Deluxe Reverb Build Issue

Discussion in 'Shock Brother's DIY Amps' started by Rock_Glenn, May 1, 2015.

  1. Rock_Glenn

    Rock_Glenn TDPRI Member

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    I have a Deluxe Reverb build that offers some terrible noises on the vibrato channel. Basically,

    The Normal Channel works perfect, though the very first time I turned it on I had a high pitch like a microphonic tube and a lot of hum, since swapping a new 12ax7 in V1 I have no problems on the Normal Channel.

    The vibrato channel gives me no sound when the volume is at 0 and the reverb knob is at 0.

    With Volume at 0 and reverb turned up I have increasing hum.

    As I turn the volume up at about 1 I get a bad farty noise, and at 3 I get the noise sometimes with a constant high pitch squeel like the microphonic tube. However over the top of the noises I get guitar sound just fine, and I even get some reverberation on all the noises and guitar.

    If I pull v3 completely the vibrato channel works perfectly, except the vibrato effect doesn't work. It only pops when I turn it on very loudly.

    I tried swapping the 12At7's and I have tried every combo of 12ax7 possible at my disposal.

    I used the weber 6a20 layout, and I notice out of the Reverb transformer hole there is dotted yellow line going to ground... I did not do anything there as I have no idea where that yellow line goes, I assumed it was the grounding of the reverb chassis to the amp chassis which is made by the output/input shields.

    I also did not do anything to the reverb can except remove the foam and plug and play, was I supposed to hook anything else up?

    I believe I grounded the reverb transformer center tap to the sleeve hole (ground) of one of the reverb jacks, could this be the problem? Perhaps that ground should be moved for hum, but could it cause what I'm hearing here?

    I can take pictures tomorrow, though I will have to remove the chassis from the head cab, which seems like such a pain. I was perhaps a bit arrogant when I mounted it in the cab before testing completely.

    Any help is greatly appreciated.
     
  2. clintj

    clintj Friend of Leo's

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    Pics please. There could be a few things going on with it.
     
  3. R. Stratenstein

    R. Stratenstein Doctor of Teleocity Ad Free Member

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    1. I think you're OK with that dotted yellow line pointing at the reverb transformer, I think it's just a diagram thing, not a wire, showing you that the wires coming through the chassis hole are from the reverb transformer. The black wire from the reverb transformer is grounded in the diagram.

    2. Unless your reverb can is one of the type with the little lever that pushes a mechanical "brake pad" against the springs for transport, once you take out the shipping packing materials, it should be plug and play.
     
  4. Telenut62

    Telenut62 Poster Extraordinaire

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    I did a Mojo kit build, my wiring was Red to B on the board, Blue to pin 6 then to 1, Green to reverb input tip, Black to vibrato pedal ground lug along with the 220k resistor.
     
  5. Rock_Glenn

    Rock_Glenn TDPRI Member

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    Telenut, my reverb transformer wiring is exactly the same, except I grounded the black on the sleeve of the reverb input jack. I have the chassis removed and will post pics shortly. Thanks for looking.
     
  6. Rock_Glenn

    Rock_Glenn TDPRI Member

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    [​IMG]

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    [​IMG]

    [​IMG]

    [​IMG]
     
  7. Telenut62

    Telenut62 Poster Extraordinaire

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  8. Rock_Glenn

    Rock_Glenn TDPRI Member

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    With this amp I got a bit lazy with heater wiring only doing a couple of twists between the preamp tubes because they are so close together. I also pulled the few twists apart for the sake of picture taking (so you could see the tube socket wiring).

    I've gone over everything with a multimeter and simply can't find any problems that would cause the symptoms I described. Poor lead dress I would think would give me a bit of hum, certainly not what I'm experiencing.

    I grounded the tremolo pot and reverb pot to the star ground next to the power transformer, along with the filter cap ground. Could some of the filter AC be sneaking back in there? Should I move the Reverb ground to the ground on the board? Or is this wasting my time and these symptoms have to be something else?
     
  9. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    "farty noise" makes me think oscillation. Oscillation makes me think lead dress problem, maybe.

    If you "chopstick" it while it makes the noise do you find that moving any wires makes it better or worse? Literally just poking with a chopstick (or other non-conductive item of your choice).
     
  10. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Interaction between leads can cause the symptoms you're describing and it's most likely not a grounding issue.
     
  11. Rock_Glenn

    Rock_Glenn TDPRI Member

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    It definitely sounds like oscillation, there is high pitched oscillation at 3 and above, and no matter where I put the volume that low pitch rumbling comes and goes.

    The Reverb transformer's primary wires and secondary wires are sharing a hole to enter the chassis, each pair are twisted together through the hole. I doubt that's the problem, but could it be?

    I'm in the process of poking around, I'm assuming that this oscillation is most likely the reverb output or recovery making it's way back into the reverb input somewhere?
     
  12. clintj

    clintj Friend of Leo's

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    Oscillation can happen anywhere the conditions are met. Anywhere. All you need is two wires close enough that signal can be induced in each other, and a net gain greater than 1. Plate lead from a tube inducing noise in a grid or cathode wire in an earlier stage will do it.

    When CBS took over, many of the circuit mods they made were to squash oscillations caused by poor lead dress, which was caused by trying to save build time. There's so much going on in a BF Fender that good dress is critical.
     
  13. muchxs

    muchxs Doctor of Teleocity

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    Yup. They generally give you enough wire for two amps. If you don't have enough left over for another amp you used too much wire.

    It matters.
     
  14. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Muchxs can't be just changing his avatar like that!!!!!!!!!

    </end thread derailment>
     
  15. Rock_Glenn

    Rock_Glenn TDPRI Member

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    Thank you all very very much.

    Problem is 100% fixed, for others who end up where I was this is what I did:

    I gave the heater wires a few extra twists.

    I made sure every wire lead going to a tube crossed at 90 degrees or close.

    I moved the black tap wire from the reverb transformer to the ground on the vibrato pedal jack, as opposed to the ground jack on the reverb input.

    Most Importantly:
    The blue reverb tranny wire was very close to the reverb output wire, probably too close and running in the same direction, I moved it well away from the input wire.

    I used shielded wire from pin 7 of v2 to the volume pot, as it also was close to some of the reverb wires, which I also separated it from and made cross at 90 degrees with other wires.

    I haven't tested the tremolo yet, as I didn't install V5 at all but that's trivial, now that I have reverb I'm happy.

    Thanks again,

    --Pete
     
  16. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Cool, congrats on getting it running right.
     
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