DIY Microphone Buzzing Noise

[Ags911]

Hi guys, I recently bought a DIY kit from a website for a U87. I don't think I can put the name on here but I put the thing together and followed all the instructions including the capsule, setting the impedance pot to the correct voltage etc. I read you must clean the flux (brown residue from the solder I believe?) from the PCB otherwise your microphone will sound noisier. The problem is I am having a noise and it is a buzzing sound (not the 60HZ ground loop hum) when I record from it. I have already tested the interface with another microphone so I know it's not that. I have attached a sample to see if anyone has any clues as to what it is? https://soundcloud.com/nodnabeats/microphone-noise

Any help would be appreciated thanks!

Darren.

[molecular]

link currently not working, at least for me...

[dmills]

Link not working.

Condenser mic capsule circuits are massively high impedance, and will pick up anything going, it is difficult to say without seeing the schematics AND the mechanical details, but the obvious thought concerns the bonding of the grill to the chassis and the chassis to pin 1, it is pretty much vital that both be low impedance and it is helpful if the grill is bonded all the way around.

And yes, the fet gate and bias resistor area is not somewhere you want any dirt at all (Also, when handling components in this area avoid any fingerprints (Use finger cots or surgical gloves).

Regards, Dan.

[Hugh Robjohns]

I suspect Dan has hit the nail on the head. I would pay very close attention to the grounding of the metal case work and, especially, the way in which the head grille is grounded.

H

[John Willett]

As U87 kits don't exist - this can only be an April Fool

[Hugh Robjohns]

As U87 kits don't exist...

I think he's referring to the 'Vintage U87' DIY kit -- presumably a Chinese look-alike kind of deal.

http://micandmod.com/en/complete-kits-u87/45-u87-diy-kit.html



H

[Ags911]

Sorry try this one: https://soundcloud.com/nodnabeats/micro ... se/s-6eYtU

[Ags911]

Sorry try this link: https://soundcloud.com/nodnabeats/micro ... se/s-6eYtU

[Ags911]

This is the link I followed to clean it. http://microphone-parts.com/diy-electronics-tips/insulate-high-impedance-connections/
I can take photos of it now and assure you it is clean to my eye. The board was initially sticky in removing the flux but I flushed it down with PCB & Flux Cleaner from Maplin a few times in order to get the stuff off. After a while I decided to use a new toothbrush to clean it out again and now I am at the stage I am. Feel free to analyse the audio. The gain is being turned up from 0 to 10 to highlight the sound. Thanks for all your replies so far.

[dmills]

I have not managed to hear the recording yet (This machine has no speakers), but if it is buzzing, as opposed to hiss, then it is interference not noise, and is probably a bonding issue with the grill.

Regards, Dan.

[SimonZ]

Now that I've heard the file, I would definitely say earthing.
As said above, you need shielding continuity throughout the body and head basket grille to pin 1.
There may be other problems, but you need to fix the hum first.

[Ags911]

Do you reckon? Because I had grounding issues before when I forgot to screw the body on tightly enough. The sound was a bassy hum rather than a buzz like this but I will try checking the grill and re-assembling it.

[Hugh Robjohns]

Yes! As I said earlier, the sound on your track is very typical of interference getting into the capsule through an imperfectly grounded head grille. There could be other causes, of course, but that's certainly where I'd start looking for the problem based on experience of similar issues with other mics.

It might also be worth noting that both Dan and Simon are very experienced in this area. Dan works for the company that makes the Soundfield mic, and Simon repairs high end mics...

H

[Ags911]

Here is the link of the sound with the body on and the body off, the hum goes with the body being on again. https://soundcloud.com/nodnabeats/mic-test-with-body-off-and/s-se1mV

Thanks, I can see he knows what he is talking about. I have no idea what pin 1 is though, one of the 3 pins on the XLR output? Maybe I can also take some pictures if that helps.

[Wonks]

Yes, pin 1 on the XLR output - the signal ground connection.

[Ags911]

Ok thanks, I just unscrewed the grill and re-attached it but no change to the sound at all bar the hum from removing the body so I don't know if it is the grounding.

[Hugh Robjohns]

Here is the link of the sound with the body on and the body off, the hum goes with the body being on again.

I suspect the hum with the body off is simple magnetic coupling to the output transformer. The buzzy sound suggests RF interference. Grounding of the head shell (and body) is critical in this respect. Without seeing what the physical grounding arrangements are its impossible to advise further. But perhaps cleaning of any grounding surfaces might help...

I have no idea what pin 1 is though, one of the 3 pins on the XLR output?

An XLR has four connections, three on pins and the fourth via the metal shell. Pin 1 carries the ground and it is vital that the connector shell, capsule head shell, body, power and audio grounds all connect directly to pin 1 with zero resistance (milli-Ohms anyway!). Pins 2 & 3 carry the balanced audio output and receive the phantom power. A positive air pressure at the front of the capsule should produce a positive-going voltage on pin 2.

The other possibility for the buzzy noise is a noisy phantom power suppy (unlikely) or a problem with DC-DC power rail conversion (if present in the design).

H

[Ags911]

I suspect the hum with the body off is simple magnetic coupling to the output transformer. The buzzy sound suggests RF interference. Grounding of the head shell (and body) is critical in this respect. Without seeing what the physical grounding arrangements are its impossible to advise further. But perhaps cleaning of any grounding surfaces might help...

I can send some pictures if you want but nothing looks out of place to me, the grill is securely attached with 3 screws.

[Ags911]

Post deleted by Ags911

[Ags911]

[Ags911]

Thanks Dan, I have provided photos in the forum for you and I think I may have a basic idea of the schematics you speak of as there was a instruction manual with diagrams and all the stuff you might need to see.

[Ags911]

Do you still think it is the grille after seeing the new photos?

[Ags911]

Wow I found the issue! Really random but for some reason, when I took out the Mini DisplayPort/Thunderbolt to VGA adaptor for my external monitor on my macbook the buzzing sound stopped. Bang on the money with the interference suggestion, I don't know whether to be happy or sad lol. How is this possible, and does this mean I can't use my external monitor while recording again as the sound seems to be consistent regardless of range from the source?

[Exalted Wombat]

Wow I found the issue! Really random but for some reason, when I took out the Mini DisplayPort/Thunderbolt to VGA adaptor for my external monitor on my macbook the buzzing sound stopped. Bang on the money with the interference suggestion, I don't know whether to be happy or sad lol. How is this possible, and does this mean I can't use my external monitor while recording again as the sound seems to be consistent regardless of range from the source?

Does this happen with other microphones too?

[Ags911]

Well I have no other microphones to test the problem with. I have tried DI with the interface and the problem does not seem to be on that too. Maybe I can try moving around the cables or the interface but I don't know.