Official C12 Clone - Build and Support Thread

[cariocaman85]

Hi, thanks for your reply!

We bought the T14 with the kit (the same as the tutorial). The red wires (21 ohms tested) are attached to the connector, and the blue ones (939 ohms) are connected to X1/X2. Is that correct?

 

[JessJackson]

Hi, thanks for your reply!

We bought the T14 with the kit (the same as the tutorial). The red wires (21 ohms tested) are attached to the connector, and the blue ones (939 ohms) are connected to X1/X2. Is that correct?

This is correct. Make sure primary and secondary left and right sides are correct also.

 

[cariocaman85]

Checked, they're ok... no phase switching.

 

[mwrichardson]

Here are some voltage measurements in my mic builds. I did 2 mics and had same readings. 

Junction of R12 and R17 .. 120vdc,  at junction of R17  C12 and plate .. 68.8 vdc,  at junction of R12  R13 and R14  (capsule polarization) .. 59vdc,    at  R11 and connector pin  .. 1.1vdc (bias). 

Also do not feed heater voltage to unused tube section (pin 5 if not using second triode) and ground plate, cathode and grid of unused section(pin 6 and 7 and 8 id not using 2nd triode). Might help noise.

 

[baadc0de]

My build has a really low output I think. How could I verify if it's the capsule but not the amp? Could i inject a sine at the grid point and check? What kind of gain should I be expecting (probably about 25dB?). The problem is, currently my gain is about 25dB short of what I would expect...

 

[Matador]

Per above, keep in mind 12AT7 and 6072A's are NOT drop-in replacements for each other in this circuit.  The output impedance of the power supply is just too high and many adjustments need to be made.

As for low-output:  in my testing of 3 prototypes, I observed around 20-25dB of gain as measured at the tube plate.  The 10:1 output transformer throws away 20dB of this gain, so the circuit is somewhere right around unity to about 5dB.  Gain can be made higher with other tube selections and some value tweaking (per above).

The stock Alctron CCDA circuit has a lot more gain, as there is a cathode-follower output stage feeding in to a much lower ratio transformer...perhaps twice the gain if the capsule is kept constant.

My build has a really low output I think. How could I verify if it's the capsule but not the amp? Could i inject a sine at the grid point and check? What kind of gain should I be expecting (probably about 25dB?). The problem is, currently my gain is about 25dB short of what I would expect...

One can inject a signal into the capsule coupling cap, or right at the grid if there is no offset in the signal generator.  If all is well, a 1V peak sine wave should appear as a 1V to 2V peak sine wave as measured at the XLR connector outputs.

As for the noise issues:  can you make a test recording of the noise you are hearing?  A great test (which can be done without taking out the capsule), is to hard ground the grid (e.g. pin 3 if you are using the "first" half of the tube) of your active tube stage and then do a test recording with everything buttoned back up.  What you will be hearing at this point is the self-noise of the tube, and any coupled noise from the power supply and/or cabling.  It will allow you to take the capsule and it's biasing (and the high-impedance section in it's entirety) out of the equation.

If the noise goes away, then we have to look in to the high-impedance parts.

 

[cariocaman85]

Thanks for all your replies! 

We can't test and record the mike before the next week, but we'll post samples and pictures asap!

I'll try with a 6072 EH, in order to preserve the NOS one.

 

[srdigital]

in building the c-12, will the k67 capsule you sell function to tide me over until i have enough cash to buy some of mr. campbell's? trying to mod 2 of the apex 460's, but want to see if the cap is a cheap alternative until i can afford the real deal. thanks!

 

[Category 5]

in building the c-12, will the k67 capsule you sell function to tide me over until i have enough cash to buy some of mr. campbell's? trying to mod 2 of the apex 460's, but want to see if the cap is a cheap alternative until i can afford the real deal. thanks!

Since those capsules have the 8KHz rise that has to be compensated for in circuit it probably won't give you what you want, even in the interim.  I am planning on using some of these while I wait to hear from Tim.  Cheap, and only positive reviews thus far.

http://microphone-parts.com/rk12-microphone-capsule/

 

[hyde maintenance]

I am wondering, what would happen if i put a m-7 style capsule in this build?
I am loving that capsule  on every mic I have wired it up on, will it work on this build as well?

I've been hoping someone would share any experiences or opinions on this question as I'm drawn to the idea of quality unique or oddball mics vs clones. Unfortunately my budget doesn't allow for multiple capsule purchases to try a bunch of combinations.

Anyone have any thoughts?

 

[chipss36]

well i have the mic pcbs and p/s  stuffed, nos rca  tube and a russian  back up,  and the mic part c-12 capsule, I also have there 67 capsule but the deal I had on the  mic fell thorough kinda funny all the parts no mic, and have to go offshore for a month, however I guess I may be that guy, pretty sure the c-12 is going to be to bright for my taste ,  matt at microphone parts is a great guy . he did select a c-12 with less high end for me, see how it works out,  cathedral pipes has his caps on sale, I have a second, with a higher capacitance,  so it does overload a bit, however to tone is spot on for me vintage and warm, high end is sweet not ice pick like, just wondering if the voltages and such in this build would support that capsule?
also want to try matts 47 cap and his 7 if this mic supports it ill try them all and report back,  i have a feeling the m-7 is what ill like best though...

 

[wolan42]

Hello,

maybe some silly questions.

Is another 10:1 transformer like Beyer BV 351 110 005 (1:10) or Neutrik NTE 10/3 also a possibility instead the CM-2480 or the AMI T14?
My goal is not a 1:1 copy of the AKG C12. I will build a good sounding mic.

I've ordered a Dale M7 (originally for my G7, but it is hard to find a not so expansiv body for this) and will now build it into the C12.
Is it also possible?

Andreas

 

[HellfireStudios]

Hello,

maybe some silly questions.

Is another 10:1 transformer like Beyer BV 351 110 005 (1:10) or Neutrik NTE 10/3 also a possibility instead the CM-2480 or the AMI T14?
My goal is not a 1:1 copy of the AKG C12. I will build a good sounding mic.

I've ordered a Dale M7 (originally for my G7, but it is hard to find a not so expansiv body for this) and will now build it into the C12.
Is it also possible?

Andreas

I am not going to say that one capsule is better in for one circuit than another, but doesn't it make more sense to use the capsule designed for the circuit? An M7 is not going to be as bright as the C12. If that is what you wanted, why did you not just build a U-47 clone? It should still work, but seems a roundabout way to get your intended destination.

-James-

 

[wolan42]

Hello James,

thank you for the answer. You are right about the sense of the capsule alternativ.
But I'm here in the forum to learn. And as a "microphone builder newbee" there is a lot to learn.

My "silly" question about the capsule was, I have the dale capsule here.
Orginally I ordered it for my G7. But for the G7 there is no body here.
At this moment the Equinox body is to expensive for me, and so I think the M7 capsule was an alternative for the C12.

Sometimes, for a non native english spoken user, I feel like an idiot (in german: Depp) to ask such questions. ;-)

I will take your suggestion.
I put the Dale capsule into the G7 and will buy a body from Equinox in summer if I have the money.
For the C12 it is better to order a capsule from Tim or as cheap alternative a RK12 from MicParts.

But what about the transformer alternatives?

In my Takstar Royer Mod, the Beyer sounds very good. But is this also a posible "substitute" for the CM-2480 or AMI T14?
(Sorry about my english, but I am not in practice for the last years.)

Cheers

Andreas

 

[HellfireStudios]

I use and love the CM-2480 in my C12 clone, but using another 10:1 transformer instead is acceptable. Try it. The worst-case-scenario is that you will not like it, and will need to purchase an approved transformer. Good luck.

-James-

 

[wolan42]

Thanx.

I try and report it.

Andreas

 

[chunger]

I have been pleasantly surprised on more than one occasion putting "the wrong" parts together just because that is what I had on hand at the time.  This is DIY after all.

 

[Pip]

Ok the latest on the PSU front and my particular build. In short forget all that other stuff I said and Matador is the man.

I got bored and I have decided I really like what the Microphone-parts people are doing so had some cash and bought there RK-12 capsule (http://microphone-parts.com/rk12-microphone-capsule/). As my original intention still holds this project requires a Tim Campbell capsule and mine is ordered but still weeks off (really good things come to those who wait) I put this in for now.

My build was suffering from not enough B+ voltage and a maxed out adjustment pot. And after much confusion on my part I finally got the CHANGE THE VALUE OF R1 & R2 TO A HIGHER VALUE OR TO A LOWER VALUE IN AN INVERSE RELATIONSHIP TO YOUR PROBLEM DUMMY!(me being the dummy). The annoying part is I know this and I still over thought the problem, don't worry my day job does not include any work with radiation. So I changed the value of R1 & R2 to 75K and voila it is working. I have a real midpoint in my B+ adjustment and all is GOOD!

Microphone sounds great and very low noise. The new temporary capsule is really crisp and not too forward but I can hear what the TC capsule will do in this circuit and it will yield perfection. No knock on the Microphone-parts bit of kit at those prices I have zero complaints this thing sounds really good now.

So:

B+= 120VDC
Bias= -1VDC
Heater 6.3VDC Measured at mic
Plate= 59.5VDC measured at output cap  ;D

 

[mwrichardson]

Does anyone know what the actual Bias voltage is on a C12. It is not noted on the schematic and is not adjustable as R8 is a 1k resistor. Klaus H. has stated that plate should be 65 to 80 vdc. Someone have a C12 they can measure?  I see Matador recommends -1 volt. I seem to remember that -1.1 was correct. I get a 68 volt reading on my plate with -1.1 vdc bias setting. I wonder what the range in vintage C12's is.

 

[Treelady]

Hello James,

Sometimes, for a non native english spoken user, I feel like an idiot (in german: Depp) to ask such questions. ;-)


Andreas

NEVER suggest that you are an idiot when you are writing in a second language!  It is impressive that so many people know more than one language.  Your English is 100 times better that our German.