Amplifers

Discussion in 'General Electronics Chat' started by Overclocked2300, May 1, 2005.

  1. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
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    After searching the web, I wondered how people design audio amplfiers. I know how basic transtors circuits are built, but what abut something like this?
    http://www.ampslab.com/c200_1.htm

    How is something like tha built? Are there calculations? If so i want to learn on how to make my own.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    The ability to design good audio circuits comes from a really good and thorough education in electronics. You don't have to be an EE, but it won't hurt. I'm not even sure there's any formal training in audio design - you have to learn enough to synthesize the skills.

    With all things in the realm of discreet component analog designs, parts are hard to find. That can make life interesting when trying to either try out a design, or to put together something you found on the internet. Check Mike Leach's site for some really fine power amps - then try to come up with parts. My amp works great, but lots of part numbers (for the semiconductors) are different from the ones on his schematic.

    The amp you found isn't really bad, but the design is about average for early 1070's. I didn't look closely at the transistors. That is the first thing you need to check to see if it's even possible to duplicate the equipment.

    Don't listen to anyone who says tube amps are just it. They make excellent room heaters and wallet flatteners. If I had saved all the gassy 6L6's I replaced out of an old mono Stromberg-Carlson amp in the '60s, I'd could seel them for serious money right now. Think I got off the topic a bit, too.
     
  3. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
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    I was able to find the transistors btw, so ive decided to use this amp instead http://www.ampslab.com/c70.htm

    The speakers I have are 125W. I dont know if they are peak or RMS, but to play it safe Ill assume 125 W peak.

    I am in electronics at school, because i go to a tech school. I wanted to learn alot more about amplifers, smps, and Digital systems (such as microprocessors)

    I have found a book on Audio Amps, but would like suggestions on what to get also.

    http://search.barnesandnoble.com/booksearc...50656360&itm=10
    Is what i was thinking of buying
     
  4. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi,

    the circuit you posted is an off the shelf design, meaning it's very common. however if you are really serious in building this power amp go ahead, but the big question is, will you be able to trouble shoot it if in case it does not work?

    the amp that "beenthere" mentioned is better than that but it is a more complicated design.
     
  5. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
    124
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    Yea I will be able to troubleshoot the amp. The reason why it probably wont wrok is because of the PCB. When I make it, some of the tracks are dissolved into the solution, and then i have to do the PCB over again.

    I have looked into the leech amp, but its too complicated and nothing i can use. The c70 amp i should u i would have perfect use for my speakers. Pluse the C70 (in my opinion) is easier for me and a good starting project. I have TO3 heatsinks, and calculated them to be around 2-3c/W
     
  6. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
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    hi

    maybe some of the reasons why you are having problems with making the pcb are the following:

    1. traces have not been adequately covered
    2. the board is immersed too long in the solution
    3. traces are in the 1mm to 1.5mm size

    suggestions:

    1. make your traces at a lowest size of 2mm
    2. move the board out of the solution every 2-3seconds
    3. warm up the solution before immersing the board which will result to faster etching time
    4. scrub or clean the board before immersion
    5. make sure that the edges of your traces are adequately covered, this is where the solution creeps in and cuts your traces expecially if its 1mm or less in size

    as a farther suggestion, use the toshiba 2N series or the motorola MJ or MJE series as your output transistor. they have better matching current characteristics specially when the transistor temperature is already elevated.
     
  7. legac

    Well-Known Member

    May 4, 2005
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    I would recommend that you should be very carefull with this circuit because it is OCL- output capacitor less amplifier. It can smoke your loudspeaker unless you have Lab equipment to test and verify the matching parameters of the transistors.
    Otherwise the IC such as TDA 7294 will work well.
    Cheers
    Legac
     
  8. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
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    but the TDA 7294 has 10% distortion when at 100W power

    what do u mean Output capacitor less amplifer? Can i put a cap in then? If so where and what value?

    EDIT: is that 100W RMS? , and if I increased the dissipation of the heatsink would disortion be less? Personally I think 10% is alot.. Are there better IC chips with less Dissipations? And I dont know if I asked this before but the speakers are 125W should I risk using more than that?
     
  9. legac

    Well-Known Member

    May 4, 2005
    54
    0
    Hi

    Customarily in audio, an amplifier is loaded by a speaker having the wattage which is bigger than the power delivered by the amplifier. There are many reasons for that philosophy: i.e The speakers will make distortion by themselves at a certain wattage and frequency level before the distortion made by the amplifier; the owner wants to prevent the costly speaker from mechanical damage due to operation at max capacity and so on..

    OCL: on AC signal perspective, you can insert a capacitor between the output of the amplifier and the speaker. The value of the capacitor varies subject to the impedance of the speaker, from 1000uF to 4700uF/63 volts or higher, non-polar.

    At 60 watts RMS, TDA7294 has 0.5% distortion. You mention 10% distortion, that is the music power concept.
    Unless the case that you would like to get experience with an 1970 circuit, the TDA or other new IC devices would be appropriate for audio enjoyment. However my taste is the tube amplifier.
    Cheers
    legac
     
  10. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
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    hi

    looks like you're having a little problem on deciding which power amp you would like to build. which is better, a discrete power amp or ic power amp. i say they are both good but a discrete power amp is better.

    if you want to learn & understand better on audio power amps, make the discrete system. but if you want the easy way out without learning much then do the ic amp. remember ic power amps is still based on discrete parts and besides you can't do much in improving the performance becoz you're stuck with it's design.

    and besides i still have to see if there is an audio power ic that can match the performance of a discrete power amp. :eek: :huh:
     
  11. Firestorm

    Senior Member

    Jan 24, 2005
    353
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    :eek: We thought you knew everything lol :D
    is there that much of a difference in the 2 types besides the modification aspect?
    thx l8er

    -fire
     
  12. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi firestorm

    what do you mean by "we thought you knew everything"

    maybe you have miscontrued my statement :eek:

    as to your question, there is a big difference :p
     
  13. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
    124
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    such as?

    EDIT: your right..I kinda am stuck inbetween IC and discrete. Discret does seem easily though..The speakers I have use AN IC AMP. They do sound pretty good but they have this one huge speaker withg a huge magnet. I think its a woofer or something..but anyway It does sound good..EXCEPT at higgh volumes there is a ALOT of distortion.

    I would love to learn as much about electronics as I can. But does discrete sound better? And is there as much distortion at higher volumes?

    also im kinda torn with money. I need a bigger Hard Drive, which will cost 50 bucks (which is what i have in my wallet), but I want to build this amp but i dont want to use my account money. I would rather use it out of pocket.

    Also Im torn with priority...I have so much to do now and worry about. Its the last month of school (im a senior) I have to worry about college (ill be going to a Community college though since i dont kno what college I am going to go to for electronics engineering or computer engineering for a masters or Doctors degree) plus i have to worry about the project I have going on. I have 1 computer Mod going on, and Im taking a bunch of powersupplies i got from school apart. So i guess i have to prioritize. But the computer mod takes time..i guess i got a lil lazy since we got dsl...
     
  14. Firestorm

    Senior Member

    Jan 24, 2005
    353
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    Just hinting that you were a smart member of this board :)
    nothin serious, just complimenting you, thats all :D :D
    Can you explain the difference a lil' more aswell?
    thx l8er

    -fire
     
  15. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
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    hi

    DISTORTION is the vain of most audio amp designers. not much have been said about distortion, how it affects the amps signal fidelity, where it comes from, how it is generated, how can it be minimized if not totally eliminated w/c is impossible.

    one of the major reason why power ic amps have a high THD is due to very close thermal proximity of the internal input & output devices. discrete devices have large junction with high thermal inertia. as temperature increases for low freqs 2nd and 3rd harmonics distortion also increase w/c highly affects class B output stage.

    another aspect is when there is a large common-mode voltage at the input stage, 2nd harmonics distortion at high freqs will also increase even if negative feedback is increased.

    when you check specs of power audio ic they usually state THD at 1khz of say 0.05% and seldom reveal THD at 20khz which usually hits 10%. and another thing this power ic are not tolerant to resistor noise voltage, that's why they always recommend the use of at least 1%tolerance metal film resistors.

    hope this helps :D

    one of the key factor of having a very low THD in discrete power amp is in the design of the input stage. ;)
     
  16. Firestorm

    Senior Member

    Jan 24, 2005
    353
    0
    thx for the clarification moz :)
    The input stage you mentioned at the end though, what are some design factors needed to make a good input? thx again.

    -fire
     
  17. Firestorm

    Senior Member

    Jan 24, 2005
    353
    0
    :( double post...h8 it when this happens!!!
     
  18. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
    124
    0
    For the input I was just gonna use an op amp such as the TLO82 as a preamp.

    The circuit shown gives abut 28dB Gain, and the max the speaker can take is 90. Human hearing is damaged at 85 I think. Im going to aim for 50 to be safe. So IF I design the preamp for another 28dB gain and dB add (correct me if I am wrong)

    so 28+28=56dB

    its gains that multiply correct?

    The reason using an op amp for a pre amp because it has good rejection of noise, and it is also simple.
     
  19. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    if you want an even better pre-amp use NE5532. the TL082 has an IENv of 18nV @ 1khz while the 5532 has 6nV. at low freq the 082 has 4uV while the 5532 has 10nV,
    CMRR 100db, SVRR 100dB, crosstalk attenuation 110dB while 082 has a CMRR 86dB. SVRR 86dB and crosstalk attenuation of 120dB. 5532 has a unity gain bandwidth of 10Mhz while 082 has 3Mhz :D

    where's the circuit you mentioned?
     
  20. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
    124
    0
    opps sorry.... The amp I mentioned was the C200 Amp, but really i am building the C70 amp found here:http://www.ampslab.com/c70.htm

    Its really the same thing,except it has a different output
     
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