Audio amp Questions - Beginner

Discussion in 'The Projects Forum' started by veneficus5, Oct 26, 2010.

  1. veneficus5

    Thread Starter New Member

    Mar 8, 2010
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    I am wanting to build a stereo amp to power a set of speakers for my first project. I want it to be as inexpensive and as easy as possible. How well it sounds is secondary. I am looking for something under $60. Maybe under $100 if it looks nice or sounds nice as well.

    I have done at least 5 hours of relevant reading, but I think it is finally time to talk to other real people. I just can't seem to figure out what I need. I am a noobie.

    What I want (or what I think I want): Stereo amp to have dual RCA input or 1/4" stereo input that outputs to two 8 ohm speakers.

    I would like to plug a dynamic microphone ( mic is 1/4" output) into it and use it as a PA. I would also like to play music in it from an mp3 player (I'd just use an 1/8" converter). My speakers are both 8 ohms and are rated at 100w each(??). Will a 75w or 50w amp power them or does the 100w rating mean I have to have that much power for some matching purpose? I'm assuming 100w is the maximum input or max rms input, but I really don't know.

    So again, I want something inexpensive and easy to build. I found this kit called Non-Inverting LM3886 Stereo Kit - $70- http://chipamp.com/lm3886.shtml. Would this be a good one to try? I also looked through the projects on this site involving the lm3886 and lm3875. They seemed to be the cheapest option.

    I shouldn't have too many issues putting the electronics together: I can solder stuff to the PCB. Is there generally troubleshooting involved once the circuit is constructed or should they work the majority of the time?

    Finally, I need a little help on the case/chassis. What kind of tools do I need to drill into metal? It seems like this part is going to be the hardest. Can I get a pre-drilled case somewhere and then use screws to connect things up?

    I have put a priority on learning safety. I'll only work at a ground fault station, I won't build with power connected. I will use one hand if there is a risk of touching a capacitor. I will wear shoes while working. Anything else I should watch for?

    Thanks so much!
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    So basically. U want to built a 100 dollar amp for ur speakers
     
  3. veneficus5

    Thread Starter New Member

    Mar 8, 2010
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    right! I would actually rather buy an amp, but I couldn't find anything for a decent price ($100 or less). After reading about the gainclones and LM3875 stuff, I wanted to try building one.
     
  4. R!f@@

    AAC Fanatic!

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    Do u have experience on building electronics stuff?
     
  5. veneficus5

    Thread Starter New Member

    Mar 8, 2010
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    a little bit with breadboard stuff. I've done some 7seg display stuff, op amp stuff, bjt and mosfet stuff. I have no experience with soldering power devices. I'm assuming I just make big solder joints, use appropriate gauge wire, and throw a heatsink on the chip with some thermal paste?
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
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    I'd definietly go with a kit so you get the PC board.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Keep in mind that this kit includes the amp and supply boards, but does not include the transformer in the list of parts. You will still need to buy an adequate transformer. They are not cheap.
     
  8. veneficus5

    Thread Starter New Member

    Mar 8, 2010
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    I thought they were cheap? Isn't a transformer essentially the small box that plugs into the wall with two prongs? Can I use a spare one of those if it's the right specs? Or is that the problem... It won't be the right specs for this application?

    What kind of transformer would you recommend?

    Thanks!
     
  9. R!f@@

    AAC Fanatic!

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    Transformers used for power amps aren't cheap buddy.

    The type and power rating of the transformer solely depends on the amplifier.
     
  10. veneficus5

    Thread Starter New Member

    Mar 8, 2010
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    I need a transformer with dual secondaries. Preferably 2x(18-30)vac. 160 to 320 VA.

    I also read something about fuses on transformers? Something about 2A slo blos was mentioned in the guide. It didn't elaborate. Do these fuses come with the transformer?
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    No fuse comes with anything. U have to buy them.
    And the VA rating depends on the amp power.

    If U do not show the specs of ur speaker, we cannot comment on a what u will need accurately.
     
  12. veneficus5

    Thread Starter New Member

    Mar 8, 2010
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  13. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The fuse will not be included with the transformer.

    As mentioned, toroidal power transformers cost a good amount.

    Do you have a preamp? To switch input sources, control volume, bass, treble, etc?

    The amplifier in the link above is just that, an amplifier, with line level input, and output for speakers.
     
  14. veneficus5

    Thread Starter New Member

    Mar 8, 2010
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    no I don't have a preamp. I guess I am looking at building one of those too? Thanks for the insight.

    All I have are A the speakers with +/_ input and B a microphone with 1/4 output. I need to somehow fill in the gap from A to B
     
  15. R!f@@

    AAC Fanatic!

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    Wow!! Did u say u have a pair of those and u got 'em for 12 bucks.

    No way!

    If I am not wrong those speakers can deliver pretty powerful sound.
    A transformer that cud drive an amp tht can drive those speakers would cost u atleast I'll say 50 bucks or more.
    Another thing is tht the IC's u had in mind won't come close to the power limit of ur speakers.
    What u need is 300W Amp made from discrete parts. IC's cannot deliver that kind of power those speakers.

    U are way over ur head, I think.
     
  16. R!f@@

    AAC Fanatic!

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    U will be better off if u buy a kit amp.

    Everything put together, meaning transformer, caps and amp module plus a casing, will cost u more than 100.00
     
  17. veneficus5

    Thread Starter New Member

    Mar 8, 2010
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    <snip>. If I had any idea the amp was the most expensive part, I wouldn't have bought the speakers lol. I didn't think DIY would be the cheapest method either, but it seems like it is? Either that or cheap audio amps don't exist. I'd be better off buying a pair of active speakers than buying an amp to power my existing speakers it seems like.

    What to do what to do... :confused::confused:
     
    Last edited by a moderator: Oct 27, 2010
  18. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Depends on the quality of sound you'd like at what volume.

    A decently built 10W amp will sound a lot better than amps advertised as 50W/4 channels. Simply because there is more headroom on the 10W amp, and the ratings aren't inflated (10W is RMS, the 50W is peak).

    If you don't mind clipping and distortion once the volume is over 30%, get an integrated speaker/amplifier. If you want to listen to music without it being painful, It does take a bit of money. You don't need to spend $500, but $250 is about right.

    Even at the $200 level, you need to be fully aware of what you are getting. Many manufacturers add a lot of bells and whistles to the preamp side to make up for a poor amplifier (usually skimped in the power supply for it).
     
  19. R!f@@

    AAC Fanatic!

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    How much are u willing to spend and how well do u think u can assemble a circuit
     
  20. Wendy

    Moderator

    Mar 24, 2008
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    We say this a lot, but what part of the world are you in? Without that it is a guess what you can get.

    You'll not old hands have put it in their profile, where it is displayed for all to see. You don't need to narrow it down to a city, but a country is nice to know. Different areas have different parts sources.

    It's been mentioned, but adverts inflate specs a lot (misstating them entirely many cases). By building your own, you get honest specifications, which are probably better than the lies you get commercially.
     
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