[FEELER] C12 Clone Project

[Matador]

How about the current production Electro-Harmonix 12AY7-EH / 6072 Gold(pin)?

This is the tube I'm using in the first prototype.  It sounds fine, but I've found it needs to burn in for a good 72 hours before the noise is acceptable.  In fact the first tube I left for a week in my Sovtek MIG100B bass amp.

 

[micaddict]

Duh, in hindsight you did mention the EH 6072. Sorry. Was it the Goldpin version (or did you already state that, too; I couldn't find it)?

 

[chunger]

pitchers!

 

[micaddict]

;D

 

[micaddict]

Anyway, regarding those EH tubes, here they are. Both versions. For those interested.
http://thetubestore.com/ehx12ay7.html
http://thetubestore.com/ehx12ay7g.html

 

[JessJackson]

Chunger, is that the headbasket you had fabricated for this build?

 

[HellfireStudios]

That is actually a stock headbasket bought from Dave Thomas at Advanced Audio. All of this was covered earlier in the thread.

-James-

 

[chunger]

Stock t14 is en-route from Oliver at AMI for testing.  I wonder what the sonic differences are generally with a larger transformer iron (like the early C12 variant).

 

[poctop]

Stock t14 is en-route from Oliver at AMI for testing.  I wonder what the sonic differences are generally with a larger transformer iron (like the early C12 variant).

in a very short short story ,  the bass frequency range overload point is extended with larger core ,
Best Dan, 

 

[micaddict]

Yep, see reply #191. 

Now, who is willing to tell the long story?

 

[Matador]

Yep, see reply #191. 

Now, who is willing to tell the long story?

I was thinking that the plate coupling cap was purposefully chosen a bit on the small side (0.5uF) in order to reduce the bass response.  I have a 4.7uF on my Apex 460 and it has a TON of bass response!

Anyone know the transformer specs on the original?  Like how many Henries, DCR, etc?

 

[Melodeath00]

Is it the original "big T14" that has extended bass, or the big Henry Radio that has extended bass?

 

[micaddict]

Both the Hiller and the Henry Radio are much bigger than the Haufe.

And here's a quote from Oliver Archut that I just found:

All three historic x-formers are fairly well designed and do not distort in the tube mic amplifiers range, or better the amplifier distorts before the x-former.
The Henry Radio as well as the T14 go pretty flat from 30 to 20k with +0/-1dB and the historic T14/1 has a response of 60 to 15k.... Due to FM radio specs of the time!

From this REPforums thread that also has a short albeit interesting discussion between Oliver Archut and Klaus Heyne. Replies #21-23. Some info about capsules there, too:
http://repforums.prosoundweb.com/index.php?topic=16952.15

 

[Matador]

More pictures of Tim Campbell's CT12 installation.

Tim's capsule comes with pre-tinned wire stubs for all of the capsule connections.  It even has a nice flux shield on both sides!

Old capsule comes out, and a spool of 30 gauge wire comes out to make new capsule connections:

The new brass mount gets installed in place of the plastic Alctron original:

The new capsule installs with 4 REALLY TINY screws (find your smallest straight slot screwdriver, then find one smaller):

New wires are easy to attach.  This capsule has isolated backplates, so with this design, the two backplates must be tied together.  This can be done easily by just stripping a bit more of insulation from the wire, and let the extra bridge across:

Now the other ends can be trimmed and soldered to their respective teflon posts:

Now that the soldering is done, the shield can be taken off.  This capsule is gorgeous!

Before I put the head basket on:  I want to try Chunger's de-meshing out for myself.  Pull up  bait of the seam:

He's right:  once the solder blob is trimmed off, the two inner layers come off as they are just press fit in.  Once the mesh is taken out and all the sharp little whiskers pushed back down, we are done!

Success!

The next stop for this mike is the studio!

 

[mateus]

OMG!
This looks sexy guys... Going to my list for sure!

Quickly off-topic:
The Manley Reference and the Rode K2 are CDDA?

 

[chunger]

Picked up the prototype from Matador today and we have it up and running in the studio with a NOS GE6072a tube provided by Christian Whitmore.  He doth not mess around with his tube selection and more importantly rejection process.  This tube is stable and quiet as a mouse right out of the gate.  Current configuration is Tim Campbell's stock CT12 capsule, and Cinemag 2480 transformer.  Oliver's stock T14 is en-route for testing.

I always expect to do a fair amount of tweaking, but this mic in its initial configuration is sounding fantastic right out of the gate with the polystyrene caps at c10, c11, c13 and the polypropylene .5uf cap @ C12 position.

Of note was the useful amount of bass present in the mic.  Compared to the fine CCDA sample microphone (modded Apex 460) that matador supplied to the studio for testing (Advanced Audio capsule/transformer), I find the current prototype a bit smoother overall. . .  a bit more "real" and silky in the way it handles high frequencies, a bit more forward in the midrange. . . perhaps not as fast in the transients.  It sounded particularly stunning going to 2" tape.

Everything seemed to scream "expensive mic" and so it should. . .because, well, it is an expensive mic   .  Note, we were testing as mono drum drum mic (center overhead) upon initial test.  I left the mic in studio so the engineer can get a feel for the current configuration before we try a few other things.  I'm thinking to try closer-to-original pio caps at c10, 11, 13 and 1uf value cap at C12, the AMI t14 transformer.  At this point, it's really just trying stuff for the sake of trying stuff because when it really comes down to it, upon initial impression, there's not much I would see to change.  Perhaps getting a nice, original C12 in the studio as a direct comparison would inform some more tweaking, but those probably had quite a range of flavors as well.

I am really excited about this project.  I can only imagine how awesome this mic will sound w/ a yellow PCB.

 

[micaddict]

How's the structural integrity of the stock grill after the two mesh layers have been removed?

Also, with the quiet tube and circuit taken care of, could you try a less ideal recording surrounding (regarding interference), please?

 

[Matador]

How's the structural integrity of the stock grill after the two mesh layers have been removed?

Also, with the quiet tube and circuit taken care of, could you try a less ideal recording surrounding (regarding interference), please?

I was worried about this too:  however the finish plating on the outside mesh makes it very strong.  I pushed in on it and couldn't deform it.

The mike PCB has dedicated bonding to ground at the XLR jack, and also to the side rails.  I measured zero ohm between every point I tested and pin 7, so I think the shielding is excellent.  I also heard no change in noise after the head basket mesh removal.

 

[micaddict]

Thanks!

 

[desol]

Perhaps getting a nice, original C12 in the studio as a direct comparison...

Yap...