we need help

recently we came across this schmatic and we need some help on why it isnt working
mic power.jpg
Edit:Thank you for helping with the picture steve

We see a big red block. Did you intend that? Koz

I’m sorry Koz. I can’t seem to get the image to show up correctly. I attached it to the post instead but it still doesn’t display quite right.

My problem is, I’m trying to use computer headsets through a mixing board along with the game audio to record walk-through videos of video games.

I was not aware until I hooked it up that these types of elertret microphones require power from the computer audio card to operate. I found the diagram that you posted on this forum of a simple circuit using a couple of resistors, a capacitor and a 9 volt battery so I tried without success to duplicate the design.

I’m sure I am missing something but the attachment i posted is your diagram with my crude drawings of the circuit connected to a 1/8" stereo jack at one end and a 1/4" mono plug at the other.

Can you please show me the mistake that i have made in trying to copy the design?

Is this thing on? Hello?

What is it supposed to be doing?
What are the two jack pugs for?

Does this article answer your questions?

Does the “computer headset” have one plug or two?

  • Bill

Calm down people.

No, it’s not quite right. (now that the picture is visible).

The + side of the battery goes through the 2200 ohm resistor and connected to the ring of the jack. That’s the supply for the electronics that makes the electret element work. Condenser microphones produce some very nice signals in response to the air movement, but they have no horsepower at all. They must be made more powerful (not louder, there’s a difference). This lets the signal travel down a microphone cable.

The + side of the capacitor is connected to the tip of the jack. That’s the sound, but it may have battery on it (some microphones leak the battery back down the sound connection – bad for sound cards), The confusion here is your microphone has three connections and your schematic uses a raw element that only has two.

And here, in the running for the worst Photoshop picture on earth…

And of course you can still get killed here. In this picture, this pink connector is the microphone.


If you’re headed for a sound mixer, you’ll need the exact opposite of this.


It’s male instead of female XLR3 and it’s a jack instead of a plug on the 1/8" side. The notation is correct, however.

Tip to XLR3 Pin2, Shield to XLR3 Pins 1 and 3.

If you’ve been soldering correctly up until now, this adapter should be a walk in the garden. Of course, if you’re thinking ahead, you can eliminate the two 1/8" connectors in the middle and wire the battery adapter directly to the XLR3 Male.



I know you’re asking yourself, “Why doesn’t somebody build these adapters?”

Because that whole process is the price of a modest XLR microphone.

And somebody does. I think I found a supplier in Britain somewhere…

You should be putting that whole thing inside a sealed metal box. Remember, we’re talking about microphone signals. Reeeeely tiny and no match for electrical interference in the air coming from motors and fluorescent lights.



Forgive the intrusion of an unknowledgeable idiot - but is this circuit called a microphone pre-amp? If so, I know the name of the chap in the UK who builds them and can supply contact details - but not in open forum. He prides himself on their being totally noise-free.

Not quite. The circuit described does not “amplify” the signal (a mic pre-amp does), it just supplies the power that the computer mic requires.
As Koz wrote, the problem for anyone wanting to market these battery packs is that they are competing in price with the likes of these: https://www.google.com/search?q=logitec+desktop+microphone#q=logitech+desktop+microphone&tbm=shop (and these sound surprisingly good for the price). By the time that you add up the cost of parts (XLR plug $3, metal project box $3, PP3 battery $2, mini-jack socket $1, …) it’s hardly worth the effort (but fun and educational to do, and useful if you already have a couple of good computer headset mics and a mixing desk).

He prides himself on their being totally noise-free.

“Low Noise” perhaps. “Totally noise free” is impossible without exotic conditions like liquid nitrogen baths, etc. Not likely.

Electret microphone elements by themselves produce a sound signal with all the robust, crushing power of butterfly wings. Just to get the signal to go down the cable requires a way to stiffen the signal and give it a good push. The best way to do that requires a transistor with power gain, but no volume gain. That’s what the 9 volts (or 5 volts from the computer) does. It gives the transistor something to chew on while it’s working.

OK, now you have this amazingly tiny signal successfully inside the computer or mixer. That’s when the Mic Amp does its magic and boosts the volume of the signal high enough for the sound card or mixer to use it. All amplifiers of this type have noise and the juggling act is to make the noise as low as possible and the signal as high as possible. This is the exact point where many sound cards fall apart. Just being inside the electrically noisy computer is strike one for quality work. Then the sound card has to work with the same 5 volts that the rest of the noisy computer is using. Strike two. Top Quality microphone amplifiers use 30 volts, two fifteen volt supplies.

And it goes on. The best way to create a very low noise mic preamp is to tailor it to the microphone. That’s why most commercial microphones say “150 ohm nominal output impedance.” Without getting too deep into this, that is designed to exactly match the connection to most top quality microphone amplifiers resulting in the very lowest possible noise and best music quality.

None of this has anything to do with computer microphones. They do not match anything and the mic preamp inside the computer is lucky to get out of bed in the morning, much less amplify your performance with low distortion good volume and low noise. That’s why the first step in good quality work is immediately divorce everything analog from the computer. External digitizers, external mic amps. better microphones, and good quality sound mixers. Then you hit the computer, hopefully with a signal already digitized which makes most computer noise and distortion irrelevant.


That’s precisely how I work: music ripped to WAV from CD (under the terms of a copyright clearance licence), everything else (voice-over and location ambience) recorded to WAV using my Zoom H4 (giving me the copyright); then import the lot into Audacity and “slice and dice”!