Official AMI-TAB Funkenwerk-C12-Alternative-Kit

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aaquilato said:
Has anyone built this kit?

Yes I did , I actually design a PCB For Oliver for his mic body  Some time ago,  and sounds really nice ,
Actually Oliver still has My Prototype.
Best,
Dan,
Oliver Archut Hybrid C12

58d028199407c.jpg

 
Well, I can see that this thread has gotten more than just a few hits but only one reply.
So I guess I'll lead the way. There isn't much out there about this DIY kit.
There is a thread on PRW but no one has written anything one it in months, except yours truly.

http://prorecordingworkshop.lefora.com/topic/4085753/AMITAB-Funkenwerk-C12-body-kits?page=3#.UwULNKW0m5H

The "Official C12 Clone" thread is only for the "Matachung" C12.

There is some info on the CathedralGuitar.com site with some very nice pics of a prebuilt unit.
Sweet! I hope mine turns out looking that good.

http://www.m221b.com/AMI/C12Kit/C12KitHI.html

So much for sharing...


I purchased what Oliver calls the "budged" kit as I thought I would save a few $$$ and do some upgrades to the Chinese PSU and make a new cable out of GAC-7.
Oliver says there are no upgrades that can be done to the Chinese PSU.
I find that very hard to believe but for the time being I'll leave it alone.

I have a CT12 capsule, a Beeznees C12 capsule and an original AKG CK12 capsule from a very old (early serial #) 414EB (which sounds glorious). So you see why I'm so keen to build a C12 clone or two.

I made a new cable but the pinout is not 1 to 1.
If anyone out there wants to upgrade their cable using the same Chinese PSU here is the correct pinout from Oliver @ TAB Funkenwerks.

GAC-7 MICROPHONE CABLE WIRING
This follows the circuit diagram posted in my first thread.

Tuchel connector side to the mic is

Pin 1 = White audio +
Pin 2 = Black audio  -
Pin 3 = Not connected (per the build instructions)
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 the Tuchel connector body

The grey wire is snipped back and not used.

After making the XLR side I realized if I had not snipped the grey wire back I could have used it as Pin 4 below (ground). You could tie the braid and the grey wire together in the Tuchel connector above. There's plenty of room for that.
Then when making the XLR below you could use the grey wire in Pin 4 and it will already be tied to ground.



The XLR side to the Chinese PSU

Pin 1 = Yellow 120V
Pin 2 = Red Thick 6V filament Heater 
Pin 3 = Green 0 – 120V
Pin 4 =  ground                                                     
Pin 5 = White audio + 
Pin 6 = Black audio  -
Pin 7 = Blue Thick Ground
Copper Braid goes to the Neutrik connector body

So since I had snipped the grey wires back I used a piece of leftover solid wire from a capacitor. I cleaned it very well with some steel wool and tied it from Pin 4 to Pin 7 and to the ground braid. That wasn't very easy since I did that last. (Next time I'll do that first!!)
And for all I know could be a mistake. I'm new at this and I'm learning as I go.

Follow at your own risk.
Feel free to chime in if you're reading alone and have more knowledge than I.

 
Glad to see that you are posting your progress here it will be always helpfull for other micbuilder outhere ,.
Keep on the good work,

Great mic + Great Capsule = A lot of fun and a lot of enjoying studio time .

Great Post +1

Best,
Dan,

 
I find it almost impossible to believe that C2 is 47uF.  C2 forms a LPF with R2, which is probably 100M or higher.  In order to get a 3dB frequency of 1Hz, only about 1500pF is needed.  The ELA M251 standard value here is about 5000pF/5nF.  47nF would give -3dB point of 0.03Hz which seems like overkill, but probably what was intended.  4.7nF is likely what would be specified, so perhaps you misplaced a decimal point?
 
Matador said:
I find it almost impossible to believe that C2 is 47uF.  C2 forms a LPF with R2, which is probably 100M or higher.  In order to get a 3dB frequency of 1Hz, only about 1500pF is needed.  The ELA M251 standard value here is about 5000pF/5nF.  47nF would give -3dB point of 0.03Hz which seems like overkill, but probably what was intended.  4.7nF is likely what would be specified, so perhaps you misplaced a decimal point?

Thanks Matador. A 47uf electrolytic was supplied in the kit I got. As you said, it probably was a mistake. I do have a 47nf PIO I will try to fit in.
 
I have built this kit.  I had the same 47uf electrolytic in my bag of parts and I suspect it was there to be used if you decided to cathode bias the circuit and be used as a cathode bypass capacitor.  Or it could have been a mistake :)
 
ValveTone said:
I have built this kit.  I had the same 47uf electrolytic in my bag of parts and I suspect it was there to be used if you decided to cathode bias the circuit and be used as a cathode bypass capacitor.  Or it could have been a mistake :)

What value cap did you use in the C2 position if you didn't use the 47uf?
 
The schematic you posted in the OP says C2 = 47nf. The original C12 Schematic shows 5000pf, which is a.k.a. 5nf, in the same position. I think Matador's suggestion that 4.7nf is what is intended seems like a most likely answer.

My guess is that the schematic linked to in the OP has a typo and is missing a "." where it says "47nf", but it seems like contacting AMI would be the easiest way to find out exactly what they intended.
 
Matador said:
I find it almost impossible to believe that C2 is 47uF.

There are two main reasons why the C2 isn't 47uF electrolytic for sure:
- electrolytics have low insulation resistance (high leakage current)
- If we assume that the time for fully capacitor charging is 5RC, it will take more than 10 hours to change polar characteristic :)
 
trans4funks1 said:
The schematic you posted in the OP says C2 = 47nf. The original C12 Schematic shows 5000pf, which is a.k.a. 5nf, in the same position. I think Matador's suggestion that 4.7nf is what is intended seems like a most likely answer.

My guess is that the schematic linked to in the OP has a typo and is missing a "." where it says "47nf", but it seems like contacting AMI would be the easiest way to find out exactly what they intended.

Well, I have reached out to Oliver and various AMI associates but no answer.

I've started the build and used a 47nf (.047uf) Vishay Film cap per the circuit layout. I wouldn't use a electrolytic even if the right value had been supplied. Because this cap is "sandwiched between the two boards" once I finish this build changing it will be kind of difficult.

If I've got it correct, C2 is the decoupling capacitor which helps remove noise in the HT supply that may reach the capsule. So is 47nf going to be too high?
Yes, I am a noob with no EE background!

Thanks for your replies. They all help.
 
aaquilato said:
trans4funks1 said:
The schematic you posted in the OP says C2 = 47nf. The original C12 Schematic shows 5000pf, which is a.k.a. 5nf, in the same position. I think Matador's suggestion that 4.7nf is what is intended seems like a most likely answer.

My guess is that the schematic linked to in the OP has a typo and is missing a "." where it says "47nf", but it seems like contacting AMI would be the easiest way to find out exactly what they intended.

Well, I have reached out to Oliver and various AMI associates but no answer.

I've started the build and used a 47nf (.047uf) Vishay Film cap per the circuit layout. I wouldn't use a electrolytic even if the right value had been supplied. Because this cap is "sandwiched between the two boards" once I finish this build changing it will be kind of difficult.

If I've got it correct, C2 is the decoupling capacitor which helps remove noise in the HT supply that may reach the capsule. So is 47nf going to be too high?
Yes, I am a noob with no EE background!

Thanks for your replies. They all help.

The only thing that will suffer is the time to change the pattern as moamps referred to above.  The RC time constant of 100M into 47nF is 4.7 secs.  Using the 5*RC rule this would be ~30seconds to change the pattern.  Using the stock 4.7nF value means only 3 seconds to change the pattern.

So "too high" depends on how patient you are. ;)
 
moamps said:
Matador said:
I find it almost impossible to believe that C2 is 47uF.

There are two main reasons why the C2 isn't 47uF electrolytic for sure:
- electrolytics have low insulation resistance (high leakage current)
- If we assume that the time for fully capacitor charging is 5RC, it will take more than 10 hours to change polar characteristic :))

OK. Matador this is beyond me. I thought this cap dealt with noise. What has that got to do with changing the pattern?
The quote above from moamps seems to be based on what would happen using a 47uf cap which is larger than the 47nf which is larger than the 4.7nf...
How long will it take for the polar pattern to change with the 47nf cap?
The boards are not connected yet so I can order a 4.7nf cap if that's what it should be.
I certainly do not want to be in the middle of a session and call for a lunch break while we wait for the mic to go from card to omni. Oy!!


Thanks for chiming in.
 
My guess is that the schematic linked to in the OP has a typo and is missing a "." where it says "47nf", but it seems like contacting AMI would be the easiest way to find out exactly what they intended.

You know this kind of pisses me off. How can AMI sell a kit with the wrong circuit layout and supply the wrong parts as well? I had to buy the resistors and capacitor that were left out.
This kit wasn't cheap and I'm stuck not knowing what to do (partially my fault as I am a noob) where the Apex 460 FAR C12 kit from Microphone Parts had well written instructions, all the parts were properly labeled.

I truly expected more from AMI. Sorry to post this disappointment in an open forum thread but this project is a year in the making. I waited 6 months for the Campbell capsule.

Oliver, if you're reading this. Not good business practice. It doesn't matter how good your transformers are.

OK. Rant over.
 
aaquilato said:
OK. Matador this is beyond me. I thought this cap dealt with noise. What has that got to do with changing the pattern?

It is a LPF for the polarization voltage.  The problem here is that even tiny disturbances on the capsule will happily couple to the grid and be amplified.  So the capsule needs very clean DC to be quiet.  This backplate voltage is what decides the pattern.

But having a very low pole in the LPF (formed from the 100M resistor and C2) also means the circuit is slower to respond to voltage changes.  When you change from omni (0V on the backplate) to figure 8 (120V on the backplate), that cap has to charge from 0V to 120V, but it has to do so through that massive 100M resistor, which has only a tiny conductance.

So yes, it takes about 30 seconds (or about five RC time constants) to change with 47nF.  But the noise filtering is better:  the stock value of 4.7nF tries to strike a balance between speed of pattern changes and noise immunity.
 
Matador said:
aaquilato said:
OK. Matador this is beyond me. I thought this cap dealt with noise. What has that got to do with changing the pattern?

It is a LPF for the polarization voltage.  The problem here is that even tiny disturbances on the capsule will happily couple to the grid and be amplified.  So the capsule needs very clean DC to be quiet.  This backplate voltage is what decides the pattern.

But having a very low pole in the LPF (formed from the 100M resistor and C2) also means the circuit is slower to respond to voltage changes.  When you change from omni (0V on the backplate) to figure 8 (120V on the backplate), that cap has to charge from 0V to 120V, but it has to do so through that massive 100M resistor, which has only a tiny conductance.

So yes, it takes about 30 seconds (or about five RC time constants) to change with 47nF.  But the noise filtering is better:  the stock value of 4.7nF tries to strike a balance between speed of pattern changes and noise immunity.

Thanks for explaining that for me Matador. I get it now.

 
aaquilato said:
Matador said:
I find it almost impossible to believe that C2 is 47uF.  C2 forms a LPF with R2, which is probably 100M or higher.  In order to get a 3dB frequency of 1Hz, only about 1500pF is needed.  The ELA M251 standard value here is about 5000pF/5nF.  47nF would give -3dB point of 0.03Hz which seems like overkill, but probably what was intended.  4.7nF is likely what would be specified, so perhaps you misplaced a decimal point?

Thanks Matador. A 47uf electrolytic was supplied in the kit I got. As you said, it probably was a mistake. I do have a 47nf PIO I will try to fit in.

So after finally talking to Oliver, yes the 47uf cap was supplied as an alternative for the 251 type circuit build.
The 47nf C2 cap on the circuit diagram is a MISTAKE. The correct value should be 4.7nf as pointed out by Matador. Oliver is having is web staff correct this to represent the correct value.
I have removed the 47nf cap and replaced it with the correct value. Happy days!
 
I'm going to end this post by saying, don't bother with this DIY kit.
I've had more headaches with all the misinformation and incomplete packaging than any other DIY kit I've worked on.

It's just not worth it.

Thank you everyone for your help and support.
 

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