Broadly speaking, there are two main types of microphones we talk about with regards to HAM radio: dynamic and condenser. There's a third, the electret, which is really a type of condenser mic but different enough that we'll consider it separate.

Dynamic mics use a diaphragm connected to a fixed magnet which moves in and out of a coil of wire. This induces a current in the wire which we can amplify and use as our output. It's basically a loudspeaker in reverse. They are durable and easy to use but also are not generally as sensitive as electrostatic microphones due to the mass of the magnet. They are often used as stage mics and for instruments with lots of bass frequencies. They are also quite commonly used with HAM base stations because they are usually pretty inexpensive and don't need special biasing circuitry.

Condenser mics are a type of electrostatic microphone. There's a diaphragm with a conductive coating and a fix plate a certain distance from the diaphragm. This setup acts like a capacitor and when a bias voltage is applied we can measure the change in capacitance and use that as the microphone output. These can be made to be quite sensitive and are commonly used as studio microphones for voice recording. They are a little more difficult to use than dynamic mics since you need to generate a bias voltage. With a studio mic this is usually done with a standardized 48V "phantom" power option on a mic preamp. This works the same way as a bias voltage on a coax line used to power an amplifier near an antenna and a bias tee can be used to inject the voltage. This added complexity usually limits the use of these microphones in HAM radio unless you use a professional mic preamp to feed your radio.

Electret mics are condenser mics which have a static charge permanently applied to the diaphragm which provides the bias needed. An electret capsule almost always has a JFET attached to the diaphragm to provide the initial amplification. Electret mics don't need external bias voltage and are quite sensitive but they are limited to physically small devices. They are very common in small microphones like lapel mics and mics attached to headphones such as the ones on earbuds that work with cellular phones. If you have a small handheld walkie talkie style microphone or a small HT, you are probably using an electret. The other downside to an electret is the need to include a bias resistor since the internal JFET does not have a source or drain resistor. Since he JFET is generating current at the drain, this resistor determines the sensitivity of the mic by converting that current to a voltage. It also determines the impedance of the microphone. The data sheet for the electret will tell you what values are best for that capsule but are typically 1k-2k.

If we are building the mic from a capsule then we need to design the microphone stage to use a specific capsule. If we're using a headset or small commercial mic, this resistor is included in the device and we can assume we'll get a fairly standard voltage range from the microphone plug, usually 1-10mV. Earbuds and small headphones with built-in microphones are inexpensive, portable, and usually of adequate quality for a small radio, especially ones designed for cell phones since they are optimized for voice communication and clarify. I'll assume we'll be using one of these and design to this 1-10mV input range. I'll also include a TRRS (3+ground) jack since this is the usual interface for a cell phone. If you want to use a setup with two TRS or TRS+TS connectors, it's easy to connect those to the headers instead of the TRRS.

Background done, lets get designing. Since the last post, I added a split-rail power supply for he receive side audio opamps. Even though it's not necessarily the best choice for a virtual ground, I used the same opamp for the rail spliiter's virtual ground since we're already ordering the chip. Normally, I'd switch to a TLV9154 which is the same device as the TLV9152 but has 4 opamps in a single package. However, there are none available from digikey or mouser. An extra chip takes up a little more room, uses slightly more idle current, and costs a little extra but none of these should be significant, and if you can't get the chip, you can't get it so you make do. Since we've now got an unused opamp we might as well use it for our mic preamp.

Let's do some quick math. If we're getting, say 5mV from the mic into 1.2kΩ we end up with about 0.02μW or about -47dBm. We want about 37dBm (5W) output. A rules of thumb for drive needed to power a 5W power amp is probably about 50-100 mW, about 20dBm.

7dB is not a lot of gain for a microphone preamp so it should be quite easy to achieve. We'll do some equalization as well. What equalization do we need? Books have been written about the best equalization for voice, in general and more specifically for HAM radio. The biggest bang for your buck is usually pretty easy to achieve without complex circuits and depends on your expected use. Rag chewing usually opts for a flat response from about 400Hz to about 3kHz with rolloff above and below. If you are contesting or DXing and you want more "punch" then you roll off a little higher up and boost the highs a bit. This puts more of the signal power in the high-mids where the majority of speech information is carried. It is also a bi fatiguing to listen to thus the use for DXing and contesting. We're designing a low power, portable radio so extended rag chew is not likely the best application, therefore we'll emphasize these higher frequencies.

I opted for a 3 band equalizer design I've used for music processing which has the benefit of only requiring a single opamp. It's not the best design but should work well enough. I built the circuit in Micro-Cap and fiddled with the tuning potentiometers until I got a curve that was close to the shape we'd like. I then adjusted some of values to change the band frequencies and to flatten the high response to a shelf. It was more fiddle and test than proper engineering but sometimes that's the quicker method. The circuit automatically sets up a virtual ground so it's fed with +12V. The Bode plot below shows the final equalizer curve.

I was running out of room on a single schematic sheet so I cleaned it up a bit with hierarchical sheets. Double click on a block to open the expanded view. Right click and select Leave Sheet to return to the top level.