Peavey Bravo 112 background noise

Discussion in 'Amp Central Station' started by Cleantone, Sep 20, 2021.

  1. Cleantone

    Cleantone TDPRI Member

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    I am getting more background noise from my Peavey Bravo 112 than I would like (see specs and signal diagram below). I play at home at fairly low volumes, often very clean or using pedals for gain through the clean channel, so the noise is very noticeable and distracting to me. I know that I can expect some noise from a tube amp but am wondering what I can do to minimize it.

    Less than a year ago I replaced all the tubes with new JJs. Less than a month ago I replaced the stock speaker with a Warehouse G12C. There was no significant change in the amount of background noise, but I think it sounds noticeably clearer - as hoped for! The electronics have never been opened, modded or serviced. The issues I'm describing are with no instruments or cables plugged, and not detecting any typical EMF noise from phone, lights, etc.

    I noticed that the reverb adds a lot of noise as the level is increased. I disconnected the tank to isolate it as a possible source. With the reverb control at 0 this improved the background noise a little, so that is one possible source. But turning the reverb control up immediately adds noise and a significant hum the same as with the tank connected. I expected the control to be ineffective with the tank disconnected, so this seems to indicate something between the reverb tank and power stage. Is this a wrong conclusion? In the short term I can live without the amp reverb, but I do want it to work.

    With the reverb disconnected and level at 0, the clean channel is improved a little bit and is not too bad up to about 3-4 on volume, then the background noise gets quite noticeable. Adjusting the High EQ rolls the noise up/down, but the other bands do not affect it.

    On the gain channel the noise is much louder even with Pre and Post gain levels just above 0. All the EQ controls affect the noise, especially the Body (mid EQ) control. Turning up the Pre gain increases the noise. That would be expected, but I wonder if it can be reduced. Are there specific 12AX7s or compatible tubes that would be quieter? Any other steps to clean up the pre-amp?

    I noticed that with the Pre gain set at 0 turning the Post gain up increases the noise. Assuming both the clean volume and Post gain are acting on the power stage it seems like noise is being added here. Would different power tubes make a difference?

    If the easy answer is to take it to an amp technician that's fine, given the amp is 30 years old it probably needs it. But I'm on a bit of a DIY kick so would like to rule out things I can do myself - e.g., different tubes, general cleaning/maintenance that doesn't require special knowledge.

    Thanks for any advice!

    Peavy Bravo 112 signal diagram.jpg
    IMG_5638.JPG
     
  2. McGlamRock

    McGlamRock Poster Extraordinaire

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    I live in an old apartment building (with old electrical wiring) and I have all the symptoms you describe. How old is the wiring in your place?
    I sympathize, it's very frustrating.
    Sometimes rolling all the eq dials back (especially the treble) can help.
    Humbucker pups help some, but all the noise does not go away.
     
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  3. Cleantone

    Cleantone TDPRI Member

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    My house is from 1928, I suspect the wiring in the specific location is original or at best 70 years old. I can move it around the house to where the wiring is more modern and test it. But the noise doesn't depend on the guitar. I have single coils and a humbucker, same effect.

    Rolling the EQ back all the way sounds dead and muddy, especially in the gain channel.
     
  4. Ringo

    Ringo Poster Extraordinaire

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    Clean the input jacks well and if it has an effects loop clean those jacks too, try putting a jumper cable in the effects loop jacks if it has that.
     
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  5. Wally

    Wally Telefied Ad Free Member

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    The reverb circuit is all in the solid state domain, so there is no tube to change. The Reverb control is a level control for the strength of the drive signal. With the tank disconnected, it is established that the problem does not lie between the tank and the power stage, It seems to me. The problem lies prior to the tank on back through that Reverb control pot. Switching the reverb out with the footswitch has no effect on the problem, either, does it? I would think not. When the noise goes away with that Reverb control at zero and the tank disconnected, it displays a clue as to where the problem lies. Odd problem….
    There may be a bad component in the reverb circuit that drives the signal to the tank or there may be a ground problem in that area. The problem is feeding back through the circuit as opposed to being fed forward through the reverb circuit since you have the tank disconnected. You could assure that connections at that pot are proper and that it is well secured by the nut to the chassis.
    You may need a tech for this one unless you want to delve into not only tube technology but solid state tech, as well.
     
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