I need help with an audio amplifier.

Discussion in 'Analog & Mixed-Signal Design' started by ConstructionK88, Jul 28, 2018.

  1. ConstructionK88

    Thread Starter Member

    Jul 25, 2018
    148
    2
    I need help with an audio amplifier....

    To the question!

    Pretty much exactly every diagram, schematic, layout (so many analogies) I have read have described in great detail how to build a great audio amp.

    Issue: they always use the best, most common(new/er parts), or personal favorite parts. I myself, obtain my parts from old radios and tvs (ect). I have purchased a 20 pack of lm386 and tip41c/tip42c. What I would overwhelmingly appreciate is a circuit that included these parts, or at least the tip chips, to build a great but not necessarily LOUD!!! Amp. I want good sounding at slightly uncomfortable levels but nothing 16 and first car loud on a Saturday night. I have quite a bit of older and modern npn-trans(c1815), pnp-trans(a933), capacitors, diodes, essentially every component except newer ics. If I have to buy more parts then I might as well buy an amp from walmart. I'd very much love help to build this from the parts I have and can easily obtain(for free) from scrap electronics. Currently trying to power, with two 6volt 7amph batteries, two 4ohm(6inch) speakers but I'm very open to change in speaker impedance and size. P.S. really trying to justify spending 100$ on breadboards, ics, transistors, and battery chargers to my wife????????????>don't think I asked a question really <
     
  2. KeepItSimpleStupid

    Distinguished Member

    Mar 4, 2014
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    I can attest that this http://leachlegacy.ece.gatech.edu/lowtim/ is a really nice amp.

    I can also say that a TV and a radio are very different.

    I worked on a essentially what's a 30 kW CRT TV, but no way can I make a TV out of it. It raster scanned a 30 kW electron beam, so the supply was 13 kV at 1.5 Amps. The electron beam in a TV might be 40 kV at a few mA.

    That crazy e-beam evaporator had a 1 M-ohm 200 Watt resistor in it for a bleeder. Yep, had about 13 kV across it.

    The SEM (Scanning Electron Microscope) I worked on used basically 741 Op-amps. It raster scanned on the CRT and the e-beam deflection coils similar to a TV.
     
  3. crutschow

    Expert

    Mar 14, 2008
    20,208
    5,715
    Here's a Google list of amps that use a TIP41 and 42, which should be a good place to start.

    For transistors it's basically max voltage rating, current rating, and power rating that are important for replacing the other amp transistors with ones you may have.
    Electrolytic caps can generally be larger in both capacitance and voltage than those specified, but not smaller.

    The LM386 puts out less than a watt of audio power, so likely will not meet your needs.
    You could use two of them in a bridge circuit to get about 3W output, but that's still pretty small.
     
  4. ConstructionK88

    Thread Starter Member

    Jul 25, 2018
    148
    2
    I'd like to thank both of you for the help. As I've said I have seen so many audio amp circuit's out there and built several with the lm386 and using just transistors. All work well for a small room or at least a larger, quiet room. But in the end the "better" ones always use personal favorited or more expensive parts. I always come across spare/junk components. Nearly all of my junk comes from thing at work like old emergency lights and P.A systems. Especially my SLA batteries. Got like 20 of those. From experience so far I'm wondering if it's my choice in speaker impedance rather than my circuit or components. Big difference in quality between an 8ohm and 32ohm speaker with the same single transistor and lm386 amp builds. Neither can run the other well enough to justify a single circuit for a "just any speaker will do" sound system.
     
  5. MrChips

    Moderator

    Oct 2, 2009
    17,292
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    Have you considered buying a pre-built class-D audio amp readily available from Amazon or eBay?
     
  6. ConstructionK88

    Thread Starter Member

    Jul 25, 2018
    148
    2
    suppose it's possible to make a lm386 preamp with only 20 gain and tip41c/tip41c ab class power amp?

    Plan on using an old Bluetooth speaker for input
    Well the thing is I don't want to "buy" a prebuilt amp. I'd feel more proud of myself building one. Also want the experience for more complex circuit's like an at home PA system for my house and to my shop ect.. A.M/F.M transmitters/ receivers for rc control. Many many things I plan on doing besides a petty audio amp. But if I can't do this well why bother doing anything at all I feel like. I need this experience with things I have around the house so I can learn how to substitute components to make a working circuit. All about the learning rather than copying all the time.
     
  7. sghioto

    Active Member

    Dec 31, 2017
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  8. ConstructionK88

    Thread Starter Member

    Jul 25, 2018
    148
    2
    I have seen it and planned on trying it or an lm386 bridge with tip41/42 final output. Thank you for reminding me. Been trying to find it but lost my bookmarks. Do you know the watt output of a circuit like this or bridged lm386/ with or without tip41/42 for final out. Noise? I desperately need something simple yet worth building. Though I must add I am using my phone or a Bluetooth speaker for the input signal.
     
  9. sghioto

    Active Member

    Dec 31, 2017
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    The article mentioned several watts using a 12 volt supply. About the same power using a bridged amp from what I have read, but would think the max power dissipation will be exceeded.
    SG
     
  10. ConstructionK88

    Thread Starter Member

    Jul 25, 2018
    148
    2
    Several amps is all I'm looking for. Everyone mistakes that I want like 100w to 1000w.. 3 to 5 watts of output is my goal with clean sound. 10 would be cool but I'm not greedy. That's why I asked if it's possible with tip41c/tip42c. I'm guessing have those can get to at least 3w.
     
  11. whitehaired novice

    Member

    Jul 15, 2017
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    Post #3 mentions using two 386 chips bridged to get about 3 watts. Why not make two of them and have each drive a separate speaker? That would give you 6 watts inexpensively.

    If that works but is not powerful enough, make two more (don't forget you'll have to have two more speakers) and get 12 watts. If you have enough speakers you could go to 8 or 16!

    Long ago I used a dual triode (12AU7) with one half a voltage amp and the other forced into operation as a power amp. Probably got less than half a watt but it was built from what I had so it did not cost anything and sounded surprisingly good. Not screaming loud but loud enough to enjoy phonograph records.
     
  12. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    While it is not the best part for the job, an LM386 can be used as the input/driver stage for a beefier output stage using the TIP transistors. It is not a common idea, so you probably will not find many example schematics on the web. Here is one from the page Wally linked to.

    [​IMG]

    ak
     
  13. ConstructionK88

    Thread Starter Member

    Jul 25, 2018
    148
    2
    I thought about doing a bridge into a single mono output to put less strain on each lm386
     
  14. ConstructionK88

    Thread Starter Member

    Jul 25, 2018
    148
    2
    I did plan on making that one but I understand the 386 is rather sensitive being it's for low voltage. I'm not sure of my phones output voltage but I'd guess it's watt range is .5 to .7 at least considering by itself can power a 8ohm 6 inch speaker at listenable levels. Worried that all the power into the 386 would cause some awful distortion and I wouldn't have much of a range for volume adjustment even at 20 gain. But again I am a newbie so I'm not really sure what will happen.
     
  15. Audioguru

    Expert

    Dec 20, 2007
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    The input to the LM386 is a voltage signal, at very low power. If the input is 2V and its gain is 200 then its output will try to be 2 x 200= 400V(!!) and you will get horrible distortion. If its gain is reduced to 20 and the input signal is reduced to 0.2V then the output will have low distortion at 4V.

    The datasheet for the LM386 shows that if it drives an 8 ohm speaker then its max output power is almost the same if its supply is 9V or 12V but with 12V its heating is much higher. Then it cannot be used as a bridged amplifier because the doubled current will quadruple its heating without much increase of output power.

    I analysed the circuit with the added output transistors and found that its voltage losses prevent any increase of output power but the distortion is increased.
     
  16. whitehaired novice

    Member

    Jul 15, 2017
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    You say you have the parts and the time--so make a single bridged amp and listen to it.

    Your phone won't overdrive it if you have a volume control (preferably an audio taper but probably anything you have salvaged from a radio will likely work fine) at the input. It is the voltage of the phone's output which will control the end power.

    If the resulting amp is not loud enough and you don't want to make 2 or 4 (which will require 2 or 4 speakers) then buy a more powerful amplifier chip--they abound.
     
  17. ConstructionK88

    Thread Starter Member

    Jul 25, 2018
    148
    2
    You sir have singlehandedly crushed my hopes and dreams along with what little balls I had left after marriage. Aside from being neutered metaphorically, what circuit would work? Again all I truly want is is something around 3 to 5or10 watt output with little noise/distortion with the components I have or can obtain through salvaging. The sad reason I want this so bad is that my brother has a Bluetooth speaker capable of sound blasting the enterprise to dust and is still clear as polished spring water at full volume and is the size of a 25oz budweiser can. (200$ he said). My goal isn't to beat him but rather closely match it and say "I made this". Also for clean up days around the house for me and my wife to listen to.
     
    sghioto likes this.
  18. MisterBill2

    Well-Known Member

    Jan 23, 2018
    1,688
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    There is another alternative to that circuit that analogKid posted, which is to use a driver transformer between the LM386 and a pair of NPN transistors. It may even be that you will need to use a single power transistor to drive the transformer. The concept comes from the mid-sixties, when suddenly bands had to have transistor amplifiers, and rugged power transistors were very expensive and the cheaper power transistors were not so rugged. You may, possibly, find these circuits in an "electronic circuits handbook" in the reference section of your library. They were published each year, and you should check the ones from the late sixties. That is one area where you can find the circuits that use the parts that are similar to things that you and I are more likely to have collected. If you can find them, older transistor applications manuals also have circuits and in those you will find some great descriptions about HOW the circuits work, and often the calculations on how different part values were determined.
    Still another choice is on line, circuits of guitar amplifiers, some of them use only transistors, and some use tubes. Only some of the newer models use IC devices, but you have a few hundred circuits to look at and study, all for free. You can gain from what others determined by experiment, but mostly you don't get much explanation on how they work. BUT that is where the stop and think comes in.
    GOOD LUCK!!!!! and happy reading.
     
  19. whitehaired novice

    Member

    Jul 15, 2017
    238
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    I don't understand why you don't just wire up a 3 watt bridge with the parts you have and see how it sounds. You say you have the parts; you apparently have the time and the skills; if it disappoints you are not out much; if it works your have something you can be proud of.
     
  20. Audioguru

    Expert

    Dec 20, 2007
    10,605
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    Bridging two amplifiers tries to double the voltage swing across the load which tries to double the current in the output transistors in the IC and in the load. Doubling the amplifier output current is the same as using a 4 ohm load instead of an 8 ohm load so the output voltage swing in each amplifier is less and the heating is more. The maximum allowed heating in a little LM386 is only 1.25W if it is in moving air.

    The datasheet shows that with a 12V supply then a single LM386 produces 0.25W into a 4 ohm load and heats with 1.15W. Then two bridged LM386 ICs with a 12V supply and driving an 8 ohm load will produce an output to the load of 0.5W and the total maximum heating of both ICs will be 2.5W.

    You know what? You have many LM386 ICs so parallel 8 of them, use a12V supply voltage and a 4 ohm speaker.
    Use a 0.22 ohm resistor in series with the output of each LM386 so that their output powers are averaged. You will get a little less than 1W.
    Then bridge two of these monster amplifiers to drive a 4 ohm speaker to 3.4W. With many paralleled amplifier inputs then the input resistance will be low so use an opamp or another LM386 at the input.
     
    whitehaired novice likes this.
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