Amplifier Schematics

Discussion in 'OT Technology' started by canadam, Mar 2, 2004.

  1. canadam

    canadam Guest

    Does anyone have schematics/plans to build a amplifier for a car stereo ?
     
  2. 04

    04 Guest

    What type of amplifier are you looking at building?
     
  3. canadam

    canadam Guest

    just something to power 2 10'' subs
    not cause im too cheap to buy one, but i think it would be fun
    doesnt have to be 2 channel even, i would, and would prefer to build 2 one channel amps, is there ways to change the power they produce ?
     
  4. 04

    04 Guest


    You are going to have to be more specific about what kind of amplifier you want. ie Do you want a class A, A/B, D, T, etc? How regulated does the power supply need to be? What kind of load are you going to be presenting it?

    And yes, there are many ways to change the output power.
     
  5. canadam

    canadam Guest

    wow... i didnt know there was so much involved ... can you tell me the difference between the classes ??

    i havent decided on subs

    wow, i thought this was gonna be easier ! haha
     
  6. 04

    04 Guest

    Well class A has its output transistors always conducting and there is always current flowing through them. Infact, often there is much power flowing through them at idle as at full power!!! They are incredibly inefficient and are a very poor choice for car audio. HOWEVER, they are the most linear of all the amplifier classes.

    Class B has two sets of output transistors. Once set is conducting the negative waveform and the other set conducting the positive portion of the waveform. This is much more efficient than class A operation, BUT, because the current transfers from one set of transistors to another, you have a slight idle period of time (because it takes .6volts to get a transistor to conduct), and because of this you get crossover, or notch distortion. It sounds pretty bad, and because of this, class B amplifiers are rarely used for audio.

    Class A/B is by far the most popular class. They are rather efficient like class B amps, but don't have the crossover distortion. They overcome this by having a constant current (called a bias current) running through them so that there is no period of zero conductance in the output transistors.

    Class D is a design that uses a a pulse width modulated suppply (pwm) for its output. (note that the power supplies in all the other car amps are pwm) The pwm supply works by having the supply either run at full output or zero. The advantages of this is that a transistor that is either fully conducting or resting wastes little power. The pwm switches extremely fast, much higher than the audio spectrum. The output is then passed through an inductor which removes all the high frequency switching artifacts. Your output is a clean sinewave just like the other designs. HOWEVER, the disadvantage of class D amplifiers is that you have to have an extremely high frequency switching supply in order to play up to 20khz. This can cause problems with interference with things such as AM radio recievers.

    Class H has a multi-voltage power supply rail which I believe is used when the amplifier is at higher output powers increases rail voltage so that power output remains linear with decreasing load impedence. But im not totally sure on that.

    Class T is like class D but full range (has a higher pwm switching frequency) but I think it may have a totally digital control system. Again I'm not sure on this one either.

    This site has more indepth explainations: http://www.bcae1.com/ampclass.htm
     
  7. flynfrog

    flynfrog Cool isnt Cheap

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    www.aussieamplifiers.com

    im looking at building one of these

    for free electroncs sample them make a fake company

    i got a few thousand dollars worth of fets from ON semi conductor
     
  8. canadam

    canadam Guest

    those aussieamplifiers are heavy !

    i want to build something that runs off the 12 V in my car, hits a peak of 250 watts and runs abouts 100 watts rms. I'd like to set it up with rca inputs, and speaker level outputs.

    like i said - one 2 channel, or 2 one channels, i dont mind
     
  9. flynfrog

    flynfrog Cool isnt Cheap

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    those could run off of 12 volts jsut need a little differnvt power supply
     
  10. 04

    04 Guest

    A little different? ;)

    You'd have to completely redesign the power supply. The power supplies for the aussie amps are (at least the ones I saw) linear, and the car audio ones are gonna have to be switch mode.
     
  11. canadam

    canadam Guest

    So basically, noone has a basic "this amp would run a couple subs nicely" type answer then ? haha

    Thanks anyway guys
     
  12. 04

    04 Guest

    Uh not really, building an amplifier even from someone elses design is quite an undertaking.

    Ive only built one amplifier and it was quite a simple build. It had less than 30 parts total for 2 channels (it was a headphone amp). It works fine, but higher power amplifiers will typically be quite a bit harder to build.

    If you want a fun project to tackle, do a google search for "gainclone amplifier" it is a relatively easy to build op-amp based amplifier that has a pretty easy construction. However, it is not a car audio amp, nor does it put out much power.

    If you are building an amplifier simply to save money, I'd advise against it. :)
     
  13. D21X

    D21X Ownz JOO

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    yea im learning about amplifiers in my ECE 342 class and holly shit is it a biatch to learn all the crap that goes on!!!!
     

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