GROUNDING TYPES

Discussion in 'The Workbench' started by Marcomel79, Nov 22, 2021.

  1. Marcomel79

    Marcomel79 Well-Known Member

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    Hi all, i apologise if this has been discussed in another thread but i just wanted to ask what the difference is between central star ground and Larry grounding and if one is better than the other. Ive only built one amp and ive used the central star grounding. Ive attached the ground lug at the chassis next to the inputs (4 holer) and all the grounds meet at a star point which i isolated from the chassis. My amp is nearly dead quiet ecxept for a little hiss when dimed but thats to be expected.

    Thanks in advance for all the replies.

    Marco
     
  2. 2L man

    2L man Active Member

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    Larry grounding uses chassis for all return current flow. Vintage amps might use chassis for all or partial return current flow. This is not good when chassis surrounds amp circuit. Also when instrument cable uses its neutral for signal and it is connected to chassis, the electromagnetic noise there inevitably comes to amp ground, will transfer to instrument and some will come back to amp input.

    Secondary Ground should be thinked as Neutral and it is one wire/bus or few wires when Star grounding is used.

    Chassis main role is Safety Earth and secondary role is a Shield.
     
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  3. South Park

    South Park Well-Known Member

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    The star grounding is what you to use all grounds are in groups that run to the center tap lug do not link them together and run one wire to the center tap you get ground loops
     
  4. Marcomel79

    Marcomel79 Well-Known Member

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    So its better to use only one connection to chassis like the one used for my build then.... the amp is very quiet...
     
  5. Marcomel79

    Marcomel79 Well-Known Member

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    This is the layout i used for my amp and is nearly dead quiet if not for some hiss when dimed like i wrote on my first post. And absolutely no hum.
    https://www.tube-town.net/cms/userfiles/downloads/px18-layout.pdf
     

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  6. South Park

    South Park Well-Known Member

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  7. AtomicRob

    AtomicRob Well-Known Member

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    Do you mean the mains ground? The amp should always have a dedicated safety ground physically near the power entry point, with a dedicated screw and lock nut. That's the (usually) green wire corresponding to safety ground. This will only carry current if there is a short or fault but it's pretty important to protect from that.

    This sounds odd - are you sure it's really floating and not just grounded to chassis through the instrument jacks? If floating that really means your ground path is back through the instrument cable, to... whatever is eventually grounded? Your hands or pedalboard maybe? This is at best a ground loop and at worst I think would be dangerous. I've never seen deliberately floating ground in a guitar amp - typically the star or bus ground is connected to the chassis in one place (separate from the safety ground, so you essentially have two connection points to the chassis.)
     
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  8. thetragichero

    thetragichero Well-Known Member

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    so there are a number of signal/power grounding philosophies/best practices (this does not include the separate bolt for earth ground and leaving the earth ground lead longer than the others if it uses an attached cord as these are mandatory for safety). sometimes pure dumb luck will have even the ugliest grounding scheme sounding quiet
     
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  9. Marcomel79

    Marcomel79 Well-Known Member

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    Hey Rob,
    no, the mains ground is separate and is attached to chassis as it should be. Maybe my first post was a bit confusing in the way i worded it.

    The circuit ground looks exactly like the layout ive attached, where the only connection to chassis is at the star point. However, i chose to have the connection to chassis at the guitar input, therefore insulating the star to avoid having more than one connection to chassis, and creating ground loops.

    My question was more like, which one is better and why..
     
    Last edited: Nov 23, 2021
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  10. Marcomel79

    Marcomel79 Well-Known Member

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    The circuit ground looks exactly like the layout ive attached, where the only connection to chassis is at the star point. However, i chose to have the connection to chassis at the guitar input, therefore insulating the star to avoid having more than one connection to chassis, and creating ground loops.
     
  11. Marcomel79

    Marcomel79 Well-Known Member

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    Maybe a 20W jcm800/jmp 2203/4...? I wanna build them all
     
  12. 2L man

    2L man Active Member

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    Secondary Neutral/Ground should definitely have only one hard wired connection to Safety Earth/Shield/Chassis and then it is impossible to operative current to escape out of amp circuit. When all band eguipment are built like that instrunents interact other instruments less.

    And instead of hard wiring you can even use a "ground breaker" "hum eliminator" etc circuit. It consists two parallel but opposite diodes which rating is at least double the HV fuse is. And parallel 10R/2W resistor and parallel X-class capacitor. There is lots of information in internet... This circuit ties amp secondary to Safety Earth "smoother" but prevents HV voltage appear to instrument strings or microphone when HV fuse burn before diodes and resistor so it is as safe as hard wired circuit. This can make setup quieter when lots of effects are used and when a Stereo rig is used.
     
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  13. thetragichero

    thetragichero Well-Known Member

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    the answer is whichever way is quiet is better. i have preamp grounds go to the input jack sleeve/chassis (nothing soldered to pot backs) and phase inverter/power amp grounds go to chassis at the first filter cap/ht center tap ground point. works well for me
     
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  14. Marcomel79

    Marcomel79 Well-Known Member

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    Was just asking because since there are difference methods to ground a circuit, maybe one was better dipending on wattage, type of circuit etc... this forum is a great place to learn. Mine works very well as it is. Heard some people built virtually the same amp twice and had noise problems with one of them and had to change the ground scheme. I guess there are many variables too, that influence the noise...
     
  15. Pete Farrington

    Pete Farrington Well-Known Member

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    In the interests of clarity and understanding, I think it best to avoid the terminology ‘neutral’ to mean anything other than a mains neutral conductor.

    Eliminating the chassis’s use as an 0V common conductor for HT current is beneficial in achieving repeatable, reliable low hum behaviour.
     
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  16. Marcomel79

    Marcomel79 Well-Known Member

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    Zero hum on my build Pete. I guess its true that theres more than one way to skin a cat...
     
  17. Pete Farrington

    Pete Farrington Well-Known Member

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    Absolutely, but to reduce the variables, it may be beneficial to eliminate the chassis as a HT 0V return conductor, use it purely as a screen. The HT has significant, noisy current loops. Keeping those current loops confined in wires, rather than allowing them to find their own route via the chassis, can prevent them interfering with the signal path.
     
  18. XTRXTR

    XTRXTR Well-Known Member

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    I have recently been studying grounding schemes. I would say what you did follows what Merlin does for the most part. One connection to chassis at the input follows his logic as well. Using local star per stage and daisy chain the stars together in the order of the stages from input to output. Speaker common should join at the PI/NFB which is through the presence pot. This logic makes sense to me and is my plan as well.

    A difference would be the use of multi cap can on more than one stage which I had planned to ask my own question about on this forum. I did a search first and found this thread. Since you are talking about grounding I wonder if you mind that I make this nuanced discussion here?
     
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  19. Gene Ballzz

    Gene Ballzz Well-Known Member

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    @Marcomel79
    It's all good! If it were me though, I'd use input jacks isolated from the chassis (like Cliff UK or Neutrik/Rean) and attach/connect that star lug to the chassis. Six of one, half a dozen of the other! If its quiet though, leave it as is. Just personally tough, I'd shy away from depending on that jack/nut for my main connection to the chassis! As we all know, sh!t does happen! :wow:

    Once I gather my thoughts and ponder your comments a bit, I'll PM you some stuff about that DSL5C.

    Just Thinkin'
    Gene
     
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  20. Marcomel79

    Marcomel79 Well-Known Member

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    Not at all!! Ask away!
     

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