Official C12 Clone - Build and Support Thread

[Matador]

Sorry if this is off the current topic ;D
firstly thanks for the great mic matador and great instructions Chunger!!
I've been trying to understand this Build a littler better but I'm a bit confused about the capacitor and resistor choices and values used as it's confusing my (tiny!) understanding of OHMS law for example on the heater we have 12.7V after rectifier into  5W  4.7ohm  resistor Ohms law calc shows  19.202 Watts  and 2.021 AMPS so why only a 5W resistor? Also the B+ supply shows 270 volts at the rectifier so why are we using 250v filter capacitors? Any help understanding this would be awesome!!
Thanks Again!

The 6072A nominal heater current is 350mA.  So I^2R dissipation in 4.7ohms is 0.575W.  The voltage loss across this resistor is 1.645V, which leaves about 11V for the regulator.  The regulator drops 4.7V @ 0.35A which means that the regulator dissipates about 1.6W.  If you heat both sides of the tube, the dissipation doubles.

So a 5W part is specified because:  it was the least expensive part I could find at the time.   2-3W parts tend to come and go at Mouser depending on when you order, but 1W and less and 5W and greater tend to always be in stock.  It was a BOM/availability consideration, not an electrical design one.

As for the B+ supply:  the Nichicon caps we use have quite a high derating factor when used near room temps.  The manufacturers have a lot of margin built in to these parts (especially the high temp parts).  I stayed with 250V because the next size up is 315V, which only specifies 47uF instead of 100uF for the same package.  Also the preliminary transformers I tried seemed to have higher core loss, and I didn't see average DC reading up near the 270V mark in any case.

If you want to be extra conservative, you can sub in a 47uF/315V variant of the VZ line which is in the same package size.  Sonics would (probably) not be impacted to any audible degree (the filter pole is already sub 1Hz in any case).

 

[TheJames]

I've knocked a couple of other projects out of the way and it's time to pick this one back up.

I've got my PSU's mostly built, but noticed the voltage problems in the thread with the 175V transformers.  Not a big a deal...Swap out R1/R2 in the PSU with 56K.

I also thought about converting to 6201/12AT7 in the hopes of having a better supply and choice of tubes (since good 6072a's are rare and I'd rather not obsess over tubes).  The 12AT7 mod seems to require R1/R2 to be lowered to 33k (along with R17 on the mic PCB to 47k).

Without doing the math and just eyeballing it, I might need to lower R1/R2 values even more to say 20k to make the 12AT7 conversion with the lower output power transformer?

Also...I was looking to get a switchcraft XLR-M 7 insert for the mic body instead of reusing the 7-pin connector that's included.  Any leads one where to get one.  Non-stocked at Digikey and Mouser...Switchcraft claims their distributors have none.  Any thoughts appreciated.

Thanks!

 

[teacat]

Without doing the math and just eyeballing it, I might need to lower R1/R2 values even more to say 20k to make the 12AT7 conversion with the lower output power transformer?

I have one of the 175v trafo's and did the 12at7 conversion because of a noisy 6072. I left the 56k's in place at R1/R2 and since I had one, put another 56k in the mic at R17. Easily dialed in proper voltages and the 6201 (a late 50's ge 5 star) sounds fine.

 

[aaquilato]

Newbie Alert!!!
Hey guys. Since this is the Official C12 Clone - Build and Support Thread I'm posting a question or two for you knowledgeable guys. I'm not finding answers on any other thread.

Newbie Alert!!!
I need some help finishing this build and I don't want to make a critical mistake.

Here come the questions...

1) Has anyone built an AMI C12 kit?
Here's the link to the construction guide:
http://tab-funkenwerk.com/id142.html
Oliver has two types and I have his "b" kit which has the cheap Chinese PSU and a cheap mic cable. As far as I know this is the only difference between the two kits.

His construction guide page refers to the AMI PSU in the schematic.
Can I ASSUME the Chinese PSU is the same in as much as the wiring goes, etc...?
I'm building a new GAC-7 mic cable. Here's the pin out I'm using:

Pin 1 = White audio +
Pin 2 = Black audio  -
Pin 3 = Grey Not connected - snipped on BOTH ends of the cable
Pin 4 = Red Thick 6V filament Heater
Pin 5 = Yellow 120V
Pin 6 = Green 0 – 120V
Pin 7 = Blue Thick Ground
Copper Braid goes to xlr connector

Yes? The is the standard wiring config as far as I know.

That just leaves rebuilding the PSU. Can I use the Studio 939 kit to rebuilt the PSU?
Will that PSU work with Oliver's C12? The voltages are the same.

2) What are your thoughts on Carbon Compound Resistors?
The kit came with 4x 100M CCR. The rest are new type resistors. Blue metal oxide?
I have all the correct values in CCRs. Anyone want to chime in about this?

3) The Output Capacitor!!
It seems every thread I read the size of this cap is different.
Oliver supplies a 47nf / .047uf / 47000pf Dipped Metallized Polyester Film Capacitor for this.
I've seem many C12 schematics where the cap is 4.7nf / .0047uf / 4700pf.
This is a BIG difference. Or is it?
This isn't like saying put a 1uf cap in to get more low end response. Or is it?

I'll stop here for now.
I await the knowledge of this group in helping me with this build.

Thanks for your time!

 

[Melodeath00]

aaquilato, please note that the AMI C12 is not an exact replication of the vintage C12 circuit. It is different. Also, you seem to be confused abotu the output cap, which is actually C3, and 1uF, not the 47nF C2.

 

[aaquilato]

aaquilato, please note that the AMI C12 is not an exact replication of the vintage C12 circuit. It is different. Also, you seem to be confused abotu the output cap, which is actually C3, and 1uF, not the 47nF C2.

Thank you for your reply Melodeath00.

I have figured out which capacitors Oliver has supplied and there positions in the build.
He obviously assumes that a bag of unlabeled components make perfect sense to everyone.

What was confusing me and still does, is a 47uf 25V Nichicon VX was suppied as the 47nf C2 cap. Can you explain the difference to me? 47uf instead of 47nf?
Yes, I am confused about this.

So that had me going through every capacitor conversion chart to try to figure out which cap went where. I now know where they all go and see that the output cap is a 1uf (polyester film) cap. I have a .47uf PIO cap that I will try in that position.
A .047uf PIO cap would be TOO small in the C3 position, correct? I have those as well.

What about the rest of my questions? Can you shine any light?

Thanks again for the quick reply.

 

[aaquilato]

"His construction guide page refers to the AMI PSU in the schematic.
Can I ASSUME the Chinese PSU is the same in as much as the wiring goes?
I'm building a new GAC-7 mic cable. Here's the pin out I'm using:

Pin 1 = White audio +
Pin 2 = Black audio  -
Pin 3 = Grey Not connected - snipped on BOTH ends of the cable
Pin 4 = Red Thick 6V filament Heater
Pin 5 = Yellow 120V
Pin 6 = Green 0 – 120V
Pin 7 = Blue Thick Ground
Copper Braid goes to xlr connector"

I have received an answer that both the AMI PSU and the Chinese "budged" version are interchangeable.
Just is case anyone else out there needs to know.

Can anyone give me any help with the C2 47nf capacitor question?

As mentioned a 47uf was supplied with the kit.
My EE skills are limited as to what C2 does in the circuit.
Was the wrong capacitor mistakenly packaged or can a 47uf be used in place of the 47nf in this position?

Thanks again for all your help with this.

 

[Matador]

Which kit are you asking about?  If it isn't the "Matachung" C12 you are better off starting a separate thread.

 

[aaquilato]

Which kit are you asking about?  If it isn't the "Matachung" C12 you are better off starting a separate thread.

Yes, I'll do that. Sorry.

 

[Dennyp]

Hey matador

I'm having some trouble adjusting the heater voltage on the power supply.  I cant get it down from 13.60v  adjusting the trimmer does nothing and all other voltages (B+ and bias) seem ok.  I actually ordered another trimmer thinking that might have been the problem but with the new one installed I still have the same voltage as before.  is there anything obvious that im missing?

thanks in advance from a total noob,

Dennyp

 

[Matador]

Where and how are you measuring?  I would double check the soldering around R9 and R10, and confirm that D9 and D10 are in the correct orientation.

 

[Dennyp]

Ill check as soon as I can.  as far as where I'm measuring, am I not suppose to measure from the 5 pin terminal that goes to the 7 pin connector?


UPDATE:

The Joints look ok to me and the orientations are correct.  Im not the best at soldering but everything looks like it should work. 

 

[Micheal85]

Hey all.

  Just wanted to thank all of you here for this awesome build. I can't imagine how much hard work goes into all of this. Just wanted to share some pics. And let you know how well it went. It still has the stock capsule in it. I have not decided which way to go. I hope tskguy's is available soon. I have had very little interaction with him, but, so far his costumer service is amazing and hearing the sound clips from the 87 builds I think that will be a great choice. Besides having the stock capsule on it the mic sounds unbelievable. I used it in a session last week and was very impressed. I still have a few wiring lengths that need trimming down etc. And I am trying to diagnose a "popping static" problem that is proving difficult due to it rarely happens especially not when I want it to. But I'll get it.

But thanks again to every one. Matador, Chunger and everyone else who made this possible. ;D

I am also elbows deep in an 87. I will let you all know how that went when finished. On the correct thread of course.

 

[Matador]

Ill check as soon as I can.  as far as where I'm measuring, am I not suppose to measure from the 5 pin terminal that goes to the 7 pin connector?


UPDATE:

The Joints look ok to me and the orientations are correct.  Im not the best at soldering but everything looks like it should work.

Can you try grounding the end of R10 (1K) that goes to the pot?  The output voltage should go to 4.44V.

Try grounding the adjust pin (either the "other" side of R10 from above, or the + pin of C9, or pin 1 of the LM317T):  the output should go to 1.25V.

 

[Dennyp]

Can you try grounding the end of R10 (1K) that goes to the pot?  The output voltage should go to 4.44V.

Try grounding the adjust pin (either the "other" side of R10 from above, or the + pin of C9, or pin 1 of the LM317T):  the output should go to 1.25V.

This is where I apologize for being a noob....when you say ground, do you mean run a wire from the end of r10 to one of the grounds on the board? if not I apologize for not knowing what you mean. also, was I measuring from the right places?

 

[Matador]

This is where I apologize for being a noob....when you say ground, do you mean run a wire from the end of r10 to one of the grounds on the board? if not I apologize for not knowing what you mean. also, was I measuring from the right places?

You got it.  Just solder/clip a wire to ground, then carefully probe it to the various points I noted.

I would measure right at the output 5-pin screw terminal: heater plus is the second pin from the right, and ground is the left-most pin.

 

[Dennyp]

This is where I apologize for being a noob....when you say ground, do you mean run a wire from the end of r10 to one of the grounds on the board? if not I apologize for not knowing what you mean. also, was I measuring from the right places?

You got it.  Just solder/clip a wire to ground, then carefully probe it to the various points I noted.

I would measure right at the output 5-pin screw terminal: heater plus is the second pin from the right, and ground is the left-most pin.

I ran a wire from r10 to ground and I measured @ the heater on the 5 pin terminal and there was no change still 13.60v. does that mean there is a problem with that resistor? 

maybe this is related im not sure...I have an apex 460 body and power supply and the AC power section is laid out a little different than in your pictures.  I had to cross the cables from 9.5v to 200v in order to match what was on your board. I confirmed and labeled where they were connected in the original PSU...could it have been mislabeled? 

 

[Matador]

Try hard grounding the ADJ pin on the regulator itself.  The heater voltage should drop down to 1.25V.

 

[lordscruffo]

Hi guys,

    I just completed a build of the budget c12 with the new mullard tubes.    At first i had a low output issue which I resolved using Jandoste's posted fix:


"FIXED!

Thanks Category!
FB and RB linked by a jumper!
Thanks"

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

 

[ValveTone]

Hi!

Just wanted to say I completed my build and implemented all of the various 251 modifications and a few component swaps: 2.2 uf Ero MKC output coupling cap and Russian PIO treble bleed cap mainly.  Thanks to Matador and Chunger for their help!

I just did a day's worth of sessions at my place here in NYC and this DIY 251 mic killed it!  I actually preferred it over my U47 for the male vocalist I was working with, when paired with my V76 (my main vocal chain).  This DIY 251 was smoother overall for his voice. 

I also used it on female vocals, paired with an MP2NV for a little more air, and it was perfect.  I also used it on viola and violin for the hell of it and it was very nice there too!

Damon