LM358: Amplifier Selection for a Throat Mic

Selma,

Does this mic have a built in pre-amplifier. In other words does it need power? If there is a preamp already, then just about any op amp could do a decent job.

1) An instrumentation amp is used when a difference (differential) signal need to be amplified with very high common mode rejection and where DC accuracy is important. A low noise amplifier could be used for this application.
2) Noise can come from external pickup (shielding helps), power supplies (better supply filtering and better op amp PSRR over frequency), and internally generated (voltage and current noise).
3) If you know the needed specification, search for an amplifier that matches. Alternately, pick from a selected list of microphone preamplifiers. www.ti.com/.../microphone-preamplifier-product.page
4) The kit link did not work for me. What is the supply voltage used?

Hi Ron,

Ron Michallick said:

Does this mic have a built in pre-amplifier. In other words does it need power? If there is a preamp already, then just about any op amp could do a decent job.

That much is unclear, as the company who makes the throat mic has not released a data sheet to me. However, I'm tempted to say no since hooking it up to an oscilloscope didn't show a perceivable signal.

Ron Michallick said:

3) If you know the needed specification, search for an amplifier that matches. Alternately, pick from a selected list of microphone preamplifiers. www.ti.com/.../microphone-preamplifier-product.page

Thank you for the helpful link! I just have an issue knowing what parameters I need to match an amplifier to a microphone. ( I'm quite new to this.)

Ron Michallick said:

4) The kit link did not work for me. What is the supply voltage used?

And that kit required a 12 V supply voltage. I was testing it with a power supply (of unknown efficiency) in our lab, but didn't have a chance to try powering with a test bench supply.

I'm going to try and link the kit again, but I'm not sure if it'll work this time either: http://www.vellemanusa.com/products/view/?country=us&lang=enu&id=350480

Selma,

To keep noise down, keep cable from mic to amplifier short as possible and use good shielding.
The output of the LM358 kit is not made to drive headphones or speakers.
What comes after the LM358 kit?

A door answering device comes after the pre-amp. (Device linked below)

http://www.valcom.com/products/doorentry_ts/v-2900.htm

So the current system flow is

Throat Mic -> Pre Amp->Door Answering Device

To provide background, we're trying to construct an intercom system, but instead of using the door answering device's transducer for a microphone, we would like to use a throat mic.

So we're trying to build a system that will allow:

1. A person to call (using a telephone) the door answering system and choose to talk to either the person wearing a throat mic headset or the door answering device's speaker to talk to everyone

2. We also want the person wearing a throat mic to be able to talk back with the person calling on the phone.

We're currently focusing on the 2nd point.

Selma,

For item #1, does this call from a remote phone (from anywhere in the world) or does it come from a local phone connected to local wiring that does not connect to the world land line phone system? The former won't work ,but the later can work.

For item 2, your mic needs to hack to internal parts of V2900. This can be done however, I have no advise of how to do this.

Do I understand correctly?

For item #1, we are connecting to a local phone. And we have already connected our phone to the door system (it works as expected.)

For item #2, I'm not quite sure how to do that either. I was hoping to integrate a pre amp to boost the signal of the throat mic to the levels the door system's transducer would output, but I'm unsure if 1) that will work and 2) that I'm selecting the right preamps to test with.

But yes, you understand correctly.