Audacity Forum

Thanks for clearing up the wattage and terminal strip questionsis. Makes sense.

<<<The job of the (2.2K) resistor is to bring the 5 volts down to about 1.5. Anything you do over that is pushing it.>>>

&

<<<The voltage on both sides of the 2200 resistor goes up. The resistor doesn't just soak up the difference. It shares.>>>

Just a little confused here still. I thought we wanted to send approximately 5 volts to the microphone... So why do we want to get to 1.5 volts? I thought the purpose of the 2.2k resistor was to bring the 9 volts down to 5 volts so you could send that original 9 volt signal to the microphone at approximately 5 volts.

What I was wondering is if I would even need the 2.2K resistor between the power source and the microphone. If the original voltage is a steady 5v... then no resistor is needed between the 5v power supply pin and the mic right?

It's the 10K resistor that would bring the 5v from the power supply pin down to about 1.5v right?

Can't thank you enough for your patience and help! I swear I'm getting about 99% of it lol. I'll be sure to contribute as many pics and tips as possible to the forum once I'm done.

More bad graphics from Photoshop®.

This is what's going on inside your microphone. The sound waves wiggle the plates of your condenser which generates a very weak signal. The transistor makes the signal hardier and more robust (but not any louder) so it will go down the cable to your mixer. All condenser microphones have a booster somewhere. In the early days, it was actually a vacuum tube. Those wacky looking things standing up in front of Adolph Hitler were condenser microphones.

The transistor pulls or releases the Ring connection in response to your voice. It's working against the 2200 resistor. The resistor is part of the microphone, it's not optional; it's fairly critical and it's built into every soundcard. If you put battery directly on that connection you will probably fry the transistor.

Koz

All the 10,000 resistor does is "settle" the voltages and currents in the microphone circuit before you plug the mixer in. If you don't do that, plugging in the microphone will put a brief hit of battery voltage on the audio line -- and it will go straight through the DC blocking capacitor into the mixer.

When you plug the microphone in, there is still a brief hit of 9 volts on the sound line, but it quickly leaks away harmlessly into the sleeve/shield through the 10,000 resistor. By the time you plug the mixer in, there is clean audio on that wire and nothing else.

Koz

Awesome! The drawing answers my questions. I'll take a crack at it.

By the way, I had an even older (fried) power supply collecting LOTS of dust. I took everything out of it and it seems like the perfect little metal box for mounting three circuits in. Its already got a couple of small holes, some ventilation, a spot to screw the ground wires, a tight lid and it's the same size as the power supply so it should work great. I'm guessing that's exactly what the box is designed for, basically housing one really BIG circuit.

I'll probably build one circuit first and test it to see if I can hook it to house power without wierd fluctuations and pops like you cautioned me about. Crossing fingers.

I'll be sure to contribute as many pics and tips as possible to the forum once I'm done.

That would be good. We get asked this all the time and there was never a beginning to end story about how to do it.
Koz

Ok, this morning I built the circuit, and it works, but is very noisy (background hiss).

I'm using a 7805 for my 5V supply, with a 9V battery driving it. I think its likely to be my issue.

I was using the http://www.epanorama.net/circuits/micro ... ering.html under Multimedia microphones to normal microphone input
I did not include the 10k resistor between the signal and the ground, but I don't think its the cause.

So, question, is a 7805 a bad choice? Looking back at the application notes I think I used a 22uF capacitor on the input side rather than a .22uF, and I skipped the output 0.1uF capacitor. Which the application notes for "stability and transient response". Eh.

The cap bridging the audio signal path is a electrolytic similar to Radio Shack part VHT10M50. Any comments?

If I can fix the hiss I'll post the part list.

Ok, checked, used the correct value (0.22uF) for the input side capacitor, tried temporarily adding the recommended 0.1uF cap to the output side with no discernible result. Signal is clear and fairly strong, but has a strong computer style hiss.

Enclosure is a plastic box....

I'm about to take a whack at this. Been sitting on the parts for a while and finally have some time. Should have some updates soon.

Quick question about 1/8 in leads. Instead of ruining the cord on my headset/mic, I'm using a 1ft. long 1/8 female plug with bare leads to wire into my plastic circuit strip as I discussed earlier. It's a stereo cable which means there are 3 wires: red, white and green. I know all I need for the circuit is Tip and Sleeve. I assume green is ground so that's my Sleeve. Is that right? In this video (@4:36), the mic he is using only has two leads (the white wire on the left)

http://m.youtube.com/#/watch?v=JPxqluZkS2o

Which two wires should I use out of the green, red and white leads? Or should I twist red and white together? Thanks.

Ok gave it a try. I ended up twisting the red and white together and treating them as Tip. I put the extra 10k resistor and everything else where it was suppossed to go. No sound at first but I wiggled the connections and got a loud POP and peak lights on the mixer. I assume something wasn't connected tightly somewhere and whatever I wiggled fixed it. After that, I got sound!

Two problems:
1) I get sound when I tap on the mic gently, but when I tap harder I get big crackles and pops. Same when I blow into the mic. Gently is fine but louder same as tapping.

2) I have to have the level and the gain on the channel CRANKED to even get any of that at all. To the point where I can hear the hiss of the floor noise.

I also didn't ground it to the hollowed out computer power supply box I'm using yet.

So it's not even close to where I need it to be to record with it, but I'm happy to have sound. Any ideas about what I'm doing wrong?
Thanks!