lm386 amp again

Discussion in 'The Projects Forum' started by slimnick, Jan 6, 2008.

  1. slimnick

    Thread Starter Member

    Nov 25, 2007
    21
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    hello , i've built an ampilier from http://web.mit.edu/6.115/www/datasheets/LM386.pdf. also i haveen others tried and built this amp on this site also. i successfully built the diagram on page 5, with up to 200gain. my first question is also on page 5 its has a diagram of an ampliefier with bass boost. is that a circuit that will give bass to your speakers?, if so will the bass boost circuit need to connect with the 200 gain circuit?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    It's a modification of the circuit arrangement that will increase the bass output. The modified circuit is in place of the G = 200 circuit.
     
  3. slimnick

    Thread Starter Member

    Nov 25, 2007
    21
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    so it can operate solely by itself, if so the RL seen in the schematic is actually the speaker?
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    RL is indeed the speaker. At the top of page 6 is the frequency response. Note that the midband gain is 19dB, which is a gain of 8.9.
     
  5. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
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    I've tried the bass boost configuration of the LM386, and the difference is quite noticeable.

    I think the bass boost should work if the amplifier's gain is set to a value greater than 20. The bass boost network won't interfere with the gain network, since all the last one does is to "short" the internal 1.35K resistor. Notice that the term "bass boost" is not accurate. More appropriate would be to use the term "treble attenuation" instead.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    Yes the bass boost will work if the gain is 200.
    But only the 100hz bass will have a gain of almost 200. The higher frequencies will have a gain of nearly 100.
     
  7. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
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    Indeed, forgot to mention that the treble attenuation (or bass boost) is in the order of 6dB (therefore will reduce the treble to half). I think it will start at 1KHz, if I'm not mistaken.
     
  8. slimnick

    Thread Starter Member

    Nov 25, 2007
    21
    0
    i have built the bass boost circuit, its works but the bass the comes from the speaker sounds like it was puttin the pseaker to its limits. so i changed the input votlage from 9 to a lower one of 3volts. it has gotten alot better but it still is quit abit muffled, what can be the cuplrit? im not sure if it can be the speaker that im using. it is a 6 ohm impedance speaker rated at 15 watts. i had to make acouple of alternative parts within my circuit design.

    the 250 uF was replaced with a 220uF but that shouldnt cause all that problem.

    i used a .047uf for the .033uf that is inline with the 10k ohm resistor

    also i used a 0.01 uf cap as the bypass

    anything can suggest whats the matter?
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    896
    With a 9V supply and an 8 ohm speaker, the LM386 amplifier clips when the output power is over only 0.45W. A cheap clock radio has more power. a little 9v battery has difficulty to produce that much power.
    Its power output at clipping with a 4V supply is only 0.06W (loud earphone level). It isn't spec'd at a supply of only 3V.

    The amplifier is at its limits with these very low supply voltages.

    This is a dinky little amplifier IC. If you want power then use one of the hundreds of amplifier ICs that are made for car radios. Most have an output at clipping with a 13.2V battery and a 4 ohm speaker of 14W.
     
  10. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    Perhaps what you are earing is distortion caused by the clipping of the signal (the output voltage equals the rail voltages at both ends). You should decrease your gain. See if that helps.

    For that, you can use the TDA2003 from ST. It is an excellent amplifier. The only downside is that you will need more power.
     
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