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5e3: My grounding scheme may be weird!

Discussion in 'Shock Brother's DIY Amps' started by mcentee2, Feb 11, 2019.

  1. mcentee2

    mcentee2 Tele-Meister

    278
    Feb 18, 2011
    York
    Ok, another thread on my new 5e3 pre-built chassis for you to kindly offer advice on:

    I have consumed and understood nearly all the various Grounding posts/threads etc over the years, but I haven't yet come across the one in the pre-built chassis I just bought :)

    There is no dedicated ground bus at all.

    - all four input jacks are locally grounded to chassis (switchcraft)

    -v1a/b shared cathodec/r is wired to a chassis screw next to the v1 socket - this is the only thing grounded to that point.

    -v2a cathode c/r is grounded to the Normal Volume ground lug, soldered to its pot back and via the chassis at that point

    -v2b's 56k resistor and the two 6v6 220k grid leak resistors are connected to B3+ cap -ve and grounded via the Bright Volume ground lug, soldered to its pot back and via the chassis at that point

    -B2+/ B1+/6v6 cathode c/r and the 6.3v center tap are grounded via the Tone pot's ground lug to the back of the pot and via the chassis at that point.

    - The mains ground and 330-0-330 secondary center tap are connected to one of the PT mounting bolts, securely though :)

    It doesn't appear to be a noisy amp, but the above makes me nervous!
     
    Last edited: Feb 11, 2019
  2. harleytech

    harleytech TDPRI Member

    Age:
    56
    33
    Jun 5, 2017
    Wisconsin
    I didn't use any of that grounding BS you read about on the internet, And my 5E3 is as quiet as a church mouse...
     
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  3. sds1

    sds1 Tele-Holic

    Age:
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    832
    May 4, 2017
    Orlando, FL, USA
    Ultimately, this is the only thing that matters.
     
  4. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    I mean, if it works, what's the actual question? That builder found a way to make it work, so if it sounds good it is good.
     
  5. mcentee2

    mcentee2 Tele-Meister

    278
    Feb 18, 2011
    York
    Very true

    If that is the case the question turns into a useful addition to the "good" grounding schemes for others to read about on tdpri
     
  6. sds1

    sds1 Tele-Holic

    Age:
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    832
    May 4, 2017
    Orlando, FL, USA
    Well I hate to give the builder too much credit, I think it's more that they ignored some aspects of pure grounding scheme (partly at the direction of Fender-by-example), fired it up and found it to be a quiet amp, and left it be.

    This grounding scheme (or lack thereof) would probably be less successful in other builds.

    Also remember this is a fairly subjective measure of success until you start measuring idle noise with precision test gear in a controlled environment. I bet we could improve upon this amp's grounding scheme, as negligible to our ears as those improvements might be.
     
    King Fan likes this.
  7. mcentee2

    mcentee2 Tele-Meister

    278
    Feb 18, 2011
    York

    Thanks for this note of sense :)

    I suppose I was more worried about "safety" than noise really !

    The grounding is "sectioned/split " close enough to other schemes wrt the power and pre sections; in this case v1 is split off even more.

    It is just the mechanical nature of it going via each pot that concerned me.
     
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  8. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    I mean, look at all the Fender stuff. We just run a short wire from something we wanna ground over to some brass and call it good.

    There's lots of stuff that "works" - rather or not is ideal is a different question.
     
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  9. sds1

    sds1 Tele-Holic

    Age:
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    May 4, 2017
    Orlando, FL, USA
    Oooh I thought this was about noise. Usually the "grounding scheme" discussions are in the context of keeping the amp quiet.

    The first few things you listed are not a big deal but now I see the cathodes grounded thru pots... no I agree with you that is not a best practice. Signal grounds via the pots to chassis is just OK because those are signals, I'm not sure anyone would agree that cathodes should be grounded to the back of a pot like that.
     
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  10. mcentee2

    mcentee2 Tele-Meister

    278
    Feb 18, 2011
    York

    Exactly - methinks the soldering iron will be out shortly especially for these bits, and I might as well sort out the rest of the grounding as well to fit.
     
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  11. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Good discussion here. The broad issues as you say involve a) noise b) reliability. Am I thinking straight, that reliability is more the question than actual physical safety (fire, shock, etc.)?

    Your builder may have just followed two separate 'models' for grounding. Leo used local grounds all over the place in these small amps, like a single-strand-filament ground at each tube socket and a local ground to the brass plate for each sector. His amps were quiet enough, likely designed by trial and error in the shop. I'm guessing yours is far from the only modern build where someone just stuck a ground wherever Leo stuck a ground symbol.

    Leo, Jim Marshall, and many others grounded via the pots, either locally (the soldered-down ground lug) or also with a bus.

    Both models can create ground loops, but with luck (and in the millions of amps out there) these are small and may not act as antennae for noise.

    Reliability is another issue, but if your amp is quiet I *might* be tempted to simply make sure there's a big star washer behind each pot and crank the pot's mounting nut down firmly. EDIT: One reason beyond just 'keep it simple': unsoldering from pots can be a pain, or even damage the pot.
     
    Last edited: Feb 11, 2019
    mcentee2 likes this.
  12. mcentee2

    mcentee2 Tele-Meister

    278
    Feb 18, 2011
    York
    It is more safety really, reliability second, but if the loss of reliability was just a "not working" thing then I can fix it easily enough when it happens.

    If the reliability thing meant a safety thing in the future, then I am more likely to want to fix it all now.

    The various placements and separations of the grounds in themselves are probably "safe" but may induce noise at some point - I'll know where to look if it happens, and I'm not too fussed today.

    re Safety though: In particular:

    -in general: the tube cathodes and filter caps via the pots. If a pot becomes detached from the case or otherwise loses its grounding (corrosion?) then that associated cathode/cap isn't grounded

    - in particular: the main filter cap and screen cap, heater center tap, 6v6 cathode, and 220 grid resistors' ground going via the Tone pot case to ground in but..

    I am not clear if that is a safety concern ?

    and:

    - The PT 330-0-330 center tap being grounded via the PT corner bolt
    - The Power cord ground bolted to the same one.

    Is that safety concern ?

    Does any of the above lend itself to danger of shocks or overheating, sudden current rush etc ?
     
  13. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    I'll tackle this one -- you're right to think about true safety first.

    On the one hand, many modern builders ground their *CT* to a PT bolt, and if you use two star washers and some thread lock, it will likely work OK. But experienced amp repair folks note PT bolts do tend to loosen over the years, so a dedicated center tap / 'power amp' ground bolt is better, and would be a simple enough fix *if* you can safely fit a drill into your chassis in that area. Otherwise at least get the star washers and thread lock right.

    **But** the household mains power cord ground, also sometimes fastened to a PT bolt, is a bad idea. That is a huge safety risk if the nut ever loosens. It needs its own separate, unique ground bolt and star washers x 2 and thread lock. Luckily, it's usually easier, even in a Fender 'trench' chassis, to drill a hole high in the sidewall of the chassis where the drill bit won't contact anything even if it punches through all the way.
     
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  14. kleydejong

    kleydejong Tele-Holic

    647
    Aug 30, 2010
    Orange City, IA
    I know much of the direction is about grounding, but to touch on the mechanics of nuts and bolts.

    I brought my old Cakepan 5E3 to a gig this past weekend and noticed that a nut had come quite loose. I hadn't been grounding anything to that point, but my point is that I feel like you never quite know where a screw / nut connection to the chassis will come loose over time. This particular connection was using a standard bolt - flat washer - flat nut from my local hardware store. I had tightened it by hand using a screwdriver on one end and a pliers holding the nut on the other end. I try to tighten it down as firmly as I can without stripping the screw.

    I also currently have a wiggly pot on the volume control of my strat. So that's two out of perhaps hundreds of nut / bolt / washer combinations I've put into an amp or guitar or pedal in the last 10 years that are recently loose. Percentage wise it probably looks pretty good. But it isn't fool proof.

    If you were to be hyper conservative on this what would the very best practices be? Toothed washers, a firm tightening, and locktite? Perhaps even using something like a star head bolt and then a drill to really tighten it down? Heck let's go to an extreme and use hex bolt heads and tighten them down with a wrench or even a breaker bar like you would on a car? Diminishing returns ensue. Impractical in a tight space.
     
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  15. mcentee2

    mcentee2 Tele-Meister

    278
    Feb 18, 2011
    York
    Thanks - bolts, star washers etc will be on their way to me :)
     
  16. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    Nylon luck nuts are also a good plan. That sucker is never coming loose.
     
  17. Urshurak776

    Urshurak776 Tele-Meister

    492
    Jul 2, 2004
    Charlotte
    If it's good enough for the Submarine force and the Space Shuttle, it's good enough for a 5E3.
     
  18. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Use what you will. I would just say that I have worked in facilities where nylock nuts were forbidden on electrical connections. I recommend keps nuts, star washers, lock tight and proper torque specs for the size fastener you are using.
     
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  19. Lynxtrap

    Lynxtrap Tele-Holic

    640
    Feb 29, 2016
    EU
    Seems more like the builder found the nearest things made out of metal that looked like ground on the schematic. This fine example of how not to do grounding just happened to work by luck. ;)
     
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  20. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    For sure - after getting more details on the pots and what not it sounds sketchy. Pictures would be interesting to see the general quality of the work.
     
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