Rob Flinn

Problem with C12 clone
« on: March 10, 2019, 03:44:00 PM »
I've just got to the testing stage with a C12 clone that I started some years ago (see pic).    The insides are a Poctop pcb that I have glued in place with Araldite.  The PSU is the matching Poctop board.   It uses a Tim Campbell capsule.  The problem I have is that the mic seems to overload if I talk loudly into it.   If I hold it about 50cm away it sounds quite nice if I speak into it, but is unusable in a real world recording situation.   It's difficult to describe the sound, but it is sounds like it has reached the end of it's headroom or like a lot of wind is blowing directly into the capsule.      Since it is very high impedance it's quite difficult to test. I'm getting 1.1v bias & 117v at the mic & I have swapped the valve out with another I had.     I'm just wondering if anyone else has experience this sort of problem & what the solution was ?  Or maybe you have some suggestions as to where I should look ?
« Last Edit: March 11, 2019, 06:47:53 AM by Rob Flinn »
regards Rob


Re: Problem with C12 clone
« Reply #1 on: March 11, 2019, 02:26:22 PM »
Replace the capsule with a 50pf capacitor and see what happens. Could be the capsule.

Rob Flinn

Re: Problem with C12 clone
« Reply #2 on: March 11, 2019, 02:34:33 PM »
Replace the capsule with a 50pf capacitor and see what happens. Could be the capsule.

Is this 2 x 50pf ?  One for each diaphram ?

Also not quite sure how this determines whether it's the capsule.    It only makes the noise when there is a significant sound level, so if I replace the capsule with some caps there is no way to create the level of input at which the problem occurs since I won't have any an input at all.  Have to sub another capsule I guess.
« Last Edit: March 11, 2019, 03:27:19 PM by Rob Flinn »
regards Rob

Re: Problem with C12 clone
« Reply #3 on: March 11, 2019, 06:53:31 PM »
You can do it with two, or just one in cardioid.

Before that you could try it in omni and figure of 8 and test both sides, or swap the sides by swapping wires. Could be the voltage reaching the capsule is too high (over 60v). But I am just guessing.

I guess you are using a proper pop screen, moisture from your breath will cause the exact same effect you are describing. Is it just caused by vocal? Does it happen if you record high spl instrument?

Rob Flinn

Re: Problem with C12 clone
« Reply #4 on: March 11, 2019, 06:58:51 PM »
You can do it with two, or just one in cardioid.

Before that you could try it in omni and figure of 8 and test both sides, or swap the sides by swapping wires. Could be the voltage reaching the capsule is too high (over 60v). But I am just guessing.

Ok I will try tomorrow if I get a chance.


Quote
I guess you are using a proper pop screen, moisture from your breath will cause the exact same effect you are describing. Is it just caused by vocal? Does it happen if you record high spl instrument?

I'm not without experience of condenser mics.  It overloads at much too low a level.   However it's not out of the question that it is the dreaded moisture problem.  I will experiment further with this.
regards Rob

Tim Campbell

Re: Problem with C12 clone
« Reply #5 on: March 11, 2019, 08:55:28 PM »
Rob if it does turn out to be the capsule email me and I'll sort this out as quickly as possible.

Rob Flinn

Re: Problem with C12 clone
« Reply #6 on: March 11, 2019, 09:43:35 PM »
Rob if it does turn out to be the capsule email me and I'll sort this out as quickly as possible.

Thanks Tim, I'm fairly confident that the capsule isn't damaged.    I bought it from you a number of years ago but it's only last week that I installed it in the mic
regards Rob

Rob Flinn

Re: Problem with C12 clone
« Reply #7 on: March 13, 2019, 11:56:55 AM »
It does seem to be a moisture issue.  Although my workshop is attached the house it is an extension & it gets pretty cold out there.  Having let the mic warm up in the main house for 20 mins it seems to be working really well.   Great sounding capsule Tim even using an MBox 2 in the test for the mic amp   .......
regards Rob


 

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