU away. The noise decreases when I do that and vanishes when it's 10 cm far from the PCB.
Do you have an idea to keep the transformer inside the PSU ?? )
I take a picture of the location of the transformer in the post above.
May be the magnetic field created by the transformer is too close of the conds?
Thanks.

 

[Matador]

It's 2 micandmod kits

It's probably best if you can first figure out how to convince Yannick to support his kits.  :'(

 

[alkfalf]

Hi Matador,
Thanks for your answer.  Micandmod's boss wrote me in march that he's stopping.
So It's why I didn't contact him for this issue. More over it's not a fully micandmod kit anymore. I've had the mics for 2 years and I bought Tim Campbell Capsules last year to improve them. I was very happy with the mics on drums and with very close piano recordings but now I have a project with strings and cinematic Piano and I want them to use as room mics and I hear the noise in this kind of recording.
I think that, may be (but I'm not an electronics expert), the PSU transformer is too close from the components because when I move the transformer far away from the PCB, I hear less and less noise. One way of solving it is to keep the transformer out of the metal box (it will work like that for my next recordings). Else, I think to try to build a kind of faraday cage around the transformer? But may be someone has a smarter way to do?
I've ridden a lot of pages of this thread to find my issue and I understood  that it happened some troubles with micandmod. And even if I'm french like him and my name is Yannick like him, I would appreciate your help! Thanks

 

[rmburrow]

Hi,
I've tried to take the transformer of the PSU away. The noise decreases when I do that and vanishes when it's 10 cm far from the PCB.
Do you have an idea to keep the transformer inside the PSU ?? )
I take a picture of the location of the transformer in the post above.
May be the magnetic field created by the transformer is too close of the conds?
Thanks.

Try rotating the power transformer in the PSU box while listening for minimum noise?  Ground the transformer case with a short clip lead to chassis or ground common while doing this.

 

[micaddict]

And even if I'm french like him and my name is Yannick like him, I would appreciate your help!

LOL Any  more matches?  ;D

 

[alkfalf]

Thanks rmburrow. It's better but still audible for the first square transformer but the other toroiadal transformer is much too big for this box because of the other components.  But I will try to rotate the pcb too! thanks.

@micaddict : not so intimate with him to tell you but Yannick means John in Britanny (West field of France).... it's not a so rare forename...