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About make an audio power amplifier.

Discussion in 'General Electronics Chat' started by Nikolai Petrenko, Jan 30, 2016.

  1. Nikolai Petrenko

    Nikolai Petrenko Member

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    I
    I mean 6 pieces of 15V zenner diodes.
    I have thought about use TO-92 regulators instead of TO-220 before but sorry to say: small regulators like 78L05; 78L08; 78L09 and 78L12 are available but 78L15 and higher voltages aren't, LM317L too.
     
  2. Nikolai Petrenko

    Nikolai Petrenko Member

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    3 zenner diodes in parallel can provide current up to 60mA to feed preamps without any damage, because my zenner diodes can't allow current over 30mA or they will burn.
     
  3. spec

    spec Well-Known Member Most Helpful Member

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    Nikolai,

    No worries: it is a simple matter to configure most regulators for a higher voltage. So for example you could turn a 78L05 into a 15V regulator with a couple of resistors, if I remember correctly

    spec
     
  4. dave

    Dave New Member

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  5. spec

    spec Well-Known Member Most Helpful Member

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    Not really practical Nikolai, because 6 of 15V Zeners would all have different voltages and slope resistance so you would not achieve much by paralleling them up.

    One approach would be to make your own voltage regulator with a 15V Zenner and a couple of transistors. For low current outputs, you can even make a regulator from just an opamp and a Zener. But as said in my previous post, a standard voltage regulator is the way to go. If you let me know what regulators you can get, I will post a schematic for a good 15V regulator.

    spec
     
  6. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Given your stated load requirements, you gain nothing by using 3 zeners in parallel AND the rail voltage will reflect the Lowest of the three's BV. One zener (per rail) is preferred (as noted by spec above).

    Sample SIM:
    upload_2016-2-15_10-0-26.png
    All things considered, this circuit is at the edge of various limits.

    The 270Ω current limiters may need to be adjusted depending on the load. Choose a value that allows the zener to regulate AND still allows the circuit to provide adequate current for your OPAs. Rail voltages will also vary with load resistance(s).

    Once you have one rail working correctly, mirror it for the other rail.
     
  7. spec

    spec Well-Known Member Most Helpful Member

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    Re using a lower voltage reg to generate 15V, here is the sort of circuit to do the job. There are many variations of this:

    ETO_2016_02_15_Iss02_PREAMP_PSU.png
    ERRATA
    (1) The maximum input voltage should read 45V, not 50V (thanks Mikebits)
     
    Last edited: Feb 18, 2016
  8. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    I like that!

    Zeners seem to be prone to heat fluctuations as well, seeing as your building a super duper amp it seems a shame to ruin it by using cheap shortcuts.
     
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  9. spec

    spec Well-Known Member Most Helpful Member

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    Hi LG,

    The main problem with the shunt Zenner circuit is that it does not isolate noise and ripple that well (rejection ratio). Also the circuit does not generate a super low impedance power line, which is important for minimizing distortion, especially with a discrete pre amp, which Nikolai favors.

    spec
     
    Last edited: Feb 15, 2016
  10. Mikebits

    Mikebits Well-Known Member

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    You might want to take a look at the maximum input voltage spec of that regulator. I think it is 30 or 35v.
     
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  11. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Historically such schemes (but ONLY using single zeners - you can't parallel them) were commonplace in guitar and PA amplifiers, feeding the preamp stages from the main amplifier rails.

    However, as you would expect, this part of the circuit was always a serious source of problems and failures, due to the high amount of heat dissipated there.

    Simply use a pair of 7815/7915, or the smaller L series - it will perform FAR better, and be much more reliable.
     
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  12. Mikebits

    Mikebits Well-Known Member

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    He said he can't get those, for what ever reason?
     
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  13. spec

    spec Well-Known Member Most Helpful Member

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    Thanks Mike.

    The input output differential is as you say, 35V but as the output voltage is 15V this means that the total maximum safe input voltage to that circuit implementation is 35V + 15V =50V.

    CORRECTION: you are right the tail of the 78L05 is at 10V so that reduces the safe input safe voltage to 35V +10V = 45V. Good work :)

    Of course, it would be sensible to pop in a few protection bits here and there to legislate for turn on conditions and possible fault conditions. If the reverse diode were a 33V Zener, for example, that may help.

    Keep the comments cumming. Like I have said before, my schematics are straight off the drawing board and may be full of errors. It is a great help to know that someone is checking.

    Cheers

    spec
     
    Last edited: Feb 17, 2016
  14. granddad

    granddad Active Member

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    Hi Nikolai , had you looked at 723 Reg IC .

    The 723 Voltage Regulator IC. It consists of a voltage reference source (Pin 6), an error amplifier with its inverting input on pin 4 and non-inverting input on pin 5, a series pass transistor (pins 10 and 11), and a current limiting transistor on pins 2 and 3. The device can be set to work as both positive and negative voltage regulators with an output voltage ranging from 2 V to 37 V, and output current levels up to 150 m A. The maximum supply voltage is 40 V, and the line and load regulations are each specified as 0.01%.
    IC-723-As-positive-voltage-regulator.jpg
    Edit , Changed the original jpg circuit as it had pins 11 and 10 connected ?
     
    Last edited: Feb 15, 2016
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  15. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Just because he said something doesn't mean it makes any sense :D
     
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  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    He is in Vietnam (or on the Moon?) where common ordinary Western parts are not available.
     
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  17. Mikebits

    Mikebits Well-Known Member

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    They don't do Ebay there?
     
  18. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    They got the internet so unless its on a import ban............ Besides didnt he order from RS? I am reasonably sure RS do a couple of different regulators ;)
     
  19. Nikolai Petrenko

    Nikolai Petrenko Member

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    Oh my question spend all you a lot of time. Thank for all answers.
    I can't find 723 reg IC.
    78xx series are vulnerable to input voltage above 35V. LM317 is better anyway, will safe when input voltage below 40V. But only TO-3 and 220 version of LM317 are available, TO-92 not.
    Yes, as AG said, in my country many common Western are not available. But seem be Japanese and European parts are much popular than American ones. Japanese parts are pretty variety. Russian parts quite popular, but most are old power analog parts like diodes, transistors, thyristors in since Soviet-era (good for high power).
    Lucky! Return to my old thread "Transistors equivalent", I have found that KT135G will replace BF494 or BF109 well in RF circuits, some name-faded glass diode will replace 1N34 quite well (may by germanium diode), all of these were extract from old Soviet radio walkie-talkie :).
     
  20. Nikolai Petrenko

    Nikolai Petrenko Member

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    I realized that parts in chipdip.ru are cheaper and more reliable than in Ebay ( part of Ebay which I can reach, not all).
     
  21. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Mate you so need to move!! Life without a fully stocked parts bin is just existing and not living, build a raft ;)
     

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