Official C12 Clone - Build and Support Thread

[duantro]

Signal chain is a ua6176 that I use most of the time with my diy 251, or diy mk7

 

[shabtek]

I wonder if there would be hum if you lifted the ground on the UA box instead.
might not tell much, as it works well with other mics .
what about heater dc return;is it isolated?

 

[kazanoom]

How much would someone charge to assemble a 251 build if I provided all the materials?

 

[Delta Sigma]

@duantro

Just reading quick so I may have missed it but where in your power supply is your PCB 0V grounded? Photos?

Ground loops are extremely frustrating but just know you'll have an earth grounded IEC and no hum eventually.

Personally, I like to only ground the power supply PCB 0V at the 7 pin XLR with the cable shield (earth ground right at the IEC connector). I will sometimes ground the 0V via lift switch that would force the 0V to only be grounded to the cable shield inside the mic.

 

[duantro]

I wonder if there would be hum if you lifted the ground on the UA box instead.
might not tell much, as it works well with other mics .
what about heater dc return;is it isolated?

I’ll try lifting the pre and see if anything happens. I did try a different pre at one point, as well as a different input on the mic panel. I’ve hooked it up as the guide currently. - Pin 7 0v ground tied to shield at mic xlr, psu xlr, and 7pin psu xlr. I’ve also left mic body pcb rails screwed and making contact to 0v and shield. Heater dc return is pin 7 0v. I tried it with shield lifted at mic and with pin 7 xlr not jumpered to tab shield in psu and it buzzed worse.

 

[duantro]

@duantro

Just reading quick so I may have missed it but where in your power supply is your PCB 0V grounded? Photos?

Ground loops are extremely frustrating but just know you'll have an earth grounded IEC and no hum eventually.

Personally, I like to only ground the power supply PCB 0V at the 7 pin XLR with the cable shield (earth ground right at the IEC connector). I will sometimes ground the 0V via lift switch that would force the 0V to only be grounded to the cable shield inside the mic.

Where do you connect your ground lift switch? Do you break connection between 0v and shield tab at 7pin xlr in psu? And no shield connections to 0v anywhere else?

 

[Delta Sigma]

Yes, I break the connection between the 0V and shield ground at the 7 pin XLR.

• Earth (wall) ground to chassis at the screw for the IEC connector
• Cable shield terminated to the XLR body and its pin grounded to the chassis at the 7 pin XLR
• 0V and cable shield bonded to mic body
• 0V connected to power supply chassis at the same point as the cable shield via switch

When the switch is closed, your 0V only has a connection to the chassis ground at the 7 pin connector and inside the mic through the shield back to the same point at the 7 pin connector. When the switch is open, the only path 0V has to ground is inside the mic body, through the shield back to the power supply chassis.

If memory serves me well, I ground the 3 pin XLR to its mounting screw just like the 7 pin. I do not connect the two XLR connectors' pin 1 or shield tabs to each other. I do not bring the audio pair into the PCB, I keep the pair short, twist it and go directly from the 7 pin XLR to the 3 pin.

 

[duantro]

Yes, I break the connection between the 0V and shield ground at the 7 pin XLR.

• Earth (wall) ground to chassis at the screw for the IEC connector
• Cable shield terminated to the XLR body and its pin grounded to the chassis at the 7 pin XLR
• 0V and cable shield bonded to mic body
• 0V connected to power supply chassis at the same point as the cable shield via switch

When the switch is closed, your 0V only has a connection to the chassis ground at the 7 pin connector and inside the mic through the shield back to the same point at the 7 pin connector. When the switch is open, the only path 0V has to ground is inside the mic body, through the shield back to the power supply chassis.

If memory serves me well, I ground the 3 pin XLR to its mounting screw just like the 7 pin. I do not connect the two XLR connectors' pin 1 or shield tabs to each other. I do not bring the audio pair into the PCB, I keep the pair short, twist it and go directly from the 7 pin XLR to the 3 pin.

Thanks for this detailed reply! I've disconnected the xlr shield jumper in the psu, disconnected the 0v (pin7) from the chassis shield tab at psu ( also clipped a lead on it to see if it changed while connected, and it didn't), and disconnected pin7 from shield tab in the mic. It is better, but still present. It seems signal has a ground hum in the mic somewhere. When unpowered and I plug in mic, it buzzes loudly. When I power it up it gets better. I'll clean the solder joints again

 

[Delta Sigma]

By disconnecting the shield jumper, do you mean the shield tab on the XLR? Make sure this is always grounded well to the chassis immediately where it comes into the chassis (connector's mounting screw) since the XLR shield is always connected physically to the chassis by the screws. If the connection via screws doesn't conduct well, then you could create a ground loop.

The basic pin 1 XLR (or pin 7 on the mic connector?) theory is to always ground your shield immediately when entering a chassis or enclosure. This should be done in the mic body as well. This explains it much better than I can:
https://www.ranecommercial.com/legacy/note165.html

 

[duantro]

I found the smoking gun. After reading 70 some odd pages, I realized that you were supposed to solder the bottom 2 tabs of the tube board! I’m on page 85 now and wondering if the last board revisions are noted anywhere? There seems to be an extra turret above the tube board, that seems to go to c12. Is this the better option instead of the red wire with the grinded turret from the Chunger visual build guide?

 

[Matador]

I found the smoking gun. After reading 70 some odd pages, I realized that you were supposed to solder the bottom 2 tabs of the tube board! I’m on page 85 now and wondering if the last board revisions are noted anywhere? There seems to be an extra turret above the tube board, that seems to go to c12. Is this the better option instead of the red wire with the grinded turret from the Chunger visual build guide?

(If it's the wire I'm thinking) it was a waste, because you can go directly from the connection point right to the tube grid without needing to flow through an extra turret.

 

[Delta Sigma]

I found the smoking gun. After reading 70 some odd pages, I realized that you were supposed to solder the bottom 2 tabs of the tube board! I’m on page 85 now and wondering if the last board revisions are noted anywhere? There seems to be an extra turret above the tube board, that seems to go to c12. Is this the better option instead of the red wire with the grinded turret from the Chunger visual build guide?

Good stuff! Finally getting a mic working after dealing with a long term troubleshoot is a huge relief. I hope it sounds great!

 

[mrgrooves666]

Could someone with the most recent board post some detailed pictures of it finished. I also followed the guide with the old version and then figured somethings I need to adjust after reading the whole thread to find that things have changed. Just want to double check I have everything right before my capsules arrive. Thanks in advance!

 

[marked]

I see there are some talk about BUZZ.. And I might as well throw this out there.. I got a huge amount of noise, perhaps RF or other disturbance. I got it in both the C12 and Elam circuit, when using the C12 headbasket that came with this build. It went away completely with an Elam headbasket(bought also from studio939), with two layers of shielding, fine and coarse mesh. I did check that both baskets were connected to mic body and ground.
Any clues to why the C12 headbasket made a huge difference to the shielding of the Elam headbasket?

 

[marked]

Might as well add, no change in capsule or tube changed anything, only the change in headbasket removed the buzz. Tried four capsules and plenty tubes..

 

[mrgrooves666]

The mesh grill in the headbasket surrouding the capsule acts as a faraday cage, protecting the capsule from RFI/EMI interference. If the c12 basket was the single layer version, then this might have been the reason. The more coverage area it offers, the better rejection. This depends on the location as well. On my C12, at home, I stick to double layer headbasket at the end because all my attempts to turn other mics to single layer gaved me the same results, and I don't have the tools to install a single layer, more tight mesh myself.

 

[marked]

Yes,
That is what I gathered as well, because the main difference between the headbaskets were single vs double mesh. I was supprised though that it made such an huge impact. From silent to halfway upp on the db gauge of white noise. And got speculating if I had missed something in the grounding scheme.
Perhaps there are som ways to minimise the RF disturbance and still use a single mesh basket, dont know?
Anyways it is a good thing to know for others who might encounter the same problem and the solution is nowhere in the circuit.

 

[mrgrooves666]

Yes,
That is what I gathered as well, because the main difference between the headbaskets were single vs double mesh. I was supprised though that it made such an huge impact. From silent to halfway upp on the db gauge of white noise. And got speculating if I had missed something in the grounding scheme.
Perhaps there are som ways to minimise the RF disturbance and still use a single mesh basket, dont know?
Anyways it is a good thing to know for others who might encounter the same problem and the solution is nowhere in the circuit.

Yes I was surprised too with my own attempts. I guess its about finding the right mesh size, density, and also means to secure a good ground connection to it. Add to that, you get to small and dense and its starts to impart coloration to the sound. That was my main issue, I don't have the tools try different specs, and to form the mesh into place nicely, also my iron tip, Its not to hot to be able to solder it correctly and ensure a good ground connection, so I had to abort my single mesh endevours and just stick with double layer lol...
I believe there are some discussions here about the spec, when chunger was exploring the possibility of tweaking the HT-11A basket to be more like the C12.

 

[Recording Engineer]

Studio 939’s Type 1 single-layer headbasket has been great for me. I have four mics with them and another pair completed at some point soon.

 

[Delta Sigma]

Yes,
That is what I gathered as well, because the main difference between the headbaskets were single vs double mesh. I was supprised though that it made such an huge impact. From silent to halfway upp on the db gauge of white noise. And got speculating if I had missed something in the grounding scheme.
Perhaps there are som ways to minimise the RF disturbance and still use a single mesh basket, dont know?
Anyways it is a good thing to know for others who might encounter the same problem and the solution is nowhere in the circuit.

Have you tried the single layer anywhere else? I have a problem in my house when I'm in the room my coax cable from my ISP runs through. I have a huge hum problem with electric guitars but I couldn't localize it to the coax until I plugged in a ribbon mic.