Help with class AB amp

Discussion in 'General Electronics Chat' started by CRY&PRAY, Jan 6, 2014.

  1. CRY&PRAY

    Thread Starter Member

    Jan 6, 2014
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    I know that i keep asking the same thing, is that i'm scared.. if i burn the only one amp that works.. how will the speakers play the 15th? by screaming loud?

    I just want to be sure 100%, today i've tried to attach the bases of the transistors to the push pull stage of my AB amp, ad it worked, but i was using that +-18v, i'm a bit scared to use 2 2sc5200 and 2 complementary PNP, with a freaking 1500 watt transformer.

    it's simple i know, just wire all the resistors to the emitters then to the anti bump circquit, and 2 collectors to a rail, and the other 2 to the other, and connect the bases. But if a small drop of solder falls on the collector and then touches the heatsink? ever seen a 1500w spark? cuz i did....
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Geez, you don't get it. I give up.
     
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Exactly... So, don't do it. Sorry, but YOU shouldn't be trying stuff like this on equipment which you must have in working condition. I wouldn't do it myself....

    For more power rent something as suggested.
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    When I worked answering customer calls, uttering those words would have gotten me instantly fired......

    but you don't know how many times I dreamed of saying it.:D
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    Good point. Can you provide a more appropriate response?
    I will try to contain my frustration next time.
     
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I wasn't criticizig your response, just remembering the 20 years at national Semi that I spent answering similar questions. I think you nailed it. If you go back through the five pages of this thread, I and others have all been saying the same thing you did but you phrased it more concisely. This thread is kind of a prototype of how to waste five pages on something that is not feasible and absurd to even try for a variety of reasons. But harmless I guess.
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I wasn't criticizing your response, just remembering the 20 years at national Semi that I spent answering similar questions. I think you nailed it. If you go back through the five pages of this thread, I and others have all been saying the same thing you did but you phrased it more concisely. This thread is kind of a prototype of how to waste five pages on something that is not feasible and absurd to even try for a variety of reasons. But harmless I guess. Nobody got electrocuted and no houses were burned down.
     
  8. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Hola bounty,

    What type of customers where those? Other engineers trying to design things?
     
  9. CRY&PRAY

    Thread Starter Member

    Jan 6, 2014
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    luckily no house were burned down :3, ho well i'll go with what i have, tomorrow i'll go to but the pieces to repair the omnitoric, i'll need help there on a particular resistor that i forgot the value, if you go to see the img it's the one with some numbers and question marks. That resistor bridge emitter and base of the d669a thru a pot, but i don't remeber the exact value, i think that were all 3 red strips so a 2k2, i'll buy all the 3 probalily types and start from the bigerg one :3 i'll post here the conclusion during the repairing
     
    Last edited: Jan 12, 2014
  10. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Let's wait until February 16th.:p
     
  11. CRY&PRAY

    Thread Starter Member

    Jan 6, 2014
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    haahahahhaah, i'm not that crazy to wire stuff like i don't know how... and make my house burn with my freaking multimonitor and gaming pc that cost an eye of the head!! and a usual a freking 10 amp fast blow fuse for that amp until i got it working correctly, then it's own 10 amp slow blow fuse.
     
  12. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Mostly they were digital designers trying to figure out how to use an analog part....
     
  13. CRY&PRAY

    Thread Starter Member

    Jan 6, 2014
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    One channel of the omnitronic is ALIVE!!!

    just need a d699a transistor to set the bias correctly, now sounds like a fart at low volumes, but if i touch the collector and emitter of the d699a place where now is nothing it sounds well!!! i'll wait to get all the parts :3, as the other channel, just need to pray.... still using the famous bose psu +-18 v

    [​IMG]
     
    Last edited: Jan 13, 2014
  14. tubeguy

    Well-Known Member

    Nov 3, 2012
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    I must applaud you ... you remind me of me...
    Never give up... never surrender!!! :D
     
  15. CRY&PRAY

    Thread Starter Member

    Jan 6, 2014
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    hahaha, happy to know that, i really like eletronics :3 it's like an advanced lego and i find awesome how freaking piece of Si can stop current. Today maybe i'll go out with a friend and go get some of the parts, but the shop is pretty far away, hope they have that D699A that's pretty rare and i'll post the results, as the other channel.... need a check to the pre-amp that's not driving the 2 transistor (the one in the photo that i've placed, but to the other side) and so these transistor are not giving anything on the bases of the Power amp.
     
  16. CRY&PRAY

    Thread Starter Member

    Jan 6, 2014
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    Guys need a help!, what does that transistor one the 1 img down left with his base to the ground and a diode to the -95 v? the amp does not sound or sounds really bad on both channels (they are specular, i've tried to see if was a burned transistor) i have to connect a 100kOhm pot between the collector and the emitter set at around 40-50 KOhm in order to get sound (powerfull and well).

    [​IMG]

    [​IMG]
     
    Last edited by a moderator: Jan 14, 2014
  17. CRY&PRAY

    Thread Starter Member

    Jan 6, 2014
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    i've got today 60 euros of components :3 yay, all mounted and the amp is working well, still having that problem, now i've placed 2 resistors (one for channel) on the emitter and collector of these 2 transistor (the one who has the base grounded and kinda biased with a diode coming from the 95-)

    The question now is... is sounding this bad cuz i'm powering it with a low voltage (+- 18v) and so the diode that has maybe been thought to work with higher voltages is not biasing that transistor.. or it's a bigger problem?

    the resistors that i've placed are 2k2 Ohm
     
  18. Veracohr

    Distinguished Member

    Jan 3, 2011
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    I think it's a bias current source for the differential transistor pair above it.
     
  19. CRY&PRAY

    Thread Starter Member

    Jan 6, 2014
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    So i'm having that problem cuz the +-18 is not enough to bias the differential pair? cuz i've everything wired up now, tomorrow ill hit the switch :3
     
  20. Veracohr

    Distinguished Member

    Jan 3, 2011
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    I don't know, maybe. You might try downloading LTSpice and simulating the circuit before you try the "hit the switch and pray" method.
     
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