Official C12 Clone - Build and Support Thread

[ln76d]

Something between "sweeter, deeper, more 3D" and just better.
I modified many microphones for single layer mesh and never had problems with hum.
Also tested original C12 headbasket and also no problem.
If you have hum problem, try to improve mesh connection as also overall ground connection.
Another thing - try different input connection - without grounding capsule.
That works really better in case hum problem, even if theoretically it shouldn't be better.

 

[Matador]

There shouldn't be much difference from a hum perspective, as the wavelength of typical 60 cycle hum is astronomically high.  Even the 1/4 wavelength frequency of a 1mm opening is many hundreds of GHz, not an issue in a microphone.

However from an air-pressure perspective, I've always noticed big improvements when removing inner mesh layers and going single layer with bigger grill spacing.

 

[ln76d]

Fully agree on both if i understand correctly

I think that some people have a bigger hum with single layer (after removing the rest or when making its own) because there's no proper ground connection, between body parts.
Another thing is input topology - good test - try grounded and not gorunded capsule without headbasket at all
It's a big difference between both, so there can be also when body (or just mesh) isn't properly grounded.

Definately more open mesh, more acoustically transparent.

 

[Alexandru marian]

It is really strange as it seems to be decently well made. It made from a large siever. Not nearly as open as the akg!  One rectangle folded to cylinder and soldered, then a circle soldered on top as lid. It overlaps the mic body very tight for 1cm, i need to twist it in place and the wire ends scratch the body all over.  wrapping this bottom connection area in alu foil doesnt help so it has plently of contact.  What helps is to cover the lid with a circle of alu foil. Like this the hum halves in intensity but it is still far away from the neumann head.  That one doesn't even come super tight over the pipe but as soon as i drop it in the hum vanishes.  You can hear the 3 versions here

Soundcloud.com/user757801519/grilles

 

[Carl Cress]

This is still confusing as the v3 schematic indicates the front backplate connects to C13, not R15.
I think an updated schematic to match the V1.4A board would be helpful. 

As I am using Tim Campbell's CT12 capsule should I still bridge the backplate terminals together as this is not shown in the schematic?

Thanks.

Now I'm confused again. And also I have the same question in regards to the bridging of the backplates (CT12)

 

[Carl Cress]

Needless to say I think that the CT12 capsule wiring for the V1.4a version PCB should be updated or have a clear pictorial addendum so that there isn't any confusion. Most of the symbols in a schematic are familiar to most, even those new to building but the capsule symbol in the schematic is not and thats where my confusion comes from. After careful review of my V1.4a PCB, the build pictorial  and the V3 schematic it would look like the front backplate does come from C13 and although Chunger's pictorial shows shows the backplates bridged on the CT12 I'm still left wondering that the back capsule are insulated from each other for a reason and shouldn't be bridged. Am I overthinking this?

 

[ln76d]

Do you have two wires for each backplate connection oor just one?
If one, it should be obvious, if two - take multimeter and use beeper to see is there connection between both.

 

[Carl Cress]

Do you have two wires for each backplate connection oor just one?
If one, it should be obvious, if two - take multimeter and use beeper to see is there connection between both.

Ok, Here's the way I understand it in the physical sense (soldering points).

Front Capsule to the ground (ground side of C10 on PCB)
Front Backplate from C13 (after R15)
Rear Capsule  to R16
Rear Backplate to R14

The V3 schematic (page 1) shows separate points for each backplate (C13 and R14) but the PCB only has one labeled(BP) after C13. So do I just use one wire from C13 to both backplates (bridged) or do I run 2 separate wires from C13 and R14 and bridge or leave unbridged? At $550 CAD a capsule I'm nervous.... and 2 solder points away.

Capsules haven't arrived yet. I just want some clarity so that I can install them without issue. Thanks for the help.

 

[Matador]

Just follow the connection indicators on the PCB itself: don't worry about the nearest caps/resistors.  The nodes are labeled FC, RC, and BP for you, right next to the proper node.  Just put a wire from each one to each place on the respective capsule.

For bridging:  the C12 was designed to utilize a single backplate capsule.  If you use a dual-backplate capsule, they still must be tied together:  either bridge them right at the capsule (my preferred way), or run two wires, one from each backplate, to the single BP connection.

 

[Carl Cress]

Matador, you are a gentleman and a scholar. Thank you for your patience.

 

[pundit]

I bridged the backplates at the CT12 capsule and ran a single wire to the point labelled 'BP' on the PCB which is C13.

The mic is up and running although with a temporary JJ 12AT7/ECC81 tube installed until my GE 6072 arrives from Bowie.

I'm not a big fan of the JJ 12AT7 as I found it brighter and not as smooth as a Mullard 12AT7 I have compared it to.

Even so the mic shows promise but I'll know for sure when I fit the 6702.

The Cinemag CM-13114 transformer is a quarter of the size of the transformer fitted to my Bock 251.

A transformer swap may be another area I might  look at down the track.

Ok, Here's the way I understand it in the physical sense (soldering points).

Front Capsule to the ground (ground side of C10 on PCB)
Front Backplate from C13 (after R15)
Rear Capsule  to R16
Rear Backplate to R14

The V3 schematic (page 1) shows separate points for each backplate (C13 and R14) but the PCB only has one labeled(BP) after C13. So do I just use one wire from C13 to both backplates (bridged) or do I run 2 separate wires from C13 and R14 and bridge or leave unbridged? At $550 CAD a capsule I'm nervous.... and 2 solder points away.

Capsules haven't arrived yet. I just want some clarity so that I can install them without issue. Thanks for the help.

 

[cariocaman85]

Hello,

I was wondering, what about adding voltage regulator circuit to Bias output and B+ output?
would it be good or totally useless?

(I'm not using the alctron casing psu, but a bigger one)

thanks

 

[tonzauber]

The Cinemag CM-13114 transformer is a quarter of the size of the transformer fitted to my Bock 251.

A transformer swap may be another area I might  look at down the track.

I you look at the original Haufe T14/1 that was used back in the days ,(except for the very first batches, which also used a different capsule revision with a different resonance point), and that is still available today, you will see it is a tiny tiny transformer.
Sometimes size does not matter.
More important is, that the whole system is well balanced - in case of second revision CK12, C12 circuit and T14/1 it works wonderful.

 

[micaddict]

Sometimes size does not matter.

Many will be so happy to hear this. 



Hey, but what if you want to record, say, the lower registers of a huge pipe organ?

 

[tonzauber]

Many will be so happy to hear this. 



Hey, but what if you want to record, say, the lower registers of a huge pipe organ?

then use a small diaphragm "real" omni microphone with a transformerless output stage
You can (or at least, in the past you could)  order the 4006TL from DPA with a lower cutoff frequency of 5Hz

 

[pundit]

Yes I know the C12's had several transformer changes over the years.
I was just really thinking out loud. 

The Bock 251 has a big low end, smooth mids and silky top end which sounds great however I don't want this C12 clone to totally emulate the Bock.

I'm looking for a little less lows and a bit more more euphonic sheen in the highs with this build but without any nasties.
Once the GE 6072 arrives I'll know if we've achieved that.

I you look at the original Haufe T14/1 that was used back in the days ,(except for the very first batches, which also used a different capsule revision with a different resonance point), and that is still available today, you will see it is a tiny tiny transformer.
Sometimes size does not matter.
More important is, that the whole system is well balanced - in case of second revision CK12, C12 circuit and T14/1 it works wonderful.

 

[micaddict]

then use a small diaphragm "real" omni microphone with a transformerless output stage

True. Nothing will beat a pressure mic in that regard.

But that's cheating.  ;D

 

[cariocaman85]

Hello,

I'm currently trying to build another C12 with high end parts (capsule, tube, capacitors, resistors, regulator, etc).

I bought a big psu case and I'm trying to optimise the power supply with the space I have left.
I'm wondering about adding a Schaffner EMI filter in front of the transformer (custom wired).
Do you think it's wise? What would be the Amperage needed in that case?

By the way, regarding the bias supply, I ran over this link http://www.acoustic-dimension.com/DHS-modules/DHS-active-bias-supply-ABS.htm
Do you think It could be implemented in the circuit and would it have any benefit to do so?

Thanks

 

[Matador]

Wow! 100 pounds for a bias supply?  I am in the wrong business.    In terms of the EMI filter: are you having EMI issues?  Can you describe the problem you are trying to fix?

As to benefit of a separate bias supply, you should try it out.  It would make swapping tubes much easier.

 

[cariocaman85]

I 'm not having particular EMI issues, it's just that I don't know which perturbation can occur in the future. The more the power line is cleaned, the more the PSU should be efficient, I am right? Or does it have bad sides too?

Regarding the bias, yes it is expensive... But I'm willing to pay if it could benefit to the sound. If it is good only for swaping the tubes then I have no need for that, as I intend to keep the 6072.
I understood that it could help regulating the bias and reducing the ripple, but maybe it is just audiofool... 

I have already built 2 of your C12 design with TC capsules and they're absolutely fine! I'm just wondering what I can do to go another step further, as I have more space in the PSU case.

Thanks

Remi