Help with strange AC30 out-of-tuneness.

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Grant Ferstat, Mar 21, 2006.

  1. Grant Ferstat

    Grant Ferstat Some guy in obscure bands in a far away place... Silver Supporting Member

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    Hi All,

    I have an AC30 Reissue which seems to be exhibiting an out-of tuneness particularly noticeable on my B string. This doesn't seemed to be helped by substituting different speakers or all valves. According to the tech the wave looks symmetrical on the bench.

    Any ideas?
     
  2. PaulC

    PaulC Member

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    Hey Grant,

    It could be a problem with power supply ghosting. These amps have very little filtering in the power supply allowing high enough levels of ripple voltage to modulate the audio. Your tech should be able to see that on a scope as a "wiggle" to the tops of the waves. It really shows up when the output tubes are starting to square up a bit.

    Bad grounds can also do this, but it's pretty common for these amps to ghost. A cure is to up the filtering, but it will change the feel of the amp a bit (not for the worse - just different).

    Later, PaulC
     
  3. Grant Ferstat

    Grant Ferstat Some guy in obscure bands in a far away place... Silver Supporting Member

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    Thanks heaps Paul,

    I think he may have mentioned looking at this "wiggle" thing but I'll pass on the information about the grounds also.

    Cheers,
    Grant.
     
  4. Grant Ferstat

    Grant Ferstat Some guy in obscure bands in a far away place... Silver Supporting Member

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    An update,

    I checked with my tech and he has tried all of Paul's suggestions-any other enlightenment?

    Has anyone else experienced this?
     
  5. mbratch

    mbratch Member

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    Do you have any other amps to try your guitar out on? It could be your guitar strings. I had the same problem recently and it went away when I changed strings. It was the low E string, though, which may have had issues with its winding.
     
  6. Grant Ferstat

    Grant Ferstat Some guy in obscure bands in a far away place... Silver Supporting Member

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    Good suggestion mbratch-first thing I thought of though.

    We've changed the guitar and the player! My tech gets the same sound when he plays through the amp also (335 or Strat).

    BTW, I've experienced the string thing before too, and I think it happens when the string gets a bend or kink in it such as when you pull the saddle back a long way to intonate. As a result of noticing this when I'm adjusting intonation on guitars I prefer to pull the saddles back towards the back of the bridge further than I think they'll need to be before I restring meaning that I'm only likely to have to move the saddle forwards and any little kinks in the string will be behind the saddle.
     

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