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Background hiss

Discussion in 'Amp Central Station' started by VintageMike, Dec 25, 2014.

  1. VintageMike

    VintageMike TDPRI Member

    Dec 16, 2013
    Imlay City, Michigan
    I have a Blackstar Stage 60 and was wondering how much hiss coming from amp is normal? When playing clean there is none. Channel 2 gets some hiss and channel 3 gets more. And that is when the guitar volume is 0. Is there something wrong with it? It sounds like a T.V. with no signal.
  2. OneyedK

    OneyedK TDPRI Member

    Apr 18, 2014
    Mechelen, Belgium
    I've never seen the insides of a Blackstar Stage 60 so I don't know how much noise is to be expected.
    The more gain, the more noise, so far, that sounds normal...
    The power stage seems ok, so you don't have to look there.

    The primary reasons for excessive noise are:
    1) large (or poor quality) resistors in series of the grid of the tube of a gain stage.
    2) the preamp tubes themselves can be noisy.
    3) a failing cathode bypass capacitor

    (3) given time, the tube will fail and the problem will show itself. It can be detected by a tech with proper measurement equipment (a voltmeter will show the real bad caps, but it won't show the ones causing noise)
    (2) changing tubes with new ones can lower the noise, use known good tubes or buy "premium select" from a source like the Tube Amp Doctor.
    (1) a bit harder to solve without the schematic, you can change the resistors to low noise types, but you cannot alter their values or your Blackstar Stage 60 will no longer sound like as its old self.

    Merry Xmas!!!
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