0
\$\begingroup\$

I'm working on a two way amplifier/intercom for my parents to use in the car because of road noise and hearing problems.

I got a couple LM386n-4 and I've tried the circuit layout from here: http://www.learningaboutelectronics.com/Articles/Microphone-amplifier-circuit.php

enter image description here

I've also tried the really stripped down version from this answer:

https://electronics.stackexchange.com/a/473553/76121 enter image description here

For a microphone I want to use a computer headset with ear cup for the speaker, and a boom mic for the microphone. It has a 4 section jack for left, right, mic, ground, and the plug also has 4 pins.

Unfortunately I can't get it to work. With one plug I get a weird tone, and when I tried a different one I only got silence.

I'm trying to get some electret mics, but I don't think I will be able to get them delivered in time for Christmas. So, is there a reason that the ones I have won't just work?

enter image description here

\$\endgroup\$
9
  • 1
    \$\begingroup\$ An electret microphone does need a pull-up resistor to operate and give an output signal. Judging from the photo of your setup, if the red cable is coming from the mic then it's quite normal you're not hearing anything because there's no pull-up resistor there.. If you don't know the pinout or you are not sure if it's coming from the mic, then you can test the cables with a multimeter by measuring in resistance mode. Low resistances (e.g. 4, 8, 16, or 32 Ohms) indicate that there's a speaker there. Common is always ground. \$\endgroup\$ Commented Dec 14, 2020 at 6:42
  • 1
    \$\begingroup\$ Stick with your first circuit because it biases the microphone properly. However, it can easily turn into an oscillator due to how you might wire the circuit on breadboard. \$\endgroup\$ Commented Dec 14, 2020 at 10:26
  • 1
    \$\begingroup\$ It's typically illegal for the driver to wear headphone; there might (?) be an exception for a single ear, but consider if this is wise. \$\endgroup\$ Commented Dec 14, 2020 at 10:28
  • 1
    \$\begingroup\$ You apply power to the LM386 first, then tee-off power to the microphone and possibly add another RC filter for extra power line filtering @AndyD273 \$\endgroup\$ Commented Dec 14, 2020 at 13:56
  • 1
    \$\begingroup\$ @AndyD273 That's good news. As for the noise issue, yeah, hooking up a circuit on a breadboard when even millivolts are important is a terrible idea. Plus, 10k as a bias resistor for electret mic may be a bit high as it can lead to higher offset voltage and thus early clipping. Most electret mics are happy with 2k2 to 4k7 for Vcc = 5V. Maybe you can try decreasing the 10k to something around 2k2 or 3k3. \$\endgroup\$ Commented Dec 16, 2020 at 3:58

1 Answer 1

Reset to default
0
\$\begingroup\$

So apparently the big problem was that the microphone jacks I bought were mislabeled as to which connector went to which ring on the plug.

Big thanks to the commenters that helped point me in the right direction!

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.