Official C12 Clone - Build and Support Thread

[Reverend]

Guys, I built two Matador/Chunger C12 Clones. On the second, I wired it to use the right side of the tube. However, somehow, the microphones are out of phase. Can someone give me an idea on the best way to re-wire/re-solder one so they are both in phase with each other? Thanks.

Just swap the wires on either side of the output transformer (one side only), or swap pin 2/3 on the output of the inverted mic'a PSU.

Thanks Cat 5! It did the trick. I swapped the blue wires of the mics output transformer as I didn't want to mess with making the PSU something that I couldn't interchange with my other C12 clone.

 

[jasavoy]

Guys, can someone please help me? I finished building Matador's C12 and I've got a problem- I get almost no voltage at the capsule even though I've got +120VDC coming in at the B+, +0-120VDC on the polarization, and -1VDC  for bias, and I get about 50V at the plate, but barely 3VDC at the backplate. I cannot figure it out! I've tried without tube, with capsule disconnected, with output cap disconnected and then with output tranny disconnected. PLEASE HELP!

 

[Matt Nolan]

Guys, can someone please help me? I finished building Matador's C12 and I've got a problem- I get almost no voltage at the capsule even though I've got +120VDC coming in at the B+, +0-120VDC on the polarization, and -1VDC  for bias, and I get about 50V at the plate, but barely 3VDC at the backplate. I cannot figure it out! I've tried without tube, with capsule disconnected, with output cap disconnected and then with output tranny disconnected. PLEASE HELP!

Are you trying to measure the voltages at the capsule? The circuitry is so high impedance here that your meter causes a serious load on the voltages, thus pulling them down. Measure at the other end of the big resistors.

 

[jasavoy]

Thanks, Matt! So I can't actually measure the voltages at the capsule then, but my plate voltage is low as well- it's only around 45V. Is that the same issue?

 

[Matt Nolan]

Thanks, Matt! So I can't actually measure the voltages at the capsule then, but my plate voltage is low as well- it's only around 45V. Is that the same issue?

Others can probably chime in about this specific build, but I would say that you should be somewhere near 0.5 * B+ for your anode voltage. If you are not, it could be a biasing issue (adjust the relative voltage between grid and cathode) or it could be a poor tube.

 

[Phrazemaster]

Strange thing. I finished putting together this project, installed the CT12 capsule, adjusted voltages. Everything looked good, buttoned her up and no sound.

Tube glows.

I removed the microphone round housing and...it passes signal that way.

When I put the round tube covering back on, no sound.

Very strange. I've got to figure out what's shorting.

Anyone else have an issue like this?

Thanks,

Mike

 

[Phrazemaster]

Well back in the studio today, this issue is nonexistent. All I can think of is that some cleaning solution may have needed to dry. Microphone passes audio.

However another issue has presented itself. The capsule cuts out when medium-loud plosives are spoken near it. The audio cuts out for 1/2 a second, then returns.

I thought this only happened if the capsule was dirty, or was old or had a problem. This is a brand new capsule.

Anyone else have a thought about it?

Best,

Mike

 

[Tim Campbell]

Hey Mike, I have addressed this with you by email and asked you to return the capsule so that we're sure that it's not that.
Without the mic body on does it do the same thing? Could it be a short that only shows up when handling the mic as you do when you are close to it?
Just in case check that the connections on the capsule are snug and check for poor solder joints.

 

[Phrazemaster]

Thank-you Tim.

I am certain it is my doing somehow; I know your work is impeccable! That's also why I stated the question generically and kept your name out of it. I just didn't know with your heavy workload when I might hear back; that you would post here speaks volumes to your integrity, so thank-you. I see too many posts around here putting great manufacturers such as yourself on the defensive, when 99% of the time it's user error.

I will take your suggestions, and let you know; thanks for stellar support when I'm sure you're very busy.

Best,

Mike

 

[jasavoy]

Hey guys, what's the noise floor of this mic supposed to be like? I just finished mine and it sounds great but there is a lot of noise, even after swapping tubes to a known quiet tube. It's just an airy noise, but not exactly high frequency- just def easy to tell it's on- I don't know what it would be. Any thoughts?!
Thanks!

 

[Matador]

Can you post an audio clip of the noise?

 

[jasavoy]

Matador it won't let me upload WAV or MP3s. Can I email you?

 

[TLRT]

Hello All,

I have a problem, my mic started to do this random crackle noises(especially when turning the pattern switch pot), I changed the tube, removed the capsule and soldered a 80pf ceramic cap between the grid connection point and the ground, but the problem still exists. Do you have any idea? The second interesting thing that the polarization voltage starts to rise up to 135-140 volts when I turn of the mic. (it is not doing it when I put a resistor between pin 1-7 with no mic)

 

[chunger]

I had similar symptoms on a build and traced it to a faulty capsule.  Are you using a known test capsule to confirm mic function?

Hello All,

I have a problem, my mic started to do this random crackle noises(especially when turning the pattern switch pot), I changed the tube, removed the capsule and soldered a 80pf ceramic cap between the grid connection point and the ground, but the problem still exists. Do you have any idea? The second interesting thing that the polarization voltage starts to rise up to 135-140 volts when I turn of the mic. (it is not doing it when I put a resistor between pin 1-7 with no mic)

 

[Tim Campbell]

I changed the tube, removed the capsule and soldered a 80pf ceramic cap between the grid connection point and the ground, but the problem still exists.

This capacitor would substitute for another capsule. If the problem still exists without a capsule present I don't believe it's the capsule.

 

[gyraf]

Agreed.

Replacing the capsule with a 60-100pF capacitor (rated 63-100V) is about the best way to figure out if you have a capsule- or electronic problem.

Noise problems - when you can rule out a noisy tube - is nearly always down to contamination or solder flux residue. Remember that a finger print can easily screw up a 1G grid path...

Jakob E.

 

[Matador]

You can hard ground the tube grid with a temporary jumper.  This will tell you if the noise is pre or post tube amplification stage.

 

[TLRT]

Thanks all,

Looks like it was a mic circuit problem, it is hard to work with acrilic boards...

 

[Phrazemaster]

Hey all, I've got a strange issue with my C12. With the microphone body buttoned up, no signal passes. Unless I jiggle the connector at the base, then I get some little low level bursts.

If I remove the round tube housing around the microphone, it passes signal (plus all the expected noise).

I've looked and I've looked, but I can't seem to find what might be shorting out here. It's a very clean build, and the design is already so simple I can't figure out what might be happening. H+, B+, and Bias all are in spec.

This is strange. Any thoughts on this?

 

[Matador]

Unless I jiggle the connector at the base, then I get some little low level bursts.

Is the screw that secures the XLR plug in the bottom of the housing fully "backed out"?  This set-screw "loosens" (aka. counter clockwise) to tighten the XLR to the base of the body metal.

I'm guessing that the stress of screwing the end bell is stretching the bottom of the assembly, and then you are loosing circuit ground.