AKG C12 point to point build

[Coop]

Today I finally received the FLEA body and the last parts for the PSU. First of all, the body looks and feels amazing. Can't wait to put some parts in it.

I put in the last parts of the PSU, switched it on and the lamp started to glow. No smoke no bang. Good sign. I measured B+ and the Bias and both seem to work. B+ is a little bit high, but that is probably because the transformer delivers 220V and not 200V. Need to address that later. But the weird thing is the heater line. I didn't get any voltage there at all. So I started to troubleshoot and it seems that there is something really wrong. The diode bridge rectifier seems to be bad. And what is even weirder, it is doing the same thing on both PSU boards I built. When set to AC I can measure ~60V coming out of the heater line. I double checked all the components, but they all seem to be installed in the right way. What could cause this issue? As it is on both boards, I don't think it is a bad diode or so...

 

[soapfoot]

B+ is probably high because it’s unloaded—no mic attached—right?

 

[Coop]

Nope, I did strap a 180K resistor across Pin 7 and 1 to mimic an attached mic

 

[Coop]

Figured the issue with the power supply out. Had to wire a jumper between the negative heater and ground terminal. Now I do get 6.3V out of the heater output. Also did change R1 and R2 to get the voltage down and be able to reach 120V B+

PSU is now almost finished. Just missing some minor adjustments in cable management.

And I did start working on the mic itself. I think I got everything right so far. Only missing the tube and the capsule. I do have an old capsule from a Blue Bluebird laying around. Looks like a CK12 type capsule. So maybe I use that as a test capsule first. Also still not sure wether I should use a NOS GE 6072 or a Mullard 12AT7. Not really sure what fits my capsule, transformer and output cap setup the best.

Cable should be here next week, so I can attach the connectors to it as well and test that out too.

Here are some pics

 

[Coop]

Short update

PSU is finished, cables are all tied up nicely and I finally ordered both a capsule and a tube for the mic. I also finished the cable which brings me to one question about the shield/ground.
I do have a 3 XLR and a 7 pin Tuchel on the PSU side. Right now I do have 0V coming from the supply entering the mic at PIN 6, the cable shield is connected to both connector housings of the cable but the connector housings inside the PSU are not connected to each other. Should I tie them together and should I connect 0V to the cable shield inside the mic or the PSU?

 

[lampas]

Short update

PSU is finished, cables are all tied up nicely and I finally ordered both a capsule and a tube for the mic. I also finished the cable which brings me to one question about the shield/ground.
I do have a 3 XLR and a 7 pin Tuchel on the PSU side. Right now I do have 0V coming from the supply entering the mic at PIN 6, the cable shield is connected to both connector housings of the cable but the connector housings inside the PSU are not connected to each other. Should I tie them together and should I connect 0V to the cable shield inside the mic or the PSU?

As far as I remember I tied 0 to the chasis inside the PSU and also tied 0 to the chasis inside the microphone. Then there wasn't hum anymore. I think that this could be seen from the photos I did send you, but I'll check again as I could not remember anymore what I did exactly (I did this 7 years ago ...) .

 

[andYz00m]

Why did you need to jumper the negative heater to ground?

 

[Coop]

@andYz00m

The PSU board layout is meant to be used with mics that use positive or as negative heater voltage. For +6.3V you have to connect heater- to GND and for -6.3V you have to connect heater+ to GND.
So in order to be able to use it with a C12 style mic, you have to jumper the negative heater terminal to ground.

 

[maxwall]

Has anyone tried the Beezneez CK12 capsule, opinions ?

 

[Recording Engineer]

A friend bought one in 2015 to put it in a C12 type mic with a 6072 and AMI T14. Insanely open and bright without any harshness at all to be found anywhere.

Boutique capsule builders’ skills, tastes, and techniques change over time, so who knows how they are now, but I’d love to have that exact same mic added to my arsenal sometime!

 

[aaquilato]

I have put one in a PTP build that was from an Australian DIY site some years ago. It’s my Aussie C-12.
It’s a beautiful sounding capsule IMHO.
Not at all harsh.
Ben does a very good job.

 

[doqmemory]

Has anyone tried the Beezneez CK12 capsule, opinions ?

I have several and they sound wonderful in both C12 and ElaM 251 microphones. BeesNeez ships pretty fast to US and they are a pleasure to deal with.

The sound is in the same ballpark as the Tim Campbell CT12 (wish I could order a few of those, but I never get a reply from @Tim Campbell ).

 

[Igor_Zg]

Short update

PSU is finished, cables are all tied up nicely and I finally ordered both a capsule and a tube for the mic. I also finished the cable which brings me to one question about the shield/ground.
I do have a 3 XLR and a 7 pin Tuchel on the PSU side. Right now I do have 0V coming from the supply entering the mic at PIN 6, the cable shield is connected to both connector housings of the cable but the connector housings inside the PSU are not connected to each other. Should I tie them together and should I connect 0V to the cable shield inside the mic or the PSU?

Hi @Coop,

may I ask you what kind (model) of polarity switch are you using?
thnx

 

[Coop]

@Igor_Zg

I did use a Lorlin 12 position 1 pole non-shorting switch

 

[daristiguieta1]

Hi @Coop, any updates? Thinking of taking the plunge with this exact build! Looking great from what you've posted so far!

Dan

 

[dirkjanheemskerk]

Hi @Coop, any updates? Thinking of taking the plunge with this exact build! Looking great from what you've posted so far!

Dan

Hi all,

Same here, so would love to see an update.

Cheers,
DJ.

 

[soapfoot]

I’ll make that a +2

 

[Coop]

Hey all,

Sorry for the late reply. I did finish the mic, but I didn't have time to really test it so far. There is so much live work to do at the moment. No time for using the C12.
But I do have a session coming up in June where I will be using it. Will be sharing some sound files

 

[soapfoot]

Out of curiosity--what did you use for a power transformer in your PSU?

 

[robinhuntmusic]

Just to chime in, I bought 2 OPR ck12 capsules. Im very happy with them. Super silky and none of that harshness.