Official C12 Clone - Build and Support Thread

[Melodeath00]

I pulled out my C12 for the first time in probably 3/4ths of a year today. Wow, it really sounds good. I had forgotten.

 

[TNO73]

pls help troubleschoot....

With no load, the B+ will be very high...that's normal.  Passive PSU's need load current to establish their working output voltages.

The proper test load is 180K (not 200K) for a 6072A tube.  You want to pull about 0.7ma through the test load @ 120V, which is 171K (180K is closest standard value).  200K will pull 0.6mA, and that small 0.1mA difference in current will translate to +18V higher B+.  Subtract 18V from your measurements above and you'll be in the proper range. 

If you cannot adjust down enough after changing to the proper load then it means that the series PSU resistors (R1 and R2) need to be higher in value.  Stock value is 91K:  I would change them to 100K and you should be able to get it down below 120V.

all right, thank you very much - just tried with a dummy load of 178K(thats what i could establish) which took my voltage down to 123VDC. Still a little to high!

Gonna try to change R1+R2 to 100K, looking forward to report back on this issue.

Tom

I´ve tried now changing R1+R2 to 100K! Now i cant get to trim it up 120VDC, used dummy load 178,5K!
Speak there anything against using R1 as 91K and R2 as 100K?
thanks

 

[TNO73]

Hi again!

I´ve added some pics of the the Elam 251 build, could you pls. have a look if there is anything obviously  wrong! Especially the reused c10 which is now going from backplate to ground!?
Thank you very much for support!!!
Tom

 

[Matador]

I´ve tried now changing R1+R2 to 100K! Now i cant get to trim it up 120VDC, used dummy load 178,5K!
Speak there anything against using R1 as 91K and R2 as 100K?
thanks

No problem: use whatever gives you the right trim range.

 

[Melodeath00]

Matador, I decided to check some things in my C12 today, and noticed something that seems odd.

Pin 4 of the tube is for the heater. When I measure DC between the body rail and Pin 4, I get 6.3V. However, I am getting continuity between Pin 5 (the unused triode heater) and the body rail as well. Is this correct? I can't see why Pin 5 should be grounded. I thought it was floating.

Secondly, should the Bias voltage be measured at the tube or the PSU? The AKG schematic doesn't show reference voltages. I get -1.1V in the PSU, which becomes -1.37V at the tube in the mic. Plate voltage is 69.8V.

 

[Winetree]

The stock Chinese Tube cable has 7 wires and an overall shield connected to the tab.
I using Mogami 3172 mic tube cable with 6 wires, 1 twisted pair for audio, 2 large, and 2 regular, and an overall shield.
With the 7 pin connectors, there seems to be one wire short.
Would the following  wiring guide be correct? 
Pin 1 = B+            - Large
Pin 2 = heater    -Large
Pin 3 = pattern  - Regular
pin 4 = bias          - Regular
pin 5 = audio      - Twister Pair
pin 6 = audio +  - Twisted Pair
pin 7 = ground"  -Overall Shield
Tab    =connected to pin 7 or not?

 

[chunger]

The stock Chinese Tube cable has 7 wires and an overall shield connected to the tab.
I using Mogami 3172 mic tube cable with 6 wires, 1 twisted pair for audio, 2 large, and 2 regular, and an overall shield.
With the 7 pin connectors, there seems to be one wire short.
Would the following  wiring guide be correct? 
Pin 1 = B+            - Large
Pin 2 = heater    -Large
Pin 3 = pattern  - Regular
pin 4 = bias          - Regular
pin 5 = audio      - Twister Pair
pin 6 = audio +  - Twisted Pair
pin 7 = ground"  -Overall Shield
Tab    =connected to pin 7 or not?

A couple of my GAC7 cables are wired with overall shield connected to pin 7 ground and with pin 7 jumpered to the housing.  If I recall correctly,  Klaus may have posted somewhere his cables wired in this fashion.  From what friends have told me, a more "proper" way to do it is with the 7 conductor cable independently wired with one of the larger gauge conductors at pin 7.  . . then, you have the option at the PSU or microphone to figure out your grounding scheme.

Built as pictured in this thread, I have not experienced noise problems (or sonic differences) interchanging cables wired both ways on C12 clones and on mk47.  I have read that you may need to adjust some parameters if you plan to use the same cable for a DU67 build.

 

[Winetree]

From what friends have told me, a more "proper" way to do it is with the 7 conductor cable independently wired with one of the larger gauge conductors at pin 7.  . . then, you have the option at the PSU or microphone to figure out your grounding scheme.

That's the way I was going to connect it, with a large wire going to pin 7.
But because there's only 6 wires,  I'd have to use the overall shield for one of the 7 pins.
With one?

P.S. Returned the Mogami cable and I'm going with Redco 7 conductor cable.

 

[JeromeMason]

Edit:

Actually I was told the info I requested, now I'm trying to figure out if I have either a defective xformer or output cap.

All my voltages in the PSU and inside the mike are perfect, but the mic is not outputting hardly any signal to the XLR. I can rule out xformer by measuring the ohms from the red/blue leads. However, I'm not positive on how to tell if it is the output cap that is causing the problems. If anyone has had this problem before and it was something simple, or if it was either the xformer or Output cap please chime in and let me know what you did to find it.

Thanks,

Jerome

 

[Matador]

Edit:

Actually I was told the info I requested, now I'm trying to figure out if I have either a defective xformer or output cap.

All my voltages in the PSU and inside the mike are perfect, but the mic is not outputting hardly any signal to the XLR. I can rule out xformer by measuring the ohms from the red/blue leads. However, I'm not positive on how to tell if it is the output cap that is causing the problems. If anyone has had this problem before and it was something simple, or if it was either the xformer or Output cap please chime in and let me know what you did to find it.

Thanks,

Jerome

Hey Jerome, was this particular mike + capsule combination ever working properly?

 

[JeromeMason]

Edit:

Actually I was told the info I requested, now I'm trying to figure out if I have either a defective xformer or output cap.

All my voltages in the PSU and inside the mike are perfect, but the mic is not outputting hardly any signal to the XLR. I can rule out xformer by measuring the ohms from the red/blue leads. However, I'm not positive on how to tell if it is the output cap that is causing the problems. If anyone has had this problem before and it was something simple, or if it was either the xformer or Output cap please chime in and let me know what you did to find it.

Thanks,

Jerome

Hey Jerome, was this particular mike + capsule combination ever working properly?

At one point yep it was working beautifully, then I removed the components for Ela m mod and added the other few components and that is when the issue started with basically hardly any output. So, I put it back together as the C12 and it's still having that same issue. Just very low output. It was suggested that it could be one of the 5000pf caps, but if it did this when they were not on the board I don't see how it could be them. I can test the capacitance of them though, check to see if they are ok.

You have an idea of what it could be Mat?

 

[Matador]

You have an idea of what it could be Mat?

Do you have any way of injecting signal to various points in the circuit?  Or measuring signal amplitude (e.g. a scope)?

 

[JeromeMason]

You have an idea of what it could be Mat?

Do you have any way of injecting signal to various points in the circuit?  Or measuring signal amplitude (e.g. a scope)?

I don't have that type of equipment, I could send audio via an interface output and then run back into PT where I can read the amplitude.

 

[kotopees]

Hello everyone!
I assembled C12 Microphone Kit Complete
it worked the first time. There is a problem on the omni pollar there is no noise when I switch on the figure of eight appears high frequency noise: the lower frequencies noticeably missing. High-frequency noise increases when switching from the circle to eight.
All voltages are set up well, as indicated on the first page.
https://soundcloud.com/alexandr-burakov/sets/polar-pattern-test

Please tell me what could be the reason?
thanks in advance

 

[zandru]

Greetings Group DIY'ers ,

Do I need to bridge or connect the two back plate terminals of the budget 34mm K67-based edge terminated
capsule that I purchased from Studio939,

in regards to the multi-pattern (FB/RB/FC/RC) 4 capsule connection pins on the Matador Mic PCB ?.

Will be most appreciated for a timely reply.

Much Thanks….ZANDRU…………

If not!;  (Please Help) explain my shortcomings...........

 

[chunger]

Bridge front and rear backplate either at the capsule or at the PCB.

FB = front backplate
RB = rear backplate
FC = front capsule
RC = rear capsule

 

[TheJames]

Well...I finally got one of the mics completed.

Here are some of the build variables..

175V PSU transformer
Setup for 12AT7
Chunger's select AT7 tube
AMI transformer
1uf Cap
Beesneez CK12 capsule
Single layer C12 type head basket
Stock tube mic cable

I originally setup the mic with a basic EH 12at7 which in some cases sounded as good if not better than the select tube (a tad warmer) but it's downside was noise.  The "select" tube I got from Chunger was significantly quieter than the EH tube.  I'm sure that could vary.

Here's a couple of sound files to listen to comparing a stock mic with a modded one.  Obviously both mics cannot sit in the same physical space, the stock mic is a hair bit higher with it's capsule as close to the modded mic as possible.

This is the same performance, both mics going through a Presonus ADL600 into an Orion 32 for conversion.  Recorded at 24/96.

The stock mic used 40db of gain, the modded one 50 db of gain.  I had to trim a little to get the levels the same. difference in level is a little more than 6db.

http://www.madsonics.com/wp-content/uploads/2014/11/C12_test_A1.wav
http://www.madsonics.com/wp-content/uploads/2014/11/C12_test_B1.wav

 

[Matador]

What is "stock" in this case?  Just the plain Alctron HT-11A up without changes?

 

[micaddict]

First impression on cans: A is fuller down low.

BTW good to see the AT7 tubes showing up in these builds. I remember asking Matador for the circuit changes for that. I think he answered in the White Market thread.



Henk

 

[TheJames]

What is "stock" in this case?  Just the plain Alctron HT-11A up without changes?

That's correct.  Alctron out of the box with the single layer head basket.

Side note....I added a couple of other mic details in the original post (transformer and output cap).