Official C12 Clone - Build and Support Thread

[Matador]

Any advice? I have scheduled a recording session, last time I used the mic was distorting easily. I want to use it in this session.

If you inject a signal, it needs to be injected into the coupling cap (just like a replacement capsule).

A few things:

1) Make sure the scope probe is grounded against the mike frame properly
2) To eliminate the xformer, read the signal directly from the output of the coupling cap wrt. ground (after C12, where the output cap goes to the transformer).
3) Make sure that the XLR ground (pin 1) of your signal source is connected/grounded to the mike body
4) If the signal from C12 is distorted, you can try lifting C12, then probe directly at the tube plate.  Make sure that the probe is set to AC coupling otherwise the output signal will be biased way up at 50-60V DC (be careful doing this, this can make the circuit oscillate)

You should be able to get a clean signal from the output of C12.  If not, I would disconnect the transformer primary, then place a 100K resistor from the output of C12 to ground.  Then measure the output of C12 again.  You should be able to get a 20-30V peak signal cleanly out of the amplifier with no distortion (assuming 1V fed in).

 

[barbaroja]

Any advice? I have scheduled a recording session, last time I used the mic was distorting easily. I want to use it in this session.

If you inject a signal, it needs to be injected into the coupling cap (just like a replacement capsule).

A few things:

1) Make sure the scope probe is grounded against the mike frame properly
2) To eliminate the xformer, read the signal directly from the output of the coupling cap wrt. ground (after C12, where the output cap goes to the transformer).
3) Make sure that the XLR ground (pin 1) of your signal source is connected/grounded to the mike body
4) If the signal from C12 is distorted, you can try lifting C12, then probe directly at the tube plate.  Make sure that the probe is set to AC coupling otherwise the output signal will be biased way up at 50-60V DC (be careful doing this, this can make the circuit oscillate)

You should be able to get a clean signal from the output of C12.  If not, I would disconnect the transformer primary, then place a 100K resistor from the output of C12 to ground.  Then measure the output of C12 again.  You should be able to get a 20-30V peak signal cleanly out of the amplifier with no distortion (assuming 1V fed in).

So capsule has to be disconnected?

 

[Matador]

So capsule has to be disconnected?

Yes, it makes it easier.

 

[barbaroja]

So capsule has to be disconnected?

Yes, it makes it easier.

Quick question. I am not using a external scope, just recording the mic output into my soundcard and analyzing it with a VST oscilloscope plugin. Just connecting the xlr#2 (+) pin to the grid gives me back the signal into the soundcard input. Tried grounding the body, no change. With this particular config, is something special that has to be done? I am going C12 - Vintech X81 preamp at minimum gain - TC Electronic Konnekt live.

 

[ValveTone]

Hi!

Just wanted to share a fun photo.  Here's my 251-wired version of this kit (with a few tweaks), up in Avatar's Studio A. 

Notice the vintage 251 off to the side?  Why?  Because my mic beat the vintage one out in a shootout for this particular vocalist (at least as far as tone, it was a bit noisier than the vintage 251, any thoughts?).  This is a session with a Grammy nominated jazz vocalist run by a multiple-Grammy winning engineer (he borrowed the mic).  His call, not mine. 

In all fairness, both mics were a bit too noisy for this vocalist's softest passages, so the Lauten is up there as well (a fine mic).

So, these kit-built mics can hang with, and on some days beat, the big boys!

Damon

 

[Matador]

Just wanted to share a fun photo.  Here's my 251-wired version of this kit (with a few tweaks), up in Avatar's Studio A. 

... (at least as far as tone, it was a bit noisier than the vintage 251, any thoughts?)...

Thanks for sharing!  Very cool!

Can you describe the noise in more detail?  Or have a recording of background silence that shows it?  What list of modification instructions did you follow to convert it to a 251?

 

[stelin]

Thanks for sharing! What tubes do you use?
I have built two C-12s and tested both 6072A's and Mullard 12AT7's (all NOS from Christian Whitmore). The 12AT7's have about two db lower noise level in the upper mids (the 6072A's have a 'brighter', more audible noise). Go figure! The cheap ones works better for me!
I have also tested two 6072's from electro harmonix, and they could be used as 'backups', but they are not as quiet as the NOS tubes.
I'm also interested in your 251 conversion. What did you do? There has been several suggestions about how to hook up the capsule.

 

[mgronroos]

I have also used a few EH 6062A tubes, and have had that bright noise on two of them.

I did some burn in tests though, and one of the noisy ones was noticeably quieter after 72 hours.
After 96 hours of burn in time, it was almost quiet. It actually sits in one of the C12s now.

So it may be worth a try to leave the mic on for a few days, and maybe the noise floor will go down to an acceptable level.

Best,
Michael

 

[wave]

Hello all,
Im building up one of the kits and I'm getting some resistor values that don't align with the version 3 BOM. I've been testing with 2 different meters to make sure that i wasn't crazy.
Has anyone else experienced this? did I look up the wrong BOM? I got it from the build info on the first page of this thread

Thanks,
Dave

 

[chunger]

Hello all,
Im building up one of the kits and I'm getting some resistor values that don't align with the version 3 BOM. I've been testing with 2 different meters to make sure that i wasn't crazy.
Has anyone else experienced this? did I look up the wrong BOM? I got it from the build info on the first page of this thread

Thanks,
Dave

Do you mean the resistors are mispacked? If that is the case please let me know which ones are swapped or missing.

 

[wave]

Hey Chunger,
I spoke with Eric and he said he had the same problem. He told me to just match the numbers with the way you have them oriented in the build pics...

Thanks!
Dave

 

[wave]

Hey Chunger,
Another question: In the build pics and text you state:
"And the wire leads on the 7 pin XLR trimmed to length, stripped, tinned, and installed.

Pin 1 = B+
Pin 2 = heater
Pin 3 = pattern
pin 4 = bias
pin 5 = audio -
pin 6 = audio +
pin 7 = ground"

In The schematic that Matador posted in the thread it shows bias and pattern being swapped. Also how does the label for this terminal block (X1) correlate? The legend shows a P5 P6 and P8. Maybe I'm an idiot....

Dave

 

[chunger]

Hey Chunger,
Another question: In the build pics and text you state:
"And the wire leads on the 7 pin XLR trimmed to length, stripped, tinned, and installed.

Pin 1 = B+
Pin 2 = heater
Pin 3 = pattern
pin 4 = bias
pin 5 = audio -
pin 6 = audio +
pin 7 = ground"

In The schematic that Matador posted in the thread it shows bias and pattern being swapped. Also how does the label for this terminal block (X1) correlate? The legend shows a P5 P6 and P8. Maybe I'm an idiot....

Dave

The XLR pinouts are whatever you determine them to be. . . just make sure you either have a consistent system throughout your "fleet" of microphones or you assign a specific PSU and cable to each microphone and never swap them.

The terminal block designations are labelled on the PCB screen printing.

P6= GND
P3= Pattern
P4= Bias
P8= Heater
P5= B+

These correspond to the screen printed labels/solder-pads on the microphone PCB as well.

 

[wave]

Thanks for clearing that up buddy! I usually use a different 7 pin for each mic. This one will def be unique as I'm using the 7 pin XLR at the PSU but I'm going to modify the mic to use an Amphenol.

You rock!
Dave

 

[Category 5]

Anyone have any output TX bell housings from HT-11A?  The new ones Chunger has don't come with em, and well, I like em.

 

[Matador]

Hello all,
Im building up one of the kits and I'm getting some resistor values that don't align with the version 3 BOM. I've been testing with 2 different meters to make sure that i wasn't crazy.
Has anyone else experienced this? did I look up the wrong BOM? I got it from the build info on the first page of this thread

Thanks,
Dave

Can you be more specific?  I may just need to update the BOM.

 

[junkface]

Built up my first c12 and had no problems getting it running and biased. Big ups for such a well documented build thread.  Sounds great even with the old capsule in there! My next step is swapping out the original capsule for the HK 12 I just got in the mail. Was wondering if anybody could talk me through the mounting/ wiring, as this will be my first capsule swap, and the ct12 section of the build here doesn't really spell it out. Apologies for being a total n3wb, the HK 12 just looks so sexy and I really don't wanna muck it up.

Mainly I'm wondering which 4 places I'm connecting to on the capsule and which of the 4 solder pegs they run to. Thanks so much for the help!

 

[chunger]

You may want to make a post over on eric heiserman's white market thread for clarification.

Based on the latest revision thati received, carefully remove one screw  on the front face.  Attach the included wire tab to this screw.  This will not effect the membrane tension as the mylar is glued to the ring.  Do the same on the back side.  These are your front and back capsule leads.

There should also be 4 screws attached to the edges of the capsule.  These are your backplate electrical connections.  Select one from each side (front and back), remove the screw and attach wire tabs to these.  These are your backplate connections.  In the C12, these must be bridged together.  You can do so right near the capsule or at the PCB.

Next, select 2 empty holes around the perimeter to as mounting points to your capsule saddle.  This capsule uses a wide 45 degree saddle and the diameter is 34mm.  Use the oncluded 0-42 self tapping screws to mount the capsule with 2 of the empty holes on the outer edge.

 

[gyraf]

(side note: I just got to play with two REAL 1953 C12's in our studio. Now I understand the prices they fetch on the used market)

 

[Category 5]

I can't imagine the anything sounding better than the pair I built with Tim's capsules last year.  They are honestly the best sounding mics I have ever laid ears on. Been trying to contact Tim
to get another capsule pair for a few weeks now but haven't heard back.  I'm dying for another pair but trying to hold out for CT12s again. Has to be the smoothest capsule I've ever heard!