Required parts to build a stereo amplifier?

Discussion in 'The Projects Forum' started by kingkona, Aug 27, 2016.

  1. kingkona

    Thread Starter New Member

    Aug 19, 2016
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    Hello,

    I am interested in learning electronics and love audio systems. My goal is to take a project-based approach to learning electronics. Hopefully, backing into electronics from a high level to a low level by studying the components will prove effective. If I'm setting myself up for failure, please let me know (I appreciate constructive criticism). I'm decent at soldering, but my skills with high density, tiny components is limited.

    I did some research regarding the required components for a stereo, but I'm not certain if I have everything. Online vendors assume a certain degree of knowledge (which I don't have) about the other components such as power supplies and transformers. I have inquired with various vendors and either did not getting a response or they don't know what's required to build a complete system (which seems strange). I'm hoping I can get feedback on my parts list and anything I may be missing.

    My ideal stereo system (e.g. a boombox) would include multiple inputs such as a CD Player, Bluetooth for streaming and USB interface for mpeg files. Below is a components list that seems to be favored by many on the internet given the sound quality and low cost.

    Other than speakers, does it look like I have everything to build a basic stereo with an external input (e.g. CD player)?

    -- Qty 1: Non-Inverting LM3886 kit (assume a kit that includes all parts - Res., Cap., Amp, etc.)
    -- Qty 1: Power supply kit (again, assume a kit that includes all parts - Res., Cap., diodes, etc.)
    -- Qty 1: AC inlet IEC Socket
    -- Qty 1: Alps RK27 100KAX2 Potentiometer and PCB for Volume Control
    -- Qty 1: Grayhill Selector Switch + PCB
    -- Qty 2: Speaker Binding Post Pair
    -- Qty 2: RCA Jacks - Chassis Mount
    -- Qty 2: Terminal Blocks to connect power supply (may be included in PS kit above)​

    I believe I need a power transformer, correct?

    Can this system be run off of batteries (for a portable system)? If so, any suggestions on what I need (e.g. rechargeable battery types, etc.)?

    I'm assuming that I will need crossovers for my speakers, correct? Any suggestions?


    Thank you for your help.
     
  2. #12

    Expert

    Nov 30, 2010
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  3. kingkona

    Thread Starter New Member

    Aug 19, 2016
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    Thanks for the reply and information #12.

    Let me take a step back. Rather than listing parts, perhaps a better approach would be to ask what are the basic required components to build a stereo system (excluding speakers). Naturally, numerous options exist and I’m sure the universal answer of “it depends applies.” However, please assume the following is based on a class D amp with dual woofers and tweeters, AC power only and nothing fancy like Bluetooth or a USB interface.

    1. 2-channel amplifier kit with PCBs and components
    2. Power supply (with terminal blocks to interface power wires)
    3. Power transformer??????
    4. AC inlet socket for power cord
    5. Volume control (i.e. potentiometer)
    6. Selector switch for various inputs
    7. RCA jacks to attach external components
    8. Speaker binding posts to attach speakers

    Regarding Q3 above, is a separate power transformer always required in addition to the power supply? (I’ll worry about sizing it correctly later).

    I have already done some research and the parts listed in my original post are available in kits. I have seen the Instructables page before and it has served as a good reference guide. I decided not to follow that plan for a few reasons. First, it is my understanding that a class AB amp is relatively power inefficient. Second, I’d like to build a dual-woofer system. The LM3886 system is a class D amp (higher efficiency) and seems to be held in high regard.
     
  4. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    The LM3886 isn't class D.

    And yes, a transformer is a necessary part of a linear mains to DC power-supply.
     
    Last edited: Aug 27, 2016
  5. BR-549

    Well-Known Member

    Sep 22, 2013
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    I would start off small and no ac power. And unless you are willing to study, go with audio ic chips, not discrete components. You can find sample circuits on data sheets and application notes.

    Build a small stereo audio amp with 2 small speakers off a 12 volt dc supply. Use your computer aux line out for a signal source.

    Get something like that going.....and then decide how far you want to go.
     
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  6. #12

    Expert

    Nov 30, 2010
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    There's a thousand ways to go about this. My first recommendation is to work backwards.
    You might start with the Sound Pressure Level you want to produce because that's the very last thing that happens.
    One less would be the speakers you want to drive.
    From there you find the power you need.
    From that you find the voltage and current you need (the power supply).
    Working backwards from the output stage you find the gain you need in the pre-amp.
    Then there is the option of a tone control stage and what is called a recovery stage to boost the voltage back up after the tone stage.
    In other words, do the math first.
    After you have the block diagram with the gains figured out, you get down to the nitty gritty with resistors, capacitors and frequency response.

    Right now, you look like you started in a hardware store and hope all the parts get along with each other.
    If you've done this before, intuition and experience go a long way, but it seems you don't have much experience, so math is the way through the woods.
     
  7. kingkona

    Thread Starter New Member

    Aug 19, 2016
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    Thanks to everyone for your feedback!! I will be taking a step back and go about this project using a more gradual approach. I'll also stay away from AC power initially.

    Depending on what route I take, I'm sure that I'll have additional questions. Regardless, I'll report back on my results in hopes that it'll help another newb like myself ;).

    Thanks again!
     
  8. #12

    Expert

    Nov 30, 2010
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    An afterthought...
    This place is populated with some serious nerds. When you say you want to do an audio amplifier, a whole encyclopedia of options flash before my eyes. If you said you want to put 10 watts through some 8 ohm speakers, hard answers come quickly. Hit us with some numbers.
     
  9. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    Unfortunately, you really can't go to the electronics distributor (e.g. Digikey) and expect to come back with all of the parts to build a stereo amplifier.

    You can, package or put something together from mini-kits.

    Here http://leachlegacy.ece.gatech.edu/lowtim/ is an example of an amp that I used as a reference design with changes that I saw appropriate. It is a really nice amplifer.

    To bad, this http://www.ilpelectronics.com site is not up and running. Their modules are potted.

    To give you an idea of how weird you can go, here is just a passive attenuator: http://jos.vaneijndhoven.net/relaixedpassive/index.html or "volume control".
     
  10. wayneh

    Expert

    Sep 9, 2010
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    I think a better and more methodical approach would be the one followed by so many of us here. Get a breadboard and hookup wire, a wire stripper, some component collections (including a bunch of resistors, various capacitors, diodes, transistors, etc.). Start using your stuff to build simple, battery powered circuits. Really simple, like transistor switches, LED flashers, and so on. Work through the basics.

    The first thing most hobbyists build is a power supply with a regulated voltage, such as one based on a LM317 circuit. You can use the power supply from an old computer as an excellent starting point to replace your battery, but from that it's nice to be able to adjust voltage. Another common option is to repurpose an old wall-wart transformer and make yourself a DC supply with it, a bridge rectifier and a filtering capacitor, followed by the LM317.

    Once you've worked through these basics, you're ready for an application that interests you. With audio, I'd start with the LM386 audio amplifier integrated circuit. It's old, widely used and widely documented on the internet. Just don't expect to go too far with it.

    You'll eventually want to actually build a project. Many of us use protoboard or strip board for our builds. This spares us from making our own printed circuit boards. You can certainly advance to doing that too, but it's not really efficient for one-time builds. You'll also need a soldering iron and solder at this point.

    Along the way, you'll learn a lot of things about the suppliers to use, techniques that work for you, how to read a data sheet, and so many other things.

    I think trying to jump to the end – building an amplifier with decent quality – is likely to cause frustration if you run into trouble and cannot diagnose it. Can you get away with it and succeed? Absolutely. But shortcuts don't always save time in the end.
     
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  11. kingkona

    Thread Starter New Member

    Aug 19, 2016
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    Wayneh, thank you for the thoughtful reply. I really like how you broke down the broad steps that one could follow so as to learn more about electronics. This sort of electronics project is too complex to back into it as I originally described.
     
  12. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    I hit it from the "complex method" . The TS (Thread Starter) really seemed to want to make the project more mechanical than anything else.

    Not saying that you cant find a "happy medium", You have to pick something and then be guided. Unfortunately, the days of Heathkit are nearly over.
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Who are you calling a Nerd ?? o_O
    I am a serious Audiophile but not a nerd :D

    TS..listen to #12. He is right about how I go about it.
     
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  14. #12

    Expert

    Nov 30, 2010
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    Myself and several others.:)
    Like it or not, many of us are considered nerds. The general population is so ignorant about electricity and electronics that I am on the computer because I don't know anybody, face to face, that I can talk to about these things. I just got back from a repair job and I couldn't get the customer to understand that I moved the safety switch to only shut off one, critical part of the machine in order to avoid the way it was originally wire to control all the current to all the parts. The switch went bad from too much current so I replaced the safety switch and I changed the wiring so it would survive in the future. Trying to explain that is nearly impossible for many people to understand. They call me a nerd.:p
     
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  15. wayneh

    Expert

    Sep 9, 2010
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    Ditto. "In the valley of the blind, the one-eyed man is king". We nerds appear godlike to the blind.

    I accept that there is specialized knowledge and not everyone will know "everything". The sad thing is, there are so very many people that don't seem to have any specialized knowledge about anything.
     
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  16. dannyf

    Well-Known Member

    Sep 13, 2015
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    How to move forward will depend on your goal.

    If you want to learn, a lm3886 or similar chip amp is a good starting point. Once you are more advanced, you can build discrete amps, like jlh1969m or aksa50.

    If you want to have a functional unit, starting with a fully built kit is better.

    Or get a used amplifier. Older Harman kardon avrs for example go for next to nothing, and offer great sound.
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
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    ST have a nice range of class-D chips - the LM3886 is probably one of NS's BTL range.
     
  18. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    #12. At least you and I are on the same page. Fix stuff so it's less likely to happen again.

    Locktite #222 happens to be a really buddy of mine. Every pair of new glasses I got recently, the screws fell out, so now I do it automatically as soon as I deam the lenses are OK.

    I hate having to re-wire a vapor dryer with a heavier gauge wire because the manufacturer goofed or equally as stupid , Make the common of a 22 Amp circuit travel 3" on a PCB instead of tied to the same lug.
     
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  19. kingkona

    Thread Starter New Member

    Aug 19, 2016
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    Sorry for the really long winded reply. This is a great conversation. Even though I don't know diddley about electronics, I think I'm among people of like mind. I work in the data networks/security environment. I recently changed jobs from a wireless LAN / RF focused environment. RF is awesome because it forces you closer to the physical layer which is really interesting. Sadly, it doesn't pay the bills as well, so I made a change.

    Unfortunately, I find electronics to be difficult to learn. Like anything worth knowing, electronics requires a lot of time, focus (time) and experimentation (time). However, I stumble with electronics. I tend to understand mechanical systems and love to build things; however, I'm fascinated by electronics and really want to learn about them. I'm open for suggestions on how and where to start learning electronics, hopefully well before I retire.

    I have found that I learn more and remember things better when I'm immersed in a project that I can research as I build it. The first project may be a turd, but I generally do better the next time. This is why I wanted to build an amp (I also love music and audio). I don't have much time because my job demands a lot of me, along with my younger kids. It's funny, my oldest kid picks this stuff up like it's nothing making dad feel like a real dolt :confused:.

    Regarding Weyneh's comment, I couldn't agree more that most people don't have specialized knowledge of anything anymore. So many people don't know the first thing about what makes their lives go. What's interesting is that as technology advances, the lower level knowledge gets lost because it's so abstracted by easy to use software. The more technical lower level stuff has become the domain of the esoteric.
     
  20. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    Here's http://connexelectronic.com/index.php/ another spot to browse for audio.

    ==

    One idea, I had was to say:
    1. Find a small kit - thru hole
    2. Try to reverse engineer it
    3. Try to duplicate the PCB - have the PCB made (Eagle is a suggestion)
    4. order the parts and assemble.
    5. Convert the layout to surface mount
    6. Do the same.

    You can spend some time in simulation with the free LTSPICE program and then try to build your circuit.
     
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