Here is the schematic

I checked the circuit 1 million times. I got it from a website. Everything is correctly connected. The sound is loud, but it is very distorted. I use a 9 V battery.

Where is the problem? :(

EDIT:I used an LM386M-86 CHIP and not the LM386N-4 CHIP that is used on this schematic.This may have caused he problem??

  • 2
    \$\begingroup\$ You haven't told us what signal you are feeding in and what voltage it is. \$\endgroup\$ – Transistor Jun 8 '19 at 20:02

LM386 needs an AC coupling capacitor on its input.

If your input circuit is DC coupled, you disrupt the input biasing arrangements built into the amplifier. Instead of being centred, the output voltage is probably close to one of the supply rails, clipping the positive or negative half of the AC waveform, resulting in severe distortion.

Insert 1 uF (or 10 uF) in the path labelled "Mono_Audio" on the schematic.

EDIT : Peter Mortensen is absolutely right to ask for references - my memory was way off here.

What I got wrong : it is NOT essential to eliminate a DC path between +In (Pin 2) and GND.

What still matters : it IS important to keep the DC source impedances similar on both input pins (pin 2 and pin 3). to keep the inputs roughly balanced and the DC output voltage roughly Vcc/2 (4.5V wit a gV supply.

Since Vin- (pin 2) is connected to GND here, that means Vin+ must be fed from a fairly low impedance to GND, say 10K or less. So my previous suggestion may be a step in the wrong direction (unless you also allow Pin 2 to float) - instead, you may need a DC path to GND such as a 5K resistor from "Mono_Audio" to GND.

Be guided by the DC voltage on VOut (pin 5).

  • 1
    \$\begingroup\$ Perhaps add some numbers and references? From the datasheet for TI's version, page 4, "Recommended Operating Conditions", "VI, Analog input voltage", minimum -0.40 V, maximum 0.4 V. \$\endgroup\$ – Peter Mortensen Jun 9 '19 at 10:15

Probably because the input signal level is too high. To test this, add a 100 ohm resistor from pin 3 to GND. The output volume will be reduced, but, if high input level is the problem, it also will be less distorted. Consider adding a volume control at the input. It is shown on the datasheet applications.

Also, pay very careful attention to the power supply decoupling. Add a 100 nF ceramic capacitor in parallel with the 100 uF electrolytic, and make sure the leads are as short as possible and as close as possible to the device pins 4 and 6

Also, there should be a coupling capacitor between the junction of the two input resistors and pin 3. This is to remove any residual DC on the incoming signals, which can affect the output voltage range.

Also, there should be a 10 ohm resistor in series with the 100 nF capacitor on the output to ground. This is called a Zobel network and works to reduce high frequency oscillations, which can sound like distortion.

Note: it is much easier to discuss the components of a circuit if the schematic has a unique reference designator for each one.

  • \$\begingroup\$ the input signal level isn't high. It is from a mp3 player \$\endgroup\$ – Stelios Liakopoulos Jun 8 '19 at 20:19
  • \$\begingroup\$ i burned both of my LM386 chips. The first because i did wrong connections and the second because i thought the problem was the 9 volts of the battery and i used a 24volt adaptor to power the circuit(i am stupid). When i buy new ones and build the circuit again i will try your solutions \$\endgroup\$ – Stelios Liakopoulos Jun 8 '19 at 20:22
  • 3
    \$\begingroup\$ The output level from an mp3 player can be too high for this amplifier. You have the gain set to 20, the maximum output it can provide is probably about 5-6V pk-pk, the maximum input will, therefore be about 1/4 V.Turn down the volume on the player. \$\endgroup\$ – Kevin White Jun 8 '19 at 21:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.