Official C12 Clone - Build and Support Thread

[Matador]

I hooked up my C12 through a preamp and directly into my monitors. I only hear low-frequency hum. The hum doesn’t go away when the body tube is installed, so I don’t think it’s RF. I’ve replaced C12 and C13 just in case they were passing DC. When I ground the grid the hum goes away. The capsule seems to be working but the audio is overwhelmed by the hum.

If I inject a 50mv sine wave at the grid, I get a sine wave at the output cap (C12) of about 1V. As soon as I attach the signal generator lead to the capsule side of C13 the hum goes away and I can hear the sine wave through my speakers. So, I think the tube circuit is working correctly.

Attaching a signal generator to the grid will overwhelm the grid resistor...I also assume you clipped the ground lead of the signal generator somewhere to the mike as well.

Try injecting the sine wave through a 100pF cap into the capsule side of C13.  I bet it sounds the same as the capsule.

You have the headbasket in place while you are trying all of this, yes?

 

[kcatthedog]

snap

 

[JessJackson]

This mic sounds so much better with a fully passive power supply like original c12's

Most of you who built this mic with supplied psu board aren't hearing it's full potential.

What's the difference Jess?  The Mataching PSU is just like the original except for the regulated heater isn't it?

Yes, B+ is passive just like the original, with the exception of using a full wave bridge rectifier rather than a half-wave rectifier.

I await to hear how it's different, other than using an LM317T to regulate the heater supply rather than a Zener diode.

Try it... makes a bigger difference than I would have thought.

I got two vintage c12's here at home and couldn't figure out why the clones weren't as silky  smooth so i powered them off the vintage psu's and there we have it.

I guess it's not always about the amps and the volts.

J

 

[Winetree]

Most of you who built this mic with supplied psu board aren't hearing it's full potential.

Is there something that could be done to the P.S. to mod it like the orginal.

 

[skidmorebay]

Attaching a signal generator to the grid will overwhelm the grid resistor...I also assume you clipped the ground lead of the signal generator somewhere to the mike as well.

Try injecting the sine wave through a 100pF cap into the capsule side of C13.  I bet it sounds the same as the capsule.

You have the headbasket in place while you are trying all of this, yes?

Thanks Matador, that helped. Installing the headbasket and a little more cleaning with a q-tip did the trick. It's quiet and sounds wonderful.
I never would have thought that the headbasket does so much to reduce noise, even after the body tube was on.

I'm reminded of a saying someone told me a long time ago: "If something you are doing isn't working right, look at the parts you thought weren't important."

 

[skidmorebay]

Try it... makes a bigger difference than I would have thought.

I got two vintage c12's here at home and couldn't figure out why the clones weren't as silky  smooth so i powered them off the vintage psu's and there we have it.

I guess it's not always about the amps and the volts.

It would be interesting to learn what voltages the vintage PSU is putting out and compare them to the B+, heater, bias, etc. of the new one. Maybe the difference is just in the adjustable parameters...

 

[Matador]

EDIT: nevermind.  The only winning move is not play.

 

[JessJackson]

EDIT: nevermind.  The only winning move is not play.

Not playing is deleting.. saw your previous comment, change is just as egotistical.

anyway.. make some platinum records.... or not.

 

[JessJackson]

Try it... makes a bigger difference than I would have thought.

I got two vintage c12's here at home and couldn't figure out why the clones weren't as silky  smooth so i powered them off the vintage psu's and there we have it.

I guess it's not always about the amps and the volts.

It would be interesting to learn what voltages the vintage PSU is putting out and compare them to the B+, heater, bias, etc. of the new one. Maybe the difference is just in the adjustable parameters...

Voltages are the same.

its quite a few things that contribute to the large 3d silkiness that you get from the vintage c12's

Full passive PSU (people will tell you regulated heater is an improvement.. blah bla bla) regulators sound stiff to me in tube mic circuits.. especially in non self biased circuits. (it shouldn't coz your science degree and volt meter says so?.. ok)
PIO bosch coupling cap (people will tell you film is better.. blah bla bla) if u want a clean audiophile mic you build a transformer-less TLM 10whateverthefuk.
Original carbon wire wound resistors (people will tell you they are more noisy.. blah bla bla) Sometimes a little hiss comes with a lot of beauty.
nos 5 star tube
original haufe t14/1 transformer
original CK12 (although Tims capsules give me the same silk when i install in my vintage c12's)

J

 

[chunger]

Voltages are the same.

its quite a few things that contribute to the large 3d silkiness that you get from the vintage c12's

Full passive PSU (people will tell you regulated heater is an improvement.. blah bla bla) regulators sound stiff to me in tube mic circuits.. especially in non self biased circuits. (it shouldn't coz your science degree and volt meter says so?.. ok)
PIO bosch coupling cap (people will tell you film is better.. blah bla bla) if u want a clean audiophile mic you build a transformer-less TLM 10whateverthefuk.
Original carbon wire wound resistors (people will tell you they are more noisy.. blah bla bla) Sometimes a little hiss comes with a lot of beauty.
nos 5 star tube
original haufe t14/1 transformer
original CK12 (although Tims capsules give me the same silk when i install in my vintage c12's)

Hmmm. . . I'm not the circuit guru, but there are statements here that I think are categorically incorrect (those who know better can verify or correct me here).

- The original C12 PSU is passive B+ with regulated heater supply.  It is not passive/passive as JessJackson implies.  The general topology of this clone tracks with the original in that it is passive B+ with regulated heater supply.  (2 key notable deviations are full wave rectification on B+ as opposed to half wave, and the use of LM317T for heater regulation on the heater instead of zener.)

- The original C12 as well as our clone is NOT  fixed bias design.  It is a self-biasing circuit that contains some of the components that generate the bias voltage  inside the PSU and sends it to the mic via cable to the mic.  This clone's trim pot allows precise setting of the base idling point (ballpark), but the circuit pushes and pulls based on program. . . .as does the vintage original C12.

 

[chunger]

on a tertiary note, nobody is denying that PSU (even between 2 copies build with modern BOM) can sound different from unit to unit based on variances in components.  But, useful discussion requires the use of that science stuff! 

It is about as practically unreasonable to suggest everyone "simply" go out and try some vintage original PSU's as it is to say "simply" run the clone PSU for 50 years and then report back on how it sounds.

It is widely accepted among people who have tested a lot more PSU's than myself that the method of heater supply has a nearly imperceptible effect on the sonic footprint of the microphone.  Which is an even more mute point in our scenario because this was comparing regulated vs. unregulated HEATER supply.  Our clone is the same classification as original (regulated).

The B+, however can have an effect on tone, and the effects are more profound in circuits that derive heater supply from the B+ (a la U47).  But, it is generally agreed that any good implementation of the same topology will shift the footprint sideways retaining the original sonic markers of the original as opposed to destroy all resemblance.  Many people cannot tell the differences.

As for carbon comp resistors vs. metal film, the sonic differences increase as current increases, and we are dealing with very small currents in these circuits.

We have put together what we feel is an excellent (uncompromising even) "package" of components and chosen our deviations from the original design based on sonics, budget, physical layout, continued availability of parts, noise performance, ease of assembly, etc.

Each layout and BOM is a direct reflection of the experience and preferences of the designer.  My webstore is set up to not "penalize" anyone who wishes to use their own PCB, BOM, power supply, capsule, and any other variable they do not see eye to eye with Matador on.

Hit one out of the park, and I'll change the kit. . . it's evolving.  Or, post your BOM and people who agree with your tastes and/or reasoning  can give it a go!  We are making a major revision now since our rev. 1.2 PCB's are almost sold out, and our parts kits are also sold out and being re-ordered.  But, in my experience, controlled testing and obtaining concrete sonic results (teflon isolated HiZ, transformer, etc.) have been difficult to lay out and the results inconclusive and murky at best.

FWIW, if seeking "silk" in this circuit, take a long-hard look at Eric Heiserman's capsule which was actually developed on this clone.  Coordinating now with hired talent for a "proper" test session.  These have not been released that long, and they are just now getting out "into the wilds" in some quantity and in a variety of studios, but my initial impressions of it are outstanding.  One thing we know for sure. . . the capsule by far, has the most profound impact on tone in regards to tiniest of spec changes in this mic and in most mics.

 

[gyraf]

Thanks Chunger. You saved me quite a lot of typing here.

Jakob E.

 

[JessJackson]

Lol ... I was mearly saying that a couple mods could be made and I get jumped on like a fly on shit.

I forgot that there are two bias "excuse the pun" people making money out of this project.

People get sensitive when their money could be effected.

Yeah ok it's not TRUE PASSIVE or
Incorporates chokes like u47

317 on H just doesn't sound good to my ears.

Anyway we can continue this in 50 years.

 

[Spencerleehorton]

Hi all,
I for one would definitely welcome a comparison between what is considered a better sounding psu to one which sounds worse, same mic and capsule.
All good food for thought, very good points from everyone on this.

Regards

Spence.

 

[gyraf]

People get sensitive when their money could be effected.

We are getting close to the edge of our no. 1 rule on this board: NO PERSONAL ATTACKS

Jakob E.

 

[JessJackson]

I want to add that I don't hear "as much" of these differences when listening on NS-10's or KRK E8's at normal listening levels...

I hear the harshness mainly when cranking the Augspurgers. This is when gear and mixes either shine or break up.

J

 

[Matador]

Here is my experience is what really impacts the tone of a microphone (based on all of the prototypes I've built, of this and other designs), ranked from most significant down to least significant (with other things held equal):

First and foremost:  the room the microphone is in dominates everything.  A solid gold C12 in a crappy room in front of crappy talent will always be crappy, debates about differing type of DC heater voltage aside.

Next we have:

1) Capsule
2) Capsule
3) Capsule
4) Capsule
5) Capsule
6) Tube (this is more a noise consideration, however a tube has many real parasitics that play down in the audio band)
7) Coupling Cap size
8) Transformer
9) Polarization scheme
10) Tube Bias point
11) Coupling cap type
12) B+ level

After this you get into quaternary effects, the differences of which double blind ABX testing (and yes, testing must be done in this fashion for audio, no exceptions) would need to vet out.  I'm not interested in debating quaternary effects, because filtering them out properly and controlling them is almost impossible, and then the debate becomes solely about "impressions" and "gut feelings" which differ from person to person.

Now for full disclosure:  this list is using my ears, on the prototypes I created and listening in my rooms with the equipment available to me.  If anyone else has another list, with the effects dominated by the kind of DC voltage on the heaters, by all means, post a BOM and an ABX comparison and we can have a debate.

Believe it or not, a lot of what was done design-wise in the 50's was done by necessity and lack of alternatives, not hard product requirements (compromise is at the heart of all engineering in reality).  I would guess that if you went back in time and brought AKG engineers into the present and sat them down in front of a modern Mouser catalog, different decisions would have been made.

I feel like a regulated tube heater design is in some very good company:  the C12A (look at that huge PNP shunt regulator in the heater section!), the ELA M251 (another PNP shunt regulator!), the Gyraf G7 (even with a 317!)...to speak nothing of the plethora of tube mike preamps, and tube guitar amps with the same.

 

[kidvybes]

on a tertiary note, nobody is denying that PSU (even between 2 copies build with modern BOM) can sound different from unit to unit based on variances in components.  But, useful discussion requires the use of that science stuff! 

FWIW, if seeking "silk" in this circuit, take a long-hard look at Eric Heiserman's capsule which was actually developed on this clone.  Coordinating now with hired talent for a "proper" test session.  These have not been released that long, and they are just now getting out "into the wilds" in some quantity and in a variety of studios, but my initial impressions of it are outstanding.  One thing we know for sure. . . the capsule by far, has the most profound impact on tone in regards to tiniest of spec changes in this mic and in most mics.

...it's interesting you bring up the "2 PSUs built from the exact same PCB/BOM" argument...I have one built by Matador and another built by Eric Heiserman...they are essentially identical in terms of components, yet when coupled to the same mic, they offer slightly different voicing character...Matador's build has that airy vibe you look for in a C12, and oddly, Eric's PSU offers a slightly thicker, warmer but silky tone, more like a 251...they both work fine, and since I only record a single mic at a time and have no need for a matched-pair, I'm happy to have the option to choose which PSU to pair with one of my C12 mics (which have 2 different capsules as well)...they both sound quite nice!

...one of my C12 mics employs Eric's HK12 capsule, and it sounds very smooth and airy (particularly when paired with my Matador-built PSU), shy of any excessive essi-ness/sibilance...sounds somewhat similar to a friend's mic which employs the Campbell capsule...very pleased with Eric's work...

 

[Melodeath00]

So we're saying PSUs can sound different, but it is less caused by the design, and more by the tolerances of the parts? I really need to get my C12 out again.

 

[Matador]

For the passive portion of the circuit (e.g. the stuff feeding the B+ voltage), it becomes quite a bit more complicated (which is the main drawback of passive designs).

For example, if I had to reason about potential differences in the B+ line, I would hazard that C4 would play the largest role to any change in sonics.

If you are the tube, "looking back" through the plate resistor into the PSU, the C4 filter cap is the first component you encounter.  Given the RC time constant of the filters is so very long (the last filter resistor into C4 gives a time constant of around 7 seconds):  any short term audio current demands at a given voltage are really served by C4.

Big electrolytic caps have a lot of tolerance:  20% in fact.  One PSU's C4 could be down near 80uF real value and another could be closer to 120uF, which would have a sizable effect on the effective AC output impedance of the supply.