Official C12 Clone - Build and Support Thread

[Volume11]

Hey guys, I'm having trouble digging up info on the gac7 wiring in the search section. Am I correct by using the thicker blue and red wires for the heater and B+ connections? Also, should I ground the shield to the correct ground pin, or do I use one of the colored wires? If the second option is correct, do I ground the shield to the xlr housing, or just leave it out of the circuit all together?

Sorry if this has been mentioned already, but I had trouble finding any info for this specific mic.

Thanks,
Chad

 

[Matador]

Ok I read that a few times and couldn't get what you were asking...but a quick Google search tells me you must be asking about Deltron GAC-7 power supply cable.

Here's how I would use this:  the two thick cables (red and blue according to the datasheet) I would use for heater and ground, since these have the lowest resistance per foot.  So declare red for heater+ and blue for ground.  The current flow through B+ is minuscule compared to the heater so your ohms are best spent on heater and ground.

Here's the ground scheme:
1) Inside the PSU:  PSU board ground connects to the 7-pin XLR connector.  The docs use pin #7 right in the middle.  This ground is also connected to the PSU enclosure via a short jumper to the brass tab on the XLR connector which goes to the chassis via the housing itself.
2) Inside the PSU, the 3-pin XLR connector has pin 1 connected to the shell via a similar brass lug.

Inside the mike:  pin 7 goes to the PCB "P6" node and transmits the PSU ground right to the PCB ground.  The shell of the XLR cable (which is the cable shield) is tied to the microphone body via the 7-pin connectors brass retaining screw, which is also strapped to the ground wire to pin 7.  The circuit ground is bonded to the microphone body via the PCB mounting screws as well.  Thus all of these things become "ground" when it's all bolted together.

 

[Volume11]

Ok I read that a few times and couldn't get what you were asking...but a quick Google search tells me you must be asking about Deltron GAC-7 power supply cable.

Here's how I would use this:  the two thick cables (red and blue according to the datasheet) I would use for heater and ground, since these have the lowest resistance per foot.  So declare red for heater+ and blue for ground.  The current flow through B+ is minuscule compared to the heater so your ohms are best spent on heater and ground.

Here's the ground scheme:
1) Inside the PSU:  PSU board ground connects to the 7-pin XLR connector.  The docs use pin #7 right in the middle.  This ground is also connected to the PSU enclosure via a short jumper to the brass tab on the XLR connector which goes to the chassis via the housing itself.
2) Inside the PSU, the 3-pin XLR connector has pin 1 connected to the shell via a similar brass lug.

Inside the mike:  pin 7 goes to the PCB "P6" node and transmits the PSU ground right to the PCB ground.  The shell of the XLR cable (which is the cable shield) is tied to the microphone body via the 7-pin connectors brass retaining screw, which is also strapped to the ground wire to pin 7.  The circuit ground is bonded to the microphone body via the PCB mounting screws as well.  Thus all of these things become "ground" when it's all bolted together.

I really appreciate you taking the time to look that up, and for giving such a detailed explanation as well. Thank you!

That is indeed the same cable, which I ordered from chungers online store. So, I believe that I get everything that you are saying but, I just wanted to double check. If pin seven is taking care of all of the grounding for the psu to mic cable, then I don't need the shield of the gac-7 cable connected to anything. Correct? Sorry if this is a silly question, I just like to be sure of things before moving forward. Thanks again

Chad

 

[Category 5]

Both my mics went together and calibrated without a hitch, even the one with the lower rated power transformer (thanks to Matador's for coming up with the replacement values for R1/R2).

I used a 5 star GE I got for 30 bucks off ebay to get things rolling then switched to the two JAN GE tubes I got from Bowie.  All the tubes worked great, and I do feel the 5 star might have sounded a little bit silkier.

I can't believe how good this circuit made the stock capsules sound.  Now I am more eager than ever to finally get my CT12s!

The 180K dummy load got B+ and Bias voltages pretty much dead on, and I had to raise the heater to 6.59 (at the PSU) to get 6.3 at the mic.  This was in both mics.  Switching to the other tubes didn't change much at all, but I did some fine tuning to get to 120/-1 again.

I do have a little body resonance coming from inside one of the mics and I wonder if it could be the way I mounted the T14s inside the bell housing.  I used the smller inner holes to thread a zip tie through and fix the transformer to the bell housing, then ran the wires through the corresponding outer holes.  It kept things very clean and aligned for sure so I hope I can keep it this way.

Luckily no noise, crackling, or intermittent issues to speak of.  Other than the hiccup with B+ on one of the PSUs (due to the lower output transformer) these mics went together like legos.

Thanks so much to Chunger and Matador for putting together one of the simplest projects ever.  Legendary IMO.  I can't wait for the 251 and the regulated supply.

Also wondering if the upcoming regulated version of the supply will be usable with ioaudios MK47 and upcoming U47 projects.

I'm expecting Tim to contact me any day to get my capsules.

 

[jandoste]

Hey Chunger,
OMG! Please tell me which one is right? I already soldered them as like
Pin 5 +
Pin 6 -

Thanks

Good catch. . . I've corrected the discrepancy.

Pin 5 -
Pin 6 +



Next, because I foolishly disconnect the stock wiring, I need to re-solder the 3 pin xlr. 

Pin 5 is audio +
Pin 6 is audio -
pin 7 is ground

 

[Matador]

Hey Chunger,
OMG! Please tell me which one is right? I already soldered them as like
Pin 5 +
Pin 6 -

Thanks

Good catch. . . I've corrected the discrepancy.

Pin 5 -
Pin 6 +



Next, because I foolishly disconnect the stock wiring, I need to re-solder the 3 pin xlr. 

Pin 5 is audio +
Pin 6 is audio -
pin 7 is ground

It really doesn't matter:  the mike will work exactly the same either way.

 

[Category 5]

Hey Chunger,
OMG! Please tell me which one is right? I already soldered them as like
Pin 5 +
Pin 6 -

Thanks

Good catch. . . I've corrected the discrepancy.

Pin 5 -
Pin 6 +



Next, because I foolishly disconnect the stock wiring, I need to re-solder the 3 pin xlr. 

Pin 5 is audio +
Pin 6 is audio -
pin 7 is ground

Just make sure the mic is wired the same and you're fin.  It's arbitrary what pins you use.

 

[jandoste]

Thanks! so all is good here

 

[wolan42]

Putting "the wrong" parts together ... it is diy ;-) like Chunger said


A few weeks ago I asked about an another transformer for this build. In my case a Beyer 1:10.
Today I finished the mic with the Beyer, a RCA 6072 an a Mic&Mod MK-12 capsule.
I compare it with a T.Bone SCT-2000 I have here at the moment.
The C-12 Clone sound fantastic.
Airy, not harsch and a with a good basement.
In the opposite, the T.Bone sound muddy and very crispy in the high freq. And I liked it before.
When I find time in the next weeks, I will make some records and compare it with a cinemag transformer.


Now I wait for Tims capsules I ordered in spring. (I have time)
Last week I request boards for the next mic.
I look forward to the new power supply.


Thank you Chunger, Matador and the other people who made this available.


sincerely


Andreas

 

[Volume11]

The CT12 capsule has isolated backplates which we will bridge together at the solder terminals on the capsule.  With this capsule being scavenged from a previous prototype, Matador already soldered in wires for the front diaphragm, rear diaphragm, front/rear backplates, as well as bridge the front and rear backplates together.

So, another noob question here. Do I actually solder the two terminals on the side of the capsule together? This doesn't make much sense to me. I did this and I tested the mic polar patterns and Cardioid doesn't work correctly. So, I'm guessing that this is because I soldered the two plates together. Cardioid basically works like figure 8. Before I start unsoldering this thing, I wanted to double check with you guys. This capsule is way too expensive to risk any damage.

Thanks,
Chad

 

[Category 5]

I'm testing some tubes, all 6072.  How important is it to re-bias for each tube when testing.  Can be cumbersome when switching a lot.

 

[Matador]

So, another noob question here. Do I actually solder the two terminals on the side of the capsule together? This doesn't make much sense to me. I did this and I tested the mic polar patterns and Cardioid doesn't work correctly. So, I'm guessing that this is because I soldered the two plates together. Cardioid basically works like figure 8. Before I start unsoldering this thing, I wanted to double check with you guys. This capsule is way too expensive to risk any damage.

Thanks,
Chad

The C12 design is for a 3-terminal capsule - TC's is 4-terminal.  So you have two choices:
1) Solder a wire and bridge the two backplates at the capsule.  Then run one of the wires to FB, and the other to RB.
2) Run two separate backplate wires from the capsule, and run one to FB and the other RB, and tie them together at the PCB.

The choice is yours as they are electrically equivalent.

The only difference between cardioid and figure-8 is the backplate voltage.  Measure the "P3" node right where it enters the mike.  It should read 60V when set to cardioid, and 120V when set to figure 8.  Also confirm the junction of R12 and R13 reads 60V as well.

 

[Matador]

I'm testing some tubes, all 6072.  How important is it to re-bias for each tube when testing.  Can be cumbersome when switching a lot.

Most tubes are within reason and the operation won't be effected in-between tubes.  Remember that the stock C12 isn't fixed bias, so it will settle to a reasonable operating point in most cases.  Even if you don't end up changing anything, you can always just spot-check the voltages.

 

[kcatthedog]

hi,

if i want to use a mullard 12at7, do i need to mod the mike ?  I have been told voltage should be ok ?

thx!

 

[micaddict]

hi,

if i want to use a mullard 12at7, do i need to mod the mike ?  I have been told voltage should be ok ?

thx!

This was covered only last week.
Reply # 913. 


(... and more elaborately in replies # 872 and 874.)

 

[Volume11]

So, another noob question here. Do I actually solder the two terminals on the side of the capsule together? This doesn't make much sense to me. I did this and I tested the mic polar patterns and Cardioid doesn't work correctly. So, I'm guessing that this is because I soldered the two plates together. Cardioid basically works like figure 8. Before I start unsoldering this thing, I wanted to double check with you guys. This capsule is way too expensive to risk any damage.

Thanks,
Chad

The C12 design is for a 3-terminal capsule - TC's is 4-terminal.  So you have two choices:
1) Solder a wire and bridge the two backplates at the capsule.  Then run one of the wires to FB, and the other to RB.
2) Run two separate backplate wires from the capsule, and run one to FB and the other RB, and tie them together at the PCB.

The choice is yours as they are electrically equivalent.

The only difference between cardioid and figure-8 is the backplate voltage.  Measure the "P3" node right where it enters the mike.  It should read 60V when set to cardioid, and 120V when set to figure 8.  Also confirm the junction of R12 and R13 reads 60V as well.

I tested the mic in the studio last night, and everything is perfect. My initial test was through a venues live PA, so it was kind of hard for me to tell the polar patterns apart, with the limited time I had to test it. I'd like to thank all of you guys (especially Matador and Chunger) for making this project available and for the support as well. The mic is in a session right now, I'll report back with the results.

 

[Category 5]

hi,

if i want to use a mullard 12at7, do i need to mod the mike ?  I have been told voltage should be ok ?

thx!

Looks ike you might just need to change r17 to 47k in the mic and re-bias.

The other stuff was for the silver mica conversion only, right?

 

[Matador]

hi,

if i want to use a mullard 12at7, do i need to mod the mike ?  I have been told voltage should be ok ?

thx!

Looks ike you might just need to change r17 to 47k in the mic and re-bias.

The other stuff was for the silver mica conversion only, right?

Its all outlined in 874.  The caps are orthoganal to the 12at7 conversion.

 

[chunger]

hi,

if i want to use a mullard 12at7, do i need to mod the mike ?  I have been told voltage should be ok ?

thx!

Looks ike you might just need to change r17 to 47k in the mic and re-bias.

The other stuff was for the silver mica conversion only, right?

Please read the relavent posts carefully.  The B+ section of the power supply is passive.  2 resistors in the psu also need to be changed to account for the new tube.  This was explained in detail a few posts back.

 

[jandoste]

Hey guys,

I'll use the peluso CEK 12 capsule... what do you think about it and did anyone try it?

Thanks