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Audio Amp

Discussion in 'Electronics Homework Help' started by sdw26, Mar 23, 2011.

  1. sdw26

    sdw26

    5
    0
    Dec 5, 2010
    Hello everyone,

    I wanted some feedbacks/suggestions/corrections/alternatives, or whatever it might be that would help me with my project.

    My project is to build a speaker board.
    I know the basic gist of what to do, but what I am having trouble with is choosing the right chips!
    power supplies i have are : 5v and 3.3v
    I got 8 bits in parallel, V_H = 3.3V
    frequency range : 250Hz to 4.5 Khz

    For the DAC I found two chips, AD7801 and AD7302
    For the OPamp, I found LM4990 (If you know any other op amp chip that works in +5v range please do let me know, also I want an output power of 2W)
    For Speaker I found CMS0361KLX (Link: http://products.cui.com/CUI_CMS0361KLX_Datasheet.pdf?fileID=1113)
    I also found another speaker AS06608PS-WR-R but this needs about 4W of power so i would have to change the op amp.

    I would really appreciate if anyone can tell me if i got the chips right.. Or if anyone could suggest different chips. This is a very small projects, i do not need high performance chips, cheaper the better. All I need is for the speaker to output the sound in the given frequency range and a potentiometer to control the volume.

    Any help appreciated!
    Thank you so much!
    SDW
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    You're not being clear on one particularly important point.

    What is the input signal?

    Is it a digital signal (hence the DAC)?

    Is it serial or parallel (or something else)? (if you don't know, then the source of the signal may help us).

    For an amplifier, low voltages tend to limit your choices, and especially limit your power output. Do you know what impedance speaker you have> or can you spec that out later?

    Tiny, high performance, cheap -- choose any 2. Seriously, you'll find that higher performance devices tend to be more expensive.

    What are you doing this project for? School?
     
  3. sdw26

    sdw26

    5
    0
    Dec 5, 2010
    Thank you for the reply.
    Yes digital signal, 8 bits in parallel.
    Impedence of the speaker I chose is 8 ohms.
    Although the driving load for the opamp I choose is 4ohms for 2 watt supply, I thought I could have an extra resistor in parallel w/ the speaker so the resistance drop down to 4.

    Here is the link so you have an idea of the project http://reaper.ws.binghamton.edu/ctwigg/eece387.shtml
    We are doing the speakerboard part.
    This is a very simple project. I don't need to do anything fancy as long as it does it's job.

    Thank you!
     
  4. sdw26

    sdw26

    5
    0
    Dec 5, 2010
    I'm designing the whole board that would take The parallel bits and output the sound. I have to design the pcb for it. But I can't go any further not having the right chips. It's hard to find a low power op amp that would drive a speaker with the frequency range I need.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    OK, first things first. This is homework help, so I will move it there.

    Excellent. I understand that :)

    Now, you realise that for 2W output, you're going to have to drive the output very close to the supply rails. That will give you very little dynamic headroom, and thus you'll only really be able to achieve 2W on peaks, not on the average of a complex signal. (I note that your project only has to produce sine waves -- and they're as simple as it gets)

    That really doesn't make sense. the op-amp may require a 4 ohm load if it is to DELIVER 2W to a load. Your statement is worded so that it seems like your power supply is rated at 2W.

    Well you could, but that resistor will be turning your output into heat, not sound. Your output will be around 1W max in that case.

    I note the requirement to achieve a stated sound level. You may wish to consider the various variables which will affect that (such as the speaker efficiency) .

    I note the reference to academic honesty in those documents. Please read the rules of our "homework help" section and note that they are there to help you avoid a penalty in your studies.
     
  6. sdw26

    sdw26

    5
    0
    Dec 5, 2010
    Thank you for the reply.
    Well it is my junior design project, cant really consider it as homework.

    I think I understand a little bit more on what to do.
    Yeah the resistor wont do any good like that.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    OK, note that your amplifier doesn't need to operate from 5V. It's only the board which mist be supplied with 5V. You could step it up with a DC/DC converter.

    However you'll get some hints from looking at the demo video on your school's site. It's pretty clear that their demo is not doing that, so you probably won't have to either.

    As for frequency response -- I can't imagine that's an issue. you're producing audio frequency sine waves!

    Go to the digikey web site. Type in "audio amplifier" in the search box. Select the obvious category from the list (it has over 4000 hits). Use the parametric search to narrow down what you need (I selected output powers from just under 2W to around 3W and power supplies with ranges that included 5V at to near the top end). I then end up with over 200 parts that I can look through. Perhaps limiting them to mono would narrow that down even more.

    edit: This is the first hit I see. It may be nothing like what you need, but it does illustrate that parts fitting these specs are not awfully hard to find (nor that expensive).
     
    Last edited: Mar 24, 2011
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    But we do.

    edit: As does your school.

    It's not that we don't want to help you, it's just that we don't want to help you get a grade of zero. I note that a category 1 offence has pretty major implications, and that a category II offence must be even worse.

    We would aim to give you help that doesn't really require you to disclose it in your final submission (but whether it is appropriate for you to do so, we could not say)
     
    Last edited: Mar 24, 2011
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