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help with volume control circuit

Discussion in 'General Electronics Discussion' started by DaveParker, Apr 28, 2012.

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  1. DaveParker

    DaveParker

    4
    0
    Apr 28, 2012
    Sirs,

    I have an Ipaq which has an earphone out 3.5mm socket
    I wish to put a volume control between the Ipaq and my amplifier.

    Would it be OK to use a 10k log potentiometer?
    If so should the high ohmy end go to earth?

    Sorry for my non-tech speak ... as you may guess ... I am not too well-up on all this stuff.

    Any advice you can give would be most helpful.

    I have read somewhere that if it has to be a 100k log pot, then I could use a 100 lin pot with a 16k resistor strapped from earth to the slider.

    If anyone could point me to anywhere which would give me a baxendall tone circuit with volume control included as well I would be forever grateful. ... I can't find one anywhere.

    Sorry if I am wasting your time.

    regards
     
  2. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    Never heard of a ipaq.

    A 10k log potentiometer would be OK to put across tha output of your device. The output should be taken from the slider and ground.
    If you get the pot the wrong way round, the volume will change very fast at one end of the control.

    I Googled Baxandall and got a diagram of his filter from duncanamps.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    I think he meant an iPack.

    [​IMG]

    It is described as

    It also has an option to display the amount of lunch money in the backpack so that bullies don't unnecessarily target poor kids.

    If his device has a typical output (for headphones etc) and your amplifier has a reasonably high input impedance, then the 10k pot should be fine as suggested above.

    However you might also want the hack which shows your lunch money balance always at zero. :D
     
  4. DaveParker

    DaveParker

    4
    0
    Apr 28, 2012
    Thanks folks.

    I have found the passive Baxendall circuit, but it doesn't show a volume control,.. none of the ones I have found thus far, do show one.

    Can I assume it just straps on after the slider and earth of the volume control output?
    Should I use a capacitor in ether, or both of the input and output of the volume control, and if so, what values would be recommended?

    The iPAQ is an old Hewlett Packard handheld PC, running Pocket Windows operating system. This allows me to run Windows Media to get the required output to my earpiece.

    I do appreciate your help ... thank you
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    Care to post a link to what you've found? I will be easier for us to take a look that way.
     
  6. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    Looking at the duncanamps site, it appears that the tone control should be fed with a low impedance. You have this.
    The circuit should feed into a high impedance, there are components for 1M or 2.2M. You could try a 1M log pot but will need an amplifier with a high input impedance, do you have this?

    I do not think that input and output capacitors will be necessary.
     
  7. DaveParker

    DaveParker

    4
    0
    Apr 28, 2012
    Thnaks folks.

    The URL I was looking at was
    http://www.41hz.com/forums/content.php?279-Passive-tone-control

    It describes itself as
    ######################
    Simple tone-control circuit. Low + Highs. Baxandall type.
    No active components: simple, always works, with any amp !!
    And very effective!
    #####################

    Sounded good to me!

    I was wondering about where to put the volume control, and thought it should probably go in before the tone circuit.

    I am going into the 1/4" input jack of a Marshall MG3dfx amplifier.
     
    Last edited: Apr 29, 2012
  8. davenn

    davenn Moderator

    13,866
    1,958
    Sep 5, 2009
    OK also I hope you realise ... as the output of the laptop will be stereo, you will need dual supplies ?

    anyway here's that tone control cct modified to include a vol control this is ONE channel ONLY :)

    [​IMG]

    a 50 KOhm log pot would prob be ok for the volume ( you need a dual pot!!)

    cheers
    Dave
     

    Attached Files:

  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    Thanks.

    The most important thing to note is that the output is relative to a 20db attenuation of the input signal. You need at least 20db of gain to bring your signal back up to the same level.

    It has an input capacitor already, so that would not be needed. As an entirely passive circuit, the output will not benefit from an additional capacitor.

    To help reduce noise, you might want to ground the case of the pots, and probably house the entire thing in a metal box.
     
  10. davenn

    davenn Moderator

    13,866
    1,958
    Sep 5, 2009
    True true ... would not just turning up the output of the laptop make up for that ?

    good thought, I neglected to comment on.... also use decent twin screened lead between laptop output and tone/Vol controles and also from there to amplifier input

    D
     
  11. DaveParker

    DaveParker

    4
    0
    Apr 28, 2012
    Thank you , all of you.

    Not what I was expecting at all. So well worth me asking your advice, for which I am very thankful.

    I am only concerned with mono, so dual pots/circuits will not be required.

    Interesting about the gain loss ... perhaps I should consider an active circuit, but that means running power, or using a 9volt battery, I expect.
    Any further advice would again be appreciated, especially if it was linked to a circuit that an idiot could build.

    P.S. ... I was just thinking ... my iPAQ has a 5volt plug available, could I run something from that .. it is rated at 1amp

    PPS this is the iPAQ device I am using ..

    http://www.amazon.com/HP-iPAQ-2215-Pocket-PC/dp/B00009RL1X

    except mine is about 6 years old now!
     
    Last edited: Apr 29, 2012
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