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Deluxe Reverb - Reverb Hum

Discussion in 'Shock Brother's DIY Amps' started by h4ck.b0x7, Mar 11, 2018.

  1. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    Any ideas why I’m getting this hum from my Deluxe Reverb? If the reverb knob is all the way down there is no hum. As the knob is turned up the hum increases. None of the other knobs affect the hum. There is no change in the hum if I disconnect the reverb send. However, if I disconnect the reverb send there is a change as shown in the second video.



     
  2. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    I should clarify, this is a Hoffman AB763 build using a cannibalized ‘65 DRRI.
     
  3. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    Have you inspected the tank connections, and tried swapping both reverb tubes with others?

    Swap V4 with V1, which is preamp for the normal channel. Chances are you may not even use that tube much.

    If that don't fix it, swap V3 with V6, the PI.

    If one of these fixes it, you may find you want to get a new tube, or you may find no issue with the tubes swapped.

    Another quick test is if you have another amp, place them back to back, and run that amp through this one's tank, and then this amp, through that one's tank. Which time does it hum...
     
  4. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    I don’t have another tank but I ordered a new MOD tank. I’ll swap tubes and report back.
     
  5. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    Swapping tubes makes no difference.
     
  6. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    I went a step further and connected the footswitch. The hum goes away when I turn the reverb off via the footswitch. It comes back when I toggle the switch again.
     
  7. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    I meant to post this picture as well.

    EBCBA8D9-A190-4FB4-9A7C-FBB4F4189299.jpeg
     
  8. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    It's hard to tell how loud it actually is in your video. Did it just start happening? Reverb is a noisy circuit, no matter what. Some level of noise when turned up high is to be expected.

    See what happens when your new tank arrives. Try new cables, if you have them.

    That's the limit of my remote troubleshooting skills, I'm afraid. Hopefully someone else will chime in.
     
  9. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    It’s LOUD, playing easily covers it up but you would never be able to record with it.

    I ordered vintage style cables as well, which I’ve been meaning to do.

    This has happened since I built the thing. Since then I’ve built a couple more amps and acquired 6 or 7 guitars. To be honest, I’ve been preoccupied/lazy and just haven’t gotten around to fixing it.
     
    asnarski likes this.
  10. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    Could be wire dress.
     
  11. dunner84

    dunner84 Tele-Meister

    270
    Jul 15, 2014
    Victoria, bc
    So far, my experience building amps with reverb has proved them to be troublesome circuits. There will always be noise, but not so much that you can't record. I would post pics of the wiring. It is most likely lead dress. I've had to fuss with all of mine post build to get them reasonably quiet.
    Also, it's possible that you have all of your RCA jacks grounded. They should be isolated from the chassis, and take a look at how they are grounded on the tank.
     
    Fiat_cc likes this.
  12. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    It’s not lead dress, I’ve done the chopstick charade.

    Both of the RCA jacks are grounded to the chassis...

    The tank is whatever comes in a DRRI. It is soon to be replaced by a MOD 4AB3C1B.
     
  13. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
  14. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    Here’s some pictures for posterity.

    5925B06D-F87F-43CD-BE4C-D59F0736BC25.jpeg 634D1A89-4C1F-4305-9E28-8CF21BCE31D2.jpeg
     
  15. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    Does anybody have any other ideas?
     
  16. Fiat_cc

    Fiat_cc Tele-Holic

    Age:
    35
    510
    Oct 8, 2016
    Melbourne, Australia
    I'm not an expert, but that grounding scheme goes against what I've heard lots of other experts say is best practice, however given the way Fender did it in the originals I doubt the scheme itself is going to be your issue. Possibly a bad or missed ground, or a simple mistake. I once had a problem with low distorted output and eventually found I'd mistakenly connected two pins on my phase inverter back to front. Triple check components, layout etc and if you're 110% there are no mistakes, recheck lead dress. Those big filter caps are quite close to pots and sensitive wires. What happens if you move the reverb control wires up in the air, a loooong way away from them?
     
    moosie likes this.
  17. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    I'm not kidding when I say I have checked the wiring like 6 times in the past. If I move the reverb wire way up nothing happens. I've checked the lead dress on more than one occasion.

    In what ways does that grounding scheme go against "best practices"? The only thing I can think of is that the buss wire is connected to the back of the pots, however, that shouldn't really make a difference.
     
  18. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Are the filter caps grounded to the back of the pots?
     
  19. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    I assume your pots are mounted directly to the chassis, right? No insulating washers / bushings?

    As has been mentioned, the filter caps are very close to the reverb pot, and wires leading off it.

    If your pots are not isolated from the chassis, then grounding your bus to them eliminates the benefit of the two bus wires. Your preamp common return path is not directed away from the power section by only touching the chassis at the input jack. Instead, it connects to the chassis all along it's length, effectively at the intensity pot, which is right near the power supply.

    Yes, Fender did this, and it works. But they also routed the filter caps separately.

    At this point, I'd probably replace the reverb control wires with shielded coax. If you've already shielded these, that's good, I just can't make it out from the photo.
     
    Last edited: Mar 13, 2018
    Fiat_cc and asnarski like this.
  20. h4ck.b0x7

    h4ck.b0x7 Tele-Holic

    778
    Nov 29, 2011
    United States
    The filter caps that are close are the preamp filters, the B+ filters are off to the side and run to the far PT bolt. I got that layout straight from Hoffman examples.

    Honestly, I can’t remember if the buss wire is soldered to the back of the pots or not... I haven’t opened it up in a year and a half.
     
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