Resistors and filters for stereo amplifier based on TDA2822 chip

Discussion in 'The Projects Forum' started by El Zu, Mar 1, 2016.

  1. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    Hi!
    Working on low power stereo amplifier built around TDA2822 chip. It has 2 sources: External source (audio in from RCA_1) and Internal from another digital part (C3 and C4 are decoupling capacitors for supply this part). Very simple project, but I have some questions before layout it:
    1) About volume pots resistance (10K or 100K?) and the value of R5 and R6 (1K, 10K or nothing?)
    2) I add C6 capacitor for better protection, so should I add some additional filters to make it work better.
    3) Should I add some impedance resistors for the "internal digital audio source" (nets R_INTIN and L_INTIN).
    4) And maybe I've missed something else?
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    1) 10k is fine for the pot resistance. You don't need R5 and R6.
    2) No additional caps needed.
    3) No additional resistors needed.
    4) Why are C9 and C10 only 470μF instead of the 1000μF shown in the data sheet?
    That will roll off your bass some if you are using 8 or 16 ohm speakers.

    What is the purpose of the low value resistors R3 and R4? :confused:
    They will shunt most of the input signal to ground.
     
  3. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    I've made it! It's so loud, and a little noise is hearing.

    I would like to make it more quite. Even when my pot is turned off, I'm still getting some music through the amp. And its too load at 10%, couldn't amaze what will be at 100%! :eek: Thats why R5 and R6 have to be there, I think.

    In my data sheet C9 and C10 are 470μF. I saw some schematics with 1000μF capacitors right before the signal out. Don't know why (?)
    See the attachment.

    I've made a mistake. Its 10K, not 4,7.

    So, how to made it work not so load? And whats the mess with the pot?
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    Are the pots audio taper (logarithmic) types?
    If not, that would explain why the volume sounds so high at only 10% of the pot adjustment.

    If the pots are indeed the linear type, you can make them act similar to an audio pot by changing the values of R3 and R4 to between 1kΩ - 2kΩ as discussed here.
    If that low resistance loads your source too much you can change the pots to 100kΩ and R3 and R4 to 10k-20kΩ.
     
    Last edited: Mar 1, 2016
  5. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    I use A pot, and change it to 100K, try to replace R3 and R4 from 10K to 100k as well. It makes the load low, but at 100% it distort a little bit anyway. Is there kind of protection from the distortion or overload? And white noise is still hear a little, I think I should separate supply gnd from audio gnd to avoid looping. In the layout I make an general plate for both, and I guess it is a mistake.
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    If the pots are 100k, then R3 and R4 should be about 10k to 20k.

    Distortion is normal when you overdrive the amp. You just need to keep the volume below that point.

    A ground loop would cause 50-60 cycle hum, not white noise.
    White noise is from the intrinsic circuit noise which generally can't be reduced.
     
  7. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    Ok, try to find the way out the problem. Or try to make another one with another chip. Thanks.
     
  8. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    I skip it to amplifier on OPA2134. But couldn't decide where the gain pot should be: R3 or R4, or before C1 or C2?
    Don't want to make a new post about it :rolleyes:
     
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  9. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    The OPA2134 is an operational amplifier with a low output current (its minimum rated load is 600Ω).
    It cannot be used to drive speakers or a headphone as the TDA2822 can.
     
  10. El Zu

    Thread Starter New Member

    Jan 13, 2016
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