Forgotten connections

Discussion in 'The Projects Forum' started by cockney, Feb 7, 2014.

  1. cockney

    Thread Starter New Member

    Mar 6, 2013
    2
    0
    Hi all,
    I took a small amplifier circuit board out of something that was being thrown away and probably almost instantly lost what wrote down regarding what the wires were connected to
    In the attached image you can see a circuit built around a jrc 4580dd.
    The strip of wires that you can see are labeled as the following...
    Cont
    -15v
    +15v
    R
    G
    L

    So I get the +/- 15 volts is my power in and R & L are for left and right speakers ?

    Am I right in assuming G is ground and cont would run to the unocupied lugs on the left and right speakers.

    I want to use this to build a little portable amp to plug my phone into I have the case design in wood all sorted but I am at this little bump and would really appreciate some help with the amp. This is my first project and ultimately want to build my own amp to fit the case probably a bit more powerful than what this circuit is capable of but im reading the jrc chip is a rather capable bit of kit, is this correct ? Also where does a ground go in a wooden case? I only ever see them screwed to a metal clip attached to a metal case, does this become void ?

    Thanks for any help especially as a lot of this is probably really simple to some, I have forgotten pretty much everything bar ohms law from my electronics training 25 years ago as its a field I never went into but now need a hobby due to an illness that requires long periods of sitting around ignoring pain.

    Cockney
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,730
    759
    R,L are in the signal inputs with respect to G
    ±15V are supply with respect to G

    G is ground used for supply and signal and is common to input, supply and to speaker as well.

    There is one more pin {CNTL}. I presume this is the control pin and might or might not be used.
    Possibility is that it is the mute pin or enable pin to switch on the IC
    Need to see the data for details.

    I believe 500mA supply is enough to power the chip.

    Wooden case might or might not be suitable depending on the amp sensitivity.

    Metal case are grounded ( connected to G ) to eliminate external interference .

    You can use a wooden case. Use foil to cover the internal and ground it. Proper PCB mount is necessary to avoid shorts or PCB touching metal ( foil ) in metal housing.
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,730
    759
    The data I got is NJM4580

    I believe it is the same chip.

    And yes it can drive headphones but not low Z speakers.

    What I said about 500mA might be overkill, you can be good at lower current I believe.

    It is a preamp so I think a metal case would be needed and some shielding is necessary.

    CNTL is not part of the chip. It could be another circuitry to mute the external speakers when HP is plugged in. So I think it is an output.
    Leave it alone and check for sound.

    Remember not apply POWER in reverse cause you might blow the chip
     
  4. cockney

    Thread Starter New Member

    Mar 6, 2013
    2
    0
    Thats great thank you for your help.
    So it looks like the JRC chip isn't up to much amplification then. I took it out of something with a mic input and the circuit has a volume and balance control but I don't think it was a headphone amp.
    Has anyone got any ideas of how to better utilize this chip if i was to remove it from it's current circuit ?
    If not i may keep it for a later project as it seems its highly sought after in guitar distortion pedals.
    I would rather build this little amp for my wife though she likes the look of the external case :)

    Thank you for your current and hopefully future input

    Cockney
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,730
    759
    This is not the case. It cannot directly speakers but headphones, no problem. Audio level will be enough.

    Then it is wired as a standard Preamp to amplify low level signals. It might not be configured to drive low Z. Like headphones.
    Need to study how the circuit is laid out and compare it to the data sheet.
    With a few changes it might be possible to drive a headphone.
    Like input resistors and some other parts like capacitors.

    If you remove it or not, The chip can be only be used for OP AMP based projects. Mainly it is designed to operate for Audio frequencies.

    Distortion Amp is different. But I'm not familiar with guitar amps as I have not attended such units.

    You wanna use this IC for an amp for your wife.
    What do you wanna drive. Speakers ?
     
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