overdrive box grounding schemes

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by booj, Feb 4, 2008.


  1. booj

    booj Member

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    Anybody know of a website, or info pertaining to ways to keep the p. s. hum from coming through on a DIY high gain stomp box? I use a DS-1 in series with it and the Boss doesn't change its background noise when the p. s. is unplugged.
    The noise level itself doesn't get too much higher, but the hum sounds different.:NUTS:)
     
  2. HipKitty

    HipKitty Silver Supporting Member

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    I think this post may be in the wrong spot, however, in the DIY,are your in's and out's shielded with the shield grounded on one end only? Also, are they separated..(i.e. the input jack to switch on the input side of the box and the output jack to switch on the output side of the box)?
     
  3. booj

    booj Member

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    Thanks for responding HipKitty!
    After perusing the effects threads I was impressed by the brand names. This box has none. I feel that it is a theory type query and the more hip tech people are on this thread, although I am probably wrong, as you have pointed out. Anyway..
    The Rean style jacks are both grounded to the box by the sleeve connector only.
    The nuts holding the jacks use 3 steel washers instead of plastic washer on the outside of the box. (pretty) The Circuit ground is connected to the boards' hold-down screw/metal spacer/chassis.
    The LED, Level control, tone control cap, diode snubber circuit,and bypass ground are formed by a wire from the two jack ground lugs.
    The power supply jack connects to a full wave bridge to allow either polarity of power supploy into the box. That's grounded to the circuits hold down screw also.:confused:
    It really is pretty quiet. I just want it silent. :bkw
     
  4. HipKitty

    HipKitty Silver Supporting Member

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    You'll definitely want to use shielded wire (we use RG-174 coax) at least from the input and output jacks to the switch and keep them seperated..as I questioned in the post. The braided shield can be separated out of the braid, twisted together, soldered into a single "wire" then connect it to the ground lug of the input jack...do the same for the output jack, but (obviously) with a separate piece of shielded wire. The wire inside will be soldered to the tip leg of the correlating jacks. On the switch end of these, strip the shielded wire so that no braided shield is exposed, shrink wrap it, but leaving the "internal" wire exposed so it can be soldered to the correct legs of the switch...maybe leave about 1/8" of the "internal" wire (plastic) sheath from the stripped "internal" wire to the shrink wrapped section of the coax..I hope this makes sense...

    Then comes the issue of whether or not you are grounding the switch itself...if not, it needs to be done.
     
  5. booj

    booj Member

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    Thanks once again for the reply HipKitty,
    I'm thinking the problem could be a groundloop created by the current from the power supply traveling through the aluminum enclosure via the same route that the audio is using for its ground. Since you can't see the box, I guess the question is in your experience have you seen this happen? The noise is definately 60 HZ, although the power supply goes through a full wve bridge before it gets to the circuit.:YinYang
     
  6. HipKitty

    HipKitty Silver Supporting Member

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    First, look for a loose or ungrounded ground and/or solder joint.

    Honestly, I don't suspect a missing ground in the signal path, otherwise the unit (most likely) wouldn't pass signal. However, this doesn't always apply to some circuit designs. The same pretty much applies to a missing ground on the power supply...if it weren't there, there'd be no power. This brings up the issue of testing voltages on the power rail. Not only check that the correct power is where it's supposed to be, make sure that there is no power where it shouldn't be.

    What kind of voltage and how are you powering the unit?

    Verify the circuit build by continuity tests and correct component values. Also, verify that any caps that are positional (i.e. electrolytic) are positioned correctly. Essentially, re-trace the entire build.

    I truly suspect a proper shielding issue (or lack there of). What enclosure are you using? Also, you may need to do the shielded cable coming from the switch to the input of the fx as well as going from the fx to the switch (via volume controls).
     
  7. booj

    booj Member

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    Problem solved. I looked at a boss schematic of a BD-2, and found that the ground for the output jack went through a 100 ohm resistor to circuit ground. I did that and the 60 hz noise was eliminated.
    However, with that noise gone, I could then hear a 120 hz p.s. noise. I fixed that by adding, coincidentally, another 100 ohm resistor in series with the p.s. jack and the boards d.c. supply line. The boxes internal filtering was more effective and I only lost a fraction of a volt of supply voltage.
     

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