Official C12 Clone - Build and Support Thread

[micaddict]

I know. 
You even had a famous tennis player with that name.
Come to think of it, quite a few younger French men may be named after him.

 

[alkfalf]

You are right! But the young french people don't know that Yannick Noah was a famous tennis player. Here, they think he's just a singer. )

 

[micaddict]

Yeah ...

To get back on topic, this is a great forum with lots of folks who are very happy to help. 
But it is understandable that Matador has somewhat mixed feelings about this one.

 

[alkfalf]

I understand

 

[Matador]

It's hard to imagine how two different transformers would give such drastically different results unless there was some construction or winding differences between the two.

The only thing I can suggest is:

1) Buy a replacement transformer - you might PM Chunger and see if he has any transformers available for sell

2) Maybe try and improve the shielding on the PSU case.  Remove the transformer, and make sure the paint underneath where it makes contact with the case has the paint scraped away.

There's little if any magnetic shielding on the stock transformer but it may help some.

For #2, also make sure that:
a) That the PSU ground node is properly connected to the chassis somewhere (this typically happens right at the 7 pin binder connector
b) that the IEC ground is attached solidly to the PSU chassis.

Maybe you can upload a few photos of these areas?

If you look at Chunger's photo's, you'll see this (on the right side):

Circuit ground goes to pin 7 of the 7 pin connector, which bridges up to the large metal tab (which is the 7-pin housing outser shell), then wire jumpers over to the same shell tab on the 3-pin XLR connector, which then gets tied over to pin 1.  All of these nodes need to be tied together.

 

[alkfalf]

Thanks Matador,
I red a lot of your post in this thread and I already checked the pin 7, and the pin 1 of the XLR.
Grind off the metal box under the tranformer with a dremel for a best contact. I even built cables with alligator clips to be sure about the contact.
I moved  the toroidal transformer away and I have no hum at all. I've tried to move  the other transformer away and the result is excellent too. No buz at all with both mics.
I will send you a picture inside the PSU soon but I can't do it this week because I'm recording.
I send you the picture of the modification. I know, it's a very ugly assembly ))

 

[lyricalgeek]

Matador,

Love this project and the ability to "hack" it into a 251 circuit (almost), but also love the greater granularity of the pattern switch.

Was looking over the original C12 schematic and comparing it to the 251 schematic and had a couple of questions.

C11 in the 251 schematic seems to be the path by which the RC passes it's signal on to the grid (with C11 blocking DC and allowing the AC signal through), is that correct?

Also  notice that the 251 shows the polarity voltage hitting the filter cap (C5) before hitting the resistor R16.  This differs from the C12 schematic where the polarity voltage hits the resistor R16 before hitting the filter cap (C11).  Do C5 in the 251 and C11 in the C12 circuit perform the same function?  Namely filtering the Polarization voltage?

I'm really striving to understand each part of this circuit.

thanks for all you have done for this community.

 

[Matador]

Which exact schematics are you referring to?  Can you link them?  Otherwise I'm not sure which caps are being referenced.

My version of the 251 is different from the original in that the original supported pattern switch right on the microphone.  The way the original did this is quite different from my version, as I wanted to retain the 12 polarization step scheme that the C12 uses right on the PSU unit itself.

 

[lyricalgeek]

Which exact schematics are you referring to?  Can you link them?  Otherwise I'm not sure which caps are being referenced.

My version of the 251 is different from the original in that the original supported pattern switch right on the microphone.  The way the original did this is quite different from my version, as I wanted to retain the 12 polarization step scheme that the C12 uses right on the PSU unit itself.

Sorry guess I could have been more specific.  I'm referencing your version 1.4 C12 schematic from post #1 in this thread, and your latest M251E conversion schematic  from post #2301.

http://musicalsparks.com/images/c12/c12_schematics_1v4.pdf
http://musicalsparks.com/images/251/m251_ht11a_schematic_only.pdf

 

[Matador]

Sorry for the delay.

In the 251 schematic, C11 AC couples the front and rear diaphragms together - otherwise you only get one half of the capsule in omni mode.

C5 is indeed a filter, however if it's moved post R16 it becomes a pad due to C11 and the input capacitance of the tube.  Given it's 5nF it becomes one hell of a pad too.

 

[ln76d]

For both circuits, especially with use of bright capsules, C414 input configuration works nicely (C2 from 414 schematic  isn't needed).  If both PCBs allow that type of wiring then I recommend to try

 

[shot]

I've used C12 kit and some guidelines from this thread (thanx to Category 5) to build a perfectly working ELA M251

Since I had a new camera I went to take pictures of every step.

I've posted it here - https://groupdiy.com/index.php?topic=66993.0

Thanks goes to Matador, Chunger, Category 5 and all the rest of you who made this build possible!


Luka

 

[Spencerleehorton]

plugged this C12 mic in the other day, been using ELAM 251 and U67 for a while.
My C12 is really hissy!!!????
Is there a mod or a fix to reduce the hiss of this mic?

 

[sr1200]

Mine is pretty dead silent... you sure there aren't some problems in there somewhere or perhaps a bad tube?

 

[Patrick from Davis]

You are right! But the young french people don't know that Yannick Noah was a famous tennis player. Here, they think he's just a singer. )

Or the Dad of an NBA player...

 

[ribor92]

Has anyone tried putting the PSU in something like this?
https://www.don-audio.com/tube-mic-power-supply-enclosure-MPS-700

Would it be possible? It would look so damn good! I live in europe so it woul be a pretty good deal to

Edit: just saw another poster using what looks to be the same chassi! So thats good, would be interesting to see how one have placed the transformer in there!

 

[TillM]

It will work cause martin (rainton) do this chassis for us with multiple pcb options.
You can also buy it on the white market.
Aaron just purchased it from martin.

 

[ribor92]

It will work cause martin (rainton) do this chassis for us with multiple pcb options.
You can also buy it on the white market.
Aaron just purchased it from martin.

Thanks! That is so awesome! Any recommendation on which transformer that will work well? It would be the only thing left to replace from the alctron stock one. 

 

[vinylwall]

SOLD

 

[MatthiasAnton]

Hi everyone,

I just recently finished a C12 build with a GE 6072 tube. The mic has two problems that occur about 80% of the time and only in combination, never separately :

1) when switching between patterns, the audio output becomes noisy (wind noise) for about 2 - 3 seconds, then the noise fades away.
2) the back diaphragm sounds very dark compared to the front. When the problem does not occur, both capsules sound very similar. The capsule is a Tim Campbell CT12.

Has anyone ever experienced similar problems or knows what could be causing these issues?

Thank you all!