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stereo potentiometer question

Discussion in 'Off Topic Threads' started by wireguy, Sep 14, 2013.

  1. wireguy

    wireguy TS Member

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    The left/right speaker control potentiometer on my stereo receiver died on one side. Does the replacement need to be linear or logarithmic? I would think in this application linear would be fine but maybe not. It's 200k ohm.
     
  2. larrystrollo

    larrystrollo Member

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    Linear makes sense to me.
     
  3. Brian in Oregon

    Brian in Oregon Well-Known Member

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    That's a very good question.

    And the answer is, unfortunately, it depends.

    I'm assuming that by "left/right speaker control potentiometer' you mean the output amplifier and not the left/right balance control. The balance control should be linear.

    A little background for volume control: Logarithmic controls work better for audio gear than linear. There are two reasons for this. First, the human ear has a logarithmic curve, so a log pot matches that better. Second, logarithmic pots give finer control at low volume, especially for headphone use.

    So one would think that the manufacturer would simply use a logarithmic pot, right?

    The problem is, the manufacturer may need a custom curve not available in an off the shelf logarithmic pot.

    So what some manufacturers do is use a linear pot and parallel resistors on it to make a custom curve.

    How do you tell this?

    One way would be to carefully look at a schematic to see if there are two resisters paralleling the pot.

    The other would be to measure the pot being replaced. Is it a single pot or are there two that are ganged? Usually a ganged pot is used in older equipment, one for each amplifier or preamp. In more modern equipment with digital control, the pot controls a digital circuit that then controls the amps. If it is a ganged pot, then likely one of them still works, allowing you to measure it. If it is a linear pot, then the 1/4, 1/2, 3/4 and full settings will be in linear proportion to each other. A log pot might be on a log scale or more, but whatever it is, it will not be linear. You'll have to have it removed from the circuit to measure. But you may be able to measure in circuit to see the curve if it had resistors paralleling it. I'll assume you know how to use an ohm meter.

    I've posted a link to a page that does the math for custom log pots using a linear pot, so you can see how using a linear pot in a log application works.
     
  4. wireguy

    wireguy TS Member

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    It's left right balance.

    I can see where the "human ear curve" make sense on volume control, logically, at least from my ignorance of the subject, there's nothing to be gained from logarithmic on left/right. I can also see the possibility of something more going on in left/right control than I'm aware of though.

    This is a 40 year old Technics receiver and it doesn't appear anything but a straight forward pot is being used.
     
  5. Brian in Oregon

    Brian in Oregon Well-Known Member

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    If it's left/right balance, then yes, go with a linear pot.

    The reason is, the center point is "zero" and you would go left or right in a linear line from there.

    If it was logarithmic, the scale would not be balanced from the "zero" or center point. It would have one side get louder suddenly, and the other would take excessive movement.
     
  6. wireguy

    wireguy TS Member

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    Thanks Brian. I should be able to get that locally then.
     
  7. halfmile

    halfmile Well-Known Member

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    Audio taper if the volume attenuator is the culprit. This is most likely 2 controls on one shaft, each controlling the input to the driver sections (L & R) of the amp.

    If you got a schematic when you bought it (common before the 90's) Newark might have an exact replacement.

    A lot depends here on the quality level of the equipment. If it's high end stuff, you may want to send it in.

    Just about everything got to be audiophile quality in the 90's when more IC's and fewer transistors were used.

    In the 70's there were great variations in quality, with Kenwood, Sansui, Sony, and Pioneer being the good stuff and the 23 percent better than that cost twice as much.

    there was a lot of crap being sold then too.

    HM
     
  8. wireguy

    wireguy TS Member

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    OK, I put a new pot in and the left side still won't work. In the trash it goes. I've been down this rabbit trail before.
     
  9. grntitan

    grntitan Well-Known Member

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    Time for a new stereo. They have changed a bit in 40 years. For one, they are a 1/4 the size. Two, they don't have 8 Track players. LOL
     
  10. Brian in Oregon

    Brian in Oregon Well-Known Member

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    What is the make and model of the receiver?
     
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