Hello, & Help!

[ulterior_modem]

Hello, all. I'm sorry for the lack of detail; I usually stick to the software side of things. I'm looking for a bit of help with what I thought was a simple change.

I've got a GE desk phone I've been using for ages. It does not have a headset port, so I thought I'd add one. I 've rerouted the output for the speakerphone to a 2.5mm minijack. I've done the same thing with the speakerphone mic input.

When I went about testing I found that the output is fine; however, the input is at greatly decreased volume. I have to practically chew on my headset's mic.

It had an electret mic attached to the input. Do I need to build and amplifier circuit, or...?

Thanks,

ulterior_modem

[Whales]

Hello there!

Hello, all. I'm sorry for the lack of detail; I usually stick to the software side of things. I'm looking for a bit of help with what I thought was a simple change.

Don't worry.  A more descriptive thread title would help us help you, however 



Most likely the signal level generated by your headset mic is very poor compared to the original mic for the phone.  You have a couple of options:

(1) Find the amplification circuity in the phone and adjust it
If you are lucky, the phone design already has an amplifier in it you can adjust.  Either by a twisting a potentiometer (hopeful) or by replacing a resistor (more realistic) with a different value.  If you are unlucky, then you mic's output is directly digitised without amplification, so the next option is your only bet.


(2) Make your own pre-amp (not as hard as it sounds)

• A single op-amp in feedback and a few resistors will do
• Using a potentiometer will allow you to have variable volume control, if you want it
• It will need to source power from somewhere, so you will probably want to put this in the phone's plastic body

If you are unsure what I'm talking about, look up using 'op-amps' as amplifiers and 'op-amp feedback'.

[Stonent]

What's the ohms rating of the microphone?

[lapm]

What's the ohms rating of the microphone?

Modern phones use microphones that are more like capacitors. You can get those very small ones... Thing in OP's case is that hes headset probably has microphone that is not as sensitive as the one in phone. So he need pre-amplifier for the signal.

Also just remembered this: Make sure your wires are correctly. Ground wire on headsets negative side and signal wire on microphones signal side... I have seen some of these capacitor microphones loose sensitivity if connected wrong way in...