Replacing mini electret mic with a headset

[JJ94]

Hi, I've been building an intercom circuit based on the design by colin55 found in this thread:

https://www.electro-tech-online.com/threads/lm386n-1-elecret-mic-amp.121819/#post-1004570
**broken link removed**

I was wondering how it would be possible to replace the miniature microphone with a 3.5mm microphone jack. Any advice would be much appreciated!

 

[djsfantasi]

Assuming that at the other end of your 3.5mm connector is a microphone - what type of microphone is it?

 

[alec_t]

Assuming the mic to be plugged in is also an electret type, just remove the mic and connect 1) the jack tip contact to the 100n cap, and 2) the jack sleeve contact to circuit ground.

 

[JJ94]

Assuming that at the other end of your 3.5mm connector is a microphone - what type of microphone is it?

At the moment it's a standard PC mic picked up from Poundland, packaging was so basic I can't tell if its electret or dynamic. I'm hoping that the circuit will be compatible with any PC headset

 

[JJ94]

Assuming the mic to be plugged in is also an electret type, just remove the mic and connect 1) the jack tip contact to the 100n cap, and 2) the jack sleeve contact to circuit ground.

Great cheers, I did try that with my £1 headset but didn't work so I'm assuming it's not an electret headset. Will try to get a better headset and try again.

 

[alec_t]

My bad; I was thinking 'just mic', not 'headset'.
Your £1 headset almost certainly has an electret mic, but you may need to use a multimeter to identify which of the connections are for the earpiece(s) and which for the mic.
This setup may or may not apply to your headset.

 

[JJ94]

My bad; I was thinking 'just mic', not 'headset'.
Your £1 headset almost certainly has an electret mic, but you may need to use a multimeter to identify which of the connections are for the earpiece(s) and which for the mic.
This setup may or may not apply to your headset.

I should have mentioned that the headset has 2 3.5mm jacks, one mic and one earpiece. The earpiece one is already connected using a chassis mount like this and is working fine, the mic one doesnt seem to work when using the same mount

 

[alec_t]

Have you confirmed that the mic itself isn't faulty?

 

[JJ94]

turns out it was faulty. I have two identical headsets and the one I happened to have connected doesn't work. The other works in the circuit just fine. Time to invest in a slightly better quality headset, thanks for your help much appreciated!

 

[alec_t]

Good to know the problem's solved.

 

[audioguru]

The full duplex intercom circuit was originally from Red Circuits. Colin simply copied it and changed the audio amp ICs.

 

[Ron1406]

Hello,
Actually , I am looking for a circuit , some sort of intercom ; where one side is a telephone line and the other side is like a handfree talk and hearing set. Could I use the schematic of this intercom as the
microphone amplifier and the line amplifier for the loudspeaker? As here is some circuit that prevents that the microphone has influence on the loudspeaker. Could this be done with this schematic?
Ron1406,

 

[audioguru]

A "handsfree talk and hearing set connected to a telephone line" is usually called a speakerphone. A cheap speakerphone prevents mic to speaker acoustical feedback howling by using "voice switching" that cuts off the mic when it detects sounds from the distant end then cuts of the speaker when sounds are detected at the mic, called half-duplex. It also frequently cuts off voices. An expensive full duplex complicated circuit uses an acoustical echo-canceller circuit like used in a Polycom speakerphone. The echo-canceller circuit makes a model of the acoustical environment including the phases and levels at various audio frequencies then cancels them when they are the same in the mic and speaker. Then you can talk at the same time the distant end is talking and you can both hear each other, called full duplex.

It sounds like you tried to attach a schematic of an intercom but it is not here. Maybe it is this one? Here is a handsfree intercom that cannot be used on a telephone line: