Can a cap go bad and cause a short (humming)?

[lafromla1]

So I get the new strat all wired and it sounds freaking awesome, quiet as can be until picked, strummed or whatever.  Then I go to play with the tone and no change, so I look back there and the capacitor had come lose from the soldering point.  I resolder the cap back and now it hums like a there is no tomorrow.  The only way to get rid of the hum completely is to put my hand on the trem claw or grab the strings.  If I touch either the Area 58 or the VV 54 when engaged, it hums like a beast. 

Can this be a bad capacitor or just a cold solder joint causing it to hum?

 

[Cagey]

Neither. Somehow, you've got it wired wrong.

 

[lafromla1]

What is wired wrong?  I am only asking as before I resoldered the cap, all 3 pickups were working perfectly, there was just no tone control due to the loose cap.

Should I remove all the ground wires and start that process over to make sure that there isnt a cold joint somewhere?  I dont need to unhook any of the leads as they all act properly when the 5-way and mini-switch are engaged.

 

[Cagey]

Cold solder joints manifest themselves as intermittent or open connections. If you lost the tone control connection, you'd simply lose tone control. If you lost a ground, depending on where it's lost, you might either get noisier or lose signal altogether. If touching the pole pieces on your pickups makes things noisy, then it's likely the hot/gnd are reversed at the output jack. If you get that same symptom only on certain pickups, then they're wired backwards. As simple as guitar wiring is, it's difficult to say what could be wrong without being able to see it.

 

[lafromla1]

I'll go over the diagram DiMarzio sent me again, but after looking at it multiple times, I think everything is where it should be.  Strange that when the cap was loose, the guitar was silent and played perfectly. and when I reattached it is when everything bad started to happen.

What a pain in the butt.  I didnt have these issues when I wired my boat, but then again everything is scaled larger and I could use connectors, so there was nothing to solder.

If I just create a common ground wire attached to the inside of the cavity, can I avoid having to connect any ground wires to pots?  just attach all the pickup grounds and one side of the capacitor to the one common ground wire, connect the output jack to that same common and ground it to the trem from there?  I dont believe that there is any reason to ground the actual pot is there?

 

[stubhead]

This is actually several questions, and diagnosing wiring long-distance is notoriously difficult*, but:

The best way is to think of the signal as akin to water, or something ALIVE.... :evil4: The pickups generate a signal, and they have a ground. The signal goes crawling off to get dicked with at each stage along the way, so as to make something happen to it. It's rolled off with a pot through a capacitor to ground to change the tone, or rolled off with a pot directly to ground to change the volume.

2nd Q: A common ground will work just fine, but if everything except the tone control was working fine, demolishing the whole thing to start over is kinda drastic. You have isolated the problem at one particular point, and the grounds you already have (to the volume pots?) were OK.

So, maybe: It's very easy to fry capacitors with too much heat, far more so than frying pots - I always put little Radio Shack alligator clamps on the connecting wires as a heatsink, and only heat the lugs - if your soldering iron even touched the cap it may well have gone to heaven to sleep with the fishes.
That, fishy capacitor heaven. :guitaristgif: A partially-murdered cap could very well do what your'e describing. Plz refer to *, though.

 

[Cagey]

One side of the volume and tone pots needs to go to ground because that's how you control the signal. The volume pot gradually bleeds more and more signal to ground as your rotate the thing, and tone pot bleeds just higher frequencies to ground the same way. Grounding the body of the pot is redundant if the rest of the thing is wired properly, as it ends up grounded anyway either through the foil ground plane the pots are mounted to, or via the lugs you should be using instead to ground all that.

 

[drewfx]

1. If the tone control pot is wired properly and you're getting hum regardless of how it is set, the problem isn't the cap. But disconnect the tone entirely from the circuit to verify this.

2. If touching the strings makes the hum go away, the first question always is "Is the bridge grounded properly?"

3. If touching the PU's causes more hum (and you don't have the jack wired backwards entirely), the PU's bare wire may not be grounded correctly.

 

[Cagey]

Sometimes, a schematic makes more sense than a wiring diagram. Unfortunately, wiring diagrams seem to be the standard in the music industry, because so many people don't understand electronics, or at least the symbology used on circuit drawings. But, it's pretty straightforward, and gives you a better view of what the signal paths are instead of just where the parts and wires are. Below is a bit cribbed from GM Arts...

Here's the schematic for a standard 3-pickup strat. Probably the most special thing about this circuit is the 5 way switch. It was originally a 3-way switch that had a "make before break" design. This means that when switching from, say, the neck to middle pickup, the middle pickup connects before the neck pickup disconnects. Players soon became adept at balancing the switch between selections to use the additional sounds (neck with middle and middle with bridge). These became known as the "in-between sounds" and are often incorrectly called "out of phase" sounds. The pickups are not really out of phase, but the sound has a nasal quality similar to certain out of phase sounds. Eventually, Fender started using switches with 5 positions that are electrically identical to the original 3 position switches; they just make it easy to select the in-between positions.

Another unusual feature is that the two tone controls share the same tone capacitor. This has the advantage that additional highs are not lost in the neck + middle position when both tone controls are set to zero. It also saves on the cost of an extra capacitor!
Standard Single Coil Wiring

On all of my diagrams, the small circles show the physical switch stops. So there are 5 stops for a standard strat 5-way switch. Because there is no electrical connection for the 2 in-between positions, these are shown grayed out. Note also that the switch arm shows a wiper instead on an arrow to signify this is a make-before-break switch. This means that in the in-between (grayed-out) positions, the middle is connected to one of the sides as well as the switch arm connection.

There are 2 of these switches drawn in the schematic above, labelled S1a and S1b. This means there are 2 banks for switch S1: banks (a) and (b) are 2 switches are physically joined so that they move in unison. For this schematic, this ensures that pickup selections align with the active tone knobs.

 

[Cagey]

Incidentally, I modified one of the schematics at the site linked to in my previous post to show how to wire a Strat with a single master volume and master tone, which makes more sense than what Fender's been doing for all these years.

With Fender's (standard) scheme, you never had a tone control on the bridge pickup, which is arguably the one that sometimes needs highs rolled off. It also misbehaved in the #4 position, where you'd have the two tone controls in parallel. Adjusting one affected the other. With this scheme, you always have a tone control, and it affects everything equally. Plus, you need one less pot. Cleans things up, works better, costs less money, easier to wire. What's not to love? Unless, of course, you don't feel like buying a new pickguard to eliminate the leftover hole you'd have on an existing fiddle. But, Strat pickguards are so common, they're the least expensive of any extant, and who doesn't need a new 'guard once in a while?

 

[drewfx]

Please! Everyone knows the best way to wire a strat is with 1 tone on the neck, 1 tone on the bridge and none on the middle. :icon_biggrin:

 

[lafromla1]

Please! Everyone knows the best way to wire a strat is with 1 tone on the neck, 1 tone on the bridge and none on the middle. :icon_biggrin:

That's the way the Jimmie Vaughan strat is wired.

 

[AutoBat]

i never use my tone pots, they're there to keep the volume knob some company.

 

[Cagey]

i never use my tone pots, they're there to keep the volume knob some company.

That's pretty much what mine is for, but it really only needs one.

 

[Super Turbo Deluxe Custom]

That's the way the Jimmie Vaughan strat is wired.

That's a common mod done by a lot Strat players.

 

[lafromla1]

OK, here is the diagram that I got from DiMarzio.  Everything is done as it is shown.  I think they mean the red wire from the neck and mid (not bridge) should be grounded to the volume pot as the red from the bridge is already accounted for on the mini-switch.

It still hums like a beast over and above what my tube amp gives off.  When I touch the trem claw, the amp is dead silent.  When I touch the strings, the amp is dead silent.  When I touch the screws on the 2 single coils, they hum louder (when they are engaged on the 5-way).  When I touch the screws on the humbucker it is a little more quiet, but I can still hear a slight hum.  For comparison, I plugged a strat in that has VN's and there is no hum at all through the amp.  I plugged in a strat with tex-mex single coils and there is the usual single coil hum.  Again, just for a point of information, when the capacitor came disconnected from its solder, the guitar sounded perfect, just had no tone adjustment when the knob was turned. This may be a coincidence, but those are the facts.

I'm at a loss....

 

[drewfx]

My first guess would be 1 or more of the grounds came disconnected when you were working on it (or reassembling it, particularly if it's a top route). Also possible something could touch where it's not supposed to when reassembling, and short (bare wires are particularly bad with this).

Without taking things apart, if you jumper (clip/tape/whatever) a wire from bridge to jack plate, does everything work perfectly? If so the problem is definitely your bridge ground.

Do you have (or have access to) a multi meter?

 

[lafromla1]

Your idea of jumping wires gave me an idea and I started playing around a little more this morning and this is what I found; when I jump the open tab on the tone pot to a ground, the humming goes away entirely for all pickups.  However 2 things occur, 1) when I touch the screws to the 2 single coils (not that there would be any reason to do so when playing), there is a slight hum and, 2) when I turn the tone knob to 10, the sound cuts out entirely.  From 1-9.5, the sound is exactly where it should be.  I am wondering if this relates to the fact that the original schematics had me putting in a no-load pot instead of using a regular pot (as the shaft was too short on the Fender no-load) or should that not matter?

 

[Cagey]

You shouldn't have an "open tab" on any of the pots. We're back to "wired wrong". You need to either very carefully review what you've done, or start taking pictures so others can do it for you. Something is being lost in translation.

 

[lafromla1]

You shouldn't have an "open tab" on any of the pots. We're back to "wired wrong". You need to either very carefully review what you've done, or start taking pictures so others can do it for you. Something is being lost in translation.

And that can be the issue.  If you look at the schematic that DiMarzio sent me, the tone pot has an unused tab (as one is connected to the volume pot and one is attached to the cap).