adding volume pot to small amp

Discussion in 'The Projects Forum' started by campbellkd14, Jul 26, 2010.

  1. campbellkd14

    Thread Starter New Member

    Jul 26, 2010
    It's been a zillion years since electronics school and I've forgotten way too much basic analog theory. Any help would be greatly appreciated.

    I have a small stereo amp kit that uses a TDA2004 chip to which I must add a volume control. The input is line level from a PC sound card (application is an upright videogame cabinet).

    I have a 10kΩ stereo audio-taper pot. Please see attached snippet from the spec sheet for the TDA2004 chip. Could I just insert the 10k stereo pot inbetween the existing input capacitor and the chip input leg for each channel? That would be main pot legs from input to ground and wiper leg to chip input.
  2. JDT

    Well-Known Member

    Feb 12, 2009
    Put the pot before the capacitor. So connect your line input across the track and connect the capacitor to the slider (centre pin).

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  3. campbellkd14

    Thread Starter New Member

    Jul 26, 2010
    do you mean like the picture attached below? (of the circuit diagram of a similar amp - mono and using a different chip, but wiring would be theoretically similar). Won't putting the pot BEFORE the cap bleed some of the signal off to ground? If so, enough to matter?

    The schematic in the pic originally had the cap before the pot, I edited it to move the cap to ensure I was correctly understanding what you meant. Thanks.
    Last edited: Jul 26, 2010
  4. campbellkd14

    Thread Starter New Member

    Jul 26, 2010
    It works as intended. If any signal is being bled off to ground, it's inconsequential for this application. I don't fully understand why, but I'll accept that it works and thank you profusely. Now I can finally FINISH this project.
  5. SgtWookie


    Jul 17, 2007
    Note that you should use a ganged dual audio taper or log pot, rather than a linear pot.

    If you have the "ends" swapped on a log/audio taper pot, you will have very little control over the volume; just change the end wires around to fix it.
  6. Audioguru

    New Member

    Dec 20, 2007
    The polarity of your input capacitor C1 is shown backwards. The input pin of the IC has a positive voltage so the (+) wire of the capacitor should go there.
    The datasheet recommends 2.2uf, not 1uF so that the POP when the power is applied is not too loud.
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