Grounding schemes

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by J.T., Dec 23, 2002.


  1. J.T.

    J.T. Supporting Member

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    Anyone care to share their favorite grounding scheme for amps?......i am building a JTM45 and i am decinding on a grounding scheme to 1- minimize any hum or noise and 2- to asthetically look neat
     
  2. tonedaddy

    tonedaddy Member

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  3. J.T.

    J.T. Supporting Member

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    Thanks Tonedaddy!
     
  4. JacksonAmpworks

    JacksonAmpworks Member

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    Thanks for the link to my amp Tone Daddy!! Yes, I did build that amp, and I just sold it to a guy on eBay a few weeks ago. For that amp, I used a single point ground and it was very quiet.

    Right now I'm experimenting with a true star ground on my prototype amps that I'm building, and I have nothing but good things to say about them. The layout is a lot cleaner than with a single point ground, and the noise floor has been further reduced.

    From the experience that I have had with my prototypes, I will be offering all my amps with a true star ground that ends with one connection to the chassis. The only other ground on this amp will be the safety ground from the line voltage ground straight to the chassis.

    Thanks again for your post!
     
  5. kwright

    kwright Guest

    Randall Aiken has a great paper on his website.

    www.aikenamps.com

    Go to Tech Info-->Advanced (Aiken)-->Star Grounding.

    This is where I got the most info for my "Homebrew".
     
  6. JacksonAmpworks

    JacksonAmpworks Member

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    I second that kwright.

    Randall Aiken's site has been an invaluable reference for me. He is also one of the nicest guys I have ever dealt with. Once I left a message for him on his phone and said that he could email me back to save long distance charges and he called me back within 10 minutes.

    He's a very cool guy and a great source of knowledge.
     
  7. Carol-AnnAmps

    Carol-AnnAmps Gold Supporting Member

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    I keep reading that grounding schemes are not an exact science, that's not exactly true. They are rarely understood making it mysterious to many, but it actually is a very simple science. Understanding current flow paths of the various AC and DC supplies and signals dictates the best grounding scheme for a particular design. THe chassis is your largest conductor, use it wisely and it will beat any ground bus.
    Typically keeping heavy current grounds like heater grounds and speaker grounds, short and away from small signal grounds, always knowing the flow direction allows the chassis to be used a common ground point, with multiple star connections for each 'circuit' made to it. It's easy to visualize if you actually think of the true direction of the flow of electrons, from negative to positive, not the other way around.

    I build multiple channel high gain amps that also incorporate some digital microcontrollers, so I have the extra issue of digital grounds, which have a whole different set of other issues than a current ground.....and I use the chassis as the main conductor for everything with zero noise.

    1. I use the following star points on the chassis.
    a) Safety Earth. Always as close as possible to the IEC connector and never shared with anything else.
    b) Filament Ground. Close to Power Transformer.
    c) Main Power Supply Ground. Located near the power transformer. HT C/T if applicable, bias supply if applicable, 12V supply. Main Power supply caps.
    d) Preamp Power Supply. Located a couple of inches away from the main power supply ground. All stages of the preamp Power Supply caps ground to this one point.
    e) PI Ground, Used for grounding the high signal level audio PI and efx return stages. Located close to the PI circuit.
    f) A separate star point for every two triode stages. All aspects of each pair of stages are grounded to the same point. Located close to the respective stages.
    g) Input Jack, this is generally connected to the same ground as the first two preamp stages, located close to the jack.
    h)Digital Ground, the digital power supply uses the 12V supply line and regulates it to 5V. The grounding for this is located next to the actual board in an area of the chassis where there is very little chassis current.

    The secondary side of the OT has a heavy ground current, wire this directly to the speaker jacks to avoid the flow through the chassis. If your amp has feedback you need a ground reference point to the PI, so you can take a small wire from the speaker jack ground and run it to the PI star ground. Only a very small current will flow in this circuit.

    The audio signal grounds and the power supply grounds are never located together. Some texts tell you to locate each power supply ground and associated regulation components right next to the audio stages they serve. I've always found this somewhat problematic from a practical sense. The heavier power supply current can induce noise in the audio grounds. Again if you think in terms of negative to positive, my rationale makes more sense.

    Modifying any old Marshall or Fender to this type of scheme, makes is a lot quieter.

    Anyway, hope this is useful. Just use some common sense and visualize where the currents flow and avoid mixing small audio and heavy power on the same ground and you will find you can break some of the rules you will read on the internet about grounding., with much better results that tacking a separate ground line in there. Chassis is the king conductor, use it !!!!!
     
    Last edited: Aug 13, 2014
  8. pdf64

    pdf64 Member

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  9. donnyjaguar

    donnyjaguar Member

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    Pay attention to what CA Amps is saying, there some sound advice here.
     

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