Official C12 Clone - Build and Support Thread

[mwrichardson]

I used wire jumped instead of SMD device. I am not a fan of them.

 

[Gearsix]

Thank you, I have lost that post!
Another thing: someone has used 4700pf capacitors instead of 5000pF?
Cheers

 

[mwrichardson]

4700pf is fine. They are just filters. and.. I got on Tim Campbells capsule waiting list!! Thanks Tim!

 

[Category 5]

I got on Tim Campbells capsule waiting list!! Thanks Tim!

How?!  Lucky!

 

[Gearsix]

Someone has verified differences using the 100M Ohm resistors instead of 30M Ohm and 250M Ohm?
Best

 

[chunger]

Just got word from the motherland.  The production run for the custom headbaskets is complete.  These should become available shortly.

 

[mwrichardson]

Where and why are you using 100M resistor? It is not on schematic or BOM.

 

[Gearsix]

In the version 3 of the BOM (you can download it in the first page af this thread) the 100M ohm resistors are indicated as alternate to 30M and 250M resistors
Best

 

[Matador]

I tried the 100M versions in the second prototype and could not tell any differences.

They also save almost $10 from the BOM cost alone.  ;D

 

[Gearsix]

Thank you!

 

[baadc0de]

How much of a difference in low cut does a 0.15uF capacitor make vs. 0.5uF or 1.0uF?

 

[mwrichardson]

If you double the cap from 0.5 uf to 1 uf the low end is extended about an octave.

 

[Winetree]

If you double the cap from 0.5 uf to 1 uf the low end is extended about an octave. I might try this.
But aside from this, I read a capsistor review, rating many caps on their sound,
and the ERSE caps were rated 6.5 with some as high as 12.
The cap prices when up with the ratings.
Would a better rated and more expensive output cap (C12)
make a difference in the sound of the C-12?

 

[JessJackson]

If you double the cap from 0.5 uf to 1 uf the low end is extended about an octave. I might try this.
But aside from this, I read a capsistor review, rating many caps on their sound,
and the ERSE caps were rated 6.5 with some as high as 12.
The cap prices when up with the ratings.
Would a better rated and more expensive output cap (C12)
make a difference in the sound of the C-12?

The Elam 251 used a 1uf cap, the c12 used a .5

1uf adds saturation at transformer also, I have not done sonic tests on this yet but many have.

Coupling Cap Reads...

http://www.neumann.com/forums/view.php?bn=neumann_archive&key=992691654&v=f

http://prorecordingworkshop.lefora.com/2011/02/16/c12-v-ela-m251-differences/efora.com/2011/10/23/franken-u47-opinions-welcomed/

 

[chipss36]

I am wondering, what would happen if i put a m-7 style capsule in this build?
I am loving that capsule  on every mic I have wired it up on, will it work on this build as well?

 

[baadc0de]

Guys, I'm a bit at a loss here with my build.

I have built both the PSU and the mic. In the mic, I have substituted the output cap for a 1uF PIO and the two 5nF styrenes with two 8.2nF films. In the PSU, the pattern switch is built from 390k resistors instead of 400k resistors.

My multimeter has 10M input impedance in voltage measurement mode. With a dummy load (182k resistor) I can get 111V easy. With the mic I can only get about 80V. On the mic, basic voltages check out ok (bias, heater, plate). I have tried injecting some signal after the output cap (before the xformer) to verify that it's working OK and I can certainly get the signal out (so cables, leads, xformer, etc.. are all OK).

But I can't get any signal if I inject at grid. EDIT: with capsule disconnected.

The signal is direct from D/A through a 1uF/630 poly cap, to block DC.

 

[baadc0de]

Found what the problem was... the wire going from plate on the PCB to tube was pinned down by a PCB mounting screw, stripping off a bit of the insulation and making contact to ground. So the tube wasn't getting any voltage on plate, since the electrons didn't feel like going there, instead opting to return to ground. Funny chaps. I'd think the opportunity to visit a springboard was better than home, but there you have it.

My next problem is super-low output, but from some testing it seems to, sadly, travel with capsule. Darn.

 

[baadc0de]

And here I am again. The mic works and sounds nice. The output is still very low (barring my preamp at home not working well - that will need to be checked out in the studio), but it does not in fact travel with the capsule (instead, hum travels with capsule, so some capsules seem to work better as radio antennas than other, hmmm). Anyway, I am now suspecting the tube or preamp. I've tried both -2, and -1V bias and settled on -1V.

 

[cariocaman85]

Hi,

I built the mic yesterday with a friend. We were very, very careful and kept everything cleen at each step according to the tutorial (with 70% isopropyl alcohol).

PSU worked fine I think. We can easily get +120V on B+ with a 180k screwed beetween B+ and ground; and 6,3 for heater, -1 for bias, checking from the PSU blocks.

Then we removed the 180k resistor and we ran a test with the mike (stock capsule and groove tube 12AT7, FB and RB linked by a jumper). We adjusted the heater from the mic, and B+ and Bias, checking from the PSU blocks. Everything went fine. Then we powered it off, closed the mike's body, plugged it in a preamp (without phantom  ), and powered on.

It took about 40 seconds before we could ear a sound but finaly, sound appeared! It was ok, except the noise seems to be too loud, and the audio signal, a little bit to tiny, regarding the stock Alctron we tested in comparison. I thought it was the tube/voltage, so we adjusted B+ and Bias (heater was fine 6,28V) with the same method I described before. The mike was still a little bit noisy and low output.

Maybe we (ok I  : ) made a mistake, I thought the tube as a problem, so I switched it for the 6072 nos tube. We readjusted voltages (B+ was down to 104, we put it at 120V), always checking the heater from the mike and the others (B+  and Bias) from the psu blocks, according to the tutorial. While everything seemed to be fine, we ran an audio test.

And... Still the same: not a lot of audio signal ( stock alctron is at least 5/6 dB higher in comparison ), and constant noise. The noise is not so loud, but enought to be a problem while recording. We tested into several preamps, with the same conclusion.  :'(

Then it was 3am and we didn't want to destroy something, so we stopped...

What do you thinks this could be? Is it normal? I don't think so but maybe someone as already encoutered this issue?

Some help will be very appreciated 

thanks,

Remi

 

[mwrichardson]

Cariocaman85.. What transformer are you using?  You need a T14 style. Check that the winding attached to the tube is the higher resistance winding.