LM386 amp gain input

Discussion in 'The Projects Forum' started by frenchie29, Apr 25, 2009.

  1. frenchie29

    Thread Starter Active Member

    Nov 28, 2008
    134
    0
    How can I pad down the gain input?
    http://www.kitsrus.com/pdf/k17.pdf

    At line level it's way too hot I barely touch the pot and it's distorting Right now I am using an inline pad and -20 -30db and it's pretty good.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You may have connected the pot backwards, or not have a good connection to ground.

    Try swapping the end connections.

    If that doesn't work, you may have a bad pot.
     
  3. frenchie29

    Thread Starter Active Member

    Nov 28, 2008
    134
    0
    When I reversed the pot wiring it sounds distorting and the does the opposite volume decrease instead of decreasing, so I know for sure the pot wired properly and is good I have like 10 of those pots. Here's what I have to use to pad down line level.

    http://www.directproaudio.com/product.cfm?directid=53336
     
    Last edited: Apr 26, 2009
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The jumper in the circuit increases the gain 10 times to 200 so don't use it. Without the jumper the gain is 20.
    A log volume control has an output that is about 1/10th the input level when set to half-way. Maybe your volume control is linear by mistake then its output is half when it is set to half-way.

    What is your power supply voltage? If it is 6V then the output at clipping into an 8 ohm speaker is only 0.2W which is not much volume. With a 9V supply it is 0.45W and with a 12v supply it is 0.53W and the chip heats a lot. A cheap clock radio might be louder.
     
  5. frenchie29

    Thread Starter Active Member

    Nov 28, 2008
    134
    0
    I'm using a 9v with a 025w 8ohm speaker. You're right a cheap radio clock is louder.
     
  6. frenchie29

    Thread Starter Active Member

    Nov 28, 2008
    134
    0
    How could I split the difference between with the jumper and without?
     
  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Use a 20k ohms pot in series with a 10uf capacitor connected from pin 1 to pin 8. Adjust the pot for a voltage gain of from 21 to 200 then measure the pot and replace it with a resistor with the same value.
     
Loading...