Official C12 Clone - Build and Support Thread

[Tim Campbell]

The PCB's are easily gotten from a couple of sources and people have posted BOM's.
It's not a complicated build.

 

[aronaut]

I'm following the 250 circuit but using a 12AT7, however, since the 250 is self biased and doesn't use the bias adjust (R3) do the the below rules still apply?

Microphone:  Change R17 from 100K down to 47K
PSU:  Drop R1 and R2 down to 33K.  Adjust R3 down to about 900ohms, then tweak with the actual tube.
Test load: decreases from 180K down to (120V/1.35mA) = 88K.  91K would work as a substitute for a real tube for PSU testing.

Thanks
A

 

[Matador]

I'm following the 250 circuit but using a 12AT7, however, since the 250 is self biased and doesn't use the bias adjust (R3) do the the below rules still apply?

Microphone:  Change R17 from 100K down to 47K
PSU:  Drop R1 and R2 down to 33K.  Adjust R3 down to about 900ohms, then tweak with the actual tube.
Test load: decreases from 180K down to (120V/1.35mA) = 88K.  91K would work as a substitute for a real tube for PSU testing.

Thanks
A

R3 is used as the cathode resistor - everything else applies.

 

[aronaut]

Right, so jumper R3 (I'm using your psu board), and cathode resistor remains 1.8K (R11) up in the mic.

 

[Matador]

Right, so jumper R3 (I'm using your psu board), and cathode resistor remains 1.8K (R11) up in the mic.

Not quite - 1.8K is more appropriate to the 6072A as the schematic indicates.  Also you don't need to jumper R3 if it's already installed - just dial it down to 0 ohms.

I would change R11 to 1K and try experimenting from there if you are using the 12AT7 tube.

 

[aronaut]

Oh right, I see. When experimenting with different R11 do I taking amperage or voltage reading at the cathode? and what should it be?

Thanks!

 

[Matador]

Voltage at cathode.  You want it to idle at about 0.9V-1.1V: lower resistance = lower voltage.

 

[aronaut]

Awesome, thank you

 

[mellsonic]

Hello guys, i need some advice: i want to built 2 x c12  microphones. I have almost all parts, the only part missing is the rotary switch (pattern selector). Mouser can deliver it only in 2 months time. Does somebody know elsewhere i can find it in the EU or Germany? maybe as well also an substitute/similar type i can use to built my microphones? Thank you very much in advance for your feedback
cheers
Mario

 

[tonzauber]

Why not re-use the stock switch that is fitted in the PSU? It is actually quite a sturdy metal beast...
If not, I think I have one or two switches as spares... I can check tomorrow.

 

[mellsonic]

Hello Tonzauber
i don't want to desolder  the resistors .
Cheers

 

[Matador]

The stock switch will work, even if you don't want to change the stock switch resistors.  The values are slightly different but it won't impact the polarization functionality.

 

[mellsonic]

Thank you Matador
why you replaced it with a new one in your build?

 

[Matador]

Because this is DIY!

The Lorlin replacement is higher quality IMHO, and is much easier to turn, and the force required to turn is consistent around the whole circumference.  But it's strictly not necessary to replace the switch to get the design to work. 

If you want an even higher quality option, look for Grayhill switches, which can be easily found in the EU:  they are about twice the price of the Lorlin, however (often) have metal bodies as well.  It's a very nice switch if you find you are changing patterns frequently.

 

[mellsonic]

Thank you again Matador !!
the Problem is that i  don t know  which switch  is the  one that i need .
i am a beginner in DIY. maybe somebody have a link where i can buy it in EU.
cheers
Mario

 

[Bowie]

Thank you again Matador !!
the Problem is that i  don t know  which switch  is the  one that i need .
i am a beginner in DIY. maybe somebody have a link where i can buy it in EU.
cheers
Mario

Hi Mario, I ordered this one recently.  Haven't tried it yet but I believe it should work fine;
http://www.mouser.com/Search/ProductDetail.aspx?R=A10015RSZQvirtualkey61110000virtualkey611-A10015RSZQ

 

[Matador]

Thank you again Matador !!
the Problem is that i  don t know  which switch  is the  one that i need .
i am a beginner in DIY. maybe somebody have a link where i can buy it in EU.
cheers
Mario

The switch variant is called a 1p (1 pole) 12t (12 throw).  However in this design, only 9 stops are used.  You can use all 12 if you really want, so long as the halfway point is aligned to the middle, you will get a few other intermediate patterns as well.

Or, you can also use a 1M center-detent potentiometer, and have essentially infinite patterns between omni and figure 8 (so long as you can reliably stop in the middle which is cardioid) - however these can be difficult to find.  If you are careful with alignment, you can rotate the pot for exactly 500K, then tighten the locknut so that this point is facing "up" towards the cardioid mark on the PSU case.

Many ways to skin this cat.

 

[Haberdasher]

Hi

Can anyone from studio 939 comment on how soon the C12 and ELA M251 Microphone Parts kits will be back for sale in the store?

Thanks!

 

[Haberdasher]

Hi again

I was thinking about possibly sourcing my own parts for this, but I need some additional info.

The zero ohm smd resistor isn't listed in the BOM, so I'd like to know the package.  Would 0805 work?

Also, does anyone know if the parts bag from 939 includes the tube socket?

TIA

 

[Phrazemaster]

Yes socket included.

Can't speak to zero ohm size, but you can even use a wire jumper, which is what I did since I biffed the smd part.