Official C12 Clone - Build and Support Thread

[Pip]

No defects that i can tell in the headbasket.  Only thing i can think of is that the chrome bath that it got made that screen mesh just REALLY hard.  (kinda like when you tune a drum head)

(sorry im trying things as i type this so it may seem all over the place)

I "massaged" the mesh a little (hearing the chrome crackling a bit as i did it) and it actually seems to have helped.  Maybe it was just to solidified from the chrome plating.  To answer your question Chung, no didn't get it with the original head basket and its 15 layers of mesh lol.  Im only hearing the ring now if i tap it with my finger, and if anyone taps this with their finger during a session im gonna be pretty annoyed anyway lol.  So, cheers n beers to you and matador for putting this awesome sauce together!!!! 

Hey, the mic sounds AMAZING!!!!  I have one small question/gripe and perhaps its something that i did.  The new head basket has a helluva resonant frequency around 430 cps.  Anyone have a good way to dampen that? (besides EQ)

Yes, i have a great way to dampen that, go to home depot, go to the electrical section, find box/duct seal, It comes in the shape of a giant candy bar w/white wrapper, it costs under $2, its for sealing the back of electrical boxes from weather. roll up a small amount into mini hot dog shape the width of the vertical posts, then line it up and push it into the offending rails from the inside. Works awesome, and poses no threat of falling off or damaging anything, and soaks up those resonances. I've done this to a dozen mics with great results. It's not too sticky and messy at all, just make sure you wash your hands before handling the re assembly of the mic.

good luck

anyone know the exact value of R1 R2 resistor change? my B+ is maxed at 113.4V

thanx
T

Sorry first thing is I am going to share something that was beaten into me by one of my mentor/teachers a true sage in the HIFI community, so forgive me if this is misdirected but it is an important distinction. DAMPENING involves water and a sponge usually, DAMPING is the effect of a force on oscillations. He would still grit his teeth to this day if I said one when I ment the other. Thanks that felt good.

430CPS is rather low this mic is always going to be somewhat vulnerable to handling noise. What capsule and mount are you using and also what tube. It sounds to me like you might have a microphonic issue.

 

[tonycamp]

Using 400K is fine.

There is obviously much higher tube tolerance than the original datasheets suggest.  Getting more current through the bleeder is one way to get more current flowing through the bias network.  In reality, the original C12 schematic shows a 300K resistor (R9) as the B+ bleeder, but that design was also only half-wave rectified, so it's not apple to apples in any case.  This had to be done in order to make use of the stock transformer in this circuit.

[size=14pt]As a general principle, if the B+ voltage is too low (can't be trimmed high enough), then one has several options:  a) reduce R1 and R2 in value, b) increase the value of the bleeder R6, or c) make the bias voltage more negative.  B and C reduce the current through the network which increases B+, and A reduces the voltage drop while keeping the current roughly the same.
[/size]
If the B+ voltage is too high (can't be trimmed low enough), then reverse the direction of everything above.

I was on the fence about making the B+ part of the supply regulated (with a MOSFET pass element and a Zener diode bias with feedback), however this is a drastic departure from the original supply and likely has more sonic implications.

Hey fellas, which option is best? my B+ is low at 113.4V, is there an exact value on R1 and R2 for a 6072A?, is a,b,or c a better option? I'm a first year newb, i'm getting better, but i'm just not comfortable making these decisions on my own

help a brother out?

http://www.groupdiy.com/index.php?topic=51377.msg666445#msg666445

I think this is best option. Again 75K was my choice with the same problem.

Pip

Thanx brother! So here's what i did just because, i new the mic was working ok(no smoke or sparks or flames ect. ;D), so I backed my B+ trimmer off to about 95v, pulled my tester 12at7, put in the 6072A, and trimmed it up, and now i get B+120v(trimmer is still wide open though), bias -1 and heater 6.3, go figure? Is a 12at7 a poor choice for testing? I must admit, i kinda had a little panic attack sticking a $100 tube in it, but i had a feeling it would change things, Now alls good apparently. Im gonna trow da Tim Campbell capsule in and give her a go, i'll report tommrw.

thanx for the reply Pip

 

[tonycamp]

Check this out my brothers of DIY, considering we are at only 5% of this cost with our builds, even utilizing the best parts available! It truly brings a  to my heart, as i have a hard time believing it sounds $19,000 better than my Matachung C12(i'm aware the listing is an ELA M251)

Thank you Matador and Chunger for bringing the dream of Unobtainium to reality! (make sure you scroll down the page, there are some great pictures!)


http://www.ebay.com/itm/TELEFUNKEN-ELA-M-251-E-VINTAGE-ORIGINAL-CLASSIC-TUBE-MIC-MINTY-LQQK-SIR-380-/290774086590?pt=US_Pro_Audio_Microphones&hash=item43b37c73be

 

[Gus]

Be careful with duct seal.  I would use something else.

IIRC it out gasses and anything that out gasses is bad to place by a condenser capsule

 

[tonycamp]

Be careful with duct seal.  I would use something else.

IIRC it out gasses and anything that out gasses is bad to place by a condenser capsule

I don't know what kind you're talking about, I was concerned about that before i used it also, so i looked into it.  I use "IDEAL" duct seal from home depot(thats all they carry out here), a quote from their site

"The Duct Seal formula is completely nontoxic, and unlike many other chemical-based repair materials on the market, you can handle it without gloves or fear of skin irritation/chemical absorption. It’s also completely non-corrosive, so it’s safe to use on both plastics and metals. Ooooh, and one more thing: Duct Seal also has a relatively high flash point (590°F), so it’s helpful in preventing electrical fires"

I sealed every outlet box, switch box, door knob, damped lamps, and a lot of other things that resonate in an undesirable fashion in my studio. I've put it into a lot of mics, they all still work great, I used bare hands to install all of it, no skin irritation, cant smell it unless you put your nose right on it, and i forget which mics its in until i tap on the basket, so??

 

[Gus]

I have used duct seal in the past for damping things like turntable headshells.  IIRC it left a residue when I removed it from the headshell.

Just because you can't smell or it is nontoxic it does not mean it is not outgassing. 

 

[tonycamp]

Ok then, i'm gonna pull my Thiersch Blueline PVC M7 capsule out of my mic, because PVC out gasses like crazy! And while i'm at it, i'm going to pull out the wire from my mics because they have chemical insulation on them, my carpet, air ducts, paint, acoustic foam, this Mac computer, and every product in the house that contains some form of petroleum based plastic, including my food containers. Also the plating process on my mic bodies is so toxic it's ridiculous, i should throw those away also.

IMO, its no big deal, besides, I'd rather deal with a little poison in the air than a harsh upper mid resonant frequency any day!lol

I'm not forcing anyone, don't use it.  it works really nice though

 

[Gus]

I believe you are misunderstanding my posts.

I have worked on older microphones that had a coating on the mylar, as best I could tell without a test was the foam inside the headbasket broke down and was a part of the coating on the mylar.

Anything that has a plasticizer added can outgass like in a new car. 

My point is what is in the duct seal might/will coat the mylar of the capsule possible causing issues.

I agree duct seal damps very well.

 

[tonycamp]

I have(had) 2 vintage sm81's that are complete junk now due to the shure microphone cases, the foam in them dissolved into oily goo, destroying the mics. I had them perfectly stored with all my other mics.
I believe duct seal is too dense in it's formulation to be flyaway like foam and stick to a capsule. I will just agree to disagree with you, as my results have been problem free and excellent.

BTW, i like a lot of the posts you've done, always informative

Thanx
T

 

[JessJackson]

I still have very low output.

Question, what is the common reason in this circuit for low output level? I feel that I may have the xformer wired wrongly or something simple like that.

on Pg 9. i post images of my transformer. I wired the high number to the circuit board and the low number to the XLR but forgive me if i'm being an idiot but shouldnt the higher resistance go to XLR and lower resistance go to board since its a step down xformer.

Also should my green wires be tied together. like most ela m / c12's are?.. i think im going to have to pull the xformer and re-measure.

 

[sr1200]

Got the same tube that chunger used in his photo documentary of the build.  Purchased from tube depot, ordered low microphonic yadda yadda.  Its definitely NOT the tube though, since when i swap the head basket for the old one, the issue is not there at all.  As I stated earlier, the problem isn't really a problem anymore since i bent the screen around a little.  The body resonance is way down near about 100 or so best i can tell from handling it.  (not very scientific tests here for this lol)

BTW chung... how did they buff the nickel to a shine on the screen lol (totally looks like chrome to me and even has pitting like chrome!) ??  Bout to use it for a session in about 20 min.

 

[chunger]

Got the same tube that chunger used in his photo documentary of the build.  Purchased from tube depot, ordered low microphonic yadda yadda.  Its definitely NOT the tube though, since when i swap the head basket for the old one, the issue is not there at all.  As I stated earlier, the problem isn't really a problem anymore since i bent the screen around a little.  The body resonance is way down near about 100 or so best i can tell from handling it.  (not very scientific tests here for this lol)

BTW chung... how did they buff the nickel to a shine on the screen lol (totally looks like chrome to me and even has pitting like chrome!) ??  Bout to use it for a session in about 20 min.

I didn't do any of the buffing!  The factory did.  I believe it's surface treatment prior to plating that makes the difference.  Also, it is MUCH more forgiving to do bead blasted matte finish because the blasted surface hides imperfections (and at this price-point, it will have imperfections).  The main reason I ordered the polished nickel finish instead of bead blasted nickel was different factories may have different formulations in their plating process and I did not want to risk the colors being different between the microphone body and the headbasket.  By doing the polished finish on the basket, it contrasts either way so even if the color of the plating is a little off, the mic still looks nice.

 

[Matador]

I still have very low output.

Question, what is the common reason in this circuit for low output level? I feel that I may have the xformer wired wrongly or something simple like that.

on Pg 9. i post images of my transformer. I wired the high number to the circuit board and the low number to the XLR but forgive me if i'm being an idiot but shouldnt the higher resistance go to XLR and lower resistance go to board since its a step down xformer.

Also should my green wires be tied together. like most ela m / c12's are?.. i think im going to have to pull the xformer and re-measure.

It's a step-down, meaning the primary has a lot more turns than the secondary.  Since that wire has resistance, you want the side with more resistance on the primary, and the low resistance on the secondary. 

What green wires are you referring to?

 

[JessJackson]

I still have very low output.

Question, what is the common reason in this circuit for low output level? I feel that I may have the xformer wired wrongly or something simple like that.

on Pg 9. i post images of my transformer. I wired the high number to the circuit board and the low number to the XLR but forgive me if i'm being an idiot but shouldnt the higher resistance go to XLR and lower resistance go to board since its a step down xformer.

Also should my green wires be tied together. like most ela m / c12's are?.. i think im going to have to pull the xformer and re-measure.

It's a step-down, meaning the primary has a lot more turns than the secondary.  Since that wire has resistance, you want the side with more resistance on the primary, and the low resistance on the secondary. 

What green wires are you referring to?

ok, cheers matador, so i have it wired correctly in that case.

Wonder what else could be causing the low output.

Im referring to the 50ohm green wires. I have an original Haufe T14. the images are on page 9 of this thread.

 

[baadc0de]

I still have very low output.

Question, what is the common reason in this circuit for low output level? I feel that I may have the xformer wired wrongly or something simple like that.

on Pg 9. i post images of my transformer. I wired the high number to the circuit board and the low number to the XLR but forgive me if i'm being an idiot but shouldnt the higher resistance go to XLR and lower resistance go to board since its a step down xformer.

Also should my green wires be tied together. like most ela m / c12's are?.. i think im going to have to pull the xformer and re-measure.

It's a step-down, meaning the primary has a lot more turns than the secondary.  Since that wire has resistance, you want the side with more resistance on the primary, and the low resistance on the secondary. 

What green wires are you referring to?

ok, cheers matador, so i have it wired correctly in that case.

Wonder what else could be causing the low output.

Im referring to the 50ohm green wires. I have an original Haufe T14. the images are on page 9 of this thread.

I also have extremely low output. Voltages are OK, transformer is wired properly (AMI), tube swaps don't seem to be doing anything..

 

[HellfireStudios]

Hey, I got one of the first-run C12 headbaskets as well, and I had the same ringing problem. My fix was to use Loctite Go2 Glue as a dampener. It reminds me of hot glue when wet, and rubber cement when dry, but dries crystal clear. I added it to the inside of the rails and around the base ring. It seems to have brought the ringing to a dull thud.
I would use painter's tape to cover the visible screen (not covered by rails, etc.) before applying glue, and removing the tape 10 minutes later as the glue tends to settle. Be careful to not use too much glue, and work with one section at a time to avoid dripping.
Sorry to be so long-winded, but I wouldn't want anyone to ruin their brand new headbasket...

-James-

 

[JessJackson]

I still have very low output.

Question, what is the common reason in this circuit for low output level? I feel that I may have the xformer wired wrongly or something simple like that.

on Pg 9. i post images of my transformer. I wired the high number to the circuit board and the low number to the XLR but forgive me if i'm being an idiot but shouldnt the higher resistance go to XLR and lower resistance go to board since its a step down xformer.

Also should my green wires be tied together. like most ela m / c12's are?.. i think im going to have to pull the xformer and re-measure.

It's a step-down, meaning the primary has a lot more turns than the secondary.  Since that wire has resistance, you want the side with more resistance on the primary, and the low resistance on the secondary. 

What green wires are you referring to?

ok, cheers matador, so i have it wired correctly in that case.

Wonder what else could be causing the low output.

Im referring to the 50ohm green wires. I have an original Haufe T14. the images are on page 9 of this thread.

I also have extremely low output. Voltages are OK, transformer is wired properly (AMI), tube swaps don't seem to be doing anything..

Post all your voltages measured at mic, i'm gonna do the same and try to figure this low output issue.

 

[Matador]

Can we quantify exactly what "low output" means?  How many DBFS is it lower than what you are expecting?

 

[baadc0de]

Can we quantify exactly what "low output" means?  How many DBFS is it lower than what you are expecting?

Another build I just did seems to be ~ 20dB louder. I'll test at the studio soon to be extra sure. From my measurements, the voltages seem to be OK and since tube swaps are not working, I guess it's either the capsule or transformer. I can probably inject signal on both and see if the gain drop still occurs. If it does, it should be the transformer, if not, the capsule. Let me know if you guys have any other suggestions.

 

[tonycamp]

Can we quantify exactly what "low output" means?  How many DBFS is it lower than what you are expecting?

Another build I just did seems to be ~ 20dB louder. I'll test at the studio soon to be extra sure. From my measurements, the voltages seem to be OK and since tube swaps are not working, I guess it's either the capsule or transformer. I can probably inject signal on both and see if the gain drop still occurs. If it does, it should be the transformer, if not, the capsule. Let me know if you guys have any other suggestions.

Double check your bridge on the back plates??