Official C12 Clone - Build and Support Thread

[Jaybird]

Can't wait to build one of these, just waiting for the next run of donor mics to be in-stock at 939.. My question is: would it be possible to fit a small switch or jumper to select what side of the tube you are using? This can be hidden in the mic body since this is something you would not want to change while the mic is in use, if it's possible how would i do it?

 

[Reverend]

I'm still not getting proper voltage readings from my PS.  On the 7 pin connector, I took out the wire ground bridge that went from the 7 to the 4 pin as per instructions (or as I read them), did I do the right thing. STUCK!

 

[Matador]

I'm still not getting proper voltage readings from my PS.  On the 7 pin connector, I took out the wire ground bridge that went from the 7 to the 4 pin as per instructions (or as I read them), did I do the right thing. STUCK!

Yes that's right.

How are you measuring, what are you measuring, and what were the readings?

 

[Reverend]

I'm a total newbie. I'm really not sure that I have my DMM on the right settings. I'm measuring the B+, GND, Polarity, etc. as pictured in Chunger's pics. Since I'm a newbie, and I've only got a couple of other builds (less complicated than this, but I've done PCB work, still), I was super, super careful to make sure that I populated the PS PCB exactly as necessary. Then, I double checked it. Then, I used my DMM to make sure that all of the connections were made. The only 2 things I'm thinking now are....I used too much heat and ruined a capacitor, or, I've got a bad transformer. I really, really soldered quick at about 300 degrees (or at least that's the setting on my Hakko). Wow. Hope I'm not in over my head here. Still having fun and I love a challenge. I even found another PS for an Apex 460, but it's older and different. I'm thinking now that I may try to fix what I have before getting that thing torn apart. For a newbie like me, getting this working will be monumental.

 

[scott_humphrey]

Outstanding project and documentation! Well done, Matador!

 

[Gearsix]

Hello,  someone knows if it is possible to use 390K Ohm resistors instead of 402K Ohm for the position pattern rotary switch in the power supply?

 

[MicDaddy]

My mic is having some weird behaviors while in Omni (it's possible that it is misbehaving elsewhere, but Omni is most obvious for me to observe)

While in Omni, the front diaphragm (FC) gets extremely 'thin' with insanely low output.  It sounds like a room mic far off in the distance.  The rear diaphragm (RC) gets extremely boomy, woofy, just a lot of low end and sounds muffled.  The difference between the two halves in Omni is not good.  They are supposed to be identical mics back to back, but unfortunately something is not playing right.

Last I verified PSU voltages as follows:
B+ 120V
Bias -1.1V
Heater 6.3V

Polar:
Omni 0V
Card ~60V
Fig 8 ~120V

These voltages are what I expected to see but the sounds are not what I expected to hear.

I've yet to swap the RC/FC connections and see if the problem follows the capsule or the amp circuit.

I've used a Beesneez K12, with a single back-plate connection to FB/RB which I've tied together at the PCB.

One thing that has me still puzzled, tonycamp pointed out on page ~3(?) a discrepancy for audio + & - regarding pins 5 & 6 on the 7 pin XLR.

On page 1 there is still a discrepancy.

See at reply #5:
"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"

Scrolling a tad further down we find:
"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"

Scrolling down further we find reply #7 saying:
"Before installing the transformer, do a quick test to verify which side is the capsule side and which side connects to the pcb and which side connects to the output XLR connector on pin 5 (-) and pin 6 (+)."

I'll have to back track and see if I have a (several) polarity flips going on but I don't suspect this would be the issue behind my polar switching observations.

 

[MicDaddy]

I swapped the connections at the pcb, RC & FC.  The only change being my formerly rear diaphragm is now the front diaphragm. 

The audible issues while in Omni follow the capsule.  Meaning, the side which sounded thin, still sounds thin.  The side which sounded woofy still sounds woofy.

I'll stick the stock capsule back in and see what happens.

 

[Matador]

So long as you use the combo of pin 5 and 6, the polarity doesn't matter much, and certainly wouldn't cause what you are hearing.

One thing that comes to mind:  some capsules I've seen place the backplates on a screw on the retaining ring, or actually connect to the diaphragm on the opposite side of the capsule.  I would ask for a terminal connection diagram from Beesneez for your capsule.

The reason I bring this up:  a muffled quiet sounding side is a sure bet that the polarization is reversed, and that the capsule is actually trying to pick up the sound coming from inside the chambers.  It's like if you flipped two cardioid mikes and pointed them inwards towards each other (to the center of the capsule!).  It makes a cardioid mike sound like the front is actually what you would hear from a properly wired mike on the "wrong" side (distant, muffled, dark, etc).

Use the stock capsule as a test, as the center-terminated capsule makes it very clear which connection belongs to each capsule side.

Hello,  someone knows if it is possible to use 390K Ohm resistors instead of 402K Ohm for the position pattern rotary switch in the power supply?

Yes this is no problem.

 

[Gearsix]

Thank you Matador

 

[scott_humphrey]

As I dive into this, I decided to search for a schematic of the C12 where the AC701K tube was used, but had no luck finding it. If anyone has this, could you please share?

The reason that I want to see it is that I want to experiment with using a 5840 tube (yes, I'm aware that it is not a direct substitute for the AC701K) in this circuit to take advantage of  the "fixed" biasing technique that was used here with the 6072a tube. I'm just curious to see how AKG approached it with the AC701K. If there is anyone who has played around with this please share your experience.

Thanks,
Scott

 

[Pip]

Unless I am mistaken the C12 never had AC701. The  M251 did but only in europe.

http://www.coutant.org/akgc12/

http://www.saturn-sound.com/Curio's/elam_microphones.htm


http://mixonline.com/recording/applications/audio_microlution/

http://fr.audiofanzine.com/construction-de-micros-amplis-pr/forums/t.517913,ou-trouver-des-petites-capsules-pour-projets-diy,p.9.html

I do have to say I can't remember seeing one for the 251 with ac701 now that i think of it.

 

[scott_humphrey]

Unless I am mistaken the C12 never had AC701. The  M251 did but only in europe.

Ah,  …well    (cough, cough)    …that would explain why I can't find it. Thanks.

Anyone have the schematic of the M251 with the AC701? Curious to know if it's cathode biased. Thanks in advance.

-Scott

 

[Pip]

Well only to chime in with all the others who have the same understanding I now  do. I just installed my Tim Campbell Capsule and it is well worth the wait. It truly is a beautiful thing and Tim is an awesome guy you can just telll by the way he writes his emails.

 

[JessJackson]

Unless I am mistaken the C12 never had AC701. The  M251 did but only in europe.

Ah,  …well    (cough, cough)    …that would explain why I can't find it. Thanks.

Anyone have the schematic of the M251 with the AC701? Curious to know if it's cathode biased. Thanks in advance.

-Scott

 

[Woot]

Well only to chime in with all the others who have the same understanding I now  do. I just installed my Tim Campbell Capsule and it is well worth the wait. It truly is a beautiful thing and Tim is an awesome guy you can just telll by the way he writes his emails.

Hey Pip,

Good to hear about the TC capsule, and congrats on the build. Did it take Tim long to reply to your emails? I emailed him about 4 weeks ago but no reply, and no luck on either phone number either. Any advice in contacting him would be appreciated.

Cheers,

Matt

 

[Pip]

Well only to chime in with all the others who have the same understanding I now  do. I just installed my Tim Campbell Capsule and it is well worth the wait. It truly is a beautiful thing and Tim is an awesome guy you can just telll by the way he writes his emails.

Hey Pip,

Good to hear about the TC capsule, and congrats on the build. Did it take Tim long to reply to your emails? I emailed him about 4 weeks ago but no reply, and no luck on either phone number either. Any advice in contacting him would be appreciated.

Cheers,

Matt

Did you put in a request for a capsule. If so it takes about 8 to 10 weeks to get one. Basically all I did was email him saying I wanted one and then when it was ready he emailed me back. But it was at least 8 weeks between the two.

best

 

[Woot]

Hey Pip,

Thanks. Yeah I wrote an email requesting a pair, asked about a deposit etc. I just presumed he'd write back a confirmatiOn email or whatnot.

So I suppose based on your experience I have a couple of capsules on the brew. Sweet

Regards,

Matt

 

[Gearsix]

Hello, I have just realized the power supply but I can't obtain a B+ voltage higher then 105 Volt
I had no problems to regulate the heater and the bias voltages but as I want to use the original capsule that needs 200 Volt (I have read so in the first page of this thread) I need to increase the B+ voltage
I have read that if the B+ voltage is too low (can't be trimmed high enough) I can reduce R1 and R2 in value in the power supply
Someone can suggest to me the right values for these resistors?
Thank you in advance

 

[Matador]

Hello, I have just realized the power supply but I can't obtain a B+ voltage higher then 105 Volt
I had no problems to regulate the heater and the bias voltages but as I want to use the original capsule that needs 200 Volt (I have read so in the first page of this thread) I need to increase the B+ voltage
I have read that if the B+ voltage is too low (can't be trimmed high enough) I can reduce R1 and R2 in value in the power supply
Someone can suggest to me the right values for these resistors?
Thank you in advance

No capsule should require a 200V B+.  120V should work with any capsule.

What is the adjustment range for B+ that you are seeing (between R4 dialed to minimum and R4 dialed to maximum)?  Of course this voltage also depends on a real load so test with the tube installed.