Official C12 Clone - Build and Support Thread

[Biasrocks]

Modern day Mouser catalogue aside.

I'm curious, if you have listened to the original PS vs your redesigned PS?

After all, the 'ears' have it.

Mark

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):

 

[Category 5]

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.

When doing matched pairs of mics would it then be advisable to match this part?  or at least source them within a higher tolerance?

The PSU I have that sounds different is the one with the 175V power transformer rather than the regular 200V one.  I dropped the resistor values to get the same B+, but wonder if that could have something to do with it or maybe it's C4.

I have also heard about undervolting the heater slightly to get an increase in harmonic distortion from the tube.  Know anything about that?

 

[JessJackson]

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.

What exactly is your experience mate because from what you've written it sounds more technical than musical (no personal attack.. a compliment, its good to be technical), I only produce records for worldwide platinum selling artists, using the best rooms in LA, New York and London, never had the opportunity and wouldn't know what its like to work with "crappy talent".

Your trying to say that the PSU is last in line in terms of how the mic's sound is effected but have you actually heard a vintage supply on a c12 clone?

Until you turn the PSU on, the mic will have no output .. That instantly puts PSU 1st in terms of how the mic sounds! 

The electrons in which are outputted to the mic are directly passed off to the pre amp. Whatever way you want to look at it or reason it in your head, the order of those electrons are important.

Yeh everyone knows that the choices made back in the 50's and 60's a lot of the time were made out of necessity. Tubes not being available for elams hence the 6072. small electrolytic caps not invented yet. transformer windings and cores not downsized, no small metal film resistors, the list goes on... but not everything thats made smaller is an improvement. unless carrying it in your shirt pocket is important to you.

We love these mics because of what they did then not because what they do now. I don't see anyone going crazy over a TLM. in 50 years you think people are gonna be saying damn, i wish i could get the parts to build a tlm like they did back in 2010. I think not. 

I've built a u47 supply with 3 chokes which is heavy as f**k, and someone like me who is always trying to downsize because of how much i travel and tour, i'd be the first person to not take a tube mic on the road.. maybe id take a psu sized like your alcatron psu on tour but I just can't deny the sound.. those heavy chokes do their thing. And therefore I'm willing to drag it through customs at every airport.

Anyway, I know what works for me. Maybe try it on your "talent" next time.. or not.

J

 

[Matador]

What exactly is your experience mate because from what you've written it sounds more technical than musical (no personal attack.. a compliment, its good to be technical), I only produce records for worldwide platinum selling artists, using the best rooms in LA, New York and London, never had the opportunity and wouldn't know what its like to work with "crappy talent".

After all, the 'ears' have it.

Ah yes, "Golden Ears":  how can I possibly argue with that.

I'm curious, if you have listened to the original PS vs your redesigned PS?

I'm guessing any and all testing I did with original microphones is irrelevant to this discussion, which seems to be more about truth than fact.

I'm glad you like your original C12:  I hope you continue to do great things with it.

 

[Matador]

When doing matched pairs of mics would it then be advisable to match this part?  or at least source them within a higher tolerance?

The PSU I have that sounds different is the one with the 175V power transformer rather than the regular 200V one.  I dropped the resistor values to get the same B+, but wonder if that could have something to do with it or maybe it's C4.

I have also heard about undervolting the heater slightly to get an increase in harmonic distortion from the tube.  Know anything about that?

Very difficult to source higher tolerance at these voltages:  it's better to buy extra and try to get them close with a capacitance meter if you care about them being exactly the same.

As for under-volting, I would experiment with it:  the heater can be adjusted down to about 4V with the stock values.

 

[Biasrocks]

After all, the 'ears' have it.

Ah yes, "Golden Ears":  how can I possibly argue with that.

No one said anything about golden anything.

All great gear in my experience is tuned by ear.

I'm curious, if you have listened to the original PS vs your redesigned PS?

I'm guessing any and all testing I did with original microphones is irrelevant to this discussion, which seems to be more about truth than fact.

I'm guessing that the answer to my question is no.

Last time I checked the title of this thread is 'C12 clone'.

Great design is large part of the battle, evaluation of a design by ear is another.

Perhaps a comparison side by side for your own enlightenment would be a good starting point for further discussion.

Mark

 

[chunger]

Seems like there is an awful lot of posturing and chest thumping going on here with very little actionable data to work with!

It would help everyone if we all stayed within our various areas of actual proficiency and not make wild conjecture outside of that.

The basic assertion is that one version of the vintage PSU (2 samples exact) sound better on the clone microphone. . . period.  The qualification is the sonic differences may not be clearly audible unless you are using a ~$20,000 monitoring system in a meticulously-tuned control room on world-class caliber artist talent.  It can be reasonably inferred that under these test conditions, we are chasing the last few percent qualitative difference between the vintage original and the clone.  At the highest levels of music production, these are the percentages that people pay inordinate amounts of money to achieve small gains.  We do not have inordinate amounts of development budget, but are serious about making the best available clone and do test and chase improvements.

- I would assume JessJackson is positioned quite well to produce and share a few high-quality exemplar sound clips in a controlled environment so we can all hear what the differences are.  This would generate our first actionable data point.

If JessJackson had left it at that, no credibility would have been lost, but the subsequent gross mis-interpretation of how the circuit actually functions discredited him in the technical discussion.  Kindof like saying,  "I like V8 engines better because the torque response of my Subaru turbo is so awesome."  It becomes nonsensical and will quickly turn off anyone listening who does have the technical understanding of how the circuit works.

This is a support thread for a specific kit.  Accuracy of information matters for people reading here for information, so yes, the people who directly design and support this kit will jump in and make corrections of inaccurate information quickly.

Matador makes a prioritized list of possible factors in the circuit and is in turn "complimented" about his lack of real musical experience. .  . ok. . . this again, produces no actionable data. . . like:

- The actual present-day values of the 4 filter capacitors and resistors in the vintage PSU particularly C4.  These are very old and what is being heard could very well be a PSU that is now out of spec.  If that is the case, the "out-of-spec" configuration can be cloned

- The specific year and internal photos of the vintage PSU (there were several iterations with major internal component changes).

- The actual output of the vintage transformer and dimensions of the core.

- The type of resistors used throughout the B+ section of the vintage PSU and their present-day values.


. . .ACTIONABLE, accurate information instead of conjecture and chest thumping.

 

[kidvybes]

Seems like there is an awful lot of posturing and chest thumping going on here with very little actionable data to work with!

It would help everyone if we all stayed within our various areas of actual proficiency and not make wild conjecture outside of that.

...true...it's clear that there's two parallel realms being discussed here, but if there's an opportunity for both sides to benefit, it's best if the conversation stays amicable and continues in a productive manner...I'm sure Jess' schedule is very tight and opportunities to gather soundfiles (representing the same clone mic coupled to both an original and modern BOM PSU) are scarce, but if possible I would love to hear the comparison...some of us here do have access to high-end monitoring systems, so it would be helpful to hear (or at least attempt to hear) what Jess is hearing...

...my only hesitation comes from the fact that I own two of the MataChung PSUs, built by two very experienced techs, with identical components, that sound different enough to hear on "not-so-high-end" monitoring, so how do you standardize the "sound" of the modern BOM PSU enough to draw a measurable conclusion?...

 

[JessJackson]

there is an awful lot of posturing and chest thumping going on here with very little actionable data to work with!

If JessJackson had left it at that, no credibility would have been lost, but the subsequent gross mis-interpretation of how the circuit actually functions discredited him in the technical discussion.  Kindof like saying,  "I like V8 engines better because the torque response of my Subaru turbo is so awesome."  It becomes nonsensical and will quickly turn off anyone listening who does have the technical understanding of how the circuit works.

Mate don't get ahead of yourself... I said the c12 is fixed bias and you said its self biased, therefore I'm discredited from the technical discussion?... I'll allow my friend the late Oliver Orchut put you straight.
( http://repforums.prosoundweb.com/index.php?topic=34443.msg508369#msg508369 )

My friend Klaus Heine also refers to the c12 as being fixed bias.
( http://prorecordingworkshop.lefora.com/reply/46982651/AKG-C12-Questions#reply-46982651 )

and Mr Bock can further explain to you why its refereed to as fixed bias
( http://prorecordingworkshop.lefora.com/reply/46982702/AKG-C12-Questions#reply-46982702 )

I remember when you first started building mic circuits on here as a newbie... you've educated yourself fast and made a few pennies out of Chucks China connects and unfortunately we lost him from these forums over that drama. I'll leave the "actionable data" to you and you leave the Credible Opinion to me.

anyway.. Out today on iTunes, ( recorded with my version of Dany's u67 - http://groupdiy.com/index.php?topic=50021.0 )

https://itun.es/i6BX8xR

We'll leave it at that.

J

 

[trans4funks1]

Hi Matador,
Do you think you could lend some advice to people who might want to try a zener diode regulated heater supply?

I have been interested in trying that and after reading up on it several times I still feel like I just need to build a couple, of designs that are known to work, before I actually get the idea.

Thank You.

 

[kidvybes]

...it benefits all if cooler heads prevail...maybe time to regroup and address the issue (sans the egos)...
...way too much talent in the room on both sides of the issue to let the conversation go south like this...just my .02c...

 

[Matador]

Mate don't get ahead of yourself... I said the c12 is fixed bias and you said its self biased, therefore I'm discredited from the technical discussion?... I'll allow my friend the late Oliver Orchut put you straight.
( http://repforums.prosoundweb.com/index.php?topic=34443.msg508369#msg508369 )

I encourage you to fully read your quotes before putting them forth as evidence of absence.

In the above Oliver doesn't even mention any bias terms, only that the negative voltage is delivered from the PSU to the grid via a resistor.  Nobody is debating that: there is much more to biasing than simple circuit topology.

And since he's not here to participate in the discussion (and never can), I won't ponder what else he might have meant.

My friend Klaus Heine also refers to the c12 as being fixed bias.
( http://prorecordingworkshop.lefora.com/reply/46982651/AKG-C12-Questions#reply-46982651 )

Indeed he does use that term:  perhaps he can come here to this thread to debate this himself?  Or do you speak for him?

What do you think is correct, and why?

and Mr Bock can further explain to you why its refereed to as fixed bias
( http://prorecordingworkshop.lefora.com/reply/46982702/AKG-C12-Questions#reply-46982702 )

A strange thing to quote:  if I understand David correctly, he is arguing that "it must be fixed bias, because otherwise why would AKG put in an extra connector on the PSU, and use an extra 30M resistor otherwise?"  David hangs around here occasionally maybe he can clarify what he meant.

So, again, do you have anything substantive yourself to add to this discussion?

In case it helps readers of this thread (and to try desperately to extract something meaningful from this discussion), I'll again put forth my definition, my reasoning, in my words:

Fixed bias is any biasing method where the bias voltage is independent of a) collector current (for a transistor), b) drain/source current (for a FET), or c) plate current (for a tube).  Self bias is any biasing method where the bias voltage is dependent on the same factors.

I don't think my definition is out of line from any of the common texts on the subject:  from the 1975 RCA Receiving tube manual, page 84 (emphasis mine):

Grid voltage may be obtained from a fixed source such as a separate C-battery or a tap on the voltage divider of the high-voltage supply, from the voltage drop across a resistor in the cathode circuit, or from the voltage drop across a resistor in the grid circuit. The first method is called "fixed bias"; the second is called "cathode bias" or "self bias";

Similar wording appears in the 1930 Radiotron Designers Handbook (probably on someone's table at AKG when the C12 was designed):

It is sometimes desired to operate the valve with fixed bias, either from a separate bias supply (battery or rectifier/filter combination) or from a voltage divider across the plate supply.

In either case, external batteries or separate supplies cannot be modulated by the current of the active elements (unless the supplies are poorly designed).

Further, from Tom Wheeler's book The Soul of Tone, page 90 (emphasis mine):

Fixed Bias: Grid voltage obtained from a fixed source, such as a tap on the voltage divider of the power supply.  By far the most common method of biasing power tubes,  fixed biasing entails an independent supply of negative voltage connected to the tube's grid.  It sets, or "fixes", the control voltage at a consistent level.

There is an absurdly easy test that follows from these definitions:  pop in a different tube that runs at a different quiescent current point, and see what happens to the bias voltage.  If it changes based on the tube, it isn't fixed bias. 

In the C12, tube return current sets the bias, which flows across R3 (R3 in my schematic, R8 is AKG's original schematic):  the higher the plate current, the more drop there is across R3, which means the more negative the bias becomes, which means plate current tries to decrease.  It's is the exact same negative feedback mechanism as an un-bypassed cathode resistor, and it if you asked the tube what biasing conditions it sees, it wouldn't be able to tell the difference between the C12 method and an unbypassed cathode resistor method.  Hence from my reasoning, the C12 isn't fixed bias.

Do the exact same test in a Fender AB763 "Super Reverb" amp (or one of it's many derivatives):  set the bias for -40V, then start subbing in different output tubes.  The -40V never changes (provided those tubes aren't driven into positive grid conduction, at which point all bets are off), regardless of the actual tube in the socket.  Hence, it is fixed bias.

Jess, do you have anything to refute any of this?  Or can I expect some more "proof" in the form of JPG's of album covers?

I'll say it again:  I get it!  You like your original C12!  I hope you continue to do great things with it.

 

[Matador]

I'm guessing that the answer to my question is no.

That's the funny thing about guessing:  if nothing else, you're right about 50% of the time.

 

[Biasrocks]

I'm guessing that the answer to my question is no.

That's the funny thing about guessing:  if nothing else, you're right about 50% of the time.

I had to guess, because you did not provide a clear answer.

Semantics and cherry picking aside, I'll ask again.

Have you compared an original AKG PS sound to your PS???

Mark

 

[Matador]

I'm guessing that the answer to my question is no.

That's the funny thing about guessing:  if nothing else, you're right about 50% of the time.

I had to guess, because you did not provide a clear answer.

Semantics and cherry picking aside, I'll ask again.

Have you compared an original AKG PS sound to your PS???

Mark

Actually I had three on my bench over this timeframe.  My impressions of them:  I was surprised how different they were from each other.  The third one I had a lot less time with, as it was a repair for a friend who works at a studio in San Jose.  The second one was a crackly mess (something in the binder connector at the microphone), however the owner didn't want me to fix it.

The first one was the "best" IMHO:  it was much more detailed sounding than the third one.  All three of them had a similar "vibe"...if I had to describe it, it would be with the "gangly keys" test.  All of them recorded this sound without sounding too piercing, where the same test with a cheap Chinese microphone would make you want to claw your eardrums out.  All three were from the early 60's if memory serves.  If I was buying one, I would have picked the first one.

The third one had the most pronounced bass response:  if you thumped the boom mike, it's THUD was much stronger sounding that the first two.  Midrange response seemed to be roughly the same across all three:  when compared directly to a U87, the differences in the signatures seemed quite obvious.

The PSU seemed unremarkable to me:  most designs of this era look the same:  rectifiers, RC filters, maybe chokes, etc.  I used the first two mainly to probe around the various circuit voltages, and I connected a few test loads to see how much current I could get at various voltages.

I can't say that I ever connected a new mike to an old PSU, but I'm positive I did the reverse:  the original mike to the new PSU.  Most of the mikes continued to sound different in relative ways in the various combinations.  Since I changed the topology of the heater connections I wanted to listen closely for additional noise or oscillations keeping the old mike constant.

What I learned:  different old mikes sounded different to each other, they sounded different to the new ones, and all things in-between.  All seemed to have the same "high lift" signature (both old and new).  My personal favorite mike out of all the combinations was the new one with Tim's capsule and the CM-2480 output transformer:  it's seemed to be the most evenly balanced out of everything I tried (and I tend to prefer the "HPF" sound in the bass region).

However my ears are not Grammy nominated, so I'm probably not able to render an opinion on any of this in any case...anyone can feel free to ignore it.  Maybe Chunger can provide more details on the studio tests and sample recordings, most of which are here previous in the thread.

So do I win a prize?

I'm pretty sure nowhere in the 75+ pages of this thread (or any other) that I guaranteed that each and every microphone would sound perfectly identical...this would be a fools errand, as even the capsules can't be guaranteed to do this, and they aren't even part of the "circuit design".  If the aim was to minimize PSU-to-PSU variation I would definitely *not* have implemented a passive B+ supply to start off with.

 

[Matador]

Hi Matador,
Do you think you could lend some advice to people who might want to try a zener diode regulated heater supply?

Sure.  Removed everything "after" C8 (including IC1 and heatsink, D9 and D10, and R9, R10, R10, and C9).  You then need to find an appropriate Zener (get a 5W one) and place it in parallel with C8.  Then you'll need to tap the new supply right from the new Zener.

You'll probably need to adjust the values of R7 and R8 though, as the Zener will fight the transformer to hold a steady drop across itself:  given those resistors are pretty low, they can make the supply look like a short circuit and the Zener will cook itself over time.  You'll want to adjust R7 and R8 (e.g. increase it) so that the Zener just turns on when the heater is connected.  If you use a 6.1V Zener, paper napkin calcs say you want about 17 ohms between R7 and R8:  pencil in a 10 ohm for R7 and a 6.8ohm for R8 and you'll be very close.

 

[tonycamp]

It would be interesting if Jess did some measuring in his old PSU to see what is? My Matachung C12  is absolutely killer on acoustic instruments, but a little sharp on my voice, if I could get that  sharpness smoothed out just a bit without  changing the stellar parts of its current sound, I'd be stoked beyond the happy I already am 8)

I'm using a C Whitmore ge 6072 and TC capsule.

 

[MicDaddy]

Let's keep it classy guys & gals (are there any gals here even?)

This is a place where we can have valid positions even not in agreement and still be able to share in a :guinness: at the end of the day, at least this is something I subscribe to within the realm of groupdiy.  Don't make it like the purple forum.

I'm listening very intently to all contributors, and appreciate everyone's input. 

 

[Tim Campbell]

Tonycamp,
Short of getting me to tweek the capsule you could try moving the pattern switch towards fig.8 a notch or two, substitute an RCA 12ay7 or an EF86 tube.

 

[JessJackson]

My friend Klaus Heine also refers to the c12 as being fixed bias.
( http://prorecordingworkshop.lefora.com/reply/46982651/AKG-C12-Questions#reply-46982651 )

Indeed he does use that term:  perhaps he can come here to this thread to debate this himself?  Or do you speak for him?

Grow Up.

Jess, do you have anything to refute any of this?  Or can I expect some more "proof" in the form of JPG's of album covers?

I heard the difference, I reported to benefit everyone. Your fear created your ego to refute. I don't need to come back with anything other than the fact that I think everyone on this board should be forced to use their real names and this is for you:

Jiddu Krishnamurti - "Knowledge gets in the way of vision, creativity and art" ( https://www.youtube.com/watch?v=jOVblLPzJ-E ) enjoy

I'll say it again:  I get it!  You like your original C12!  I hope you continue to do great things with it.

I don't ever use it, its more a collectable piece. not really a fan of the C12 in general. We use my vintage elam 251 most of the time over c12. Sits better in a mix.

J