Electret Capsule Connection to Mic Case

[thespecificocean]

I'm playing around with some cheap Aliexpress parts and trying to put an electret microphone together. I'm having issues getting everything connected properly. The only way i've been successful getting everything working is to have the body of the capsule touching the inner part of the mic body. I also have to not be touching the microphone case or the xlr connector housing. Otherwise, I just get a nasty electrical buzzing sound. I've tried basically every connection option that I can think of but i'm hitting a brick wall. So, I need some help from all of you

 

[Khron]

Well, with everything exposed like that, that's no surprise.

There's a reason (most) microphone bodies are metallic - to create a Faraday cage, and shield the sensitive circuitry from the ocean of RFI we live in.

 

[thespecificocean]

Well, with everything exposed like that, that's no surprise.

There's a reason (most) microphone bodies are metallic - to create a Faraday cage, and shield the sensitive circuitry from the ocean of RFI we live in.

Thanks for the response, but I have been testing within a mic body. I just took this photo to show what components I'm working with. I just feel like I'm missing something simple. Let me know if you have any ideas.

 

[Khron]

Questionable circuitry? Improper ground connections (XLR, circuit board, mic chassis / headbasket / body)...

Close-up photos of the back of the capsule, and (separately) both sides of that board?

 

[thespecificocean]

Questionable circuitry? Improper ground connections (XLR, circuit board, mic chassis / headbasket / body)...

Close-up photos of the back of the capsule, and (separately) both sides of that board?

Photos of components attached. Also the issue is the same using two different other capsules and a duplicate 48v power supply board.

 

[Khron]

Did that XLR connector ever have a screw in there? And is there a wire connecting that wide tab to the XLR pin 1, on the back of the connector?

But if the same happens with other capsules AND other boards, the body issues become more suspicious. Semi-related to my question above, though...

 

[thespecificocean]

Did that XLR connector ever have a screw in there? And is there a wire connecting that wide tab to the XLR pin 1, on the back of the connector?

But if the same happens with other capsules AND other boards, the body issues become more suspicious. Semi-related to my question above, though...

Yes on the screw. Just tried tying XLR pin 1 to the tab (this should be the body connection ) and got the same issue. I also tried bypassing the negative connection to the preamp board and going directly from the capsule shell to pin1 and got the same.

 

[Voyager10]

OK, when it's assembled there should already be a connection from the capsule shell to the mic body. If not you'll need to check with a meter: capsule shell -> '-' terminal on PCB -> XLR pin 1 -> XLR tab -> XLR screw -> mic body, and figure out where the disconnect is.

(It's often astonishing how two metallic surfaces can appear to be touching each other and yet have no electrical continuity between them).

 

[ccaudle]

This tab appears to have solder, but I cannot tell where it connects:


The PCB does not appear to have any mounting holes, so the only connection between the PCB reference node and the case would be that tab, or possibly the capsule housing.

That would explain this observation:

The only way i've been successful getting everything working is to have the body of the capsule touching the inner part of the mic body

The PCB appears to have the classic "pin 1 problem" so I would expect it to possibly be RFI sensitive, but addressing that would probably take more PCB surgery than warranted at this stage of your project.

As a first step you could put a short piece of copper braid between the tab connected to the screw and pin 1.

 

[Khron]

This tab appears to have solder, but I cannot tell where it connects:

And is there a wire connecting that wide tab to the XLR pin 1, on the back of the connector?

Just tried tying XLR pin 1 to the tab (this should be the body connection ) and got the same issue.

I wonder if we're all "speaking the same language", as it were...

 

[Rob Flinn]

I used that same pcb when I built my pzm's but I'm pretty sure it didn't come with the middle tab of the xlr connected to the pcb, & I didn't need to connect it for it to work well.

 

[ccaudle]

I wonder if we're all "speaking the same language", as it were...

Yes, sorry I had just missed some of the earlier discussion while skimming and trying to catch up. Basically covered by the euro time zones guys while I was sleeping.

I think I do see why just connecting the PCB to the shield pin was not successful, and the capsule itself had to be connected to the upper part of the body:



The tab with the screw will get the lower part of the body connected to the shield, but the upper part will still be floating because it is insulated from the lower half. Someone forgot to spec out where masking should be applied when the body is painted or powder coated.

 

[Khron]

The tab with the screw will get the lower part of the body connected to the shield, but the upper part will still be floating because it is insulated from the lower half.

That was more or less my thought too