Pre-amp circuit for high frequency mic

I have a microphone that is externally similar to the Electret type mics, but is designed to pick up the frequency of 38 kHz +/- 1 kHz. Link is http://www.mouser.com/ProductDetail/Kobitone/255-328SR16M-ROX/?qs=%2Fha2pyFaduhjPDaN57Th6BWwB9YLUCmPAhi50ajSVD5S3CG7NdhYmA%3D%3D.

Obviously I need to build a pre-amp circuit for this mic. However I'm not an electrical guy, so I do not know how to determine what the values of the resistors and capacitors in the circuit should be in order to amplify the frequency range I care about.

Can anyone point me towards a general pre-amp design site that could provide some guidance on resistor and cap selection, and what the circuit should look like?

Most op-amps can go well over over 100kHz, so the frequency shouldn't be a problem. You can build an [u]amplifier using an op-amp[/u] with just the op-amp; and two resistors. Plus you need a bipolar power supply and a bypass cap (~0.1uF) on both supplies.

Do you have any idea how much gain you need? (It's probably going to take some experimentation.)

I would start with 100x amplification as a guess. If I remember enough from my college lab classes I can use a variable pot for one of the resistors to adjust the gain.

Could you explain what you mean by a bipolar supply? I would want to run the circuit off the 5V or 3.3V line directly from the Arduino board to keep things simple.

If you want to run the op amp from the 5V Arduino power supply, you want a "single-supply" op amp circuit, and you'll want a "rail-to-rail" op amp.

A typical general purpose op amp can drive its output to within a couple of volts of its negative supply and its positive supply. For 5V, that means that the output voltage will be between 2V and 3V; for 3.3V, it will hardly vary, if the op amp can work at all at that voltage. A "rail-to-rail" op amp can drive the output voltage to within a few tens of millivolts of either of the supply rails.

You'll also need a "virtual ground," sometimes called an "artificial ground." Typical simple op amp circuits are designed to amplify the difference between the input voltage and ground, and ground is normally between the positive and negative supply voltage. You don't have a ground in that range, so you need to generate a voltage reference that's between your two supplies - typically, that would be 2.5V for a 5V supply, and 1.67V for a 3.3V supply. A virtual ground can range from a simple and not-particularly-effective voltage divider, to an easy-to-use 2.5V reference IC, or lots of other kinds that are harder to implement.

Here's a link to Texas Instruments' collection of single-supply op amp circuits: http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=sloa058&fileType=pdf&track=no.
There are plenty of examples, and you don't have to be an electronics wizard to follow most of it. There's some discussion of virtual grounds, but it doesn't look to be overly clear or demonstrative. If you need more, just googlit.

Here's a link to adafruit's rail-to-rail op amp: http://adafruit.com/products/808.
You can find a bewildering array of rail-to-rail op amps at DigiKey by searching for "rail," and selecting Integrated Ciruits / "Linear - Amplifiers - Instrumentation, OP Amps, Buffer Amps."

Fantastic advice, thanks!

I ran across this page last night, which seems to be what you're talking about with a common rail design: Battery Powered Electret Microphone Pre-Amplifier – Electronic Circuit Diagram

My local radioshack had most of the parts except for the right op-amp. I got some more info on the LMV721 this morning so I'll swing by this afternoon and see if they have anything that would work. I did see an LM386 audio op-amp, but that's a more complex beast by the look of things, and is geared more for driving speakers instead of amplifying mic signals.

To avoid disappointment, be sure to verify the gain-bandwidth product (GBP) for the op amp that you select. That parameter is a maximum value for the op amp. To see if your circuit complies, multiply the gain - you said 100 - by the highest frequency at which you want the circuit to operate - I think you said about 38kHz - and compare it to the specified gain-bandwidth product for your op amp. The adafruit example has a GBP of 4 MHz. Your gain - 100 - times your frequency - 38kHz - translates to a GBP of 3.8MHz, so it barely fits.

Just keep in mind that unless you are doing something non-audio / non-hearing based, no humans hear over 20k. Last I checked I could hear up to about 15k. I'm 32. Older guys go quite a bit lower than that. Much of your favorite music is probably mixed by these old guys with aging hearing. It's no big deal.

If you are doing some kind of scientific testing or something with your mic then your 38k number may be worthwhile.

Brandon

Brandon,

I'm using an ultrasonic mic/driver pair as a homing system for a small robot. Selecting a frequency well out of the audible range was done on purpose.

tmd, I wasn't aware of that, thank you.