Newb Hum elimination question

[heywood]

Yes I have searched extensively, but I hope to get better advice here.

I am changing out my pick up covers (Thread on general board) and I decided I would try to mitigate the noise.

Mojotone 60th anniversary set pre-wired with a blender assembly. ( Middle PU rev wound)

Noise when not touching the strings, less when contact is made.

Slight hum in 1/3/5

Basement has Dimmers and LED bulbs, but no real difference seen when rotating or moving about.

Ground wire seems to be a good joint on the bridge.

Since I am taking it apart I will shield all of the cavities with copper foil, and solder the joints (not sure the adhesive is conductive)

Does this have a chance to help with the noise I am getting?

I don't want to replace all of the wires with shielded wires.

I also read about people shielding the inside of the covers, I would think that would kill the tone, but since 1/3-1/2 of the pick up is above the guard, I can see the temptation.

 

[stratamania]

You will probably get some mixed answers, but here is my view. Shielding will help radio interference to a greater or lesser degree depending on pickups, shielded wires etc.

But it won't get rid of ground hum as such if that's being caused by loops in your signal and amp chain. For that you need ground lifts or a hum eliminator.

 

[Cagey]

Those Mojotones are single coil pickups. There's very little you can do to mitigate the noise. Shielding the cavities won't do jack, as you essentially have 3 half-mile long antennae sticking out of holes in the shield. You can shield the internal wiring to get rid of some hum by using shielded cable, but the amount of noise that internal wiring is picking up relative to those pickups is small enough that you might not notice it. You'll notice many single coil manufacturers don't bother with shielded cable on their parts. You'll also notice almost no commercial guitar manufactures shield pickup or control cavities. It's an exercise in futility.

Even on a noiseless pickup installation, to get truly quiet you have to use shielded cables. But, it's very effective in that case. Even with 16 CFLs and 3 or 4 computers running, I don't generally have noise issues. I can crank the hell out of things and not know the amp is even on unless I start hitting strings.

I don't think LED lamps radiate a lot as they essentially run on DC, but I don't have any installed near the playing area so I'm not sure. I do have a lotta CFLs, and those things are a screaming bitch at single coils. I intend to replace them with LED units soon. But, in your case, the dimmer may be emanating. You could turn it all the way up, or turn the lights off altogether to see what kind of difference that makes. It's usually the in-between points that radiate the most.

If you must use single coil pickups, your best bet is to invest in a good noise gate. Before I got the Axe Fx, I had good luck with Rocktron's Hush unit.

 

[line6man]

Those Mojotones are single coil pickups. There's very little you can do to mitigate the noise. Shielding the cavities won't do jack, as you essentially have 3 half-mile long antennae sticking out of holes in the shield. You can shield the internal wiring to get rid of some hum by using shielded cable, but the amount of noise that internal wiring is picking up relative to those pickups is small enough that you might not notice it. You'll notice many single coil manufacturers don't bother with shielded cable on their parts. You'll also notice almost no commercial guitar manufactures shield pickup or control cavities. It's an exercise in futility.

And when shielding does its job, it helps with high frequency electrical noise, while doing NOTHING for 60Hz hum.

 

[Cagey]

No. Shielding works by taking induced currents to ground before they can induce currents in the signal conductors the shields are wrapped around, hence the name: shield. How effective it is depends on how porous the shield is and the wavelength of the interfering signal. High frequencies, such as RF, have relatively short wavelengths and are more difficult to shield against as they can make it through a shield with small breaks in it. Low frequencies are easier to filter out, even with fairly porous shields, as their wavelengths are longer.

Look at the shield in the window of your microwave oven (that's what that mesh is). It has a buncha holes in it that are sized and shaped so that they're smaller than the wavelength of a microwave. They tie that mesh to ground, and you're safe to watch your keilbasa turn into a horror movie when you set the time too long. Otherwise, you'd cook your eyes  :laughing7:

On a serious note, that happens. Guys who do radar antenna work on military ships get burnt up if they aren't careful. Those are some powerful microwaves and they'll cook your ass RFN.

So, you can sort of think of your shield as a shelving filter. The larger the openings, the lower the frequencies that are allowed through, as well as everything above them. In the case of single coil pickups, there's no shield at all. Of course, there's no shield for humbucking/noiseless pups either, but they use CMNR (Common Mode Noise Rejection) to eliminate noise, which is pretty effective. With them, you still have to use shielded cable to wire them, as even in the few inches of exposed hookup wire you still have exposure. Since we're generally dealing with a high impedance input circuit, they're sensitive to anything. But, RF usually isn't a problem as the amps aren't sensitive to it, and even when they are humans can't hear it. We're pretty limited to 20Khz, and that's only with perfect babies. That sensitivity deteriorates over time, and starts early on. Few people can make it past their teens and still be able to hear much over 17Khz, which is a million miles away from RF.

 

[The Hun]

Those Mojotones are single coil pickups. There's very little you can do to mitigate the noise. Shielding the cavities won't do jack, as you essentially have 3 half-mile long antennae sticking out of holes in the shield. You can shield the internal wiring to get rid of some hum by using shielded cable, but the amount of noise that internal wiring is picking up relative to those pickups is small enough that you might not notice it. You'll notice many single coil manufacturers don't bother with shielded cable on their parts. You'll also notice almost no commercial guitar manufactures shield pickup or control cavities. It's an exercise in futility.

And when shielding does its job, it helps with high frequency electrical noise, while doing NOTHING for 60Hz hum.

A lot in this thread, but this is basically true for shielding tape and conductive paint that uses a thin layer of metal with no gaps. That is good for shielding high frequency. At low frequency you can have huge gaps in shielding, but you need metal thickness to absorb the higher energy at low frequency, and that must be drained away from your signal correctly. Thick metal pickup covers can be effective at shielding the pickup windings from low frequency E-field signal reception with proper grounding. I can't imagine much impact from using a thin layer of shielding tape in the control cavity though.

 

[heywood]

Covered the control box and pickup routing as well as the inside of the pick up covers.

Might have reduced the string hum, but seems a bit noisier overall, and possibly more sensitive to dimmers.

The pick ups are not at the exact same height as before, so I still need to tweak.

(This is with all pedals removed, straight into amp)

with tone knob below 10, noise reduced ( Kind of like early Dolby- hiss is gone but highs are rolled off as well)

 

[Super Turbo Deluxe Custom]

A guy posted a thread here a while back about shielding a P-90 to be hum free.  The logic being that the shielding path and ground path for signal path be dedicated and isolated from each other until the most distant point in the guitar; a single "star" ground.  I haven't replicated to see for myself, and the forum electronics gurus haven't chimed in to say why it does or doesn't work, so I'm left wondering if the bigger, better mouse trap works.

However, much ado is usually made of 60 cycle hum.  The pleasing musical sound a single coil pickup makes should be enough to negate any hum.  After all, it only hums when the guitar isn't being played.  We're generally more concerned with the sounds they make when they are being played.

 

[The Hun]

Yeah I'm the one proposing dedicated grounds separate from signal returns, the idea being to drain hum away directly to the output jack -. There's no reason to couple through stray capacitance and contaminate your differential signal by taking a longer path to the same point. Rivers don't tend to cross themselves.

Hum typically isn't a huge problem. If it is distractingly bad then you may have a bad solder connection in the wiring that you need to hunt down.

For P90's (that I've seen) there's a thick metal cover that can be an effective shield for the winding, but only if correctly drained with good grounding practices. For single coil pickups the plastic covers won't help, and shielding inside the plastic will be too thin to be effective even if grounded properly.

Fortunately your bridge is grounded, and through it your metal strings. If the bridge drain wire drains away the noise (ie NOT soldered to a potentiometer cover with stray capacitance to your signal) then the front of your pickups become shielded...almost. Because the strings are parallel the hum is actually polarized, but still significantly reduced.

The real problem is the back of the single coil pickup winding. Your body is an antenna for the hum to reach the pickup coils from the back side. Move your guitar away from your body without touching metal parts and you can hear the hum get quieter. When you touch the bridge or strings then your body is grounded and no longer acts as an antenna.

I have an incomplete solution I've been working on, but I've found the metal baseplates do nothing for shielding even when grounded correctly. Maybe because they're zinc? I don't know, but you may not want metal baseplates anyway. Generally speaking, the hum I get from a single coil pickup isn't much of a problem, but I'll keep poking at it because I enjoy poking at it.

 

[bagman67]

Okay, I'm no engineer, and I have to assume what I've read from our local electrical engineers has been accurate... but I'm under the impression that the chance of stray capacitance and suchlike in the realm of a guitar control cavity, where the voltages are so tiny, is what we call de minimis in my own field.  In other words, truly negligible to the degree it's not worth even really attempting to accommodate.


Cagey?  Trevor?  Joseph?  Help me out here.  Did I understand your teachings correctly, or am I pulling this out of my fundament?


That said, you acknowledge that you like tweezing this problem, and it makes you happy, so knock yourself out.  It's not a problem I'm willing to bother with overmuch - I just accept that there's at least some noise I'm gonna get with single coils, and I like the single coil bite enough to just deal with it.  Others, for example our resident alpha curmudgeon Cagey, find the prospect of single-coil noise wholly unacceptable, and so go with hum-cancelling variants on the traditional single-coil design.  De gustibus non est disputandum.

And no, I don't usually go around spewing Latin lingo.  It just seemed to fit here.

 

[Cagey]

Your understanding is correct.

Really, the best way to deal with single coil noise is with a gate, unless it doesn't bother you at all, in which case you just live with it as it's the nature of the beast. In some cases, the signal-to-noise ratio is wide enough that you don't need to care. You develop a reflex for quickly cranking the volume knob back when you're not actually playing a note.

Also, parametric EQs can be pretty selective about taking a notch out at a particular group of frequencies so you don't lose everything above or below some point like a shelving-type filter as is found on most amps or graphic EQs will do. Then you might not need the gate. It's not as effective as a gate, but then gates can be a pain in the shorts if you have a particularly noisy source. You can end up losing dynamic range. They don't compress things, per se, but they only allow operation above certain levels so it sorta has that effect.