Official C12 Clone - Build and Support Thread

[geekmacdaddy]

I don’t resemble the “smarter” claim, but I’m pretty sure you have the common filth issue, get some alcohol and while being super careful to avoid and not melt your polystyrene caps, clean the living heck out of the PCB, Especially where your capsule connects to the PCB, that might help, the cord grounding scheme is exactly as you’d expect, I did nothing out of the normal on mine and it’s noise free

Thanks Tony. I have done multiple alcohol cleanings...I'll keep at it. Can you be more specific about the 7pin Jacks? Is there is or is there ain't grounding to the jack bodies?

 

[tonycamp]

Thanks Tony. I have done multiple alcohol cleanings...I'll keep at it. Can you be more specific about the 7pin Jacks? Is there is or is there ain't grounding to the jack bodies?

Yes there is grounding to body with testing, I get continuity on my mic pin 7 to the outside of the mic body, unfortunately no visual on the inside, I have the bell shield cover on the tranny which covers the 7 pin jack from the backside and it’s a pita to pull that off, Hope this helps

 

[Delta Sigma]

Did you burn in your tube? Is the noise constant? If you disconnect your capsule and replace it with a 80pF or so cap, does the noise persist? Could it be hum (low f noise, 120Hz or so)?

Did you wear gloves when you worked in the hi-z section of the mic?

 

[geekmacdaddy]

Did you burn in your tube? Is the noise constant? If you disconnect your capsule and replace it with a 80pF or so cap, does the noise persist? Could it be hum (low f noise, 120Hz or so)?

Did you wear gloves when you worked in the hi-z section of the mic?

Thanks for the response, Delta Sigma. The tube is just vintage. A 12ay7 that could very well be the culprit. I have an NOS 6072 on the way. Suckers are expensive. I wore gloves with the capsule, only. I'll try the 80pf test. Not low hum, a white noise. Here's a sample; https://www.dropbox.com/s/0po1gzyj891ork8/C12%20test%208.m4a?dl=0

 

[Tim Campbell]

geekmacdaddy what capsule? You should keep alcohol away from any CK12 type capsule.

 

[geekmacdaddy]

geekmacdaddy what capsule? You should keep alcohol away from any CK12 type capsule.

Of course, Tim. Capsules that touch alcohol shall never touch my mic   No alcohol went near the Capsule. It's a Heiserman. I did physically make ground connections in the body of each jack (pin 7 to the body) and am wondering about them. I'll disconnect and see what it does.

 

[Delta Sigma]

Make sure you do not disconnect your shield. Your mic body should always have a good ground connection.

 

[Tim Campbell]

as was said earlier. Try substituting the capsule with a  capacitor so you can hear the amplifier and see if it still hisses.

 

[geekmacdaddy]

as was said earlier. Try substituting the capsule with a  capacitor so you can hear the amplifier and see if it still hisses.

I shall. Had to order that value. I'm assuming disconnect all connections to the capsule and connect the cap at Front Diaphram and BackPlate 1.

 

[Tim Campbell]

well you can use any available value from 50pf up to 100pf. Capsule values vary a lot. Connect 2 of them, one for each half.

When you talk about hiss, how high is your preamp gain? Could you have the transformer wired wrong and so need more preamp gain to get a decent signal?

 

[geekmacdaddy]

well you can use any available value from 50pf up to 100pf. Capsule values vary a lot. Connect 2 of them, one for each half.

When you talk about hiss, how high is your preamp gain? Could you have the transformer wired wrong and so need more preamp gain to get a decent signal?

Good info thanks. Triple checked the wiring, which is correct, and plenty of output.

 

[Haberdasher]

I just built 2 power supplies using pre-owned apex 460 donor enclosures/transformers.  I can set B+ and Bias voltages no problem, but when I try to measure the heater voltage my meter just blinks some values on and off.  Same behavior on both units.
I noticed the resistance was very very low between the 2 yellow transformer wires feeding 9.5v.  1 ohm on one, and 1.2 ohms on the other.  So my meter reads it as continuity.  Is that normal, or could I have ended up with 2 bum transformers?
Does a mic need to be connected for me to get a heater reading?

 

[Delta Sigma]

Heater is regulated, so probably not. A resistive load would work, need a higher power resistor.

Edited my post because I stupidly left the "not" off of probably not. Changes the meaning slightly...

 

[Matador]

I just built 2 power supplies using pre-owned apex 460 donor enclosures/transformers.  I can set B+ and Bias voltages no problem, but when I try to measure the heater voltage my meter just blinks some values on and off.  Same behavior on both units.
I noticed the resistance was very very low between the 2 yellow transformer wires feeding 9.5v.  1 ohm on one, and 1.2 ohms on the other.  So my meter reads it as continuity.  Is that normal, or could I have ended up with 2 bum transformers?
Does a mic need to be connected for me to get a heater reading?

The PSU has a terminal block for heater-.  It's used to reference the output heater- to ground (for +6.3V operation), or heater+ to ground (for -6.3V heater operation).

For C12 you need to place a jumper between heater- and ground, like is shown here (heater- is the left-most terminal block, if the PSU is facing you, with the outputs and polarization knob pointing towards you, as is shown in the picture).

https://groupdiy.com/index.php?topic=51377.msg760350#msg760350

 

[Haberdasher]

Thanks for the help, guys.

Ah yes, thanks Matador.  I completely whiffed on that post.  I swear I've read this entire thread twice!

 

[geekmacdaddy]

as was said earlier. Try substituting the capsule with a  capacitor so you can hear the amplifier and see if it still hisses.

I rebuilt the power supply (dialed in), rebuilt the mic board, all new. redid the cable, same problem. disconnected the capsule, replaced with 2 47pf caps. Big ground hum, no more hiss.
Is the capsule the problem?
thank you
Jeff

 

[Delta Sigma]

I rebuilt the power supply (dialed in), rebuilt the mic board, all new. redid the cable, same problem. disconnected the capsule, replaced with 2 47pf caps. Big ground hum, no more hiss.
Is the capsule the problem?
thank you
Jeff

Big hum: is your headbasket removed? That would cause a big hum.

 

[geekmacdaddy]

Big hum: is your headbasket removed? That would cause a big hum.

Not removed. that loud ground hum isn't there with capsule connected.

 

[geekmacdaddy]

I have found that screwing the body in takes care of the huge ground hum. With the capsule disconnected, getting that white noise with volume on the pre up, and a low volume ground hum with volume all the way down.

any thoughts appreciated
thanks

 

[Delta Sigma]

Can you summarize your troubleshooting? Tube: burn-in and swapping, hiss with capsule and without, etc. It makes it easier for someone quickly browsing the forums to help.

Did you try a new tube? Can you grab one out of a guitar amp? Even if the noise increases with a 12AY7 from a guitar amp it may help you decide the tube is the issue.

When does your 6072a arrive? Is it a Five Star from a reputable source?