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Wiring Help! Fitting a CT12 in a C414 ULS
Old 6th February 2020
  #1
Gear Head
 

Question Wiring Help! Fitting a CT12 in a C414 ULS

I've recently picked up a C414 ULS and am attempting to upgrade the capsule to Tim Campbell's CT12, but I can't work out on the stock capsule which side termination wire is front or back?

The red and clear wires connect to a couple of through pins on the capsule mount, then to yellow wires going to the left and right sides, but I can't see which connects to the front plate once they disappear under the nylon ring. Does anyone know?

I've got the circuit diagram and have traced the wires from the capsule to the board (highlighted) but still can't tell as it's so tightly packed on there.
Attached Thumbnails
Wiring Help! Fitting a CT12 in a C414 ULS-c414-internal.jpg   Wiring Help! Fitting a CT12 in a C414 ULS-c414-uls-circuit-diagram.jpg  
Old 7th February 2020
  #2
Gear Head
 

I found the answer from the images of the stock capsule on Saturn Sound: http://www.saturn-sound.com/Curio's/...%20capsule.htm, it appears red wire is connected to the rear backplate (the righthand solder pin when viewed from the back of the capsule)

But, ahem, the next problem... I've gone ahead and carefully fitted the CT12, reassembled the mic and powered it up but to my horror it was just noise

Cardioid, Hypercardioid and Figure of 8 are all just masses of noise with a faintly audible audio signal. Omni however is crystal clear, just at a lower level to the stock capsule.

So, my next question... have I in fact got those backplate wires the wrong way round and the noise is indicative of this? Am I risking capsule damage if I reverse the wires if it is correctly wired at present and the problem lies elsewhere?
Attached Thumbnails
Wiring Help! Fitting a CT12 in a C414 ULS-c414-uls-ct12-fitted.jpg  

Last edited by Big Ears; 7th February 2020 at 08:28 PM.. Reason: Added image
Old 10th February 2020
  #3
Lives for gear
 
gyraf's Avatar
 

What you are hearing is most possibly noise from contaminated high-impedance spots in the microphone.

It looks like you replaced the wireing between capsule and electronics? If so: Why?

The spots on the PCB where capsule comes in are extremely sensitive to dirt, flux and such even remotely conductive substances. Clean really well with IPA and distilled water and see if your noise changes character - if so, you're on the right track..

/Jakob E.
Old 11th February 2020
  #4
Gear Head
 

Hey Jakob, thanks for your reply. With regards to the wire replacement, Tim Campbell had kindly attached wires to the new capsule already and it was my understanding that it's better to solder at the electronics end rather than risk damage to the capsule soldering/desoldering there?

It turns out I did wire things correctly and the noise is as you say most likely related to the dirt and flux covering the components. I must have disturbed something during soldering, I'm currently in the process of cleaning things up! Failing that I'll probably take the mic in to Funky Junk in London for repair.

Last edited by Big Ears; 11th February 2020 at 03:33 PM.. Reason: Correction
Old 11th February 2020
  #5
I'm sorry to hear this. Please make sure that you haven't shorted the backplate solder tags together and that they aren't making contact with the frame of the mic.
In the ULS the backplates must stay insulated from each other. This is critical. Also check that all connections are tight (though they should be because omni works). It really sounds as if it is a backplate short.
Old 11th February 2020
  #6
Gear Head
 

Quote:
Originally Posted by Tim Campbell View Post
I'm sorry to hear this. Please make sure that you haven't shorted the backplate solder tags together and that they aren't making contact with the frame of the mic.
In the ULS the backplates must stay insulated from each other. This is critical. Also check that all connections are tight (though they should be because omni works). It really sounds as if it is a backplate short.
Hey Tim! I did have the same thought so I double checked the backplate tags weren't bridged or touching the mesh and there's a decent amount of clearance.

I did notice a large amount of old flux/gunk that appeared to be connecting two of the legs of transistor T101 in the circuit diagram, I've cleaned it off but wonder if it's maybe shorted and blown this component? I'm not very savvy with electronic theory so I'm not sure how to test for this.

I'm considering a careful attempt at removing the PCB tonight to check the underside as my other thought was if a large blob of solder had collected underneath where I'd desoldered and re-soldered the rear diaphragm ring wire to point D.

I need to say though the capsule sounds beautiful in omni, the top end is incredible!
Old 12th February 2020
  #7
Try reversing the backplate connections.
Old 12th February 2020
  #8
Gear Head
 

Quote:
Originally Posted by Tim Campbell View Post
Try reversing the backplate connections.
I did give that a go, it still had the noise only the pickup pattern was the wrong way round
Old 12th February 2020
  #9
You may have a poor or dirty solder connection on the 1 gig resistors tops. You do need to scrape the non-conformal coating off to get a clean connection. It's also common to have one of the three 1 gig resistors develop a bad connection or to break down internally. Replacing all of that is difficult work.
Old 13th February 2020
  #10
Gear Head
 

Quote:
Originally Posted by Jim Williams View Post
You may have a poor or dirty solder connection on the 1 gig resistors tops. You do need to scrape the non-conformal coating off to get a clean connection. It's also common to have one of the three 1 gig resistors develop a bad connection or to break down internally. Replacing all of that is difficult work.
Thanks for the tips, Jim. I redid my soldering again tonight, as some of it did look dirty around those resistor tops, but no lucky sadly.

I also did a some testing just to rule out the backplate short Tim mentioned and it's definitely ok on that front.

I don't feel confident enough trying to replace those resistors myself, so I think it's time to take it in for repair.

Incidentally, the service manual notes those resistors as 3 gig. Does it matter if they're replaced with 1 gigs?
Old 13th February 2020
  #11
Use 3 gig. Have fun finding them. That entire assembly is coated in polystyrene dope. You will need to remove all of it before stripping off the parts and replacing them.
Old 14th February 2020
  #12
Gear Head
 

Quote:
Originally Posted by Jim Williams View Post
Use 3 gig. Have fun finding them.
It would seem their availabiliy is about on par with the original CK12
Old 1st March 2020
  #13
Gear Head
 

Just to update, I've still had no luck getting the CT12 to work in the ULS so I decided to put the stock nylon capsule back in...and to my amazement everything works fine again, no issues at all with the mic!

Was it a fluke, had I just done some bad soldering before? I swapped the CT12 back in...same problem again, lots of noise and rumble. Back to the stock capsule and all's well, which makes me wonder is the CT12 actually compatible in the ULS with its 4-wire configuration?

Not that it really matters anymore as I've gone and fitted the CT12 into a Rode K2 and it's working perfectly and sounding beautiful! All's well that ends well
Old 3 weeks ago
  #14
Gear Maniac
Well.... maybe the backplate was grounded or shorted via the mounting screws?! The original capsule is isolated because it is a nylon assembly...
Old 2 weeks ago
  #15
Check for shorts between backplates with a DVM set to meg ohm settings. Sounds like a short or leakage to me.
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