difference between potentiometer A and B

Discussion in 'General Electronics Chat' started by frenchie29, Apr 23, 2009.

  1. frenchie29

    frenchie29 Thread Starter Active Member

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    I totally forgot about that one

    What's the difference between potentiometer type A and B?

    And the one that's the most used for audio?
     
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  2. bertus

    bertus Administrator

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    #2
  3. frenchie29

    frenchie29 Thread Starter Active Member

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    There's no mentioning of A or B type!! Unless I didn't see it. I remember well A=audio taper log. But I am not sure anymore.
     
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  4. frenchie29

    frenchie29 Thread Starter Active Member

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  5. SgtWookie

    SgtWookie Expert

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    That's a log pot. You could use an audio taper pot.
     
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  6. frenchie29

    frenchie29 Thread Starter Active Member

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    So type A??? The thing is that trimpot that came with that kit says 10KB on it. That's why I'm a bit confused. Also I want to use a TRS female connector for the audio input.

    Tip to audio in
    Ring to audio in
    Sleeve to ground audio

    Is that right?

     
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  7. Darren Holdstock

    Darren Holdstock Active Member

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    I don't recall ever seeing a log trim pot - they seem to have specified a log pot in the schematic, but supplied a linear pot with the kit. It won't matter if you're just using the pot to set the gain just the once, it's only if it's being used as a working volume control that it might become annoying as the relationship between pot rotation and perceived loudness is non-linear with a linear pot.

    An old trick to make a lin pot a bit more loggy is to add a resistor from wiper to ground - it quite often makes a more repeatable pot, as log pots are very hard to make accurately, and the tracking between dual log pots can be poor. Bertus' link (above) explains more about this technique.
     
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  8. frenchie29

    frenchie29 Thread Starter Active Member

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    I have both 10k A&B 25kB and 50k audio log (A) Now I know that the A type is for audio it says it on the 50k pot Which one would work best? I don't really want to use the 50k they cost me like $5 each
     
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  9. SgtWookie

    SgtWookie Expert

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    You need to use a 10k Ohm pot, otherwise you will have an impedance mismatch. Line-level audio is designed for 10k Ohm impedance. Using an incorrect resistance pot may result in distortion.

    If you use an audio taper pot but install it backwards, it will seem like you have almost no control over the volume for most of the pot's travel; the volume will suddenly go from almost nothing to almost full blast. If that's the case, you'll need to swap the two outside leads on the pot.

    The center lead is the wiper; it must be connected to the input of the amplifier IC.
     
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  10. frenchie29

    frenchie29 Thread Starter Active Member

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    I think I have the wiring right I used a 10k pot. The thing is, when the pot is barely open I get major distortion then when I turn it clockwise it gets cleaner and the volume increases. Is the distortion cause by not enough audio signal? That's weird I've never heard that before.
     
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  11. frenchie29

    frenchie29 Thread Starter Active Member

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    How can I pad down the gain input? Line level is way too hot.
     
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