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LM358 to make FM Audio Receiver

Discussion in 'Audio' started by Xyq, Mar 23, 2017.

  1. Xyq

    Xyq

    19
    0
    Mar 23, 2017
    HI folks,

    Can i use LM358 to replace LM386 to make FM audio receiver. I am new on electronics, I look thought datasheets of LM358 and LM386 , the big difference is LM386 have enough output voltage for speakers, I know LM358 is bad for audio, noise, crossover distortion...,
    if i want to use LM358 to replace LM386, i think i need to add with extra components, power transistors ? BJT ?
    I can find any circuits so far
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,277
    1,878
    Nov 17, 2011
    No:
    The LM386 is a complete audio power amplifier, the LM358 is a dual operational amplifier. When using the LM358 e.g. as a pre-amplifier, you will have to supply a separate power amplifier.
     
  3. AnalogKid

    AnalogKid

    2,299
    647
    Jun 10, 2015
    Yes:
    You can add external components to an LM358 stage to boost the output current enough to drive a small speaker, but it is a lot of effort compared to using an LM386 and the result will not be as loud.

    ak
     
  4. Audioguru

    Audioguru

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    585
    Sep 24, 2016
    Do you know Ohm's Law? Voltage divided by resistance = current? Assuming that the speaker is 8 ohms and you want a peak voltage of 3V in it then the current is 3V/8 Ohms= 375mA.

    The datasheet for the LM386 power amplifier shows that it can produce a little more than 375mA but the datasheet for the LM358 dual opamp shows that some of them cannot produce more than only 10mA. You will barely hear it if you held the speaker against your ear.

    The power output from an LM386 is not much, about like a cheap clock radio. There are a few higher power amplifier ICs that are high fidelity.
     
  5. Xyq

    Xyq

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    0
    Mar 23, 2017
    Thanks all:), I am going to add 2N4401 (1 pic) and 2N4403 (1pc) to boost output current. hope it will work.

    BTW, I have built one FM transmitter, but this frequency is around 46-50Mhz (FM is 88 -108 Mhz)-why . I use normal radio devices that can only receive noise.

    I used same circuit diagram and same value of components (attached image),

    I think there are 2 reasons :

    1. FM transmitter is made on the breadboard. - solution: it will be solided on PCB.
    2. Antenna is not enough long (it is around 20 cm length.)- Not sure?

    can your guys give me other ideas ? Thank a lot, I really appreciate it.
     

    Attached Files:

  6. davenn

    davenn Moderator

    13,288
    1,755
    Sep 5, 2009
    that is the major problem
     
  7. Audioguru

    Audioguru

    2,580
    585
    Sep 24, 2016
    An LM358 is no good for audio because it was made to have very low power consumption then its output transistors do not have enough idle current which causes crossover distortion, hiss noise and poor high frequency slew rate. An LM358 has trouble with normal audio frequencies above 2kHz.

    The output swing of an LM358 is shown in its datasheet to be about 2.5V less than the supply voltage. Adding a 2N4401 and 2N4403 will cause the output swing to be 4.5V less than the supply voltage so the maximum output power will be small.

    The FM transmitter circuit you found was posted on another website 12 years ago and it had 4 problems. I fixed each problem and called mine "FM tx mod 4" and here are my 4 mods:
    1) The mic preamp transistor was not biased correctly so it was saturated when the battery is new and was cutoff when the battery is old. I fixed it by biasing it correctly and adding a 5V low dropout voltage regulator.
    2) The radio frequency changed as the battery ran down so I powered the oscillator from the 5V regulator.
    3) The radio frequency changed when something moved towards or away from the antenna so I added an RF amplifier to isolate the antenna from the oscillator.
    4) The sounds heard on any FM radio were muffled with no high audio frequencies. I added audio pre-emphasis like all FM radio stations have and it matches the de-emphasis that all FM radios have. Pre-emphasis has two versions depending on where in the world. Here is my FM transmitter:
     

    Attached Files:

  8. Xyq

    Xyq

    19
    0
    Mar 23, 2017
    Hi Audioguru,

    I will use this circuit to amend my FM transmitter :).

    For LM358, if one 2N4401 and one 2N4403 are not enough, Can i add more 2N4401 and 2N4403? or do u have other ideas? my project requests that I can't use LM386, I only can use LM358.
     
  9. Audioguru

    Audioguru

    2,580
    585
    Sep 24, 2016
    Why do you think the power will be increased if you add more 2N4401 and 2N4403 transistors? Show how they would be connected.

    How loud do you want the radio to play? A cheap clock radio produces about 0.5W.
    An LM386 powered by a 9V battery produces 0.45W before clipping distortion becomes bad.
    An LM358 driving a 2N4401 and 2N4403 will produce 0.25W.

    Modern little class-D amplifier ICs produce 3W when powered by a 9V battery.

    Post your schematic of using an LM358 driving 2N4401 and 2N4403 and we will make it work as good as it can.
    You know what? Use two 9V batteries to make 18V then the output power will be 0.5W.
     
  10. Xyq

    Xyq

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    0
    Mar 23, 2017
    View attachment 32915 View attachment 32913 Hi Audioguru,

    I have attached the FM radio schematic with LM386 and
    second schematic with LM358 and 2N4401 , 2N4403. I am going to give just 5V power supply . I am not sure :(.
    Thanks
     

    Attached Files:

    Last edited: Mar 30, 2017
  11. Audioguru

    Audioguru

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    585
    Sep 24, 2016
    You made many errors:
     

    Attached Files:

    CDRIVE likes this.
  12. Xyq

    Xyq

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    Mar 23, 2017
    Hi Audioguru,

    I don't have enough experience to change circuit.
    I am really need your help.
    Do u know how to use LM358 to replace LM386 based on LM386 radio receiver on the previous post ?
    I am really appreciate it.
     
  13. Audioguru

    Audioguru

    2,580
    585
    Sep 24, 2016
    Since this is your school assignment then you should learn about the basics of electronics and do the assignment yourself. I would never use a lousy old LM358 for audio.

    With a properly designed pcb then an LM386 power amplifier IC circuit is inexpensive, easy to make and sounds pretty good but its maximum output power is fairly low.
     
  14. Xyq

    Xyq

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    0
    Mar 23, 2017
    Hi Audioguru,

    I have studied this receiver circuit but I am confused how it is working process of this circuit. kindly help me.I have no idea for some part of this circuit. Thank you very much
     

    Attached Files:

  15. Audioguru

    Audioguru

    2,580
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    Sep 24, 2016
    It is not a radio receiver. The two transistors have the input (the base of the left one) shorted to the output (the collector of the right one).
    I found an awful "radio" circuit that is almost the same as the one you found:
     

    Attached Files:

  16. Xyq

    Xyq

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    0
    Mar 23, 2017
    Hi dude, thanks so much for the help.
    Perhaps I did not make this clear to you.
    We are asked to build both FM transmitter and receiver without using any of the modern ICs.
    Only simplest analog components such as resistors, capacitors etc.
    And only op-amp in the list that we are able to use is LM-358, not even LM-386 which u thought of lousy.
    We do not need to build a perfect and robus prototype, we are required to build these circuit using simple understanding logic.
    And, if possible, improve on the circuit we found to the best using all low level components available.
    Thus, bro, if you could help us in this way is much appreciated, and so, is our receiver workable this way?
     
  17. Audioguru

    Audioguru

    2,580
    585
    Sep 24, 2016
    Your receiver is hopeless because its input is shorted to its output.
    I biased the first transistor properly with a base resistor to its collector and put C1 and L1 as a parallel tuned circuit as its collector load, then I capacitor coupled its collector to the base of the second transistor that has a base resistor and a collector resistor. It might work but I have not tried it. It can feed your extremely distorted power amplifier.
     

    Attached Files:

  18. Xyq

    Xyq

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    Mar 23, 2017
    Thanks. I will try this circuit.
    For the FM transmitter circuit. I spend a lot of time to study datasheets. but I don't know how is actual role of each component, can u explain to me the work flow of this circuit? or can u provide some resources so that I can study . because I am really dont understand. Thanks a lot for your help
     

    Attached Files:

  19. Audioguru

    Audioguru

    2,580
    585
    Sep 24, 2016
    Why didn't your teacher teach you about the basic transistor circuits? Don't you have a text book about transistor circuits?
     
  20. Xyq

    Xyq

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    0
    Mar 23, 2017
    I know this is two-stage amplifier circuit, but I don' t know why use this components? I have highlight in red box? can u explain those components ? and C5 is bypass capacitor? thanks
     

    Attached Files:

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