Official C12 Clone - Build and Support Thread

[JessJackson]

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.

I don't think your capsules need tweaking, you balance them well Tim. I've had a few off of you now.

Your right, we would always go one click towards omni to give a softer / smoother sound with less proximity effect on the C12. it works well and something you can't do on the 251 circuit.

 

[trans4funks1]

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.

Thank You Matador!

 

[Matador]

stuff

Look - i'm 99% sure this forum is for discussing the design, building, use, and merits of different music technology:  and this sub-forum is for the microphone piece of this puzzle.  And none of us have been discussing microphones for the past several pages.

I'll be the first to admit wrongdoing or casting someone's words in the wrong light.  If you are honestly explaining that:

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.

followed by:

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.

was an attempt to start a conversation and to discuss "a couple of mods", and was not a statement of a deficiency in the design, then you are 100% right, it wasn't fair of me to jump on this in the way that I did.  Context on the internet is always a tricky thing, and I'll try next time to ask for context first, and then shoot later.  ;D

If this is the case, then I apologize (to everyone reading), and it's 100% on me.

Now let's get back to talking about microphones!

 

[Category 5]

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.

Hey Tony, have you tried the Cinemag Chunger has?  Just installed one and found it to be heftier and a little rolled off in a gentle but noticeable way.  It may tone your c12 down just enough.  It's definitely a much better sounding transformer than I expected.

Also, tried any other tubes?  I found Christian's 70s era GEs to be more linear sounding and they seemed to have more up top than I care for.  Like you I'm after a sound that needs no de-essing. The older 50s triple-mica black plates went a long way in smoothing the mics out for me.  After the capsule that made probably the second biggest difference. 

@tim Campbell.

I know you're busy but get me on the list for three (more 2 matched) when you can.  Thanks!

 

[chunger]

When I originally spoke with Oliver in depth about the project, his opinion was that the stock-tuned Tim Campbell capsule paired with the stock-tubed AMI T14 transformer would lack bass.  (German radio application may have influenced the original spec).  After building the configuration and running it in studio, we did not feel it necessarily "lacked bass".  Also, oliver was quite busy and could not get around to developing an alternate spec winding for test.

Discussing the issue and Oliver's opinion with Tim, although he always gave the option of alternate tuning of his capsules, felt fairly strongly his stock tuning to be optimal based on seeing more original C12 capsules than almost anyone else worldwide.  Having used a few samples, i concur that a lower voicing may loose much of what shines in this capsule topology.

In use, we find the C12 to work well on acoustic guitars, piano, sometime for drum overheads in our room, and certain specific female vocals, but it has not been a heavy-lifting "main" microphone for general use.  This finding seems to correlate with what i hear of vintage C12's as well, so we felt the kit to be a success in regards to the end goal of being a clone.

Now, if we move the goal posts a little bit and say we now want to slightly nudge the microphone towards a mainline role, ironically, the general tuning of the Cinemag CM-13114 transformer with its more linear bass response and earlier treble fall-off may be close to what Oliver alluded to as a "better" match for the Tim Campbell CT12 capsule.

Additionally, the .56uF (original spec .5uF) output capacitor is technically under-valued.  It can be easily swapped in the kit up to 3uF (Ela M251 value).  ELA also has a very small treble attenuation 100pf styrene capacitor that can be added.  Matador informs me that this value would make a VERY slight sonic change way up high in the frequency response but we are talking about slight nudges here.

Category5's suggestion to roll different vintage tubes is also certainly a big sonic influence.

 

[Melodeath00]

Just my own opinion, but my C12 with CT12 and AMI T14 is more than bassy enough. I also couldn't imagine wanting to roll any treble off, and honestly, I wouldn't mind less bass or more sheen. So overall, it probably depends very much on your particular build/components. I have also tried 3 or 4 different tubes, and did not notice any sort of drastic difference. I even made some speaker tests with the mic recording audio using the different tubes, and again, found no differences. I think they were all 50s and 60s tubes, though. Nothing 70s. When I tried doing the "tube tests" without using the constant source of a speaker, it was a fool's errand. No two take sounded alike even with the same tube, so it was impossible to judge anything when you open the mic up, replace the tube, and try to keep your relative position to the mic 5 minutes later.

I wish Oliver had made a T14/1  transformer (the later version with less bass, and the only version found in the 251). I emailed him about it, but never heard anything back, and I never heard anything back from the new guys at AMI, either.  I'd like to try it in my C12, and definitely would be what I go with in a 251 (which is what I have another CT12 on the way for,  actually)

 

[granger.frederic]

CT12 + AMI T14 = a lot of low mids/bass
i prefer CT12 + HAUFFE  T14/1 : more balanced

 

[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.

Hey Tony, have you tried the Cinemag Chunger has?  Just installed one and found it to be heftier and a little rolled off in a gentle but noticeable way.  It may tone your c12 down just enough.  It's definitely a much better sounding transformer than I expected.

Also, tried any other tubes?  I found Christian's 70s era GEs to be more linear sounding and they seemed to have more up top than I care for.  Like you I'm after a sound that needs no de-essing. The older 50s triple-mica black plates went a long way in smoothing the mics out for me.  After the capsule that made probably the second biggest difference. 

@tim Campbell.

I know you're busy but get me on the list for three (more 2 matched) when you can.  Thanks!

Thanx Shane! great stuff man, i think i'm going to stick with it the way it is, i've been reluctant to screw with it beyond what i've done because I am sooo pleased with it's performance on acoustic instruments, so what Chung says makes great sense to me. I have a pair of TC CT12 here, and i'm planning on a pair of Elam knocks, i'll be trying the Cinemags there i'm sure, i believe i will get the high end extension i'm looking for on these, with the tamed sib freq's? As far as the bottom, i'm perfectly pleased with what i've gotten so far, and i generally filter off the bottom of everything but kick and bass anyway(another rock dude 8) )

 

[Matador]

Additionally, the .56uF (original spec .5uF) output capacitor is technically under-valued.  It can be easily swapped in the kit up to 3uF (Ela M251 value).  ELA also has a very small treble attenuation 100pf styrene capacitor that can be added.  Matador informs me that this value would make a VERY slight sonic change way up high in the frequency response but we are talking about slight nudges here.

On the 0.56uF output cap - when first looking over the circuit, I wondered if this was a conscience choice by AKG to "undersize" it.  Paper napkin calcs with a typical Cinemag CM-2480 put the RLC resonance at about 20Hz, which is already pretty low.  It may be the primary inductance of the originals may be much lower than what we have on modern wound transformers (I think both the Cinemag CM-2480 and AMI T14 are both in the 125-150H range).

The 100pF cap makes a LPF with a 3dB point of about 18-19kHz using typical 6072A tube output impedance values.  This shouldn't impact the audio band to a significant extent.  Increasing this up to 220pF will move this down a bit more than one octave to  about 8kHz.  I'm guessing values of 220pF and higher will start to become quite audible in the high end.

I think there is/used to be a pilot tone at 19kHz, so that 100pF may have been added to reduce artifacts way up there that might have impacted the tone (which would have been inaudible in any case).  I'm not convinced it was ever intended to modify the audible frequency response of the microphone.

 

[TNO73]

Hello Everybody and thanks to Matador&Chunger to make this project happen!

I´m just fnalizing Matachung c12->elam251 build. ;D
But now having problems setting the PSU B+ Voltage.  With a dummy load of 200K from B+ to ground, i´m only able to trim B+ to appr. 130 VDC - and with no dummy load i´m way over 200VDC - also to mention is that the transformer secondary is giving me almost 230VAC instead of 200VAC.
Is this type of transformer primary VAC115 -115 not useable for my location, i´m located in austria and i´m measuring 240VAC at the power plug?
Where could i look into?
Thanks
Tom

 

[muffy1975]

HI,

with the Tim C capsule, which is supplied without any leads  attached.....can I remove the tabs and solder wire to the tabs  then re attach them.? Or do i carefully solder wire straight onto the tabs whilst attached to the capsule....????

i  don't want the heat of the soldering iron near the capsule itself.

this is a very expensive capsule. Naturally i don't wish to get this wrong.

Michael

 

[Category 5]

HI,

with the Tim C capsule, which is supplied without any leads  attached.....can I remove the tabs and solder wire to the tabs  then re attach them.? Or do i carefully solder wire straight onto the tabs whilst attached to the capsule....????

i  don't want the heat of the soldering iron near the capsule itself.

this is a very expensive capsule. Naturally i don't wish to get this wrong.

Michael

Leave all of the tabs.  there is a plastic protective layer that the capsule ships with that is sufficient to protect the capsules during lead attachment.  Don't take it off until after the connections are made.  I like to tin the wire tips a bit so they stick with ease.  Get the wire into place and tap it with the iron long enough to make the connection and then back off.  If you work quickly the heat will not transfer to the membrane, and the plastic will protect against any flux splash.

Enjoy!  Those capsules sound fantastic!

 

[muffy1975]

thank you for your  kind answer.

Pre tin I shall and work quickly i will.


Michael

 

[TNO73]

Hello Everybody and thanks to Matador&Chunger to make this project happen!

I´m just fnalizing Matachung c12->elam251 build. ;D
But now having problems setting the PSU B+ Voltage.  With a dummy load of 200K from B+ to ground, i´m only able to trim B+ to appr. 130 VDC - and with no dummy load i´m way over 200VDC - also to mention is that the transformer secondary is giving me almost 230VAC instead of 200VAC.
Is this type of transformer primary VAC115 -115 not useable for my location, i´m located in austria and i´m measuring 240VAC at the power plug?
Where could i look into?
Thanks
Tom

pls help troubleschoot....

 

[Matador]

pls help troubleschoot....

With no load, the B+ will be very high...that's normal.  Passive PSU's need load current to establish their working output voltages.

The proper test load is 180K (not 200K) for a 6072A tube.  You want to pull about 0.7ma through the test load @ 120V, which is 171K (180K is closest standard value).  200K will pull 0.6mA, and that small 0.1mA difference in current will translate to +18V higher B+.  Subtract 18V from your measurements above and you'll be in the proper range. 

If you cannot adjust down enough after changing to the proper load then it means that the series PSU resistors (R1 and R2) need to be higher in value.  Stock value is 91K:  I would change them to 100K and you should be able to get it down below 120V.

 

[muffy1975]

HI,

have there been many instances of broken AMI T14 Tx s?

i ask because the primaries of my T14 are reading 2mOHMs which is obviously wrong.

The 2ndries are fine however.

What could be damaging the windings of these T14s? Could it be the conneting wires coming loose?

Michael

 

[mica]

I was unlucky enough to get 2 broken T14's before i got a working one.. Chunger was really cool exchanging them quickly, but it delayed the project ofcourse. Maybe you just got a bad one? Only the 3rd i got measured correctly.

/M

 

[TNO73]

pls help troubleschoot....

With no load, the B+ will be very high...that's normal.  Passive PSU's need load current to establish their working output voltages.

The proper test load is 180K (not 200K) for a 6072A tube.  You want to pull about 0.7ma through the test load @ 120V, which is 171K (180K is closest standard value).  200K will pull 0.6mA, and that small 0.1mA difference in current will translate to +18V higher B+.  Subtract 18V from your measurements above and you'll be in the proper range. 

If you cannot adjust down enough after changing to the proper load then it means that the series PSU resistors (R1 and R2) need to be higher in value.  Stock value is 91K:  I would change them to 100K and you should be able to get it down below 120V.

all right, thank you very much - just tried with a dummy load of 178K(thats what i could establish) which took my voltage down to 123VDC. Still a little to high!

Gonna try to change R1+R2 to 100K, looking forward to report back on this issue.

Tom

 

[muffy1975]

Hi,

just swapped in a working T14 from another of my mics and this c12 sounds AWESOME.

I made it point to point using matadors psu and mic components but laid them out P2P.

The body is  a gorgeous AMI c12 body. nice and heavy.....wow...

using a Tim C capsule and a T14.

This capsule is really amazing......

 

[hitchhiker]

Hi,

just swapped in a working T14 from another of my mics and this c12 sounds AWESOME.

I made it point to point using matadors psu and mic components but laid them out P2P.

The body is  a gorgeous AMI c12 body. nice and heavy.....wow...

using a Tim C capsule and a T14.

This capsule is really amazing......

I'd like to do the same in P2P , could you post links  (or pm me if you prefer) to the matador PSU and mic schemes and any other helpful details?