Charge buildup at guitar tone capacitor?

Pickups, wiring schemes, switch techniques and onboard active electronics for guitars and basses
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Deny
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Post by Deny »

I have an Ibanez RG1570 that for a really long time had a really weird behavior: some times I would change from bridge pup to neck and when I got back to the bridge pup it would sound thin / harsh / brittle. Some times that would also happen when switching preamps or cables. Once the harshness set in, all I had to do was turn the guitar volume knob to zero for like a second and voila, it got back to normal.

Needless to say I tried lots of possible solutions from installing a brass trem block to rewiring the pickups, changing cables and whatnot. Then I realized another (Jackson) guitar I have sounded a lot punchier and did not have the same problem although the bridge pickups in them are very similar (PAF Pro in the Jackson and Fred in the Ibanez). I did a quick check and noticed the tone pot in the Jackson was disconnected. Hmmm. Ok, tried disconnecting the tone pot in the RG1570 as well and BAM! No more harsh/thin tone.

Anyone have any idea why this happens and, more importantly, does it happen to every guitar with passive pickups and a tone control (the Ibanez also has a treble bleed capacitor in the volume pot that I didn't mess with)? It may be worth to note that it happened regardless of it being connected direct to my preamp (Triaxis) or through a buffered bypass (Bad Horsie Wah).

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phatt
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Post by phatt »

Without a very clear picture of internal circuitry or better still a schematic of the wire up it's hard to help.

No it should not happen but the possible errors are endless so hard to tell. :(
Phil.

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jmraney317
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Post by jmraney317 »

Found a wiring diagram for the RG1570 on Ibanez's web site. Nothing really unusual in the circuitry, but the pickup selector wiring is a little different for a three-pickup guitar (switch is wired so any combination using the center single coil pickup cuts one coil from the paralleled humbucker).

If desoldering the tone control capacitor (the 0.022 mF) fixed the problem, then perhaps the component itself had issues. It would be worth checking if replacing it solves the problem. The other capacitor in there (the 300 pF attached to the volume control) is not usually seen in passive guitar wiring harnesses; it looks like it serves the same function as a small value cap often seen bypassing master volume controls in amps (brightens the sound at low volume settings).

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Deny
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Post by Deny »

Yep, there's nothing unusual in the controls of my RG1570 except the fact that I've replaced the volume pot with one with a push-pull switch for engaging the neck pickup, which allows me for a broader selection of pickup combinations. The 5-position switch has 2 poles and is factory wired to tap one of the coils of either humbucker when in parallel with the middle pickup, which gives it some surpriningly convincing strat tones in positions 2 & 4. And it also has the bleed capacitor in the volume pot (which I kept) so when the volume knob is rolled off it doesn't sound muddy.

Now I might get flamed for this but I'm beggining to suspect that the harshness I was hearing was because a particular patch is extremely sensitive to playing dynamics (it requires that I play lighter) so if I'm coming from a patch that requires me to play harder it takes some time to adjust. Not 100% sure but it's a possibility :oops:

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DrNomis
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Post by DrNomis »

It could be the result of a grounding issue with the volume control, if the ground lug on the volume control had a bad solder joint on it, or the solder-lug is a bit loose, the small cap would bypass high frequencies to the output socket, causing the guitar to sound thin, what's maki8ng me suspect the volume control is that turning the knob seems to fix the problem, you could also try spraying the pot with some contact cleaner and see if that fixes things too.... :thumbsup
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Deny
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Post by Deny »

Thanks for the replies guys, I still don't know what to think on this one, half the time I think my ears are playing tricks on me but then again I don't hear the same thing with other guitars. What I probably need to do is stop being lazy and rewire this thing from the ground up, maybe I'll take the opportunity to install one of the (very nice) gold-plated Planet Waves jacks I've ordered from Warmoth a while ago.

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Post by GuitarlCarl »

All tone pots rob a little from your signal even when they are fully "on"... except the Fender no load pot whichs takes the pot out of the circuit at "10". Some guitars pickups just accent this signal loss more than others, and pots like many other components have tolerances too. Better pots seem to help this. I like CTS pots, but there are more expensive ones out there that MAY be better. Good luck chasing tone, IT'S WHAT WE ALL DO. :blackeye
I want it to sound like bees buzzing around in a 55 gallon drum...

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