RTP-area local music and culture

[Chris Rossi <nospam AT spacelabstudio.com>]

It's static.  Maybe  I still haven't opened it up yet but I was 
experimenting and I found that I could make the problem go away 
temporarily by shorting the signal to ground.  I could measure a static 
voltage of zero between the signal out and ground on the guitar and play 
for a few minutes crackle free.  After a few minutes the crackle 
returns.  Measure the static voltage again and it's around 8mV.  Lather, 
rinse, repeat.  Everytime, by playing the guitar, I could get a static 
voltage to build up.  Static voltages in the right places make things 
microphonic (sort of like a condensor microphone).

It first occurred to me check this after I unplugged the guitar and 
noticed the loose cable end was very microphonic.  Roll it around and 
the sound of the cable rolling around on the floor is coming through the 
guitar amp.  Pick it up and grab the cable for a few seconds, such that 
both conductors are going through my skin, cable is suddenly not 
microphonic.  Static builds up, then I discharge it through my skin.

Actually, that doesn't make sense, though.  The input impedance of the 
amp is high, but infinite, so there should be a path for static to 
discharge to ground without building up.  In fact, the volume knob in 
the guitar should also provide such a path.  So I dunno.  I did measure 
a few millivolts voltage, though.  I'm stumped.

I'll think about it some more.

chris


grady wrote:
> I could certainly imagine getting some noise if there's signal running 
> across those springs & they're shifting in their mounts, but there 
> shouldn't be actual signal on them, and in any case, I'd expect you to 
> get the same noise regardless of pickup.
>
> Further experimentation/question: do you hear the noise if you lay the 
> thing flat on a table & pick the open strings with a pick, such that yr 
> apparently electric skin doesn't actually touch the strings or bridge?
>
> My guess right now, given that the neck pickup seems to be be both more 
> susceptible to general noise, and to this particular noise, is either a 
> bad pickup, or a bad switch, and I'm more inclined toward bad pickup. It 
> could be ever so slightly microphonic, such that the increased string 
> travel in vibration when you're picking hard is enough to get one of the 
> poles moving a tiny bit.
>
> But that's just a total guess. I'm assuming, given what/how you play, 
> that you're probably more likely to be using the neck pickup, so I guess 
> you gotta deal with it one way or another.
>
> Chris Rossi wrote:
> > grady wrote:
> > > Some questions:
> > >
> > > 1) does it act more or less the same regardless of which pickup you're 
> > > switched to?
> > Mostly neck pick up.  Occasionally the middle pick up, but to a less 
> > extent.  Couldn't make the bridge pick up do it just now, so maybe it is 
> > immune.  There's also with this guitar, like most guitars, noise that 
> > changes or goes away when you touch the strings.  Interestingly, this 
> > noise is not present with the bridge pickup--ie taking my hands on or 
> > off the strings doesn't  change the noise characteristics of the guitar 
> > with this pickup, but does with the other pickups.  I suspect some sort 
> > of electrical interaction with my body is at the root (my electric 
> > personality), so I suppose figuring out why the bridge pickup is immune, 
> > might help me figure out how to fix the bridge and middle pickups.
> >
> > Possibly the dryer sheet the manufacturer stuffed under the pick guard 
> > is bunched up near the bridge?  I haven't opened it up yet to check 
> > their handiwork.  Maybe tonight.
> >
> > > 2) how does the position of your right hand w/r/t the bridge change when 
> > > you're playing chords with the pick vs single notes or fingerpicking?
> > Not much.
> >
> > > 3) What exactly does this circuit look like (I haven't had a guitar open 
> > > in 22+ years, and that one was a real POS anyway)? Specifically, if you 
> > > took it DI through a transformer DI with a ground lift, could you cut 
> > > this ground wire entirely & still get signal, so as to confirm/deny that 
> > > the wire is the issue? Or could you readily reconfigure the circuit so 
> > > as to make that happen? I'm asking because you honestly don't know for 
> > > sure that it isn't one of the pickups, or something funky in one of the 
> > > pots. It seems mechanical, but . . .
> > Haven't opened up the main cavity yet, just the cavity in the back for 
> > the bridge/groundplate.  But here's a schematic:
> >
> > http://www.glguitars.com/schematics/Legacy_schematic_drawing.pdf
> >
> > This doesn't make complete sense to me, though, since the connection 
> > between the bridge and the ground plate is made via the springs that 
> > tension the bridge.  There is no black wire from the bridge to the 
> > ground plate as the schematic shows.  Maybe there should be?
> >
> > chris
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