# Microphone gain with LM386

I am trying to amplify audio from an electret microphone using an LM386 audio amplifier board.

However, the output of the board is very grainy and the audio is distorted.

Is there any way I can improve the audio quality, or the microphone gain?

I have used a 27k resistor from mic+ to a 9v battery to power the microphone.

I will attach the diagram of what I have done below.

Edit - I have now looked into using a coupling capacitor on the input but there are a few schematics and I am still unsure. I have attached the images below.

• This schematic doesn't match the circuit board below. Your board shows: four resisters (including the variable one), a diode, six capacitors, all eight pins are utilized, and I doubt VCC is shorted to the input of your amplifier.... Your drawn schematic only shows one resistor (that's not a variable one), you've shown six out of the eight pins utilized by the IC, and you shorted your input to the VCC rail. – KingDuken May 20 '19 at 22:10
• @KingDuken thanks for the reply , my schematic has the LM386 module in the middle , which is the circuit board about , the input and output pins are also shown on the schematic and pcb , and I have added any extra components I used in my schematic, sorry if it wasn’t clear enough 👍 – jackv12333 May 20 '19 at 22:14
• @KingDuken also when I say “LM386 Module “ I meant the whole Blue PCB module shown above , sorry for not being clear – jackv12333 May 20 '19 at 22:16
• What does "grainy" mean? Noisy (white noise like wind?) Buzzing? Constant squealing? "Grainy" is usually applied to visual things - a "grainy" picture has visible variations that look like grains of sand. Wood has grain in that it has a textured color instead of a solid color. What does "grainy" mean when applied to sound? – JRE May 21 '19 at 10:58
• The audio out to the speaker distorts easily if I speak normally. and there is also a ticking (clicking noise ) that I can hear on the output , and also a buzzing white noise in the background – jackv12333 May 21 '19 at 12:01

Here is the schematic of an LM386 board that appears to be the same as yours:-

The gain control trimpot is connected directly to the input with no coupling capacitor, so any voltage on the input will affect the amplifier's DC operating point. If your board has a similar circuit then you need to add a capacitor between the mic and amp input to block DC voltage.

The combination of this coupling capacitor and the 10k pot form a high-pass filter that rolls off below $$\frac{1}{2\pi RC}$$

A 0.22uF coupling capacitor would be large enough to pass frequencies above 72Hz with minimal attenuation.

• Thanks for the help , I’ve just looked into using a coupling capacitor and there are a few different schematics that I could use , I have attached these onto the bottom of the original question , can you advise on which combination I should use ? Thanks 👍 – jackv12333 May 21 '19 at 8:58
• #1 won't work. In #2 the capacitor has the wrong polarity. You should use #3. – Bruce Abbott May 21 '19 at 23:25

Instead of the module, breadboard the circuit based on the electret and LM386 datasheets. Maybe use a CAD program to lay it out and test analyze the circuit. I like to use potentiometers that I can tweak to enhance the overall performance when breadboarding a test circuit. Those modules are slick, but I would prefer a bit more of my direct imput into designing what I want to accomplish instead of just throwing some modules together and expecting perfect results. There is a reason the modules are so cheap from china.

• Thanks for the help I will try breadboarding the circuit , however at the moment I only have the module , I have read about putting coupling capacitors on the input but I’m not sure how this works , and I’m still unsure whether I am using the correct size resistor for powering the electret mic ? Thanks 👍 – jackv12333 May 20 '19 at 22:35
• Under what DC conditions (the electret output, the LM386 input) would you use a DC_blocking input capacitor? – analogsystemsrf May 21 '19 at 0:10