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Amp grounding/lead dress-good reference? bus? star?

Discussion in 'Amp Tech Center' started by ChuckZilla, Oct 9, 2013.

  1. ChuckZilla

    ChuckZilla TDPRI Member

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    I have recently received my weber 5E3 kit. First off let me say the cabinet is beautiful. Tweed with oxblood. Speaker also looks great. I am trying to be patient as I work on this build.

    To the question... Do you have a good reference for lead dress in the 5E3?

    What about bus grounding?

    Star grounding?

    How many ground points on the chassis do you use?

    Thanks,
    Chuck
     
  2. radio

    radio Tele-Meister Ad Free Member

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    The ValveWizard has some great instructional material : http://www.valvewizard.co.uk/Grounding.html

    Also, if you have a little money laying around, consider starting a collection of Kevin O'Connor's book series. The first one (The only one I have so far), talks about it a bit: http://www.londonpower.com/tube-amp-books/The-Ultimate-Tone
    These can be purchased in the States at several places to avoid the horrendous shipping charge from Canada.

    ValveWizard should tell you everything you need to know about star grounding and chassis grounding.
     
  3. ChuckZilla

    ChuckZilla TDPRI Member

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    So I am to take it that with the typical layout of the 5E3, the bus grounding scheme will be more straightforward than the star grounding scheme.

    I also found a nice link to a tdpri forum with pictures of the 5E3 circuit using a bus bar

    http://www.tdpri.com/forum/shock-brothers-diy-amps/355826-uk-tweed-deluxe-build.html

    [​IMG]

    [​IMG]

    It seems that this guy used two bus bars, one for the preamp, and one for the volume/tone stack.

    In addition he has not connected the bus bar to the first two filter capacitors... I have seen a bunch of people suggesting using TWO points for ground... one for the preamp, and one for the power amp...

    However, the valvewizard says you should use only ONE grounding when using the bus grounding scheme... [See page 271 Fig 15.10 of http://www.valvewizard.co.uk/Grounding.html] Also, it appears the valve wizard only approves of bus grounding on simple, low power single ended amplifier circuits.

    I would appreciate to hear what grounding scheme any of you have used in the 5E3, and with what results? How many ground points have you used in the chassis? Bus ground?
     
  4. ChuckZilla

    ChuckZilla TDPRI Member

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    I can't see for certain, but it appears that he has one ground point for the preamp part of the circuit, (the last filter cap + the cathodes of the 12AY7 and the 12AX7)

    and another ground point for the power amp. (the ground for the first two filter caps, and the cathodes of the 6V6GTs)

    [​IMG]

    I have seen this suggest before... is this classified as star or bus grounding?
     
  5. ChuckZilla

    ChuckZilla TDPRI Member

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    Actually I am answering my own questions as I read. I hope that is Okay...

    It appears that the approach that dajoth is using is a combination of bus and star grounding techniques... The contacts on the bus bar form "local stars." [See figure 15.12, 15.13, and 15.14 in valvewizards writeup.]

    I am going to think on this for a bit, and hope I can figure out the best recipe for proper grounding, star and bus. The valve wizard seems to know his stuff.
     
  6. ChuckZilla

    ChuckZilla TDPRI Member

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  7. ChuckZilla

    ChuckZilla TDPRI Member

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  8. stratman_el84

    stratman_el84 TDPRI Member

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    Here's a link to the "Build Information" thread in the "Reference Section" of the Weber Kit Builders Forum which contains information on grounding, lead dress, etc. Trying to recall if I've seen you post on the Kit Builders Forum before. If you have not joined, might be a good idea seeing as you've got one of their kits. Lots of really, really, good folks there. The Weber staff reads/posts/responds there as well.

    http://www.weberorders.com/forum/index.php?topic=54.msg5717#msg5717

    Weber's "Reference Section" has a wealth of useful info.

    http://www.weberorders.com/forum/index.php?board=8.0

    Here's a really interesting blog page documenting implementing a ground scheme in a Weber "5H15 Revibe" build, a very complex and hum/noise-sensitive outboard (sort of tweed-Fender-6G15-like with more) reverb/tremolo build that isolates signal ground from chassis ground.

    http://home.everestkc.net/jgehring/revibe1-4.html

    Lots of good examples of proper wiring/cabling, shielded wire prep/dressing, & lead-dress practices in that build diary as well as valuable insights on grounding and noise/hum reduction. When it comes to an extremely-clean and professional-appearing tweed-style chassis build, it just don't get much prettier than those build-pics.

    Tip for novice builders: Make a few hardcopies of the schematic & layout drawings. As you complete each connection, use a highlighter marker on the drawing. After you've finished all the wiring, use a fresh copy/set and go through and check each connection and again highlight it on the drawing(s) as you go.

    Good luck! Just be patient & methodical.

    Strat
     
  9. ChuckZilla

    ChuckZilla TDPRI Member

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    Thanks for the feedback, strat.

    I am still in the planning stage of my 5E3 build, but I revisited a 5F1 build that I completed this summer. Here's what I have found.

    My 5F1 build has an audible baseline hum in it. It's not terrible, but it certainly is there. I have been working with it to see if I can further reduce the hum. I have read the valvewizard's article on grounding, and from that I learned how to think about ground loops, and how they may come to contribute to hum. From that article, I rerouted some things, and tried to reduce the length of wire runs.

    I also tried the bus diagram which shows what valve wizards describes as, "an approximate multiple star ground." This was in figure 15.10.b. in his article. If you look at this layout, it is exactly a fender champ amp.

    The valvewizard suggests using ONE point for chassis ground right at the input of the preamp.

    This did not yield good results for me.

    What did help me instead was to use the grounding scheme from Hoffman amps (el34world.com). The hoffman guy suggests using 3 grounding points.

    1) one ground point for preamp including the preamp cathodes, and the preamp filter capacitor. This ground contact point is made at the input jack.


    2) one ground point for the two power/reservoir filter capacitors, the power tube cathodes, and the center taps from the power transformer. This contact ground is made to the chassis at one of the lugs on the power transformer.

    3) one ground point for the speaker. This is made to the chassis at the speaker jack.

    After using the Hoffman approach (classic approach) with three contacts to chassis ground, my 5F1 was at its quietest.

    You can read in detail abou the hoffman/classic approach to grounding at:
    http://www.el34world.com/charts/grounds.htm

    This is actually the reference I had seen before, and was hoping to get linked to when I posted this question on the forum.

    While my 5F1 still has an audible amount of hum when the guitar is not being played through it, it sounds better with the Hoffman approach.

    Bottom line for my results: Don't use star grounding, instead use three grounding points. One for preamp, one for the power supply, and one for the speaker(s). A Bus bar for the preamp is also ideal.

    Of course YMMV, but from my little experiment, three ground points work the best.

    I am hoping that my 5E3 will be quieter than my 5F1, but I'll get back to you guys on that.

    -Chuck
     
  10. iguazux

    iguazux Tele-Meister

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    Considering the hum in your 5f1, Have you made the well known heater mod (symmetrical heaters) ? If not, it can help a lot.
     
  11. Bill Moore

    Bill Moore Tele-Afflicted

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    I have an old Airline, that I rediscovered several years back, and reconditioned it, and now it's up and running. I purchased it in 1968, and since I've owned it, it had a hum. While in the Navy I had the tech's look at it, and they changed some tubes, and caps, but it was not much better.
    When I got it working again, I took a drumstick, and started moving things around in the chassis. Finally moved a couple of wires just slightly, and it got quiet. Maybe you don't have a ground problem.
     
  12. ChuckZilla

    ChuckZilla TDPRI Member

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    The transformer I am using has a center tap for the heaters. It is grounded to the transformer lug with the HV center tap and the power tube cathode.
     
  13. jefrs

    jefrs Doctor of Teleocity

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    Reference books
    Morgan Jones, "Valve Amplifiers" and "Building Valve Amplifiers"
    Self-descriptive really. Possibly too much information but all good.
    Available on Amazon and other book sellers
     
  14. chabby

    chabby Friend of Leo's

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    I have gone to Star grounding pretty much no matter what I build these days. First off, I don't use boards but rather terminal strips to build amps. It makes star grounding so intuitive and really, the whole lead dress thing much easier to use common sense once you understand what each preamp wire does. It shortens all the wires in the end makes an amp 50% easier to repair and grounding a breeze. Depending on the amp size and power, you will usually see one main star ground fairly close to the PT. The as you ground the preamp grounds individually, I connect those grounds back to the main star ground as well so the grounds are all daisy chained back to the main until the output at the far end near the a lot of guys like to isolate those grounds which keeps them less prone to noise. I like terminal strip construction because it doesn't depend on the board effecting lead dress so much. You have less opportunities for criss crossing preamp wires and massive room in the amp. Fender and all the big producers went to board construction purely for assembly workers and speed. They didn't have to know how to do but one job. In other words preamp boards were only put in amps for the purpose of your Aunty Ruth being able to solder part b all day on the assembly line. That's an extreme example granted, but the boards do nothing but take up valuable space in the amp. You just have to re-design every circuit you build, but after doing a few, you never want to use boards again. The most beautiful thing I ever saw in my amp learning was when I saw the inside of a Carr Ramble, then a Tophat who also use terminal strips. It was an epiphany for me because I'd only seen it in some very old ciruits and at first glance, it kind of looked more difficult.

    But then I tried building a little 18 watt amp that way and several others as I got the general hang of it. getting that darnn board out of your way just opens possibilities. the Board used to always dictate design, which was limiting at times. But it makes it easy to sell kits-lol It looks all neat and orderly and simple looking I think, from a marketing standpoint. But in a way I totally disagree that's true. Because with Terminal strips each screw down point can become a ground.
    You can use different size term strips and accomplish anything 5E3 is a cake walk with strips.

    Narrow Panel tweeds even look larger. I stil love Fenders traditional heater dress with them flying as opposed to their earlier designs where they laid them down like say 52 back whenever the TV panel octal and voice coils speakers deals went bye - bye. They used such tight and sturdy heater wires in the blackface era, then I think they transitioned to plastic for the SF amps.
     
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