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Help diagnose amp noise

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by jwri9790, Jan 29, 2012.

  1. jwri9790

    jwri9790 Member

    Jan 16, 2011
    Sydney, Australia
    So I am having a little trouble with amp noise and just wanted to know if anyone could help diagnose the problem. The amp is a Dr Z Maz 18 NR head. I have RCA 1958 Blackplates in V1 and V2 and a RCA 1960s Greyplate 12AX7A in V3. Output tubes are JJs and rectifier is Sovtek.

    So when the amp is on with nothing plugged in to it there is a light "shhhhh" noise when I turn the volume up. This is not bothering me. When I plug in a lead and have a guitar running in to the amp I get a really loud hiss and hum when the amp is cranked. The sound is exemplified more by the volume rather than the master volume. I don't know much about amps, but I assume if the noise was more present when I increase the preamp volume then it is a preamp tube issue and if the noise was increased by the master it would be an output tube issue?

    any ideas? i can provide more information later when i get back to my amp.
  2. Blue Strat

    Blue Strat Member

    Aug 2, 2002
    Sterling, VA (not far from Washington DC)
    If, at the same amp settings, there's more noise with a guitar plugged in than without, the noise is coming from outside the amp (guitar, pickups, effects, etc).

    If you have flourescent lighting, single coil pickups or are sitting too close to the amp (or other electrical noise source) you'll get more noise than if you don't.
  3. Rockledge

    Rockledge Member

    Jun 15, 2011
    Try different guitars for certain, and also try the amp in a different location to see if it changes.
    Another trick is to turn the treble up pretty good, and change the bass knob to see if it increases hiss. If it is high frequency hiss but the bass knob increases it, this gives a bit of a clue that it could be for example a bad cap in the eq section.
    Also check your verb. Turn the verb down and see if it goes away. A weak verb tube will make a lot of noise and it is easy to forget to change the verb while testing, many guys set their verb once and leave it be.

    You are always likely to have some hiss at high volumes. A bad tube will sometimes hiss.
    If it has more than one channel, set the gain on the clean channel high and the gain on the dirt channel low, so you are getting closer to the same level of overdrive from them, and compare the channels to see if it is one channel that is more.
    That again doesn't tell you a lot but it does give you an idea.

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