Tapping speakers -> line out - elementery questions

Discussion in 'General Electronics Chat' started by quicksnap, Jul 22, 2009.

  1. quicksnap

    Thread Starter New Member

    Jul 20, 2009
    2
    0
    Hello all! First post here.. thanks for help in advance.

    I'm looking to rework an older device, a Wulitzer Funmaker organ, to have a 1/4" output, and I have a few basic questions. I'm very new to electronics tinkering, so know that I'm very ignorant.

    I was viewing this article/schematic here: http://www.dairiki.org/HammondWiki/LineOutFromASpinet and it seems to apply to this situation, but the values of components may need to be altered, since I'm unsure if it's an 8ohm speaker.

    So, here are some of my questions.. =)

    What is the purpose of the capacitor in the above schematic?

    What exactly are the power restrictions on Line Level?

    How can I determine what values will need to be used depending on the speaker rating? If I plan to bypass the speaker entirely, or try this on other smaller/larger devices, how could I determine proper values?

    Given that I don't really value the Funmaker too much (it's only $50), is this a decent beginners project? I hope to do this so that I may plug in this organ, direct, to a bigger amp or use headphones and disable the speaker with a toggle. Am I attempting something silly, or is there a different approach?

    Any help is much appreciated. Thanks very much.

    Dan
     
  2. Externet

    AAC Fanatic!

    Nov 29, 2005
    759
    57
    Hello and welcome.

    The capacitor blocks any DC that may be present at the speaker if such unit has DC at its output.

    Line level should be around 1 mW.

    Any value potentiometer will work. A 10 microfarad capacitor should work.

    A better approach is to tap the audio from the volume control of the organ, allows the speaker to be set to any level while the 'line out' level should stay stable at probably the proper level with no addition of circuitry.

    Miguel
     
  3. quicksnap

    Thread Starter New Member

    Jul 20, 2009
    2
    0
    Thanks much! Do you happen to know how I could properly determine the value of the big resistor for different devices, say for instance if I were to tap a smaller unit with a smaller speaker?
     
  4. Externet

    AAC Fanatic!

    Nov 29, 2005
    759
    57
    If you call big resistor to the 1KΩ in the schematic; it is mostly there to prevent an 'excessive' level if the potentiometer is turned all the way 'up' by accident at some moment. Its value is more of a limiting than level setting, and the level at the output jack cannot be calculated as audio program from the speaker has a constantly varying level, besides being adjustable by the unit volume control and the added potentiometer. On a fixed level tone, could be calculated for a given fixed potentiometer position with Ohm's law.

    1KΩ is large enough for higher outputs, and small enough to be able to be compensated with the potentiometer setting in low level outputs.

    Get your multimeter and measure the audio on the AC scale, and see how it gets attenuated with different levels, values and settings.

    Miguel
     
  5. millwood

    Guest

    the capacitor and the variable resistor forms a high pass filter. you want to make sure that they don't cut out too much bass. I usually make sure that they are good down to 20hz.

    so 20=1/(2*pi*r*c) = 1/(2*3.14*20k*c),

    or c=1/(2*3.14*20k*20)=.4u. a .47u cap will do.
     
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