Yamaha Stagepas 600i power cut-out

Discussion in 'Microphones (live or studio)' started by Robatillo, Apr 29, 2016.

  1. DonnyThompson

    DonnyThompson Well-Known Member

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    Doubtful. I think that Boulder ( @bouldersound ) nailed it:


    Let's see if I can explain the basics of this - I'm hoping that Boulder ( @bouldersound ) or Bos
    ( @Boswell ) will jump in here, and either clarify, specify, or even correct me:

    While older amps had switches to select the ohms, most modern amps will pretty much automatically adjust for ohms on their own, as long as you aren't using mismatched ohms in your speakers ( using speakers with differing ratings)... BUT - if you are using an instrument cable as speaker cable; the first problem is that most instrument cable is around 26 gauge wire, designed to carry signal, and not voltage. Also, because of the mismatch between the conductor wire and the shield wire of an instrument cable, ( speaker cables do not require a shield) this can increase the resistance to your amp's output considerably, along with "confusing" it, because it doesn't know which ohm rating to switch to - and this can result in a failed output stage of your amp.

    ...waiting on clarification of the above from our resident electronics experts....
     
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  2. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

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    I'm no expert but I think it's the inductive effect of coaxial cable that screws with amps.
     
  3. dvdhawk

    dvdhawk Well-Known Member

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    Dec 18, 2008
    Location:
    Western Pennsylvania, USA
    This page by Fender covers the subject pretty well.

    The bottom line: instrument cables are for low-power / high-impedance signals, and speaker cables are for high-power / low-impedance signals. The result of using instrument cable for the task of a speaker cable = inefficient transfer of power and excessive heat for the amp. (heat kills electronics)
     
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  4. Robatillo

    Robatillo Active Member

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    Apr 29, 2016
    Location:
    Philippines
    Maybe that's the reason why my Yamaha Stagepas 600i amps died. Because i use instrument cable. I should have consulted the expert first before doing replacing that will damage my amps later on. Lesson learned
     
  5. Boswell

    Boswell Moderator Well-Known Member

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    There are several points about amplifier outputs and speaker cables. Most of them are general, but one of them is specific to the Stagepas range of amplifiers. The general ones have been covered by the excellent contributions of my fellow contributers, and include the need for using speaker cable (not instrument cable) of a sufficient gauge for the cable length required so that the proportion of power lost in the cable (I2R loss) is small compared with that dissipated via the impedance of the speaker.

    The Stagepas specific point is that it is one of a relatively new breed of medium-quality amplifiers that use "Class D" outputs, that is, designs that use a pulse-width modulation technique rather than a linear output. It's a bit like a switched-mode power supply that produces a variable-voltage output, and is a manufacturer's favourite way of producing 300 - 600 W amplifiers that run cool and fit in a small box. In order to reconstitute the audio waveform at the output and to keep the switching frequencies out of the load, there are high-current chokes and filters mounted immediately behind the output connectors. However, the correct operation of these depends on their driving the load for which they have been designed, viz. the associated loudspeakers attached via the cables originally supplied with the system. If either or both of the loudspeakers and cables are not the originals, then the load seen by the output chokes is liable to be anywhere from a little to very different from that for which the amplifiers were designed, with a result that could vary from failure to contain the excessive high-frequency switching harmonics to the output power stages burning out, taking the power supply with them. It is possible that the latter scenario is what has happened in this case.
     
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  6. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

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    Jan 23, 2010
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    Boulder, Colorado
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    I had been wondering if there was something specific to the StagePos (or maybe FauxPas would be better) systems. I suppose it's something like a powered speaker which has a precisely defined load and can run the amp right to the edge of its abilities rather than a general purpose amplifier that must be compatible with a range of loads.
     
  7. Robatillo

    Robatillo Active Member

    Joined:
    Apr 29, 2016
    Location:
    Philippines
    Hi Guys,
    Repair was done on my Yamaha Stagepas 600i, The technician told me that they replace the power amps on the board and I also replace the speaker wire cable as what you suggest for this amps that best suited for this model. I use 14AWG with 6 meter length. Sound is great again!

    I thank you all guys.

    Best regards to all!
    Robatillo
     

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