Peavey Bravo preamp issue

Discussion in 'Amp Tech Center' started by PerHAA, Oct 6, 2019.

  1. PerHAA

    PerHAA TDPRI Member

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    Hi, I'm new to the forum and Would like some thoughts on an issue with my Peavey Bravo 112

    I Bought it recently and it did work initially, but has now decided to go silent on me. I popped in new tubes, replaced all electrolytic capacitors, checked all fuses and connections. It's not the output stage as i get signal through when plugging in to the effectsloop return. When I plug my guitar into either of the input jacks, i get a bit of crackling when i jerk it a bit. I've cleaned them as well and re-soldered the connections onto the board. Still nothing....

    Anybody has any ideas what to try next?

    -Per
     
  2. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    Can you take a cable from the FX send into another amp or an interface to see if the signal is present there?. Try a patch cable between send and return too.
    As you're comfortable getting in there, a signal generator and 'scope are super useful. While you're in there, make certain all electrolytics in the -signal- path are the correct way around.
     
  3. PerHAA

    PerHAA TDPRI Member

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    Thanks for that, I'll see if there's a signal through the effects send. I did try a patch cable through the loop though so I have very little hope anything is coming out the send, seeing as I know the return path is working fine.

    What's puzzling me is that I get some noise when moving around the jack in the input socket, but can't seem to find anything wrong with it; It's tight and seems to have good connection to the jack when plugging in and the connections have been re-soldered to the board. I guess I have to go through all components in the signal path from the input to the effects send - and this, I take it is where the generator comes in handy....? Do you have any recommendations on a unit?

    Thanks again

    -Per
     
  4. Dacious

    Dacious Poster Extraordinaire

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    If you're getting crackling when the input jack is being jiggered around that's almost certainly the culprit.

    It may not be the jack but a broken board trace. PV stuff of that era usually had pretty hefty boards but a hairline crack is always possible. It might be worth jumpering the input to the next connection point on the preamp to see.

    Also, those plastic jacks can just wear out inside leading to intermittent contact.
     
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  5. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    A signal generator is a useful thing indeed for putting a known signal in. You can get apps for your 'phone, but I'm a little nervous about using my 'phone near high voltage stuff, given my proclivity to nuke things. I built one of these. They're readily available from most online vendors, cost peanuts and more or less get the job done.

    https://www.ebay.co.uk/itm/DIY-Kits...hash=item41ffee3a42:m:mvJ87qI59jJKr3w6a5YVWiw

    You can set it up quite easily to give a constant 1KHz at a reasonable level with a basic 'scope or meter that has a frequency function. I found inserting a 500K resistor in the output to provide a load gave a more stable signal into some input stages. Makes tracing easy, makes checking frequency response easy too. Far more capable units are available, but for an occasional debug tool, it'll do.
     
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  6. MrCairo46

    MrCairo46 Friend of Leo's

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    How old is the amp?
    I have a Silver Stripe and Teal Stripe Bandit. Both have similarly described issues and the culprit seems to be the input jacks that are soldiered directly to the pc boards.
    Check and reheat the joints first, then clean the jack mechanism itself with de-Oxit. If no good replace the jacks.
     
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  7. PerHAA

    PerHAA TDPRI Member

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    I'll look into getting one of those. meanwhile I've ordered new jacks and tested to see if there's a signal coming out the effects send - which there isn't. I've also dobbelt checked the caps if they're installed correctly (have the schematic and overview from Peavey).

    I found though, that when I turn up the reverb knob, a fairly loud hum comes out the speaker. So maybe I have to look at the reverb circiut for faults. Whenever the reverb unit is disconnected, turning the reverb knob shouldn't do anything, right?

    -Per
     
  8. Wally

    Wally Telefied Ad Free Member

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    You can do a voltage check to find where the signal fails. Start at the power tubes. The pops will increase in volume as you move toward the input stage. When you encounter a failure of that Pop! To be louder than the stage you just left, you have found a problem. I highly suspect the input jacks, and if the input stage pop is the loudest of all of the test points, this would point to the input jack circuit as the problem. I replace those plastic PCB mounted jacks with chassis mounted Switchcraft jacks hardwired PCB.

    and a belated welcome!
     
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  9. PerHAA

    PerHAA TDPRI Member

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    I will definitely give that a go next time I take a look at it.

    Thanks for the input!

    -Per
     
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