Dany Bouchard D-12 Build - Pattern select not working and draining voltage.

[Wordsushi]

BINGO!

Yup, upon closer inspection there was a tiny wire connecting the ground to pin 7, then to pin 4. Took it out, fired up the PS and there is voltage corresponding to the pattern selector location and if that wasn't enough, the voltage drain is gone too AND, I have correct voltage, i.e. 60v at cardioid and what appears to be correct voltage up and down the selector.

Plugged in the mic and it's all working as it should. Fig 8 to Omni all there!

I'll give the mic a good once over tomorrow, but I wanted to first say THANK YOU to RuudNL, KrIVIUM2323 and trans4funks1 for your input and guidance where to look and what to try. I had just found a mic repair tech here in LA who said he could fix it and was going to box it up tomorrow and send it off, but you righteous dudes not only saved me a bundle but also helped me learn a ton about troubleshooting this mic.

I'll message Dany about this ground wire issue to look out for that's not in the build guide. Again, thanks everybody. It feels great knowing I built this mic and it works.

 

[RuudNL]

Good to read that you found the problem!
I hope you will enjoy your microphone for many years!

 

[trans4funks1]

+1

 

[robinhuntmusic]

Build this one too. Really great with the opr ck12 capsule!!

 

[Nick6691]

Can anyone tell me why there is cables from both backplate halves.
And how that works. Do the back and front backplate see different voltage?
Does this build require a special capsule?
Nick

 

[Delta Sigma]

Can anyone tell me why there is cables from both backplate halves.
And how that works. Do the back and front backplate see different voltage?
Does this build require a special capsule?
Nick

I don't see a schematic on Dany's site, but the original C12 had the CK12's isolated backplates tied together. The front diaphragm is polarized @ 0V, the backplate(s) at 1/2B+, and the rear diaphragm is adjustable (via power supply) from 0V for omni, 1/2 B+ for cardioid to B+ for fig-8. Backplate is connected to tube grid via cap for DC isolation.

The 251 takes advantage of the isolated backplates for switching. The front diaphragm is always polarized at 1/2 B+ and the front backplate is connected to the tube grid (~0V). In cardioid, the rear backplate and diaphragm are disconnected. In omni, the rear diaphragm connects to the front diaphragm and the rear backplate connects to the front backplate. In Fig-8, the rear diaphragm is AC connected to the front backplate (through a cap to block DC) and DC connected to the front diaphragm at 1/2 B+ through a large resistor and the rear backplate is connected to 0V.

 

[Nick6691]

Thanks DeltaSigma
That’s what I thought. That the backplate were tied together internally
That’s why I wonder why there is an extra cable attached to the backplates
and then the 2 backplate cables are soldered to 2 different turrets that are tied together on the back of the pcb with a wire.
I have looked for schematic too but can only find a build guide
See pictures
Nick

 

[Khron]

That’s why I wonder why there is an extra cable attached to the backplates
and then the 2 backplate cables are soldered to 2 different turrets that are tied together on the back of the pcb with a wire.

Well, it's definitely not the first questionable design choice I've seen made by him...

 

[Nick6691]

Anyone seen a schematic for Danys D-12? Cant find a GDIY thread either.

 

[Khron]

Anyone seen a schematic for Danys D-12? Cant find a GDIY thread either.

There's not all that much to it, to be fair - there's barely a handful of parts in there, component values are visible "even" on the board, and mostly described in the build PDF, and the designators might even be the same as in the actual C12.

PSU also seems pretty standard, the only "twist" being the provision for the small negative grid bias voltage.

 

[Nick6691]

There's not all that much to it, to be fair - there's barely a handful of parts in there, component values are visible "even" on the board, and mostly described in the build PDF, and the designators might even be the same as in the actual C12.

PSU also seems pretty standard, the only "twist" being the provision for the small negative grid bias voltage.

Hi Khron
Yes, pcb cards is informative and the build guide is good. Mostly pictures and not much explanation. I understand most of it but I dont have the second wire at the backplates. My backplates are shorted internally as should be on C12 I think. Thats why I cant understand why there needs to be 1 wire from each backplate. Do I really need to get an extra cable and look under the tape on the backplate for a treaded hole and the try to find a screw that fits. Or can I just branch out the cable in two, or just solder my cable to one point on the pcb because the to turrets for backplates on the pcb is connected together with a wire? Pictures earlier in this thread.
Nick

 

[Khron]

Thats why I cant understand why there needs to be 1 wire from each backplate.

Well, it's definitely not the first questionable design choice I've seen made by him...

If the two backplates are connected inside the capsule, that's all there is to it.

My best guess is, the build guide was written for the case of isolated-backplate capsules.

Now, why Dany might've thought / decided each backplate wire needed its own isolated pin on the PCB (despite those getting wired together anyway), is best case just a brainfart, worst case severe inexperience / incompetence. Hard to say (but seeing some of those other board builds & design decisions... )

Bottom line is, don't worry about it. Just make sure your backplate wire connects to the pin where other components are soldered too.