Condenser Microphone Amplifier Circuit Direction

Hi Daryl,

Welcome to E2E.
You can take a look at LM386, this is a general purpose amplifier, you can use the example configuration for Gain = 200. I've seen some microphone amplifying stages using LM386 with this configuration. It may be similar to LM358.
If you need a JFET input amplifier like LF353 or a very low noise/distortion amplifier you should take a look at the precision amps (OPA family) like OPA1611 or OPA827.
Another option is OPA172, there is a TI Design featuring this amplifier, you'll find it at the following link:
www.ti.com/.../tidu765.pdf
Let me know if any of these looks good for you.

Best regards,
-Ivan Salazar
Texas Instruments

Let's tease apart your post...

"Any" amplifier chosen will run off the voltages you report. The devices you've been using will run "single-ended" so let's get that out of the way. There are many excellent white papers available, many right here on TI. Search "single-ended opamp". Once you have the topology for running single-ended sussed out, you'll see you don't  need "+/-" anything...

Next, you've already determined that the mic has a tiny, tiny voltage output. This needs to be amplified, obviously. However, a "fixed" gain amp probably isn't going to do it for you. Think it through... if you have low-gain, you won't pick up voices far from the mic. If you have high-gain, when someone is close, it could easily saturate the amp. You need either a system that intelligently controls gain, such as a "programmable gain amp" (PGA) in which the gain of the system changes depending on input level (determined by the results of the A/D), or, as has been done for 100 years, an "automatic gain control" or AGC. The choice becomes do you want to do this in the "digital" domain (PGA) or "analog" domain (AGC). Lot's of ways to do both...

Unless you have a real reason to do so,  rethink how many "bits" you need in your convertor. Remember, the noise on your power supply to the A/D must be lower than the LSB of the convertor. Otherwise, the first few LSB's may be nothing but system noise. Also, most A/D convertors give a "REF" pin to set the range that the A/D works over. It doesn't have to be 5 volts; it can be anything equal to or less than the supply voltage (typically). You may find that you can use an 8-bit convertor with something like a 2.5V reference. No need to "gain up" the signal unnecessarily. 

Good luck; picking up voices, clearly, in a 20'x20' room, is not a trivial task. I'm thinking howling feedback, lot's of !@#$% feedback... 

 

Mike T.

Thanks Ivan, I will look into these options.