UPDATE:

We are now on revision 1.2 of the C12 pcb set.  Only the slightest of changes was implemented on the revision.  The board was lengthened by .060" to give slightly more length to the output capacitor slot.  The V-cap 250V 1uF OIMP type capacitor now fits without mods.  Since the kit-supplied Erse units have been working superbly in stock .56uF and 1uF options, I have not had a chance to test these super-expensive caps that are likely more snake-oil than actual "sonic gold" in our application.   There was discussion about extending the PCB length all the way down to the base of the mic to facilitate easier mounting of the AMI or Cinemag transformer, but recent tests of the clone against vintage original early type C12 leave the question open about whether the larger core early-style transformer may be a better performing setup overall.  Inquiries to Oliver at AMI about possible development of such a reproduction transformer have gone unanswered so far, but I can try Cinemag and other capable transformer specialists to see.  Anyways, the short story is I would like to leave enough space at the bottom of the mic for the larger core transformer should that ...

New products are in the pipeline:

1.  "prototyping" pcb set for the HT-11A microphone.  This board is similar to the C12 PCB set but has no traces except for the tube heater supply voltage.  Teflon standoffs in press-fit configuration at the top of the mic will allow for traditional turret-board style wiring of C12, ELA M251, or any number of other mic configurations desired.  For those who would like to experiment with a point-to-point type tube mic build, this is a clean platform to do so in the HT-11A body with minimal fabrication and fitting of parts.


I put Cinemag transformer inside of the transformer case that came with the microphone, and I feel that this option should be preserved for future iterations. Seems more eloquent than using ties, IMHO....

Also, regarding the new board, there is probably no reason to have traces for the heaters on the boards. Simply run twisted cables right up to the tube. Keeping the high current heater leads off the board makes sense, at least theoretically.

Finally, I'm glad to see that the teflon standoffs will be press fit. I modified the current boards to isolate the high impedence part of the circuit from the board, and the difference in sound is subtle, but real. The modifed mic seems to have slightly more body/bass. The mic now sounds more [insert your favorite audiophool superlative here].

Thanks again for your great work!


Another idea/request: could you make a version where this type of tube socket could be used?

http://angela.com/chinapremiumninepinceramictopmounttubesocket.aspx

and maybe one where a 7 pin socket could be used (for experimenting with 6AK5):

http://angela.com/sevenpintubesocketpremiumceramicsilver.aspx

Thanks for your consideration.

-Scott
« Last Edit: October 11, 2013, 08:38:29 AM by scott_humphrey »

chunger

New prototyping pcb is in stock and live on the webstore.  Note, the circuit will need to be wired point to point on this board.  Definitely not for beginners.

DIY photo documentaries consolidated here:  http://studio939.blogspot.com

New prototyping pcb is in stock and live on the webstore.  Note, the circuit will need to be wired point to point on this board.  Definitely not for beginners.

This looks good! A few questions:

1) Is the board the same length as the original board?
2) What is the diameter of the holes for the teflon standoffs?

Thanks!

Matador

New prototyping pcb is in stock and live on the webstore.  Note, the circuit will need to be wired point to point on this board.  Definitely not for beginners.

This looks good! A few questions:

1) Is the board the same length as the original board?
2) What is the diameter of the holes for the teflon standoffs?

Thanks!

It's about 60 mils longer than the original.  The teflon standoffs are designed for the Keystone 11308 teflon turret.

Winetree

I know this is DIY, but will there be any diagrams or pictures for the Point to point boards?
Or should we just follow the traces on the regular board and connect the points?
Can't see the back side of the board. Are the 1 big &  2 small  holes in the resistor squares connected?

Matador

I know this is DIY, but will there be any diagrams or pictures for the Point to point boards?
Or should we just follow the traces on the regular board and connect the points?
Can't see the back side of the board. Are the 1 big &  2 small  holes in the resistor squares connected?

Other than the heaters, there are no pre-defined connections.  You get to build whatever you want however you want it!

That being said, yes, if we find any keepers from a prototyping setup I'll be happy to post (and I'm sure Chunger will awesomely document) wiring diagrams using the prototype board.

How would this c12 circuit sound with something like a M7/K47 capsule in it..? They run on the same voltage so it should be easy, right..?

Matador

How would this c12 circuit sound with something like a M7/K47 capsule in it..? They run on the same voltage so it should be easy, right..?

Should sound fantastic!  The C12 circuit is essentially flat so you'll get whatever the capsule gives you (no Neumann de-emphasis or Telefunken filtering, etc).

Thank you for the respons.

Interesting. Have you tried such a combination? Anyone..?
« Last Edit: October 16, 2013, 09:02:22 AM by Jkidazz »


Matador

Thank you for the respons.

Interesting. Have you tried such a combination? Anyone..?

Not that I have seen.

I'm guessing people building C12's aren't looking for that kind of sound.  C12 has a very wide response with a response peak way up in the stratosphere (like 10kHz).  It gives it a very "airy" and "hi-fi" sound with little midrange emphasis.

This is the opposite to the 47 type response, which has a midband peak from 500 up to 4-5K range.  Everything below and above this is flat to slightly down (as compared to the C12).  It's a totally different spotlight on the sound.

Thank you for the respons.

Interesting. Have you tried such a combination? Anyone..?

Not that I have seen.

I'm guessing people building C12's aren't looking for that kind of sound.  C12 has a very wide response with a response peak way up in the stratosphere (like 10kHz).  It gives it a very "airy" and "hi-fi" sound with little midrange emphasis.

This is the opposite to the 47 type response, which has a midband peak from 500 up to 4-5K range.  Everything below and above this is flat to slightly down (as compared to the C12).  It's a totally different spotlight on the sound.

Exactly. I don't care too much for the CT-12 capsule. It is a fantastic capsule, just not for me.

I like the sound of U47's, U67's and M49's. But the projects for them are way more complex and expensive.

The reason why this c12 build is interesting, is because it is very easy to build, and the instructions are very nice. Almost like Lego. I like that ;) The PSU-pcb comes with it, A BIG PLUS, and the tube used is way more ready available than say, ac701 and VF14.

This is why I am thinking in the c12-circuit with m7 capsule route.. Maybe it would turn out to be a very, very nice and allround mic. Maybe even better and more allround than some of the "classics"..? 8)


chunger

JJ Audio made a mic I believe it was their "Dutch" model which is very similar circuit to this C12 project and used an M7 capsule.  I remember being thoroughly impressed with the audio clips posted on that combination.  Truth be told, my engineer prefers the Neumann-ish sound much more in practical use, and I have a Beesneez M7 that I plan to try in this circuit once I have completed all of the obligatory and relevant  "proper" C12 tests that I need to do.

AHAAA!  My internet-fu is strong today.  I found the Gearslutz post.  This is a JJ Audio modded Apex 460 with Thiersch blue PVC capsule.  http://www.gearslutz.com/board/5977942-post38.html

There seems to be a ton of interest right now in the ELA M251 that by design was supposed to be Telefunken's answer to the NEumann studio mics. . . the circuit seems to try and tame the inherent treble spikes and such.  I suspect a lot of people would be well served to simply try a neumann-type capsule in this nice flat-response circuit.
DIY photo documentaries consolidated here:  http://studio939.blogspot.com

The Dutch is also with a CT12-type (of choice) capsule  ;)

Thank you for your insight chunger.


chunger

The Dutch is also with a CT12-type (of choice) capsule  ;)

Thank you for your insight chunger.

This particular JJ mic definitely used the Theirsch M7 capsule.  I remembered coming across these tracks when furiously researching the various HT-11A mods.  Not sure which Cinemag transformer it used though.  Also, it does not appear to have used 6072A tube.
DIY photo documentaries consolidated here:  http://studio939.blogspot.com

Yes indeed. But that is not "The Dutch" as a commercial mic, but a mic modded by JJ ;)

Sounds pretty cool.

Now that I have you. What is the biggest difference between buying a Kit like this and just modifying the original circuit?

Thank you

JJ Audio made a mic I believe it was their "Dutch" model which is very similar circuit to this C12 project and used an M7 capsule.  I remember being thoroughly impressed with the audio clips posted on that combination.  Truth be told, my engineer prefers the Neumann-ish sound much more in practical use, and I have a Beesneez M7 that I plan to try in this circuit once I have completed all of the obligatory and relevant  "proper" C12 tests that I need to do.

AHAAA!  My internet-fu is strong today.  I found the Gearslutz post.  This is a JJ Audio modded Apex 460 with Thiersch blue PVC capsule.  http://www.gearslutz.com/board/5977942-post38.html

...Jim Jacobsen (JJ Audio) is a very talented microphone builder/modder and a great guy!...I've reached out to him to see if he can lend further insight to the C12 circuit combined with K47/M7 capsule dynamic...
« Last Edit: October 16, 2013, 05:34:10 PM by kidvybes »

Cool!

I will be looking forward to hearing what he has to say.

chunger

Yes indeed. But that is not "The Dutch" as a commercial mic, but a mic modded by JJ ;)

Sounds pretty cool.

Now that I have you. What is the biggest difference between buying a Kit like this and just modifying the original circuit?

Thank you

Matador may be able to give better guidance on this because I am not the most technically versed person, but:

1.  PSU. . . ours is a full wave rectified setup with better filtering and superior components.  Cleaner/more robust in every way.  Bias voltage is handled identical to original C12.

2.  PCB quality is superior in materials and layout.  When cleanly assembled, sonic performance of the preamp circuit is uncompromising.

3.  Component choices. . . it is notoriously difficult to find parts that fit in the stock HT-11A layout. . . there is much more flexibility with our PCB for experimenting with different caps, etc.

4.  Yellow colored PCB's sound at least 37% more awesome than other PCB colors in blind test studies.  It is an undisputed fact  ;D

That being said, the stock Alctron HT-11A is one of the most popular modding platforms in existence and there is a TON of information available online detailing various ways to do it.  There are also many semi-custom mic companies that offer turn-key products that start out as Alctron HT-11A's in one form or another.
« Last Edit: October 16, 2013, 05:42:30 PM by chunger »
DIY photo documentaries consolidated here:  http://studio939.blogspot.com

hazmatstrat

Hi Guys,

The mic in question was a Apex 460 with an EF95 (6ak5w) The transformer was a 2461 NiCo transformer from Cinemag. The capsule was a Theirsch M7. The EF95 works well with this transformer. I used a Russian PIO capacitor.

I have used the Theirsch M7 capsule in a modified 251 style circuit (6072a) with amazing results.

When I set up the C12 negative bias to the grid , I use a trim pot and tune the mic and capsule for the best tone.


8) 8)


Jim Jacobsen
JJ Audio
JJ Audiomic.com