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Long time lurker and relativly new to electrical engineering but this is the first time I've had a question so I just made an account.

I would also like to start off by saying that I tried to follow this thread but none of the solutions seemed to help my problem. The audio can only be heard if you hold the speaker to your ear.

I followed this schematic from http://www.circuitbasics.com but the output of the speaker is quieter than when I directly attach the audio jack to the speaker. schematic

This is a picture of my circuit my breadboard

I'm not sure if all the extra wires is increasing the resistance to the point of muffling the output sound but it made connecting the battery and speaker easier and the 10K ohm potentiometer's pins were bending a lot to fit in the board so I just took it out and connected it via jumpers. The 9v battery is outputting roughly 8.3v and even if I add another 9v battery to the circuit in series the speaker doesn't get any louder, just more distorted.

Also the LM386 chip was getting very hot to the point where it burned my finger on contact and one solution I found was to connect pin 1 to pin 8 and that seemed to have solved the overheating problem but no difference to the audio output.

The stereo audio jack connector I purchased had two "3" connectors from the schematic (not sure what the technical term is but the datasheet showed 2 downward ports) so I had soldered them together before realizing it wasn't necessary and disconnecting them.

I looked the datasheets of the parts and nothing stood out to me as causing the problem but if someone who knows more than me could have a look I would greatly appreciate it.

The parts I have are as follows

  1. 10K ohm potentiometer (part # 296UD103B1N)

  2. LM368 Chip (part # LM386N-1/NOPB)

  3. 1000uF polarized capacitor (part # EEE-FT1C102GP)

  4. 0.1uF capacitor (part # FG26C0G2A104JRT06)

  5. 10 ohm resistor (part # CCF6010R0FKE36)

  6. 3.5mm audio jack connector (part # SJ5-43502PM)

The 8 ohm 2 watt speaker was the only one I have on-hand so I'm not sure if the speaker is the problem but I'm planning on connecting this to a 555 audio modulated fly back driver so the speaker isn't necessary.

Any help or pointers would be very appreciated for this newbie engineer. If anyone has any questions or concerns I will try to answer them.

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  • \$\begingroup\$ What decoupling capacitor are you using? If none, (and the battery's right way round!) the LM386 may be oscillating. \$\endgroup\$
    – user16324
    Apr 15, 2017 at 19:18
  • \$\begingroup\$ @BrianDrummond No decoupling capacitor. If I did get one where would I install it if I may ask. I'm new to this so sorry if this is a stupid question. \$\endgroup\$
    – Lennox
    Apr 15, 2017 at 19:27
  • \$\begingroup\$ Across the power supply pins close to the amplifier. Same value as the output capacitor would be good, and 0.1 uF ceramic in parallel with it. \$\endgroup\$
    – user16324
    Apr 15, 2017 at 19:51
  • \$\begingroup\$ It'll be a couple days before I can get another capacitor and decoupling capacitor but I will try and let you know if that fixes the problem. \$\endgroup\$
    – Lennox
    Apr 15, 2017 at 19:59

1 Answer 1

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You have to change the polarity of the battery connection. The "+" and "-" on the audio amplifier relate to the direct and inverse input. And do not indicate polarity a power supply.

The chip can be damaged through the false connection. So perhaps it is also necessary to replace it.

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  • \$\begingroup\$ Thanks for the reply but changing the polarity of the battery just makes the speaker pop loudly about once a second and with no audible music. Is the false connection the pin 1 to pin 8 connection I added? \$\endgroup\$
    – Lennox
    Apr 15, 2017 at 19:09
  • \$\begingroup\$ @Lennox, I updated my answer. \$\endgroup\$
    – AltAir
    Apr 15, 2017 at 19:11
  • \$\begingroup\$ Sorry if I'm misunderstanding but when I remove the pin 1 to pin 8 connection, the chip starts to get hot again so I don't think that I damaged it. If I did is there anywhere to test if I damaged it? \$\endgroup\$
    – Lennox
    Apr 15, 2017 at 19:23
  • \$\begingroup\$ @Lennox, Pin1 and pin8 use for change gain of the amplifier. In this case, the gain of 20 is the default value when pin1 and pin8 are free. \$\endgroup\$
    – AltAir
    Apr 15, 2017 at 19:26
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    \$\begingroup\$ I looked at the data sheet. Pin 6 should be + battery. And you should use some kind of capacitance across pins 6 and 4 to bypass the battery. At least .1 uF. I've used your circuit many times and it should work fine. Check with an ohmeter and see if your potentiometer is really working. If the input pin was seeing an open circuit that might explain the behavior. \$\endgroup\$
    – electrogas
    Apr 15, 2017 at 21:35

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