lm386/why this circuit works well with my iphone audio jack but when i connect a mic it makes so much hiss and noise

Thread Starter

skander belhaj

Joined Sep 7, 2020
7
as you can see this is the circuit that I made based on lm386N-1 whenever I connect my iPhone (it's a 5s if it makes any difference ) the sounds works great and clean only when I put it to max it has some distortions but when I connect the electret microphone it makes a lot of noise and hissing and very painful sounds I tried changing the resistor above the mic nothing changed... I even changed the output filter and nothing worked am sure that the problem is in the input stage because when I put the phone it works great so it's gotta be the part before the lm386
can someone please tell me what's the problem what to do or what to change
 

Attachments

KeithWalker

Joined Jul 10, 2017
1,222
Is your microphone picking up the sounds from the speaker? That will make a feedback loop and will cause oscillation.
Regards,
Keith
 

Alec_t

Joined Sep 17, 2013
11,645
Your phone output signal level is probably much higher than the mic signal level, so the amplifier gain needs to be turned high when using the mic. The high gain results in hiss and other background noise being amplified to an objectionable level. It seems you need a mic pre-amp before the LM386 amp.
 

Thread Starter

skander belhaj

Joined Sep 7, 2020
7
Your phone output signal level is probably much higher than the mic signal level, so the amplifier gain needs to be turned high when using the mic. The high gain results in hiss and other background noise being amplified to an objectionable level. It seems you need a mic pre-amp before the LM386 amp.
that's the challenge I want to make this work without the preamp is it possible ??
 

KeithWalker

Joined Jul 10, 2017
1,222
there is a 30cm distance between them
That is far too close! You can tell if the problem is caused by audio feedback if the sounds change when you move the microphone relative to the speaker or if you move objects between the two that will block the sound. If they have to be that close, you will have to use a very directional microphone that will not pick up sounds from the speaker and you will have to keep the gain turned down.
Keith
 

KeithWalker

Joined Jul 10, 2017
1,222
that's the challenge I want to make this work without the preamp is it possible ??
It will work without a pre-amp. If you have a 10uF capacitor connected between pins 1 and 8, the voltage gain is approximately 200. That is enough gain to get an audible output. It will not be very loud. If you need more, a simple transistor pre-amp would do the job. First you must get rid of the audio feedback between the mic and speaker. It just will not work if the mic is close enough to pick up the sounds from the speaker.
Keith
 

Audioguru again

Joined Oct 21, 2019
1,914
Of course there is acoustical feedback when the mic hears the speaker then the amp amplifies the sounds around and around.
I agree that the LM386 produces hiss when the gain is high.
Your circuit has a few other problems:
 

Attachments

Thread Starter

skander belhaj

Joined Sep 7, 2020
7
It will work without a pre-amp. If you have a 10uF capacitor connected between pins 1 and 8, the voltage gain is approximately 200. That is enough gain to get an audible output. It will not be very loud. If you need more, a simple transistor pre-amp would do the job. First you must get rid of the audio feedback between the mic and speaker. It just will not work if the mic is close enough to pick up the sounds from the speaker.
Keith
can you suggest a circuit, please
 

Thread Starter

skander belhaj

Joined Sep 7, 2020
7
Of course, there is acoustical feedback when the mic hears the speaker then the amp amplifies the sounds around and around.
I agree that the LM386 produces hiss when the gain is high.
Your circuit has a few other problems:
did you did this by yourself
thank you so much, are you 100% sure of this circuit, I will try it
 

Audioguru again

Joined Oct 21, 2019
1,914
Yes, my circuit uses properly calculated parts values and everything shown in the datasheet of the LM386 amplifier IC.
I missed saying, Your R3 is not needed and your R2 must be a logarithmic volume control that is marked "A" for audio (not linear that is marked "B"). It might not work if you make it with messy long wires on a solderless breadboard.

Even my circuit will produce acoustical feedback howling unless you have the mic in another room from the speaker with the door closed between them. Or record the mic and play it back later.
 

Thread Starter

skander belhaj

Joined Sep 7, 2020
7
Yes, my circuit uses properly calculated parts values and everything shown in the datasheet of the LM386 amplifier IC.
I missed saying, Your R3 is not needed and your R2 must be a logarithmic volume control that is marked "A" for audio (not linear that is marked "B"). It might not work if you make it with messy long wires on a solderless breadboard.

Even my circuit will produce acoustical feedback howling unless you have the mic in another room from the speaker with the door closed between them. Or record the mic and play it back later.
but I don't have any R3 in my circuit I only have two resistors
 

schmitt trigger

Joined Jul 12, 2010
320
Your schematic clearly shows a box labeled R3, next to a value 2.2 M.

If it is not a resistor then don’t label it that way. It confuses the people attempting to help you.
 

Thread Starter

skander belhaj

Joined Sep 7, 2020
7
Your schematic clearly shows a box labeled R3, next to a value 2.2 M.

If it is not a resistor then don’t label it that way. It confuses the people attempting to help you.
Sorry i did not see that but that’s actually the mic there is no resistor there at all
Sorry for the mistake i didn’t see it at all
 
Top