Project: Portable active speakers (2 X 0.3W)

Discussion in 'The Completed Projects Collection' started by cumesoftware, Jun 11, 2007.

  1. cumesoftware

    Thread Starter Senior Member

    Apr 27, 2007
    1,330
    10
    This is a basic amplifier circuit for beginners. These active speakers are to be portable, Lo-Fi, and provide up to 0.3W of RMS power for each channel. This circuit can be powered using 4 AA batteries of using a wall adaptor (6V DC, 150mA minimum). S1 serves to choose power from batteries or from the adaptor, D is to protect from reverse polarity from the adaptor. D does not protect from reverse current from batteries, since a normal rectifier diode would cause a voltage drop, reducing the functioning time in case of the circuit being fed using 1.2V batteries.
    The overall gain of this circuit is 26dB. To compensate poor bass response from the speakers, this circuit has a 6dB "bass boost" (treble attenuation actually, >1KHz).
    FTE2 corresponds to the right channel. FTE1 corresponds to the left channel and is installed in a separate box, apart from FTE2 and the circuit. The connection between FTE2 and the amplifier circuit can be made using a standard RCA/RCA plug.

    View attachment CSA300mW.pdf
    List of components (version 1):
    B1-4 - 1.2V (Ni-CD or Ni-MH) or 1.5V (carbon-zinc or alkaline) battery;
    C1 – 680µF electrolytic capacitor (10V) (typo);
    C2/3 – 100nF polyester capacitor (63V);
    C4/9 – 2.2µF electrolytic capacitor (6,3V);
    C5/10 – 47µF electrolytic capacitor (10V);
    C6/11 – 33nF polyester capacitor (63V);
    C7/12 – 47nF polyester capacitor (63V);
    C8/13 – 220µF electrolytic capacitor (10V);
    D – 1N4001 rectifier diode (D1 in the diagram, my mistake);
    FTE1/2 – 2-1/2 inch speaker (8Ohm, 0.5W);
    IC1/2 – LM386 audio power amplifier;
    R1 – 10K double gang potenciometer (10% tol., 1/8W);
    R2/5 – 4,7K carbon resistor (5% tol., 1/8W);
    R3/6 – 15K carbon resistor (5% tol., 1/8W);
    R4/7 – 10Ohm carbon resistor (5% tol., 1/8W);
    S1 – SPDT switch;
    S2 – SPST switch.

    View attachment CSA300mW(2).pdf
    List of components (version 2):
    B1-4 - 1.2V (Ni-CD or Ni-MH) or 1.5V (carbon-zinc or alkaline) battery;
    C1 – 680µF electrolytic capacitor (10V);
    C2/3 – 100nF polyester capacitor (63V);
    C4/9 – 2.2µF electrolytic capacitor (6,3V);
    C5/10 – 47µF electrolytic capacitor (10V);
    C6/11 – 33nF polyester capacitor (63V);
    C7/12 – 47nF polyester capacitor (63V);
    C8/13 – 220µF electrolytic capacitor (10V);
    D – 1N4001 rectifier diode (D1 in the diagram, mistake again);
    FTE1/2 – 2-1/2 inch speaker (8Ohm, 0.5W);
    IC1/2 – LM386 audio power amplifier;
    R1/6 – 1,5K carbon resistor (5% tol., 1/8W);
    R2 – 10K double gang potenciometer (10% tol., 1/8W);
    R3/7 – 1,5K carbon resistor (5% tol., 1/8W);
    R4/8 – 15K carbon resistor (5% tol., 1/8W);
    R5/9 – 10Ohm carbon resistor (5% tol., 1/8W);
    S1 – SPDT switch;
    S2 – SPST switch.

    Notes:
    - C1 is only for improving power supply filtering. Its capacitance values is the half of the needed for a filtering with 20% ripple.
    - To avoid motorboating, C2 and C3 should be kept close to the respective amplifiers ICs (respectively IC1 and IC2).
    - Version 2 has a smaller gain to avoid distortion.
     
  2. Yeasina

    New Member

    May 4, 2008
    2
    0
    Thanks This Is A Nice Projects , But I Need A Hifi Speaker System
     
  3. cumesoftware

    Thread Starter Senior Member

    Apr 27, 2007
    1,330
    10
    Try the Quatour project. It has a max THD of 0.2%, but the average is around 0.1%. It is not considered Hi-Fi, but I've tested it myself and it is quite good.

    This is a project aimed for portability, and not for fidelity.
     
  4. Andrew Leigh

    Well-Known Member

    Sep 8, 2008
    92
    2
    Hi,

    I know this is old but is of interest to me. Two questions?

    Could my i-Pod drive this puppy?
    Could I feed 12V into this rather than regulating down to 6V?

    Cheers
    Andrew
     
  5. cumesoftware

    Thread Starter Senior Member

    Apr 27, 2007
    1,330
    10
    Hi Andrew,

    Thanks for your interest in this project.

    You i-Pod can drive the speakers with no problem. The amplifier was designed so the input accepts the standard voltage range used for driving headphones.

    As for using 12V from an unregulated power supply, it is a bit risky if you want to use the standard LM386 (LM386N), since its maximum rated voltage is 15V. You should use the LM386N-4 instead, since it will support voltages up to 22V. As your C1, you should use a 680µF 25V capacitor instead of the recommended 680µF 10V capacitor.
     
  6. Andrew Leigh

    Well-Known Member

    Sep 8, 2008
    92
    2
    Hi,

    thanks for the response.

    I want to use this on my motor boat so the feed will be from the outboard motor battery. As the battery acts as a large capacitor surely that will be smooth enough? Should I regulate this down to 9V with a 7809?

    I happen to have two ideal speakers at 2W, how can I squeeze a little more output from this circuit? Say 0.75 to 1W.

    Thanks
    Andrew
     
  7. cumesoftware

    Thread Starter Senior Member

    Apr 27, 2007
    1,330
    10
    Yes you can, with no problem.

    You can eliminate R1 and R6, since they limit the input volume. They are only required for 6V operation, since they prevent distortion and clipping. You can also raise the gain a bit by using a capacitor. Just check the LM386 datasheet.

    Since you are planning to use this on a boat, you might be interested in the "Multimedia active speakers (2 x 4W)" project or in the "Quatour" project. The later is based on the first, but it is much better, as it has a PCB for printing. You can drive these speakers directly with 12V. The box diagrams are still missing from the "Quatour" project, but they are already planned and dimensioned. It is a matter of doing the drawings.
     
  8. Andrew Leigh

    Well-Known Member

    Sep 8, 2008
    92
    2
    Hi,

    I am now posting in the "Quatour" thread. See you there.

    Cheers
    Andrew
     
  9. cumesoftware

    Thread Starter Senior Member

    Apr 27, 2007
    1,330
    10
    Hi Andrew,

    Thanks for your feedback and for your interest in both projects.
     
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