Official C12 Clone - Build and Support Thread

[dmnieto]

Was the transformer in-circuit when you measured?  If so, disconnect XP1 and substitute in a 100K resistor for the transformer and recheck for the roll-off (the resistor goes between the XP1 and XP2 nodes, or tack-soldered from the output cap to ground).

Yes it was... what if I load the the secondary of the transformer with a dummy 600 ohm load instead of disconnecting the transformer? Would that work too?

 

[dmnieto]

Where is the plate idling?  Measure it "before" the output cap.  It should be sitting at around 50V or so.

B+ => 119.5V
Bias => -1.07V
Plate => 62.6V

The moment I put the generator on the grid the B+ collapses to ~100V and the plate drops to around 26V... I have no clue how to test like this should I disconnect the bridge between RB and FB? I do that at the pcb

 

[Matador]

Was the transformer in-circuit when you measured?  If so, disconnect XP1 and substitute in a 100K resistor for the transformer and recheck for the roll-off (the resistor goes between the XP1 and XP2 nodes, or tack-soldered from the output cap to ground).

Yes it was... what if I load the the secondary of the transformer with a dummy 600 ohm load instead of disconnecting the transformer? Would that work too?

If you want to eliminate the effect of transformer L and C then a resistor sub is best directly attached to the output cap C12.

With a low-impedance signal source directly on the grid, this circuit should be flat out to MHz until grid C starts to dominate response.  One should not see a response peak on the CDDA circuit either.

Is the capsule connected when you attach your generator?

 

[dmnieto]

Ok,

I managed to test it by lifting the FB, RB bridge and inserting the signal at the FC pin.

1) Grid->Tube gain is 26.3dB (xfrm loaded with dummy 2Kohm)
2) Grid->Tube->xfrm(2Kohm terminated) is 4.63dB
3) Grid->Tube gain is 26.9 (xfrm unterminated)
4) Grid->Tube->xfrm(unterminated) is 5.43

Frequency response plots:


Loss at 20KHz with respect to 1K, at XP1 => 2.55dB (transformer loaded with 2KOhm)
Loss at 20KHz with respect to 1K, at XP1 => 2.89dB (transformer unloaded)
Loss at 20KHz with respect to 1K, at xfrm secondaries => 0.05dB (transformer loaded with 2KOhm)
Loss at 20KHz with respect to 1K, at xfrm secondaries => 0.02dB (transformer unloaded).

At this I started to feel *really* stupid, I checked the manual of my DMM (a Keithley 2015P) and of the probe I used, I assume output tube resistance, and yep I am creating a low pass eq when I put my probe between the output capacitor and ground. I checked by connecting the microphone directly to the pre-amp... and there it goes... the circuit is flat.

So the tube is ok, other than giving a bit lower gain than I expected (only ~5dB), it is working correctly (26dB of gain, output swing at XP of around 50Vpp,...).

So it needs to be capsule... no?

 

[Matador]

At this I started to feel *really* stupid, I checked the manual of my DMM (a Keithley 2015P) and of the probe I used, I assume output tube resistance, and yep I am creating a low pass eq when I put my probe between the output capacitor and ground. I checked by connecting the microphone directly to the pre-amp... and there it goes... the circuit is flat.

Wow...that means the probe is 400+ pF.

The response bump of the stock Apex is still puzzling:  output Z of the CDDA is on the order of a few hundred ohms, so the probe shouldn't have much (if any) impact on the measurements (unless you went up way above the audio band).

 

[dmnieto]

Wow...that means the probe is 400+ pF.

I was t-splitting the signal into two different instruments, so we had the capacitance of the probe and the input capacitance of both instruments plus who knows what ...
[quote author=Matador]
The response bump of the stock Apex is still puzzling:  output Z of the CDDA is on the order of a few hundred ohms, so the probe shouldn't have much (if any) impact on the measurements (unless you went up way above the audio band).
[/quote]
I did not measure the stock APEX (with an RK12 capsule) actually, I just measured the output of both on a live source and noticed the C12  seemed to have lower high frequency components... whether it is the circuit or the capsule I don't know. I noticed on the plots that the RK12 in the modded APEX 460 was a bit brighter (maybe +/- 1dB), but on the measurements I was seeing almost 4dB difference at 10kHz.

Any suggestions? Could it be something around the circuit in the C12 that may make it a darker?

Edit:
I know that the figure of 8 pattern has an effect of dampening a bit the high frequencies, so I checked the voltages and the voltage divider in R12, R13 sits correctly at about 59.7V, while the polarization voltage is at around 59V in cardioid... I dont think such a low voltage difference could have an effect ... am i wrong?

 

[dmnieto]

Ok, I am really feeling overwhelmed.

I just received Ben's Beesneez CK12 and I am having very similar issues to the ones by category 5 in http://groupdiy.com/index.php?topic=51377.msg696944#msg696944 with the difference that in figure of 8 one capsule sounds completely muffled. I am going to ask Ben to take a look at it, but I want to also check for other possibilities.

I removed the stylene filter capacitors from the equation (removed them), and checked that the polarization voltages in pin 4 are correct for all modes (they are), also this issue does not happen with the RK12.

I am bridging the capsule at the pcb, and as i intend to send it back to Ben I rather not try to solder them...

Any help? Ideas?

so sad... I hope there is something wrong with the capsule (like one of the backplane screws being floating) or the circuit (I doubt it because it sounds correct with the RK12), because I am totally disappointed with the sound of the microphone as it is right now, I had heard C24's before I they don't sound this muffled and boomy. I actually like the sound of the RK12 better and I refuse to believe this is the the sound of a C12...

 

[Reverend]

Aren't C12s desirable because of their brightness? Anyway, I've got a Peluso capsule. Peluso told me that the red wires (front capsule and back capsule) should be in the according places. The two blue wires, they said should be hooked up to the "tube grid". I would really appreciate it if I could get clear directions as to how to solder these wires. On the PCB there are four spots

FC - Front capsule?
BC - Back capsule?
Two others that I can't remember offhand. I am a touring musician and I have to leave the project,so...I'm at a disadvantage. I'm not an electrician, but I can solder. It would be great if there were clear instructions on where to send/solder the wires for the few different C12 clone capsules that are available. Peluso, Beesneez, Advanced Audio, as well as Tim Campbell(which no one can get).
I want to believe that this is going to work, but I'm thinking that it's a wash. I don't want to just throw this mic in the trash. If it were to work, and, sound like a vintage C12 or at least sound good, I would use this mic on my next album, or, take it to a major studio to see how it stacks up. I took my Peluso P-47 to a studio and the engineer freaked out it sounded so good.
I WANT this mic. So, how the hell do I hook this f**cker up and get it to work?
Sorry for the profanity, but if you guys could get this build to be EASY for people who can read and and solder, like me, this mic would get used on big albums and tons of people would buy your product. Microphoneparts.com have great, easy to understand and execute instructions. If this C12 clone build is for electronic snobs, then you should state that in the beginning. I feel like Matador and Chunger are not snobs, and are really on to something here. But if you look at the final segments of the instructions, there is really no clear directions on how to solder the wires coming from the capsule. Do you guys want to be successful? Directions like "learn how to use a multi-meter" are not only insulting to musicians like me, but it's going to cost you the success that you've worked hard to achieve. I suggest you cater to the people who DON'T know how to even turn on a multi-meter.
So, in closing,how the fff do I hook up a Peluso capsule to your damn PCB that had gfing ground problems?

 

[mica]

I was just about to order a CK-12 from Beez Neez for this C12 project, but halted when i saw this tread.. Is there a problem with that capsule in this build?

 

[gyraf]

Aren't C12s desirable because of their brightness?

No, IMO mainly because of their detailed-ness, and their ability to take rather high amounts of EQ without sounding strange

in figure of 8 one capsule sounds completely muffled.

If you're using your own voice and headphones for testing, remember that back membrane signal is reversed polarity in fig-8 (!!!) so you need to phase-reverse if you want to listen to yourself in headphones. Another option would be to record first, then listen back later.

Jakob E.

 

[Melodeath00]

Well this seems like the perfect time to share this...

A couple months ago I took some measurements of pink noise using bi-directional on my C12 with CT12 capsule in order to compare the front and rear side of the mic. Here's a graph of the frequency response difference. Please pay attention to the EQ curve and not the colored graphs below it. I used the front as the reference, and applied its response to the rear. Meaning the front of the capsule/mic has 4dB more 15kHz, is about the same at 10kHz, a notch at 6k, less mids, more lows, etc. https://copy.com/PABXFOoBKN3I

Since I have not tried a different capsule, I do not know if this difference between the front and rear is caused by the circuit or the capsule. Tolerances for a CK12-type capsule are supposedly all over the place according to many sources, but I do not know what "all over the place" really translates to in terms of dB.  As you can see, there's as much as 4dB deviation on mine. The front sounds a lot better than the back IMHO, but as you can see, it's got a robust low-end compared to the back, which is perhaps masking the highs. This could explain why my C12 is not nearly as bright as I was expecting, but my expectations may have been unfounded based on internet chatter.

So yes, I also experience the rear being less bright than the front in bi-directional, and it's not caused by polarity and listening with headphones. However, I might experience the opposite if I flipped the capsule around. It would require a test to see if it's the capsule or the circuit. Unfortunately the wires are so tiny, it would simply be too much of a hassle at this point in time for me to give that a try and see what happens.

dmnieto, perhaps I misunderstood, though. Is your overall mic muffled in bi-directional, not just the rear?

Also, I do not know if it helps, but my completely stock Apex/Alctron was way brighter than once I modified it to the C12.

 

[dmnieto]

in figure of 8 one capsule sounds completely muffled.

If you're using your own voice and headphones for testing, remember that back membrane signal is reversed polarity in fig-8 (!!!) so you need to phase-reverse if you want to listen to yourself in headphones. Another option would be to record first, then listen back later.

Jakob E.

I did a recording using mine and somebody else's voice, at different positions and distances, side to side compared with a mic with the RK12. the CK12 was *always* darker and muffled. I tried omni, cardioid, figure of eight... The rear capsule on omni mode sounded a bit better, but there was several dBs quieter than the front.

 

[dmnieto]

Well this seems like the perfect time to share this...

A couple months ago I took some measurements of pink noise using bi-directional on my C12 with CT12 capsule in order to compare the front and rear side of the mic. Here's a graph of the frequency response difference. Please pay attention to the EQ curve and not the colored graphs below it. I used the front as the reference, and applied its response to the rear. Meaning the front of the capsule/mic has 4dB more 15kHz, is about the same at 10kHz, a notch at 6k, less mids, more lows, etc. https://copy.com/PABXFOoBKN3I

Since I have not tried a different capsule, I do not know if this difference between the front and rear is caused by the circuit or the capsule. Tolerances for a CK12-type capsule are supposedly all over the place according to many sources, but I do not know what "all over the place" really translates to in terms of dB.  As you can see, there's as much as 4dB deviation on mine. The front sounds a lot better than the back IMHO, but as you can see, it's got a robust low-end compared to the back, which is perhaps masking the highs. This could explain why my C12 is not nearly as bright as I was expecting, but my expectations may have been unfounded based on internet chatter.

So yes, I also experience the rear being less bright than the front in bi-directional, and it's not caused by polarity and listening with headphones. However, I might experience the opposite if I flipped the capsule around. It would require a test to see if it's the capsule or the circuit. Unfortunately the wires are so tiny, it would simply be too much of a hassle at this point in time for me to give that a try and see what happens.

dmnieto, perhaps I misunderstood, though. Is your overall mic muffled in bi-directional, not just the rear?

Also, I do not know if it helps, but my completely stock Apex/Alctron was way brighter than once I modified it to the C12.

You could say that I am experiencing something similar, on figure of eight the front is always "darker" than the back, independently of how I wire the capsule... it is also louder. It happens the same in omni. On cardioid, the front gets a hell of proximity effect... even at a meter from the source. It sounds a lot like a blue baby bottle actually.

I am going to wait for Ben or Veronica to contact me again to see if they can check the capsule and retune it... because as is, it is not usable. If they don't, well, look for a discounted C12 build in the black market very soon.

 

[dmnieto]

I was just about to order a CK-12 from Beez Neez for this C12 project, but halted when i saw this tread.. Is there a problem with that capsule in this build?

That is up to you, I went for Beesneez's capsule and paid the premium $100 compared with Tim's because I didn't want to wait an unbounded amount of time to get mine and based on feedback of Ben's expertise in making great microphones; my wife's studio owns a couple of Lulu's and they are totally killer. The capsule itself looks great and it is clear he had incredible skills in building these.

That said, I am not the only one that has experienced this "dark" sound on their builds, and even Melodeath00 with Tim's capsule had similar issues, so maybe there is something wrong specifically to the build itself or some of the CK12 capsule characteristics that can make it go wrong. Because I live in the Bay Area, I am totally open to lend the mic to Matador if he wants to take a look, as even if with the RK12 it sounded a bit darker and there might be some kind of coupling on the Hi-Z section that messes with the capsule polarization and response... unlikely though.

In terms of the capsule... well I hope is a tuning problem or a one off...

 

[toobnoob]

Saw this quote from Klaus Heyne on another forum, thought some here might appreciate it...

Here is Neumann's color scheme for tube mic cables, adapted from the German Broadcast System, and appreciated by any mic tech to quickly help identify what is what:

Audio (+) = White
Audio (-) = Black
Ground = Thick blue
Heater = Thick Red
B+ = Yellow
0-120v (variable pattern) = Green
snip the remaining conductor (gray), and you are done

And make sure that you terminate shield on both connectors to ground and connector sleeves.

 

[dmp]

That said, I am not the only one that has experienced this "dark" sound on their builds,

Has anyone heard a real c12 capsule?
Maybe this is misguided expectations? If your only experience is with chinese stock mics like the apex460, you might well think the c12 is dark in comparison.
In fact you might prefer the cheap chinese mic!

I did a blind mic shootout with 7 or so mics I built and several high end studio mics, and the C12 with TC capsule came in near the bottom - by consensus of all there.  Think it is a great mic, but don't expect the heavens to part when you hear it. I don't think it will blow away everything else on a solo'd voice.
I really like the Chinese C12 capsules, like the RK12 (I don't have that particular one, but comparable).

 

 

[dmnieto]

That said, I am not the only one that has experienced this "dark" sound on their builds,

Has anyone heard a real c12 capsule?

I heard a C24, same vocals.... CK12 in my build is darker.... similar to a baby blue bottle and that one starts to roll-off at 7kHz

 

[dmp]

You could say that I am experiencing something similar, on figure of eight the front is always "darker" than the back, independently of how I wire the capsule... it is also louder.

In this test you mean the physical front of the capsule? I.e. you switched the wires & rotated the capsule 180 deg and the 'back' of the mic was now darker, when before the 'front' was darker?

Or

The front of the circuit -  meaning you switch the wires, rotate the capsule, and the front was still darker than the back, without a change after rotating the capsule?

>>>
If you can clarify this, one means the capsule is demonstrating a difference, the other means the circuit / physical mic is.

 

[dmnieto]

You could say that I am experiencing something similar, on figure of eight the front is always "darker" than the back, independently of how I wire the capsule... it is also louder.

In this test you mean the physical front of the capsule? I.e. you switched the wires & rotated the capsule 180 deg and the 'back' of the mic was now darker, when before the 'front' was darker?

Or

The front of the circuit -  meaning you switch the wires, rotate the capsule, and the front was still darker than the back, without a change after rotating the capsule?

>>>
If you can clarify this, one means the capsule is demonstrating a difference, the other means the circuit / physical mic is.

It is a combination of both, actually which points me that there might be an issue with the internal wiring of one of the capsule. Let me put it this way.

Let's say that the capsule has two sides, named A and B.

A is darker and louder than B.
Either in omni or figure of 8, A sounds even darker and louder if it is is wired to be in the front than to be in the back.

The capsule in any configuration is significantly louder in figure of 8 than in cardioid mode, and cardioid is louder than omni. Whatever side is wired as the rear, in omni mode the rear is about 6 dB louder than in cardioid.

Omni front (whatever config) sounds comb-filtered. Figure of eight sounds muffled and boomy.

It does not happen with the RK12, and the styrene filter caps are lifted

 

[Melodeath00]

dmp, to be fair, in all of my replies I HAVE acknowledged the fact that my expectations for a C12 could be off. I have never heard a real C12 in person, but I have heard some clips online where they are definitely bright. My C12 sounds fantastic; it is just less bright than I thought it would be (after comparing with my other mics), and the difference between the two sides of the capsule is larger than I expected (which again, I am not sure if it's the circuit or the capsule). I never expected it to blow away my U47 or knock the socks off of my Manley Ref Card. I was just initially surprised that it didn't sound that different from the U47 design.

dmnieto, I think we have different issues. I have not noticed any level fluctuations regarding omni versus cardioid versus bi-directional. Also, I'm not sure how you're talking about front versus back in terms of Omni. The mic is picking up from all sides in that pattern, so there isn't really a "back" and "front" in that particular case.