Introduction: Condenser Microphone Power Supply
Condenser Microphones typically sound better than dynamic microphones. If you are unfamiliar with these two types of microphones you may want to read about them in this Wikipedia article.
The short version is this:
Dynamic microphones have a coil and a magnet. So they act like little electric generators. They do not require external power such as a battery to operate.
Electret condenser microphones have two little plates (capacitor), one of which vibrates in the presence of sound. The varying capacitance is turned into an electrical audio signal by a tiny built in pre-amplifier. So this type of microphone needs an electric current to operate. Besides sounding good, condenser microphones typically have better sensitivity. Also condenser microphone elements are typically smaller than the dynamic type and many condenser microphone elements are very inexpensive.
If you have been thinking about experimenting with condenser microphone elements I would suggest this one available from DigiKey:
The sound quality is comparable to the Radio Shack mic elements I have (the specific model is no longer available from Radio Shack and I have not tested the new one.) but the output signal is much higher.
At the time that I wrote this instructable I was using a mic element from Radio Shack. I had an extra one of these that was still in the package. On the back of the package it had a tiny graph of the frequency response. If you go to the Shure microphone web site, you can look at the specs for there very popular SM58 microphone, The RadioShack mic’s upper frequency response actually looks flatter than the SM58 out to about 15 Khz. It would be helpful if the Radio shack graph had more resolution so we would know exactly where the upper frequency cut off actually is. It is actually well above the 10 Khz stated in the specs on the back of the package. Don’t get me wrong. The SM58 is a great microphone for live performances where the performer is belting out a tune with the mic almost touching their face. SM58s are really rugged. If you like to swing your microphone around by it’s mic cord and occasionally dropping it on the stage (Roger Daltrey) this is the microphone for you. I own two SM57s (same mic with a smaller wind screen). It just isn’t the right microphone for some applications such as DIY audio projects. By the way. The SM58 will set you back about $100. The RadioShack mic is an ok vocal mic but a really good area mic. If you want to use it as a vocal mic you will need a foam wind screen.
Some audio equipment provides voltage at the microphone input jack so an external power supply is not needed for a condenser mic. Some equipment does not. Many off the shelf condenser microphones (complete microphone including and audio cable and connector or a connector that accepts a microphone cable) have a built in battery holder to power the microphone and some do not. So sometimes, depending on what condenser microphone you are using and what you are plugging into, you need a battery operated power supply or it will not work.
Here is one fun microphone project I did a long time ago which is one of the reasons why I made my first condenser microphone power supply. We used to feed our outdoor pets which were the wild birds. To add to the experience I wired up one of the radio shack mics onto a shielded audio cable and ran the other end into the house by closing the window on the cable (you can do this with a thin cable. The other end of the cable plugged into the power supply. The output of the power supply plugged into a battery operated audio amplifier. The microphone was attached to the underside of the covered patio roof and the food dish was on the patio, 8 feet below. We could hear all the tweeting as if we were outside next to the dish. We could also hear their little beaks tapping the bottom of the plastic dish. From time to time we could hear possums rustling around outside after dark and of course crickets. On a good night it was like camping out under the stars in the living room.
Step 1: Schematic
Here is the schematic diagram of the circuit. The circuit on the back of the package says to use a resistor up to 1k. I tried different resistors and decided to go with 10k. The battery last for days of continuous use. Probably 10 times longer than using a 1k and it sounds great. I will test the run time at a later date. There are a range of capacitors that will work. The smaller the capacitance the more treble you get and you get less bass. I did some testing with capacitors as small as 0.001 uf and as large as 0..47 uf. I went with 0.01 uf. You may want to experiment with different values. What I settled on is not high fidelity but high clarity for speaking, birds and crickets (no bass and lots of treble)..
Step 2: Part Layout
Here is a diagram with the part layout.
Step 3: Polarity
The microphone has polarity (+ and -) The minus (negative) wire is the one that connects to the metal case.
The positive (+) connection On the RCA plug is the terminal that connects to the center pin. The other terminal is negative (-).
Step 4: Microphones
Here are a few condenser microphones I have wired up. Not pictured is the hair brush mic.
Step 5: Guitar Amplifier Setup
Here is a set up that will work well for bringing the sounds in your backyard indoors. The video cable will require drilling a hole in the wall. Video cable typically works good as an audio cable. There is a limit to the length of cable you can run with this set up. Pictured is a 50 foot cable that worked fine. Off the shelf video cables require adapters to connect the F type video connectors to RCA connectors. The amplifier is First Act model MA104. I do not think these are made any more but you can still get them on Ebay.
The connections pictured are as follows. The microphone is connected to one end of the video cable, the other end is connected to the input of the power supply. The output of the power supply is connected to the input on the guitar amplifier.
Step 6: 14 Volts DC
It is handy to have an amp that uses an AC adapter to power it up. This one is ideal if you want to go off grid or power it up from a car cigarette lighter socket. You just need to make a cable.
Step 7: As Seen on TV
As seen on TV connected to the RadioShack battery operated amplifier.
Step 8: Updates
The picture shows the microphone with a RadioShack windscreen. Here is the information on the windscreen which I picked up at my local RadioShack.
Step 9: Need More Power?
If you need more gain / volume how about a preamplifier. See steps 5 and 6 of the Instructable below.
The preamps were used to amplify the signal from a photo transistor but were originally designed for use with a condenser microphone element or a dynamic microphone. The one in step 6 is quite powerful since it can be made into a stereo preamp and the output of one channel can be connected to the input of the other channel for more gain.
See also: Modify the RadioShack Amplifier to Power a Condenser Microphone Element:
This is a modification to a small 9v battery operated amplifier that allows you to connect a condenser microphone element to the microphone input. You can also connect a photo transistor to it.
Salt: Recorded with the old mic plugged into the MPSA18 preamplifier and the gain was boosted after recording. The salt is being poured from a height of about 2" onto a stack of notebook paper.
Salt2: Recorded with the new microphone with no gain adjustment.
Watch: Recorded with the old microphone plugged into the MPSA18 preamplifier. The watch is right next to the microphone. The gain was boosted after recording.
Watch2: Recorded with the new microphone plugged into the MPSA18 preamplifier. Part of the recording has the gain boosted.
Step 10: More Recordings Here
Unless otherwise noted all recordings are with the new PUI Audio condenser mic element, recorded through one of the MPSA18 preamplifiers, and recorded with the EzCap USB audio capture interface.
MISC1: Several household items including toilet paper square ripped from roll, bendy straw being bent and straightened, scotch tape, 3/4" masking tape (lots of noise trying to find the end), dinner fork tines being plucked by opposing finger nails for a tuning fork effect. No edits or gain boost. This could be a fun game for "Good Mythical Morning" (guess that sound).
Light1: I connected a CDS photocell to the preamp. The CDS photo cell can convert fluctuating light into a variable electric current. If the rate of variations of the electric current are at frequencies that humans can hear the current can be used to make sound. The first light source is a TV remote control. Some remotes just make a clicking sound. This one produces a tone. The next light source is an electronic tea light (looks like a short candle with a plastic candle flame. All of these I have listened to produce sound. Most of them produce beeps or oscillations. This one plays a song. Christmas tree lights that change colors are usually interesting to listen to also. I will probably add some of those in a few weeks.
Around the house: I am walking around the house while talking and the mic is stationary during the recording. The fridge finally stops running after about 1 min. 50 sec.
Living room hall: I edited the "Around the house" file. I cut out the parts before and after the living room and hall. Then I boosted the volume 20 db.
L Rm hall EQ vol: I started with the same source file as "Living room hall" and cut out 2 seconds off the end, used the equalizer on the EzCap software (Audacity) to lower the low frequencies and boost the high frequencies for greater clarity, then boosted the volume.
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