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Basic problem with transistors

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by giftiger_wunsch, Jul 25, 2009.

  1. Hero999

    Hero999 Banned

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    What's the highest voltage you normally get in a valve amplifier?

    I wouldn't call 300V high voltage because it won't arc very far.
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    500-600V in a high power one.

    Which is about all you get in a switch-mode power supply as well.

    From starting back in the valve days, you tend to blow far less things:

    1) Valves don't 'blow', they are FAR more electrically robust - just don't drop them.

    2) By the time transistors came along, you were experienced.

    3) Transistors were SO expensive, you couldn't afford to blow them - when I started a transistor would cost me about a years pocket money. Sp you were incredibly careful.

    4) By the time IC's and LED's came about, the 'old timers' were very experienced, and very careful about not damaging things.
     
  3. Hero999

    Hero999 Banned

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    That's fairly high impedance because of the transformer; right?

    Speak for yourself, I'm only 27. :D
     
  4. dave

    Dave New Member

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  5. giftiger_wunsch

    giftiger_wunsch New Member

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    Not to nitpick but I believe the UK standard definition of "high voltage" is >1kVAC or 1.5kVDC anyway :p I read that somewhere, anyway.
     
  6. Hero999

    Hero999 Banned

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    That's right.

    I think in the US and Canada it's 1kVDC or 600VAC which is lower because they're wimps.:D
     
  7. giftiger_wunsch

    giftiger_wunsch New Member

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    By the way, while I'm about to order a load of components anyway, could someone suggest any parts which I might need to build an audio amplifier which I probably don't already have? Don't need a schematic or anything right now, just need a general idea. I already purchased 3 x LM358N op-amps a while back, but never did get far with my amplifier project since I was focusing on others. I'm also adding phono sockets to my rapid order.

    I'm sure audioguru's expertise will be useful here if he lives up to his name? ;) The amplifier is going to be used to boost the signal from my home media server before it goes through my DVD player and into the surround sound, as I've found it is far too quiet even with the 40W amplifier in my DVD player.
     
  8. giftiger_wunsch

    giftiger_wunsch New Member

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    Of course! So it can kill you? Big deal! Our high voltage can cause mega-death (tm)!

    Speaking of high voltage and mega-death, my area recently suffered an 8-day power cut after a certain foolish individual struck a 132kV power cable with an axe in an attempt to steal the copper wiring... shall we all just agree that that is a real "NOOB"? :D
     
    Last edited: Aug 15, 2009
  9. Hero999

    Hero999 Banned

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    Probably a dumb pikey - they're always doing stupid stuff like that.

    I heard another story about a load of pikey being killed trying to steal electricity from the grid to power his caravan site.
     
    Last edited: Aug 15, 2009
  10. giftiger_wunsch

    giftiger_wunsch New Member

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    It's alright when they do stuff which puts their own life in jeopardy, but it's just plain annoying when they deprive thousands of people of power for over a week :(
     
  11. giftiger_wunsch

    giftiger_wunsch New Member

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    It strikes me that I probably want low-noise op-amps for this purpose, though as of yet I'm not 100% clear on exactly how an amplifier functions anyway; that'll be something to research when I get the time :)

    Perhaps the NE5534P or NE5532P would be more suitable. Any opinions?

    Thanks.
     
  12. Hero999

    Hero999 Banned

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    Yes those are better than the crappy LM358.

    It depends on how much power you want, the power supply voltage and the impedance of the speakers?

    For the power end you need something like: LM386, LM380, TDA7052 or TDA2003.
     
  13. giftiger_wunsch

    giftiger_wunsch New Member

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    Well as I mentioned I don't really know an awful lot about amplifiers, but this is the situation I have:

    • My sky box feeds into my DVD player's "video 1" phono ports, my server into the video 2 ports.
    • I typically require the volume to be at about 13/40 to comfortably watch sky TV, maybe up to 18 for very quiet programmes.
    • With my server, I can comfortably listen to most programmes at full volume (40) on the DVD player
    • I checked all the possible reasons why server output signal could be quiet (checked volume, ports, made sure the cable connections were firm, etc. etc.) but it seems that the output is just weak.
    • I checked the difference in signal strength using a voltmeter on the phono cable (probably would have been better to use an oscilloscope but I don't own one) and found that the server's output was usually in the range 4-12mV, while the sky box was around 250-400mV.


    I believe what I'm really trying to do is pre-amp the signal, but I need to do some looking into what that means before I can say that for sure; either way I want to boost the signal to the point that the sound from the media on my server will have a volume similar to that of the sky box. That'll enable me to watch the programmes which are already quiet, as well as preventing burst eardrums when the DVD player is changed from video 2 to video 1 without first turning the volume down :D

    Edit: Thread regarding this project is here.
     
    Last edited: Aug 15, 2009
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The LM358 is low power which makes its high frequency performance poor (full output to only about 2kHz, half of full output to only 5kHz). Also the low power causes it to have horrible-sounding 3% crossover distortion. It is noisy with hiss. The LM324 quad opamp is the same.

    Audio opamps like a TL07x, NE5532 or OPAx134 have a full output response to 100kHz or 250kHz, extremely low distortion and low noise.

    We are not wimps in Canada. Many fools have been killed with our 120VAC mains.
    The oscilloscope I built has a 2kV high voltage that I never touched.
    I poked around inside my CRT TV many times and it has 25kV. I felt it tickling when I got close but no shock.
     
  15. giftiger_wunsch

    giftiger_wunsch New Member

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    That's a definite yes to using the low-noise opamps then. I'll order some of those and unless there's anything else specific I will need to build an amplifier which I wouldn't already have, I'll worry about the details of its construction later, probably after I've got this robotic arm and microprocessor mess nailed down and working :D
     
  16. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    No, it's a transformer - and for a large amplifier will be a pretty serious amount of power, bearing in mind the abysmal efficiency of valve amps.
     
  17. giftiger_wunsch

    giftiger_wunsch New Member

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    Waiting for my components to be despatched, but in the meantime I've created what should now be the final schematic (attached) :)

    Now I just need to work out a PCB layout. If anyone spots any problems with the schematic please let me know :)
     

    Attached Files:

  18. Hero999

    Hero999 Banned

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    Have you ordered the resistors?

    The junk box I'm giving you has 100s of 10k resistors in it, maybe some 100R and 1k resistors too, I'll check.

    Sorry, I should have said before.
     
  19. giftiger_wunsch

    giftiger_wunsch New Member

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    I'll have an ample supply then :D. I already ordered the resistors with the other bits and pieces.
     
  20. giftiger_wunsch

    giftiger_wunsch New Member

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    My components arrived today, and other than the fact that they managed to address it to the wrong name even though I confirmed I gave them the correct one :rolleyes: I'm rather unamused by the molex housings. The data sheets confirmed that the pitch (2.54mm) and pin dimensions (0.64mm square) matched for both the cheap headers I looked at and the molex headers. So unless the molex housings are designed to be a very loose fit (which seems unlikely), they made a blunder in the data sheets :(

    I don't know if they'll be able to provide a decent connection.
     
    Last edited: Aug 18, 2009
  21. Hero999

    Hero999 Banned

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    Don't use any of the components just yet.

    Go through your order, looking carefully at the part numbers and what you entered in online. If you've made a mistake with the Molex connector, then it's not worth doing anything. If Rapid or the supplier of connector who have ballsed up, then contact customer services but make sure you're 100% certain it's their fault before you do.

    One thing I'm not sure about is errors in catalogues. I know that if the picture is incorrect, and it has misled you into ordering the wrong part (this has happened to me) there's nothing you can do because they do warn you that the pictures are just for indication. If it's a written description you might have more of a case. If it's a part number, then you certainly have a case.
     
    Last edited: Aug 18, 2009

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