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I got some LM4562 op-amps a few months ago and finally had time to test my audio project, and I realized that this schematic based on some others on the network is not working.

I tried to listen to the amplified audio coming from the smartphone on the 3 W, 4 Ω speaker, but I didn't hear the music; it just pushed the membrane.

enter image description here

What am I missing?

EDIT

I have read and tried to fix my mistakes, but it still doesn't work. I am starting to believe that although it says "L4562MA" on the IC, it's not an op-amp.

I also tried with a 560 Ω resistor after the output's cap.

enter image description here

EDIT2

I have made it work with the following schematic, but sadly the distortion is very disgusting.

I mark the answer as the correct one because in my question I just did want to make it work for a test, I wasn't looking for a definitive result as I had experience before with another op amp and I got also distortion; but I couldn't decide to use biasing because I was following the schematics on the internet, to make a minimum working schematic.

Thanks!

enter image description here

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  • \$\begingroup\$ You haven't followed what I said in my first bullet point. There should be another resistor from POS_A to Vcc to create a mid-rail voltage. The NEG_A input needs the same treatment (now added to my answer). \$\endgroup\$
    – Andy aka
    Jan 9 at 19:58
  • \$\begingroup\$ C1 and C4 should have their positive terminals towards the IC. \$\endgroup\$
    – Peter Bennett
    Jan 9 at 20:28
  • \$\begingroup\$ The circuit is incorrect for a single-supply op-amp, but also the LM4562 is a wrong component for driving a speaker. You don't want an op-amp circuit, you want a speaker amplifier. \$\endgroup\$
    – Justme
    Jan 9 at 21:09
  • \$\begingroup\$ A POWER AMP is designed to drive a speaker. The opamp is designed to drive a POWER AMP that has an input that is 600 ohms or more. Your added 100uF output capacitor calculates to cutout most bass frequencies below 400Hz, use 1000uF to pass most bass frequencies to a 4 ohms speaker. Most Power amplifiers need more supply voltage than only 5V. An LM386 produces only 0.1W into 4 ohms. A PAM8403 is a stereo (2 channels) power amplifier IC that produces 2.4W into each 4 ohms speaker when the supply is 5V and its outputs di not need a capacitor. \$\endgroup\$
    – Audioguru
    Jan 9 at 21:23
  • \$\begingroup\$ Nayara, it's good you finally got an output but, did you input too much signal? The voltage gain will be 21 so something around 100 mV at the input will be about right. Remember also that this chip will not drive a loudspeaker directly and doing so can create huge amounts of distortion. \$\endgroup\$
    – Andy aka
    Jan 10 at 19:22

1 Answer 1

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What am I missing?

  • Your inverting input needs biasing at mid-rail (that's mid-rail of the op-amp supplies i.e. half way between Vcc and GND)
  • This also needs replicating on the NEG_A input with a 1k resistor to Vcc
  • Your speaker needs a series output capacitor to prevent DC flowing into it (that's the "It just pushes the membrane" cure.
  • You should check whether the op-amp is capable of driving a loudspeaker. If it isn't then add a series resistor of about 560 Ω to the added series capacitor I mentioned above.

Also, check that the power rails of the op-amp are capable of working with the supplies you have given it. You should read the data sheet to find this out.

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  • \$\begingroup\$ Missing decoupling comes to mind too after fixing the above. \$\endgroup\$
    – winny
    Jan 9 at 15:39

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