WM-61A microphone noise

[kingpage]

Greetings, this is my first post here.

I would need your experience on mic noise to help me out.

I have yet to put the WM-61A capsule in a proper circuit, but I have used an audio jack to connect the capsule directly to my laptop computer's mic-in.

It works fine, except the sporadic noise the mic picks up/generates. Perhaps you can recognise the sound? I don't think it's wind noise myself. I will test it on another computer when I get the chance. It might go away by simply adding a filtering capacitor, but I'm still waiting for the mic housing to arrive.

The file is in the post below.

Please turn up the volume a bit if you don't hear it. Laptop microphone volume is maxed without the +20dB boost.

Thanks a lot!

 

[kingpage]

Here's file.

 

[jaygee]

Almost sounds like handling noise to me.

The capsule requires a dc voltage to power the internal fet. I wouldn't worry about any noise until you have in a proper circuit.

 

[kingpage]

Thanks for responding. I'm sure that it's not handling noise because I left it on the mic-in socket. The noise is semi-regular in nature; it sometims comes in waves like heartbeats, other times it's silent for a few seconds. The intervals between the sounds are not constant. The room background rather quiet, so I have yet to identify the source of the noise. I suspect it's internal.

The laptop's mic-in socket is supplying 5V (typical of all mic-in) to my WM-61A at the moment. Even when I put it in a simple circuit, I still don't think I'll put pseudo-phantom power there. WM-61a operates anywhere from 2V to 10V and its sensitivity is quite sufficient such that additional amplication is not really needed. BTW, I do have some dual channel opamps (from my earlier headphone amp project) lying around, but adding an amp stage for the mic would mean that the new mic will require external power supply which I'm not a big fan of.

I tried turning the rooms light off, switching AC power to DC battery on the laptop as well as turning off the external hard drive, turning off the computer fan, without any success. Hopefully the noise is not due to a faulty capsule, maybe it's a bad soldering job or the old audio jack.

 

[jaygee]

It could be a noisy 5V dc coming from the laptop. An additional filter network in the circuit
could be beneficial.

I have built several electret mics myself, but always derived the power from the 48v dc phantom in my interface.
The only noise I experienced was from poor component tolerances in the circuit.

Good luck and keep us updated.

 

[mshilarious]

Noise on the +5VDC or ground. Add a capacitor to filter the supply. Or it's induced interference from the laptop to an inadequately shielded circuit.

 

[kingpage]

I might have solved the riddle. I replaced the 5V DC from the laptop sound card with a 9V battery. I connected the battery's positive to the capsule and and its negative to the ground of the audio jack which is plugged to the ground of the sound card I'd imagine. The beats are completely gone to my surprise. I thought the mic wasn't working at all at first, but then I turned the volume way up and found out that the volume has gone down to nearly silence.

Before, the noise beats were at around -31dB with a noise floor of -47dB. However, with the same setting, now its noise floor is -61dB. The recording hardly goes above -47dB. Perhaps, the amplification stage in the sound card is skipped when I wire it this way.

Is there any suggestion for me at all? What circuit will clean up the noise from the 5V DC? I'm not sure the mic-in is compatible with an external power source. I wish I had a line-in to work with. Do you know if the mic-in without the +5DCV is equivalent to a line-in?