Official C12 Clone - Build and Support Thread

[chunger]

The recommendation to glue along the edge of the mesh where it meets the base plate is good.  The next production batch of headbaskets will be glued at the factory to eliminatebthe resonance.

 

[HellfireStudios]

I used Loctite Go2 Glue on my single layer headbasket from Chunger, and it did the trick. Check out my earlier posts on the subject for more details about the glue and how where to apply it. I noticed one person had a hard time finding it. I found it in both Target and Wal-Mart chains (usually in their "hardware" sections).
I realize after reviewing this post that it may look like I own loctite. I am in no way affiliated with them. I just like most of their adhesives.

-James-

BTW, here is the finished mic. Sorry it took so long to get a pic up here.

Where did you get the nice badge made for the mic?

I actually obtained this particular emblem from a knife set. It was attached to the knife caddy. I've been on the lookout for badges ever since I started modifying and building my own mics. Surplus military medals, metal clothing/craft buttons, and even the gems off of a vodka bottle have served me well as mic badges.
Most of them need modification of some sort. A dremel will do wonders when it comes to flattening the backs and/or modifying the shape of the badges.
When trying to bend the badges to the rounded shape of the mic, use a smaller diameter pipe than the mic you intend to attach it to (this will compensate for metal's tendency to flex out when the clamp is removed). Then, use a hose clamp wrapped around the smaller pipe (covered in tape to protect the badge), to apply even and consistent pressure to the badge, while using a wooden mallet to shape the piece. I recommend tightening the clamp after every whack of the mallet. Loctite heavy duty construction adhesive has worked well for me as a method of attaching the badges to the mic. If your mic is painted, make sure you sand away a little paint behind the badge to allow the glue something to bond to. Roughing up the surface of the mic under the badge location is a good idea whether the mic is painted, plated, or unfinished to help the glue adhere.

-James-

 

[Spencerleehorton]

Hi Matador,

I am testing these AKG transformers today with scope as they are ment to be 10:1, they have 4 wires each side, i have a ratio calculator and one winding measures 32ohms and the other the same, on the other side one is 720ohms and the other is 720ohms, so i can use one side in parallel and the other in series to get the highest ratio of the transformer but when i put the ohms into the ratio calculator it only says about 7:1 with this config? i have been told not to rely on this calculator and use test tone with scope to be sure.
Will check 100k trim is correct but im pretty sure the 100k trim works fine when mic not plugged in? i was getting 135v without mic plugged in and could adjust voltage but will double check this and get back to you.

regards

Spence.

 

[Spencerleehorton]

Hi Matador,

have check the PSU and 100k is correct, has 104 on top, when mic not plugged in 100k has no effect?
When mic plugged in after a couple of minutes it sits around 92v.
All other voltages seem fine.
Which way is the transformer wired cause it was said before its used as a step down so would the higher ohm connect to the mic pcb (10 ratio) and the smaller ohm ((1 ratio) connect to the 7 pin XLR?
I thought ive tried it both ways but im pretty sure i got the config of the transformer completely wrong, i now get the correct ratio at least.
Just need to confirm correct way its wired.
Should i take out the 100k and replace it to see if that sorts it?

regards

Spence.

 

[Spencerleehorton]

HI Matador,

Have just tried transformer with the higher ohms(1450) to pins 5/6 on the 7 pin connector much less audio this way.
with the low ohms on pins 5/6 it did pass audio but still very very low?
any ideas what to do next?

regards

Spence.

 

[Matador]

If you try to use it as a step-up the loading will kill all of the signal.  The mike PCB side should be the higher DCR side (you want it to step-down).

It's perplexing that with the mike installed and drawing current, that B+ isn't adjustable.  Even with no microphone plugged in, the current through R6 should be enough to at least show an adjustment range through R4.

Just to be clear:  you are saying it's 92V always, no matter how the B+ pot (R4) is adjusted?

 

[Spencerleehorton]

HI Matador,

Yes once it comes up and settles it stays at 92v and the 100k doesnt do anything, bias and heater work fine?

regards

Spence.

 

[Matador]

Ok, let's try the resistor trick:  remove the mike, and connect a 180K resistor between the B+ line and the ground line.  You can stick it right into the output 7-pin XLR jack right on the psu.

For safety, do it in this order:  stick a bare resistor into the B+ line, then bend the resistor and stick the other end into the ground line.  Then fire it up, and see if the B+ is adjustable.  You should be able to adjust B+ up and down to a 50V or so adjustment range.

 

[Spencerleehorton]

Hi Matador,

so just to make sure your saying:

connect a 180k resistor in the psu on the 7 pin xlr to pins 1 & to pin 7 then adjust the 100k?

regards

Spence.

 

[Matador]

Yes, but only if that pin definition is what you used.

To be more clear, you want the resistance between the "P5" node (that comes from pin #1 of the 5-pin connector block), and the "P6" node (that comes from pin #5 of the 5-pin connector block).  If you wired P5 to pin#1 on the XLR, and P6 to pin#7 on the XLR, then yes, that's where you want the resistor.

 

[Spencerleehorton]

Hi Matador,

yes thats how ive wired it, will do it in the morning and let you know.

regards

Spence.

 

[Spencerleehorton]

Hi Matador,

Put 180k resistor in powered up attached gnd from MM used hot onto B+side of resistor get 92.6v then tried adjusting voltage and nothing happens either way?
Dead pot?
I'm flumexed!!!

you know whats happening?

regards

Spence.

 

[Spencerleehorton]

HI Matador,

took out the 100k pot and and put in a new one, cleaned everything with Alcohol and new 100k pot works but i only get 94.5v and when i wind the pot down it only goes down to 77v.
Mic works nice now though, but would like to get the correct voltage going.

regards

Spence.

 

[chunger]

Are you trimmer pots in the correct positions?  Switching these up is a very common build error.

 

[Spencerleehorton]

Hi Matador,

the problem i was having with the low output was the transformer, i changed it and hey presto, im pretty sure all the trimmer pots are correct now, how critical are the 392R resistors? or what part of the circuit would limit the voltage supply to the 100k pot?
regards

Spence.

 

[Matador]

Hi Matador,

the problem i was having with the low output was the transformer, i changed it and hey presto, im pretty sure all the trimmer pots are correct now, how critical are the 392R resistors? or what part of the circuit would limit the voltage supply to the 100k pot?
regards

Spence.

Critical as in exactly 392 ohms?  Critical as in do you need them at all? 

The 392R sets the divider ratio for the heater supply.  Since there is a heater adjust pot it can be off by 10% and it doesn't matter much.

For the B+ voltage, it's the series drop across R1, R2, and R4 that sets the B+ value.  Increasing R1 and R2 will lower the voltage leading in to the 100K pot (R4), and lowering them will raise it.

The transformer shouldn't effect B+ *unless* you have a wonky output cap (C12).  If this cap is leaking DC current through R17 and dragging down B+ then Bad Things Will HappenTM.

If I were you, I would replace C12 as well.

 

[Spencerleehorton]

Hi Matador,

the mic is working fine now i have changed transformer, getting good signal through it, im just not getting 120v on B+, so i think i need to lower R1, R2, and R4 to raise the voltage.
R1 and R2 are 5k and R4 is 27k so should i replace with R1/R2 = 2k and R4=15k ?

regards

Spence.

 

[Matador]

Hi Matador,

the mic is working fine now i have changed transformer, getting good signal through it, im just not getting 120v on B+, so i think i need to lower R1, R2, and R4 to raise the voltage.
R1 and R2 are 5k and R4 is 27k so should i replace with R1/R2 = 2k and R4=15k ?

regards

Spence.

Both R1 and R2 are supposed to be 91K.  R4 is the 100K B+ adjustment pot.

Which schematic are you looking at?  The official version for this build is located here.

 

[Spencerleehorton]

Hi Matador,

Im pretty sure i was just looking at the wrong psu schematic and i have 91k in the psu.
what should i lower them too?
regards

Spence.

 

[cariocaman85]

Hi

Here we are again with the head basket resonance! After your advices we decided to go to the glue solution but I can't get loctite 2go glue where I live, so I wonder if this glue:

Cyanoacrylate Bond MP

Might fit for damping the ring?

On the technical data they precise this glue is for metal, resistant to vibrations, and solvent free (http://instantca.com/industrial-adhesives/cyanoacrylate/)
Do you think it is safe for the capsule?

Thanks for your replies, we have to glue it this weekend because we gonna record on Monday.

Best,
Remi