Simple project with potentiometer and amplifier

Discussion in 'The Projects Forum' started by RyanBRZ, Oct 22, 2014.

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  1. RyanBRZ

    Thread Starter New Member

    Oct 22, 2014
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    I have a subwoofer amplifier in my car which has a remote gain control that is up front under my dash. The remote gain control is in a plastic box; in this box is a potentiometer soldered onto a circuit board which also has a green LED that lights up when the amp is on. I am trying to cleanly install this control into my dash so I will have just a knob sticking out to adjust the bass gain. The shaft on the pot is really long, and it also is the type where if you press it in, it can get longer or shorter. So I ruled out the possibility of re-using this pot and decided to buy a pot with a short shaft with similar resistance to the pot that came with the amp and wire it up myself.

    I've determined so far that the pot is linear and has 6 pins on it, which from what I read means it's a dual pot typically used for stereo applications where you want to control two separate leads at the same level. The pot is a 20k ohm (reads 19.5 on my DMM using outside bottom pins).

    The wire coming from the amp to the control box is a 6-lead telephone cord. So my next challenge is figuring out which wire does what coming from the amp. I'm guessing there is a ground lead, one or two signal (input) leads, and one or two return leads (output). This amp is a monoblock that outputs to a single channel/speaker while I input two channels to the amp, this is why I say 'one or two' in my previous sentence. I am guessing the LED is powered off of the signal line? or do you think there is a separate voltage lead in the line to power just the LED?

    Does anyone have any ideas on how I can determine each wires purpose? I do not plan to use an LED on the control so I really only need to determine which wires are carrying signal from the amp, and which lines return signal to the amp.

    Here's the pot
    [​IMG]

    Here's the underside, the bottom part is where the telephone jack mounts.
    [​IMG]
     
  2. RyanBRZ

    Thread Starter New Member

    Oct 22, 2014
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    Can I just just do a line continuity test from each pin of pot to each pin of phone jack then duplicate that with my new pot? If i hear a tone then the respective pin is the correct match? I'm using a phone jack to connect my new pot.
     
  3. vu2nan

    Member

    Sep 11, 2014
    43
    10
    Hi Ryan,

    1. There is no question of signal leads coming to the remote gain control.
    2. The potentiometer is used to vary the voltage applied to the gain control pin on the amplifier IC.
    3. Yes, you may duplicate the wiring (centre-pin to centre-pin and end-pins to end-pins). End pins getting interchanged would only result in reversal of direction (CCW instead of CW to increase the gain).

    Regards,

    Nandu.
     
  4. RyanBRZ

    Thread Starter New Member

    Oct 22, 2014
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    The issue I have is determining which pin of the phone jack goes to which pin of the pot. Can I use the continuity test to determine this?
     
  5. vu2nan

    Member

    Sep 11, 2014
    43
    10
    Sure. But make sure you keep the potentiometer in mid-position before doing that!
     
  6. RyanBRZ

    Thread Starter New Member

    Oct 22, 2014
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    Ok, awesome. Do you say that so I get a valid reading on the middle pot pin if the pot is at lowest setting? And to differentiate it from the end pins
     
  7. Experimentonomen

    Member

    Feb 16, 2011
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    This thread will be closed, read the forum TOS to see why.
     
  8. RyanBRZ

    Thread Starter New Member

    Oct 22, 2014
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    Ughhhh ok, I don't understand what I did wrong but whatever . My 1 day membership here was fun..toodles
     
  9. vu2nan

    Member

    Sep 11, 2014
    43
    10
    To get valid readings on all the pins.
     
  10. RyanBRZ

    Thread Starter New Member

    Oct 22, 2014
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    I tested it with pot at 0, half, and full. I am a little confused with the results though, see below.

    At 0, I got continuity as follows (pot pin# : phone jack pin#(s) format)
    1:4
    2:4
    3:4
    4:1,3,5
    5:1,3,5
    6:6

    At half:
    1:4
    2:4
    3:4
    4:1
    5:3,5
    6:6

    At full:
    1:4
    2:4
    3:4
    4:1
    5:3,5,6
    6:3,5,6

    Also, the bottom 3 pins on the pot read correctly as I read in examples where the outside pins always read the full pot resistance and the middle /outside pin read the adjusted value based on rod position. The top 3 pins do not read this way. I thought they should read the same. Any ideas?

    Thanks so much for the help. Mods please be patient with my thread :)
     
    Last edited: Oct 23, 2014
  11. vu2nan

    Member

    Sep 11, 2014
    43
    10
    Hi Ryan,

    Only 'At half ' is valid.
    Potentiometer pins 1,2 & 3 are mounting pins connected to ground through jack pin 4.
    Active pins 4,5 & 6 are connected as follows:
    4:1
    5:3,5
    6:6
    One terminal of the LED goes to jack pin 2 and the other to 4 (ground).

    So the replacement is a single potentiometer, not dual, and is to be connected as follows:
    Middle to jack pins 3 & 5, one end to jack pin 1 and the other end to jack pin6.
    The end pin connections are to be interchanged in case the required rotation (to increase the gain) turns out to be CCW instead of CW.

    Regards,

    Nandu.
     
  12. RyanBRZ

    Thread Starter New Member

    Oct 22, 2014
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    0
    Thank you, Nandu! Greatly appreciated. Ill post my results once the pot arrives. I ordered a single and dual gang just in case, I'm glad I did.
     
  13. vu2nan

    Member

    Sep 11, 2014
    43
    10
    Hi Ryan,

    Any time!

    Regards,

    Nandu.
     
  14. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The owners of All About Circuits has elected not to host discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

    This thread is against the AAC forum rules, Chapter 6, as seen here:

    This can be found in our Terms of Service (ToS)

    Automotive modifications of any kind are strictly forbidden. Therefore, this thread will be closed.

    Please try to understand the reasons behind this action, and feel free to browse and use the forums.

    You might find answers to your questions in one of these forums:

    http://forum.allaboutcircuits.com/showthread.php?t=54400

    Another good forum that shares many of the same membership is http://www.electro-tech-online.com/ . Good luck.
     
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