Volume Pot Hiss

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by mmmatthew, Feb 21, 2008.

  1. mmmatthew

    mmmatthew Member

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    Hi, guys... I'm new hear so don't be too hard on me! (long-time reader, new poster)

    Anyway, I have an Am Dlx HSS FMT Strat (2004)... and I've been having some trouble with the pots. First off, for those who may be unfamiliar with the axe, it's got only 2 knobs: master volume and tone.

    So, my problem is that when the volume is backed down to anything lower than 10, the guitar just starts hissing. This is obviously more evident with more drive. Now, this hiss isn't really noticeable with the tone at max, but the more you roll back the tone knob, the more apparent it becomes.

    I can tell you right now that it is not the amp (tried multiple guitars with it), it's not the cable (tried various cables), it is not the wiring in my house (does it everywhere), and it's NOT dirty pots (it's not a crackling when I turn the pot, but a constant hiss). It happens on all switch positions, so it's not the pickups either. Again, with the volume at 10, there is NO hiss.

    I've been trying for the longest time to figure out what is causing this. Could it be bad caps? Just thought I should mention that the S-1 switch has a cap attached to it, but I don't really think this is causing the problem as the cap is only engaged in one position of the switch... but just wanted to throw it out there regardless. Could it possibly be poor shielding? If the pots really ARE the problem... is there anyway to fix them and not have to go out and get new ones?

    I've tried posting this on various other forums and really haven't gotten much help. So I'm turning to you guys here at The Gear Page, because you guys seem to know what you're talking about. Thanks for any help you can give me!
     
  2. walterw

    walterw Gold Supporting Member

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  3. mmmatthew

    mmmatthew Member

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    I'd definitely describe it as hiss... much harsher than 60-cycle hum if that's what your asking. Any ideas what's causing it?
     
  4. Rosewood

    Rosewood Member

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    I agree with Walter about a clarification on hiss/hum. Hiss comes from an amp or other amplifying devices but not usually associated with a guitar. Does this guitar have active electronics?
     
  5. Rosewood

    Rosewood Member

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    Does this get worse when you remove your hands from the strings?
     
  6. mmmatthew

    mmmatthew Member

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    Well, for sure, it's not the amp that's making the noise... it's the guitar. The guitar doesn't have any active electronics, and I don't believe it's a ground issue either (i.e. the hiss doesn't get any louder when I don't touch the strings).
     
  7. David Collins

    David Collins Member

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    So, the hiss sounds louder as you put your ear right up to the guitar, and it's not coming from the speaker? ;)

    My point is from what I've heard so far, I don't think you can write off the source of the hiss as the definitely being guitar. Is the sound the amp makes when you unplug it from the guitar (while holding the cable, not the ground) of any similar sound or tone to the hiss you describe? Sometimes these problems can't be so easily isolated to one thing, but rather could be a combination of factors. For example, hiss coming from the amp circuit that some problem or design element in the guitar circuit is not grounding out as well as others.

    The cable is nearly grounded (through the pickup coil) when the guitar volume is at 10, and fully grounded when it's at 0. When it's in the middle however, you may have from one hundered to a few hundred ohms to ground - giving you a his with similar qualities to the noise when you leave a cable unplugged. If you had a guitar with 1meg volume pots on a noisy amp with 500k input impedance at the amp the hiss would likely be very noticeable with the guitar volume turned to the middle. If you had 250k volume pots with a 2meg amp input impedance it would be much quieter. Keep in mind that in both of those examples, the guitar wiring is working fine.

    If you're noticing the problem at high gain and the noise goes away with the volume at 10 or 0, I have a feeling the wiring of your guitar is fine. Not sure why you're not getting the problem with your other guitars, but it could be things from pickup impedance to pot values to shielding.

    If the hiss is still there at zero though, it is just a bad ground on the volume pot or it's lower lug. That or if the volume were wired J-Bass style, rather than the usual LP or Strat style. If I understood you right the noise was only in the middle though.

    Two things you could do. First is to get it shielded. This is probably the single biggest area for improvement. Second, (and probably more importantly) is that you should take it in to be looked at by a professional. Solving these problems online can be like a doctor trying to diagnose a disease on a forum. A good tech can probably answer in about 30 seconds with an amp and a meter, what would take hours or days to work out from forum descriptions.
     
  8. Rosewood

    Rosewood Member

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    In my 30+ years of repairing and playing guitars I've never seen a guitar (without active system) hiss so I think we're talking about two different things here. Is there any way you can record it and post it for us to hear?
     
  9. EADGBE

    EADGBE Member

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    Are you playing your amp wide open when you notice this?
     
  10. tahwnikcufos

    tahwnikcufos Member

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    Wow, this is an old topic...lol. I have seen this in guitars before, especially ones that have been stored in less than favorable conditions; where temperature and humidity extremes have wreaked havoc on the electronics and hardware. Corrosion actually builds up in the pot making it act like a capacitor. It's like a haze on the wiper and contact surface. The pot will actually store some of the electrical energy from the pickups and discharge it as a hiss, not unlike that of your favorite radio station as you get further from town. A simple fix, is to remove the pot and lay it on it's side, put a very small drop of WD40 on the edge where the metal case meets the composite wafer, allow it to soak in for several minutes then run the control back forth. If this does not work, replace the pot. This happens on amplifiers that have not had there controls moved in a long time, usually the gain pot; due to the amount of signal it must impede and the fact that once someone gets it where they like it, they usually do not move it. Why doesn't it do it at full volume? Easy, how often is your guitar never at full volume, played or stored? That was a rhetorical question btw... Good luck and rock on!
     

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