Official C12 Clone - Build and Support Thread

[Matador]

My output is great now,    but i just realized that all i am hearing is crystal clear high end and mild lows.    I just flipped the polarity/phase button on my LA-610 and BAM!  There's all my bass....    is the mic supposed to be able to switch between phase like that?  Or have i mis wired the capsule wires?  The mic is currently set to Cardiod.      Any help would be really appreciated!!!

thanks,

Lord Scruffo

Hmmm....this doesn't make sense, unless you had multiple mikes in your project that you were mixing together.  There should be no change in sound by flipping the phase on your preamp on a mono source unless something is whacky in the preamp itself.

 

[Category 5]

Sounds like you wired the capsule backwards and are listening in headphones.  If the monitor sound is out of phase with your inner ear it causes weird sound.

 

[teacat]

a short clip of my build on violin. AK12 capsule/6201 tube/AMI tranny
(not the best sounding room)

https://soundcloud.com/teacat77/c12-snip

rec'd through an octa-capture, no processing.

 

[micaddict]

Sounds nice. Hey, and I hear a distant guitar, too. 

Good to hear there are others who are willing to go the 6201 route.
Any more data on that tube?

Thanks for sharing!


Henk

 

[Marc Duchesne]

Hi Matador, nice thread... Question for you, I own an AKG C12VR (Tube) mic. I went as far as to replace the capsule and the tube into it.
As I understand, the circuit is not as per the original C12 into these mics. I am looking to upgrade the electronic also.
I know there is people modifying the board but I can't find any info's on how to do it... I though stripping the electronics and replacing with your board
but I am nor sure it worth it at the end, could be better to sell and purchase something else... Any thought !! Thanks !!!

 

[teacat]

Sounds nice. Hey, and I hear a distant guitar, too. 

Good to hear there are others who are willing to go the 6201 route.
Any more data on that tube?

Thanks for sharing!


Henk

thanks! and yeah, not distant enough- they were reading from the same music stand.  :'( 
the tube is a ge 5star from the late 50's.

 

[Winetree]

I did that with a motorcycle once. I had done a lot of mods on it and then was going to replace the frame.
I said stop, I'd no long have the originial bike and would have lost that money. I sold it and started from scratch.
You need to do the same. Return it to stock and sell it. Take the money and start from scratch. JMO.

 

[micaddict]

Teacat wrote:

thanks! and yeah, not distant enough- they were reading from the same music stand.  :'(

No problem. I like some bleed.

the tube is a ge 5star from the late 50's.

Good to hear. I've got a couple of those, too.

---------------------------------------------------------------------------------------------------------------------------------------------
Regarding the AKG C12VR.

Winetree wrote:

I did that with a motorcycle once. I had done a lot of mods on it and then was going to replace the frame.
I said stop, I'd no long have the originial bike and would have lost that money. I sold it and started from scratch.
You need to do the same. Return it to stock and sell it. Take the money and start from scratch. JMO.

^
What he said.

 

[dmnieto]

Well, I finished my first C12, and I am going through some tests.

It seems that the mic seems to generate noise in the sub 50Hz, before I start probing and soldering as matador proposed ( it has been quite a long build day), can anybody guess where the issue may come from? If there is any...

 

[Matador]

Got a sound clip?

 

[dmnieto]

Got a sound clip?

Yes, C12->VP25->ADA8824->liquid saffire 56 [ADAT]. Medium gain.

Noise on low frequency ~40dB higher than in high frequency, almost following 1/f law.

https://soundcloud.com/david-martinez-nieto/noise-c12

 

[dmnieto]

This is the spectrum analysis

 

[Matador]

The snapping/crackling noise sounds like PCB contamination.  I would give it another (careful) treatment with IPA and a cotton swab around where the teflon stand-offs attach to the board.

Please also try this test:  take a short wire, solder one side to any ground point, and then tack it to the grid of the tube right where the grid attaches to the tube PCB.  Then put it back together, power it up and do a noise-floor test recording.  Hard grounding the grid completely removes the capsule and the high-impedance sections from contributing noise, and you can hear the self-noise of the tube (and everything after) in isolation.  You can also do a live microphonics test by tapping on the mike body and seeing how loud the thump is out of your preamp.  Lower microphonics tubes will have much quieter thumps than bad ones: the worst one I had still clearly picked up my voice just by talking close against the shell of the mike body!

I actually made a small wire adapter with tiny alligator clips on each end just for doing this test.  When using new 6072A tubes (like from EH), you sometimes have to go through 10 of them and select the quietest one.

 

[dmnieto]

The snapping/crackling noise sounds like PCB contamination.  I would give it another (careful) treatment with IPA and a cotton swab around where the teflon stand-offs attach to the board.

Weird, I will do it, but I scrubbed the shit out of those stands... But will do the test in any case. One question though... I did leave the leads of the capsule quite long (I am still waiting for the custom headbasket and I was not sure I had to modify the height of the capsule), so they loop around the top of the PCB... do you believe that could cause any issues?

 

[Category 5]

Hey Mat.  Quick question.  On the tube socket board you have the pins numbered 1-9 and the triodes also labeled tp1/th1/tc1.  According to the data sheet pinks 6, 7, 8 correspond to triode 1 but yours are numbered 1, 2, and 3.  I believe the numbers are backward while the labels are correct.  tp1/th1 and tc1 correspond to triode 1 and vice-versa.

Just wanted to be clear so that we can match our strongest triode to the mic built to use it.  I am finding most tubes have a stronger side.  fwiw, i was thinking backwards before i finally snipped some pins from a beater tube to verify.

 

[dmnieto]

The snapping/crackling noise sounds like PCB contamination.  I would give it another (careful) treatment with IPA and a cotton swab around where the teflon stand-offs attach to the board.

Weird, I will do it, but I scrubbed the sh*t out of those stands... But will do the test in any case. One question though... I did leave the leads of the capsule quite long (I am still waiting for the custom headbasket and I was not sure I had to modify the height of the capsule), so they loop around the top of the PCB... do you believe that could cause any issues?

I hate to eat my words... but indeed there was a dirty trace...

Noise seems *way* better https://soundcloud.com/david-martinez-nieto/noise-c12-after-cleanup

Does it looks normal now? I can try to hunt for a lower noise tube and do the grid test, but I am concerned about dirtying it again.

UPDATE: I tried to do the grounding... and the mic started hummmmming as there was no tomorrow... I may try tomorrow when I am not that tired.. but one thing I want to mention.
I did burn in the 12ay7EH for 20 hours in the G9 preamp, and it didn't exhibit a lot of microphonics when I tested it in that environment... it did not have the flicker noise either.

 

[Matador]

Hey Mat.  Quick question.  On the tube socket board you have the pins numbered 1-9 and the triodes also labeled tp1/th1/tc1.  According to the data sheet pinks 6, 7, 8 correspond to triode 1 but yours are numbered 1, 2, and 3.  I believe the numbers are backward while the labels are correct.  tp1/th1 and tc1 correspond to triode 1 and vice-versa.

I may have numbered it from a bottom perspective instead of the top (I can't remember TBH).  It's always hard with a sillkscreen as the PCB panel is supposed to be done from the "top" perspective, yet the tube PCB panel is on the panel "bottom's up".  The TG/P/K stuff should be correct however.

I'll check it, and if backwards I'll add it to my list of tweaks.

 

[Matador]

Does it looks normal now? I can try to hunt for a lower noise tube and do the grid test, but I am concerned about dirtying it again.

UPDATE: I tried to do the grounding... and the mic started hummmmming as there was no tomorrow... I may try tomorrow when I am not that tired.. but one thing I want to mention.
I did burn in the 12ay7EH for 20 hours in the G9 preamp, and it didn't exhibit a lot of microphonics when I tested it in that environment... it did not have the flicker noise either.

Looks and sounds much better.

In terms of noise:  it's really hard to predict how any given tube will react when operating with these ultra-high impedances.  The G9 uses a 1M grid resistor:  this one is 250 times larger!  We are way outside of normal datasheet specs in this case (which typically specify 100K or so).

I was thinking about building a test harness to check for these things, but I just don't build enough mikes to make it worth it.  I build the grid grounding wire so I could quickly remove the shell on a mike, install it, then use a mike to do the burn-in noise checking.

 

[dmnieto]

Looks and sounds much better.

In terms of noise:  it's really hard to predict how any given tube will react when operating with these ultra-high impedances.  The G9 uses a 1M grid resistor:  this one is 250 times larger!  We are way outside of normal datasheet specs in this case (which typically specify 100K or so).

I was thinking about building a test harness to check for these things, but I just don't build enough mikes to make it worth it.  I build the grid grounding wire so I could quickly remove the shell on a mike, install it, then use a mike to do the burn-in noise checking.

Any chance you guys are going to put the 6072A for sale in your page? I would like to match my mic a good tube

 

[dmnieto]

Still fighting the noise...

My PSU provides 160V instead of 200V, so I dropped the resitors from 91K to 48K... by doing so, I realize that I have also reduced the ripple rejection by about 10dB. Is the combined ripple rejection of the PSU so incredibly low that it really does not matter? Or should I exchange C1 and C2 for 200uF capacitors?