Hi, I'm kohanii.
In the following blog, I had repaired the speakers of the Bose QuietComfort QC25 headphones.
When I repair my headphones, I buy Chinese copies of the speakers. This is it.
I wrote the red + marks by myself.
The article above, repaired headphone side, is a removed Chinese copy. That's why it's dirty.
It would be a shame to just throw them away, so I decided to see what I could do with them.
What is a dynamic microphone ?
The photo shows a dynamic microphone cartridge I bought from AliExpress.
There is a connection terminal on the back, which looks like a replacement part for a dynamic microphone.
If you break the plastic on the case and pull out the rubber on the back, you can get this
Here's what it looks like inside.
Huh? It looks pretty much like a headphone speaker, doesn't it?
Attach a shielded wire to the microphone.
This is what a shielded wire looks like.
I soldered it. This will make it more resistant to noise than a normal line.
For prototyping, I want to use a breadboard, so I'll add a pin header on the other side.
It looks like this. Of course, the microphone is a speaker (!?)
Use an operational amplifier to create an inverting amplifier circuit.
So, the + and - of the speaker should be inverted.
The amplification rate is 47 times.
The power supply was 5V, and I used a regulated power supply.
Use the LM358P op-amp.
There is a capacitor in the power supply, it is to reduce noise from the stabilized power supply.
I recorded it right away.
The sound waveform is shown at the top of the video.
As the sound is amplified in editing, its volume is shown in the lower right corner. The waveform displayed on the top is not affected.
I asked the chicken I bought at a 100 yen store to shout.
The sound can be recorded quite clearly.
It has a maximum output of about 3Vp-p.
You can hear the noise sound because I am turning up the volume in my editing, but it is caused by the stabilized power supply.
Someday I'll try to make a real dynamic microphone with this speaker.
I also tried it outside of the headphone speakers.