Official C12 Clone - Build and Support Thread

[Matador]

Just to add a little info.
I don't claim that both halves of every capsule or that every capsule I make are indistinguishable with each other.
This capsule is complex and made in small batches and so halves are matched within reason and capsules are matched more closely when asked. AKG's CK12 capsules are notorious for sounding similar in only a general way and vary wildly from one to another. Much of my methodology is aimed at mimicing these older capsules. Sometimes striving for more nuance and detail can result in variation.
Klaus Heyne talks repeatedly about the fact that he listens to both sides of every Neumann and AKG capsule he installs and finds differences every time and so selects the better half to use as the front facing membrane.
Monitoring over headphones while listening to fig 8 will very often result in difference in timbre because of phase differences between the 2 membranes and the headphones.
Factory made capsules can result in more consistent sound because they're made by the thousands resulting more halves for selection and methodology that results in more consistent results but less nuance and detail.
All that said, I try to keep differences to a minimum and am glad to address these variations where they are problematic.
As far as the screw size I use blame AKG. I'm only following their construction (M1's).

Tim, what information (if any) can be gleamed by measuring the capacitance of each side?  Given that a lot of the sound is likely governed by the mechanical/acoustic coupling of the various pieces, I would guess it is but one variable in a long list.

Electrically, based on my simulations less capacitance means slightly less gain (50p vs 80p is about 2dB of difference), but the effects on frequency response seem to be outside of the pass band (a dip above 30MHz).

 

[Tim Campbell]

Not much can be gained by measuring capacitance since it's easily skewered by things like contamination from handling.

 

[Category 5]

Hey Mat, what do you think about those polarity voltages?  They seem a little low to me.

And regarding capsules.  I've bought plenty of mics in non-matched pairs and can honestly say they are often a poor match for stereo work.  Even though they retain the same vibe they can have very different responses.  In fact, I have a pair of AKG 450s that are both great mics but i can tell which one I am listening to blindfolded.

No harm in a little variance Tim, but regardless of my issues I think I will send these to you to get them matched.  perhaps you can even tell me which sides match the closest so i can be sure they get used for the front.

 

[Tim Campbell]

Yes, please send them to me and I'll get them sorted straight away. I'd ask that you wait until the 25th to send them. I'll be in Norway until the 26th.

 

[chunger]

I'll post a clarification about my findings on my Tim Campbell CT12 capsules. . . particularly the one where I found different tonality on the back side than the front side.

I have had this capsule running on the front "to my ear not-as-good" side for quite some time.  It was our first build prototype.  This test microphone has seen production use in 3 studios and all reports coming back to me have been stellar, so certainly, the capsule is not broken or malfunctioning.  It was also produced about half a year prior to the capsule that resides in the point to point test build. . . certainly not in the same batch.  We are splitting hairs on very good sounding samples.  It's just that when different, sometimes, a strong preference comes to light, and it can be said, "I like one better than the other". 

For my particular application and use, I have had only 1 instances where the microphone was used in any other polar pattern than cardioid, and even when stereo micing a source, for our production, it is not essential to utilize matched pairs of mics.  In fact, we often use different microphones on L and R for drums, etc.  If I send this capsule back, I will not be necessarily sending it back for any sort of matching or re-work.  It would primarily be to run back through whatever Q/C methodology Tim uses and confirm that both sides are within manufacturing specification for the "standard" model CT12 capsule.  If so confirmed, I will have a better understanding of the sonic range I can expect from sample to sample.

Per early discussions with Tim about alternate tunings of his capsule, I can hear now pretty tangibly why he was hesitant to tune the capsule down from his standard tuning.  He feathers a very fine line where the capsule "opens up" and still offers a a solid bottom end. . . and there is a magic spot in there that he is shooting for.

I don't know what the details are in terms of tuning specifications and Tim should not feel compelled to reveal any specifics of his build methodology and tuning process.  These are after all processes refined over time and separate him from his competitors.  What I do know is these are some of the best-sounding capsules I've come across, and I've let Tim know in no uncertain terms that I will buy every available excess capsule he is able to produce.  So far, he has had none to spare 

 

[Category 5]

Yes, please send them to me and I'll get them sorted straight away. I'd ask that you wait until the 25th to send them. I'll be in Norway until the 26th.

Great!  That will give me some time to see if there are any other issues in play here.  Been tough with the holidays approaching, two in diapers and my workbench covered in parts and projects.  I need to buckle down and get to the bottom of things.  I did get that third capsule from you as well, but since it doesn't need to match the pair there's no need to send it back I'm thinking.

Anyone else see slightly lower polarization voltages than expected?  My B+ is dead on 120V ut polarization exiting the PSU is about 0/55/110 and then a hair lower coming into the mic (loss along cable?  I am still using stock)

ALSO - What voltage should I see on the actual capsule?  Should I be measuring between the backplates and ground?

 

[Melodeath00]

Category 5,

I decided to test my polar pattern readings after reading your post. In the process, something inexplicable happened.

I turned the mic on and everything was working fine. Mic sounded good. I turned off the mic and opened up the PSU. I disconnect the cables, turn on the PSU, and measure the PSU unloaded. Turn PSU off. Plug mic back in and turn PSU on. I'm trying to take measurements inside the PSU, but I also notice the mic now is extremely low output in audio. I turn the PSU off and re-seat the cables - perhaps they weren't making a full connection. Turn PSU back on and measure, but mic is still very low output and doesn't sound great (nasally). Turn PSU off. I re-seat cables again and put PSU cover back on, and power up. Mic now sounds normal. I take PSU cover off and mic still sounds normal. I have absolutely no explanation for what happened. Measurements in the PSU at this stage had no effect on sound, so I don't see why they would have affected the mic output before.

If anyone has any ideas for all that, please mention them.

Regarding voltage readings... Tonight my B+ had somehow creeped up to 125V. In Bi-directional, the polar pattern is measuring 114V, a little low. In cardioid, I'm measuring 53V at the polar pattern terminal in the PSU, also a little low, assuming I'm getting the full 60V from B+ at the capsule.

 

[Matador]

Measuring the polarization voltages is at beast approximate:  the high impedances make measure these with regular DVM's inaccurate.

For example, measuring the polarization voltage right at the PSU "P3" node will cause the meter current to drop across R11 (1 MEG).  A 10MEG meter will induce a 10% voltage error.  A 1MEG meter will cause a 50% error.   So a 10MEG meter will always measure 60V (the cardioid setting) as 54V due to the meter impedance alone.  120V will measure as about 110V.  The bias node "P4" has a similar problem caused by R5, however a 10% error on 1V is only 100mV. 

If you know your meter impedance you can "derate" the reading.

You can't measure anything on the capsule, because the meter current will go across the astronomically high impedances and clobber the results:  think of a 250M / 10M voltage divider:  the series resistance will clobber 97% of the measured voltage.

 

[Melodeath00]

Thanks Matador. My DVM is indeed 10Meg, so looks like 53V for cardioid is right on target. Does measuring B+ in the PSU have a similar voltage drop? A couple of weeks ago, I was right at 120V, but last night it was 125V, and I know we're not supposed to go over 120V. I think I should turn it down a bit, but I'm wondering if I need to account for a voltage drop.

Also, since measure bias has a 10% error, should I be shooting for -.900 V instead of -1V?

 

[Category 5]

Remember B+ isn't regulated so it will go up and down with fluctuations in the mains voltage. 

 

[Melodeath00]

Right, but I didn't expect THAT much of a fluctuation. Maybe I should knock it down to be sure I never go above 120V?

 

[Category 5]

Right, but I didn't expect THAT much of a fluctuation. Maybe I should knock it down to be sure I never go above 120V?

To be safe why not?  Also, a decent AC line regulator will help as will the upcoming fully regulated supply Chunger and Matador mentioned.  I doubt you'll see it flux higher than you have though.

 

[Matador]

Thanks Matador. My DVM is indeed 10Meg, so looks like 53V for cardioid is right on target. Does measuring B+ in the PSU have a similar voltage drop? A couple of weeks ago, I was right at 120V, but last night it was 125V, and I know we're not supposed to go over 120V. I think I should turn it down a bit, but I'm wondering if I need to account for a voltage drop.

Also, since measure bias has a 10% error, should I be shooting for -.900 V instead of -1V?

B+ is different.  The output impedance of the PSU is on the order of 50K, so a 10M meter makes for about 0.5% error.

If you want to prevent the meter influence on the bias measurement, probe the side of R5 that connects to R3 (as opposed to the bias/P4 node directly).  That way the meter current will not flow across R5.

In any case, such a tiny difference will likely not impact the tube operation in any noticeable way.

 

[Spencerleehorton]

Hi Guys,

just checked my C12 pattern select and seems to be wired correctly but i only seem to be able to get Cardioid and Figure 8, no Omni? any ideas why this would be?
I am getting 0v at omni and 60v at cardioid 120v at fig8?

omni seems to be fig8.

regards

Spence.

 

[bsatriani]

Hey Matador, can the psu be used to supply a Oliver Archut Alternate U47? (B+ needs 105v and Heater +5.05v)

Changing the r6 to a higher value (for C12 6201tube swap) allowed me to get B+ down to like 70v, and up to 125v, and also saw that I can go lower than 5.05v for the heater.  But will these figures keep on for the U47 fitted with, let's say a EF800 tube?

 

[teacat]

I've finally gotten around to building this, going through the nice build step-by-step, but after putting the switch together I get no reading on any of the wires. Not a peep. Might have a bad switch, I guess? 
Also, the schematic pdf link didn't work for me.

Edit: ah, nevermind. I took apart the switch (this is diy after all) and it is fine. Then I started testing resistors and found that I couldn't get a reading on any but two: the 392 and the 1k. So I checked the manual for my fluke and it only registers up to 60k. wtf.
So I'll just assume that everything is everything and get back to work.

 

[etiefenthaler]

Hi Chunger,
Started building your kits these days. Finished one psu. Have christians high grade tubes and tims capsules on my bench.
Want to build the mic pre with insulated turrets and ordered a couple of those.
Could you please post some pictures showing your modified mic?


Thanks a lot
Erich

 

[teacat]

Hey all, could use some help on the power supply! Got it put together- the heater's at 6.3v, but B+ drops quickly from 20v to settle down to around 6v and there is no bias voltage at all. Followed chungers pictorial to the T and triple checked everything.(I think)The little electrolytics are where they should be, everything seems to be in the right place. What should I check? What did I miss?
Thanks!

 

[Matador]

Make sure the big caps are in the correct locations (the 4700uF/25V and high voltage caps look identical).  If you place a 4700uF cap in a spot meant for a 250V cap then you'll see something similar.

 

[teacat]

Thanks for lending a hand! The big caps have been now triple*triple checked and are where they should be.
Also my transformer is 175v not 200v, is that going to be a problem?