Starting a C12 clone

Rob Flinn said:

telefunk said:

Rob Flinn said:

Telefunk,

Is that why you opted for cathode bias in your clone ?

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Not really, cathode bias sounds good, too.

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I guess, but so does a real C12.............

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Absolutely. But easily the biggest factor for a good sound is the capsule...

There's cathode bias in it's sister, the 251, remember - and the C28 of course.

I know, I know - it's only a clone if it's a clone - just sayin', it's all good. 

Several people have PM'ed me for the dimensions of the body tube so here goes:

wall thickness varies between 0.85 & 0.9mm
OD 41.75mm
length 184mm

Hi Rob,



  I am pretty sure the BBC used to modify C12 to have the same sort of bias as 251. I can find out the circuit if you likey?


    ANdyP

strangeandbouncy said:

Hi Rob,

  I am pretty sure the BBC used to modify C12 to have the same sort of bias as 251. I can find out the circuit if you likey?

    ANdyP

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Yes please Andy !!

Hi Rob,


  I am going to Italy( no interweb!) and wont be back for 8 days. I'll see what I can run down, but it may take a while. Pretty sure it is same as C28, but I could be wrong.


  ANdyP

OK, I have a couple of C28's so I can take a look.  Thanks Andy

Out of curiosity, I did my C12 Apex460 mod as C-24 and that's cathode bias.. how much voltage is on pin4 of the C12 PSU? For the fixed bias.. I didn't find this info anywhere.

baadc0de said:

Out of curiosity, I did my C12 Apex460 mod as C-24 and that's cathode bias.. how much voltage is on pin4 of the C12 PSU? For the fixed bias.. I didn't find this info anywhere.

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I've no idea.    I intend to do mine with cathode bias to avoid  having to use a different PSU than the one I have.

Rob Flinn said:

baadc0de said:

Out of curiosity, I did my C12 Apex460 mod as C-24 and that's cathode bias.. how much voltage is on pin4 of the C12 PSU? For the fixed bias.. I didn't find this info anywhere.

Click to expand...

I've no idea.    I intend to do mine with fixed bias to avoid  having to use a different PSU than the one I have.

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Sorry for the misunderstanding, I worded my question rather badly. I was asking about the fixed bias voltage on a regular C12 for the 6072 triode grid.. I'm looking for either the volts ref to ground for the pin4 that the original NK12 power supply sends out to the mic or the resulting volts that bias the triode grid (after the 30M resistor etc..)

No problems with the wording of your question, but I still have no idea.  I don't own a real C12 PSU or real C12 mic so I can't measure the bias voltage for you, sorry.

baadc0de said:

Out of curiosity, I did my C12 Apex460 mod as C-24 and that's cathode bias.. how much voltage is on pin4 of the C12 PSU? For the fixed bias.. I didn't find this info anywhere.

Click to expand...

The C12 uses cathode bias.  The 'cathode resistor' is in the PSU just to confuse you.

You need to measure P4 with the mike connected & running or you will get nonsense when you measure P4 voltage.

Maybe AKG intended to use fixed bias at some future point in time but never got round to it.