ALPS Potentiometer with 4 Terminals

Discussion in 'General Electronics Chat' started by lubnaan90, Mar 28, 2012.

  1. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
    196
    2
    Hello to all the Members,

    Here is a Potentiometer which i Intend to use as a Volume control for my Pre-Amp based on LM1036 Chip. It is a 50K ALPS Motorized pot, since it has four terminals, it is unusually strange for me because i got my hands on such type of POT for the first time

    I have attached the pictures of the Motorized POT with this post.

    Now to the Trouble, When i use a Usual 50K Pot (The one beside the ALPS pot in the picture), the volume control seems to work fine, the sound level gradually rises as i rotate the Pot control. However now when i replace the usual pot to ALPS pot, the volume control acts differently in such a manner that until 50% rotation of the ALPS POT there is No Sound at all, the sound level rises gradually only after 50% rotation of the pot. I dont Understand why this would happen even though both of the Pots are of the same value (50K).

    The connections i do on the ALPS pot is same as i do on the usual pot, about the fourth Pin, i keep it Disconnected.

    I will deeply appreciate any Kind of Help.

    Thank you & Best Regards,
    SLAK
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    have you tried measuring resistance between the pins? That should tell you what is what.. Or look for the datasheet of that particular pot.
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,437
    3,360
    Pots come with different taper, linear and log. Pots for audio applications are log.
    Turn the pot to halfway and measure the resistance from the center to the two ends.
    This will tell you if the pot is linear or log.
     
  4. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
    196
    2
    Half way resistance shows 6.7K
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,437
    3,360
    Measure halfway resistance to both terminals.
    You should have two readings that add up to the total resistance.
    If one reading is 6.7K then I assume that is a log taper.

    You have two different pots. Compare the readings of the two pots.
     
  6. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,007
    1,530
    Wouldn't the extra terminals be for the motor?
     
  7. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
    196
    2
    The same readings with the second POT :-(
     
  8. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
    762
    Where that pot comes from?

    It happened that in the last weeks I disassembled 6 desktop audio amplifiers for PC (and repaired 4 of them). ALL had defective pots from "just noisy" to "disastrous". The one I had in my personal PC acted like yours.

    Move to a new one and end of the story. Life is too short.
     
    Last edited: Mar 29, 2012
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