Yet another C12 clone

[kilmister]

Hi all!

Just finished my C12 clone project.

I followed original schematic but there's slight variations though. I didn't modify Apex pcbs just made new in to veroboard.
-Capsule is orginal CK12 mounted in Apex holder
-Tube is TFK ECC801S
-Transformer is AMI T14
-Caps are russian pio's
-Power supply is my Universal Tube Mic PSU

Next step is to go in to the mic lab to make some measurements. I'll add results in the thread once I get them.
Once again I have to thank you this great community for inspiring me to build things I've once thought they are way too far from my skills.
Let's cut the BS, here's some pictures. (click for higher resolution)

Mic innards front view:


Mic innards rear view:


PSU innards:


The Fellows:

 

[letterbeacon]

Looks fantastic -top work!

 

[Biasrocks]

Looks fantastic -top work!

Nice work!

I've got a couple of CK12's in a pair of 414EB's that are just begging to be turned into a pair of C12's. Good inspiration.

Regards,
Mark

 

[saxmonster]

Very Cool,  Great Job!!!!!!!!!

 

[tchgtr]

LOVE the point2point on the circuit board.
Can't wait to see the test results.

 

[micaddict]

Very, very nice!
Some serious ingredients there, too.

Hey folks, we really need a C12-style body that is more affordable than the Flea.

 

[tskguy]

I really digg the psu where did you get it? And the mic looks fantastic can't wait to hear some samples
Eric

 

[david-p]

It looks very nice -- congratulations!

How are you going to do the measurements?  I have successfully measured the frequency response of my amplifier with RMAA, but short of renting an anechoic chamber I am not sure that I can do anything meaningful that includes the capsule.  I have to trust my ears and comparisons with the professionally built Earthworks and 4038 mics that I have.

Just a couple of points:

Radio Shack here in the USA sell perf board that has no copper on either side.  I am not sure what the little copper rings are supposed to do on the board you have, but this avoids them!

Teflon stand offs are a good idea for the high impedance points on the perf board: I am not sure how good its long term insulation is.

From what I can see, your capsule is a little high in the basket.  It seems to me that AKG capsules are often mounted directly on the floor of the compartment.  I used double-sided sticky tape to attach the teflon-style C12 capsules in my stereo pair and have had no vibration problems.

David

 

[kilmister]

Thanks guys!

PSU is all diy. Case is Hammond 1401A which is painted. Front panel is my own design and laser engraved.

I'm lucky to have an access in to nice pro quality mic lab which has anechoic chamber and B&K measuring unit for frequency response and sensitivity. There's also possibility to measure noise floor levels which are my main concern. It might take from few days up to couple of weeks before I have change to go there.
What comes to capsule height I have to agree David. It stands a bit high. I feel it's anyway good starting point. I measured mic earlier with chinese capsule mounted and frequency response didn't look too awful. Due I don't have those golden studio ears I also have to wait some feedback from my partners before making any sudden moves.

Cheers,
Paavo

 

[kilmister]

Hi!

Finally we were able to measure a microphone in a lab.
Frequency response and sensitivity measures was performed by calibrated B&K 2012 Audio Analyzer in an anechoic room.
Self noise measure was performed with Sennheiser UPM 550-1 level meter in a Neumann isolation chamber (which is placed in the anechoic room).
All measuring signals was driven at 74dB(spl) throught the Genelec 1030 speaker.
All measures was done in cardioid polar.
Unfortunately we weren't able to capture a frequency response plot to data so I took a photo of the B&K's screen.

And here's results:
Sensitivity: 9.8mv/Pa
Noise A-weight: 24dB
Noise CCIR weight: 35dB
Frequency response 40Hz-20kHz: (click for hi-rez)


Over all it's quite similar with the original one. Self noise is a bit high, might be a tube. I'm anyway a very happy man!

Cheers,
Paavo

 

[dmp]

Looks great! I just finished a C12ish mic in a Apex body as well.

I followed original schematic but there's slight variations though.

Would you mind sharing your component values? Since you used your psu design you probably changed the cathode biasing.
In my build, I used 1G resistors around the capsule. What did you use?

 

[Scrappersa]

Looks great! I just finished a C12ish mic in a Apex body as well.

I followed original schematic but there's slight variations though.

Would you mind sharing your component values? Since you used your psu design you probably changed the cathode biasing.
In my build, I used 1G resistors around the capsule. What did you use?

I second that for both of you guys. It would be great to compare my component values to the both of you.

 

[kilmister]

Would you mind sharing your component values? Since you used your psu design you probably changed the cathode biasing.
In my build, I used 1G resistors around the capsule. What did you use?

I used as close values I had around at the time of build. Like originals 5000pF is 4700pF and so on. I don't have mic in hand now but IRCC I was inside of 10% tolerance with all component values refered to original.

Since you used your psu design you probably changed the cathode biasing.

Do you mean did I change cathode biasing from Apex to fixed? Yeah kind of. I rebuild all innards of the mic so I have fixed bias which I can adjust by the trimmer in the psu.

-Paavo

 

[Scrappersa]

Would you mind sharing your component values? Since you used your psu design you probably changed the cathode biasing.
In my build, I used 1G resistors around the capsule. What did you use?

I used as close values I had around at the time of build. Like originals 5000pF is 4700pF and so on. I don't have mic in hand now but IRCC I was inside of 10% tolerance with all component values refered to original.

Since you used your psu design you probably changed the cathode biasing.

Do you mean did I change cathode biasing from Apex to fixed? Yeah kind of. I rebuild all innards of the mic so I have fixed bias which I can adjust by the trimmer in the psu.

-Paavo

The mic looks great man. I would love to hear it. You did a fantastic job on it.

 

[dmp]

Do you mean did I change cathode biasing from Apex to fixed? Yeah kind of. I rebuild all innards of the mic so I have fixed bias which I can adjust by the trimmer in the psu.

Ah, my bad. I just looked at your psu design in the other thread and realized it has a trimmer in the ground rail to bias like the original C12. Awesome!

 

[kilmister]

Exactly. I couldn't saw any good reason to invent wheel again

Cheers,
Paavo

 

[ricardo]

Frequency response and sensitivity measures was performed by calibrated B&K 2012 Audio Analyzer in an anechoic room.
...
All measuring signals was driven at 74dB(spl) throught the Genelec 1030 speaker.
...
Unfortunately we weren't able to capture a frequency response plot to data so I took a photo of the B&K's screen.

And here's results:
Sensitivity: 9.8mv/Pa
..
Frequency response 40Hz-20kHz: (click for hi-rez)

What was your reference microphone?

What distance from the source?

Mike measurements with a 2012 are done by measuring a speaker with a calibrated reference mike.  Then removing it and measuring the DUT at the exact same position.  The 2012 has facilities to subtract the reference measurement from the DUT measurement to give the true DUT response.

 

[kilmister]

Lab uses B&K's reference mike. I don't know exact model and didn't check - stupid me...
Yes, DUT is placed in same position where reference mike is located. Distance from speaker is around 3 meters.

-Paavo

 

[ricardo]

Lab uses B&K's reference mike. I don't know exact model and didn't check - stupid me...
Yes, DUT is placed in same position where reference mike is located. Distance from speaker is around 3 meters.

You need to measure and record the exact distance.  It seriously affects the LF performance of the velocity component ie cardioid types & fig-8s.

Many mike makers including the big Germans and Harman cheat by adjusting the distance to get nicer graphs without telling you.  Only DPA specify explicitly that they have done this evil trick.

The 2012 also provides 'windowing' which affects the LF accuracy too.  It's less obvious than the windowing in FFT methods but still there; just hidden.  You need to record the settings on the 2012; in particular the assumed distance of the 1st reflection.  Yes anechoic chambers have reflections too.

I'm suspicious of your measurements if the distance is actually 3m.  LF looks too good for a C12 type.

But the response above 200Hz should be good assuming the height between the wedges is greater than 2.5m

The standard distance should be 1m.  If you get another chance to do this, measure the response at 180 & 90 degrees as well.  This will give a good idea of the 'hidden errors'

 

[micaddict]

distance should be 1m.

Yup.