About speaker, amplifier & power supply

Discussion in 'General Electronics Chat' started by onlyvinod56, Nov 12, 2010.

  1. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
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    1
    Hi,
    I have few questions in my mind about audio amplifiers. Here goes...

    1. If an amplifier is mentioned 16W, what is the current required by the IC when driving a 4 ohm speaker. Is it 2 Amps??? (sqrt(16 / 4))

    2. If the current required is 2 Amps, what is the current rating of the power transformer?

    3. A transformer of detail 230 / 12 - 0 - 12, 3 Amp. What is that 3 ampere? Does it belongs to 230v or 12v?

    4. If i want to design a 5.1 amplifier (6 channel) with three ICs (TA 8215 @ 15W / channel), what is the total current required? suggest me the transformer and its ratings.

    5. Is it possible to design a woofer or speaker box with glass?
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    Ugg... You just opened a can of worms.

    Advertised "whattage" and actual wattage have nothing in common. (Except they are numbers)

    As for #5, you can build a speaker enclosure out of whatever material you want. Some materials have better resonant properties when combined with different drivers.
     
  3. marshallf3

    Well-Known Member

    Jul 26, 2010
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    If i want to design a 5.1 amplifier (6 channel) with three ICs (TA 8215 @ 15W / channel), what is the total current required? suggest me the transformer and its ratings.

    If you used all the channels on the three ICs you'd have a 6.0 instead of a 5.1 amp, 5.1 means only preamp out for the subwoofer.

    As to your voltage and current requirements simply look at the examples in the datasheet for a TA8215 then multiply that by three.

    Please note there are hundreds of ways manufacturers specify output power and most make it sound as if you're getting more power than you actually are. A truthful rating for an audio amp is in Watts RMS, all channels driven, into a X ohm load from 20 Hz to 20 KHz with less than or equal to Y distortion.
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    Amplifiers use a lot more power than just their output by geting hot. The power of the heating must be added to the output power.
     
  5. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
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    surprised.... what, can a pre amp drives the 4 ohm, 15W speaker? I thought an amplifier is required.....

    My PC is configured with 5.1 ready.....
    I need six amplifiers for six channels......am i wrong?
    I have seen TL072 based LFE filters on Google. I think i dont need it.....right?

    your single answer confused me alot. Make it clear please.

    AND still i didnt understand what transformer i have to use for this?
     
  6. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
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    ThanQ. so, i can use a glass enclosure.
     
  7. timrobbins

    Active Member

    Aug 29, 2009
    318
    16
    56,

    To get a very simplified understanding, then yes if you dissipated 16W in an ideal 4ohm speaker then yes you would need the amplifier to supply 2Arms.

    If you have 16W flowing out of the amplifier then you need more watts flowing in through the power supply. The datasheet gives you a ballpark internal dissipation within an amplifier of about 12W - so the power supply must provide about 16+12=28W.

    The 3A refers to the 12-0-12V winding's rms current rating.

    Ballpark single power supply power rating to supply 6 amplifiers (ie. 3x TA8215) is then 6 x 28W = 168W.

    The above is all very simplified - and in essence is 'unreal' if you are listening to music.

    Why do you want to use glass? If you want to see the speaker, then there are a number of 'see-throughs' - which I think use a clear polycarbonate (eg. Lexan).

    Ciao, Tim
     
  8. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    ok...

    thanks tim.

    so, what is the current rating? is it 168/12v = 14A????? shocked:confused:



    i dont know about lexan....ok..i'll search for that. ya, i need a see - through...
     
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Glass isn't recommended for woofer enclosures.

    The other thing to keep in mind is that Most of a good audio amplifier is the power supply. No matter what you use for the outputs, if the power supply isn't stiff and capable, the audio will clip and be very distorted.
     
  10. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,750
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    U going to get a big bang for sure if u use glass cabinet for a sub.
     
    Last edited: Nov 13, 2010
  11. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    Thing to remember is to standardize the readings. I assume you are talking RMS power, basic AC stuff. This means you are going to need 2.828 X the DC to handle the peak and peak to peak waveforms (again, basic AC stuff). It is important to compare apples to apples.

    Marketers lie, and ignore basic AC math (probably because they have no clue). When you talk to an engineer or a tech you will be getting real world values, instead of what sounds good so you will buy it.
     
  12. retched

    AAC Fanatic!

    Dec 5, 2009
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    Im guessing you meant a "BIG BANG". ;)

    You WILL need some nice thick, PORTED glass if you want to do that.

    There are many-a-speaker enclosure made from polys.

    Quite easy to construct too. You can get a 4x8 foot sheet of 3/4 inch polycarb and make a clear enclosure.

    Use HIGH quality, HIGH strength adhesive that is chemically matched for poly.

    I would also back that up with some thick threaded fasteners.

    Especially if you are using a long-throw woofer.

    A lot of air needs to be moved. Porting will help with pressures.

    Read about port tuning so you dont ruin the sound, or the speaker.
     
  13. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
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    Thanks for u all.....
    5.1 amplifer: I got three uPC1185h ICs
    power supply: 12V, 5Amp
    speakers: 4 ohm
    woofer: 4 ohm, 15W (small one for my small room) I need to test the woofer with the IC. LFE signal is ready at my PC mother board audio terminals.
     
  14. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    You power supply isn't nearly enough.

    The Datasheet states the 20W output is with a dual 22V power supply, which means a center tap transformer at 5 Amps (less than 1 amp per channel).

    The subwoofer has a built in amplifier, correct?
     
  15. Audioguru

    New Member

    Dec 20, 2007
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    A small woofer produces no bass. a high quality 8" or bigger woofer in an enclosure designed for it goes down to about 50Hz (-3dB).
    A little "woofer" that is only 2" or 3" goes down to about 250Hz so does not prodduce bass sounds.
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    If the woofer is 4 ohms instead of 8 ohms then it needs an amplifier that can drive 4 ohms. The power supply voltage will probably be different.
     
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