Mike Sulzer

That is right; the no load pot is a way of having a tone control, but not allowing it to affect the brightness of the guitar when it is turned to 10. Seems like a good deal if you want the extra brightness.

You could, but some people leave out the tone and do change the resistance of the volume pot in order to get a somewhat brighter sound. Some people use a tone pot, but use a "no load" pot which goes off the end of the resistance track at ten. Hmmm... I hadn't considered this since I've always had a tone pot, but my new build will have volume only. So, are you saying that a 500K volume by itself will load the pickup differently than a 500K volume + 500K tone? Should I use a 250K volume to get an equivalent loading?

Since: 1. The resistance placed across a pickup primarily affects the height and width of the resonant peak (2.5 - 10 KHZ) 2. The tone capacitor has a much smaller impedance at the resonant peak than the tone pot, yes, the parallel combination of the resistances of the two pots (250K) is what is effectively loading the pickup when both are on 10 .

OK, if it hums with the input shorted then you are not picking up rf at the input. If it hums with a battery as a power supply, then it is not the power supply. It sounds like a problem involving a ground loop with the the amp you are feeding this to.

I agree with Lovecraft; I do not think this is rf. When does it buzz? Does it buzz with the input shorted? if you plug a cable in with the other end of this cable shorted does it buzz?

[quote name='GregP' post='262034' date='Apr 3 2006, 02:46 AM'] [quote name='Mike Sulzer' post='261313' date='Mar 29 2006, 08:43 PM']It will certainly help with that, but only if it does not short out.[/quote] I coulda sworn the whole point was that the capacitor WOULD fry, thus breaking the connection between you and the current, which would be incorrectly travelling along the ground in the case of a reverse-wired outlet! Or the other reading I had, and I admit that the site wasn't clear, was that you were supposed to feel SOME current and take it as a warning to let go right away. It's just a few extra seconds saying, "Heya... you're about to get zapped!". It's definitely never described as a "bad current blocker". Greg [/quote] The capacitor is specced at 400 volts. It willnot easily burn out. The value is now .33 uf, less than the 1 uf it used to be to allow less current, and less likely to kill you. If it is to serve as a warning, the current must be big enough to feel, but small enough to be safe. Electrical things are generally not so predictable. Check your equipment at set up time.

I agree that your body becomes part of the shield as you say, but there is more to it than that. If you do not touch the strings, your body runs at some other potential than string ground (and it is variable depending upon circumstances), and so it is a source of electric field causing hum. Connecting your body to guitar ground removes that field by putting your body at the same potential as guitar ground. Have you noticed that if the strings are not grounded then if you touch them, the hum might increase? In this case you are putting your body potential on the strings and bridge, and this shows that there is a proximity effect.

If you do not ground the strings through the bridge or whereever, they have no contact with the electronics either, but you need to do it, so there has to more to it than that. I will go with Robert's proximity argument, but also repeat what has been said many times: with perfect shielding you would not have to ground any of these things.

[quote name='JoeAArthur' post='261319' date='Mar 29 2006, 09:13 PM'] Since it takes much less AC to fry me, I will certainly incorporate this modification to my guitar just in case the B+ DC of my amp makes it to the grid of the first tube in my amp. [/quote] But guitarnuts web page says this capacitor is intended to save you when the high voltage dc gets on the ground connecton of the input jack of the amp!

[quote name='Robert_the_damned' post='261262' date='Mar 29 2006, 05:25 PM'] I'll have to add my two cents now its here! I read somewhere (somewhere reliable) that it takes far longer for a capacitor to burn out than it does to fry a person...and thefore putting one in your string ground circuit is a little pointless...it'll break the circuit sure enough...after you've taken the hundreds of volts at whatever ampage the dodgy equipment feels like giving you! Robert [/quote] The capacitor should not burn out; that is why it has a pretty high voltage rating. It is suposed to limit the current to a non-lethal value. That is hard to do with 110 or 220 volt AC and still have a low enough impedance to keep the hum low. The real purpose of the capacitor, according to guitar nuts now, is to protect you in the rare case when the high voltage dc from your tube amp gets onto the cable from the amp to the guitar. It will certainly help with that, but only if it does not short out. But I think this kind of fault where you get the plate voltage on your guitar is very rare.

[quote name='Talman_Hawk' post='261171' date='Mar 29 2006, 08:42 AM'] Glad to hear that you're another happy user of the "Quieting the Beast" mod. [quote name='BeAR' post='5059' date='Mar 13 2003, 07:18 PM'] On a side note, I deleted the .33uf 400V cap and used a straight wire instead. Works just fine.[/quote]While it may "work" without the 0.33 µF cap on the string ground, remember, that cap is suggested to help protect you from a shock. Getting zapped by our equipment is one of those low incidence/high consequence events. In other words, it may not happen often, but it can be pretty nasty when it does happen. [/quote] .33uf is too large to protect you most of the time; if you make it a lot smaller, you will get hum. Note that guitar nuts tells you this now. I think you are better off not using the cap, in order to avoid a false sense of safety. It is better to check the wiring and eqipment carefully. Shielding is a marvelous thing, but your strat can still pickup hum from from your power transformer if you get very close and are in a single pickup mode. This is from the magnetic field; getting rid of it is a different matter.

It corrrectly computes the field in the situation where the magnetization in the permanents would not change significantly, that is, when the permeabilty of the permanent magnets is low, or when the permanent magnets are not very near the other magnetic material. This is a somewhat tricky concept, and I am sorry if it is not clear! I have been an engineer for many years, and I still find magnetic circuits difficult to understand.

If you look at the main site for FEMM, at the FAQs, you see that question 6 is important in showing the limitation of the accuracy of the field models predicted for some pickup magnet configurations. FEMM treats a permanent magnet as a source of magetic field, but does not allow its magnetic material to be modified by applied fields. Here is a brief explanation of the significance: A ferromagnetic material (iron steel, ferrites, some ceramics and rare earths, etc) has permeability, the ability to amplify an applied magnetic field. A ferromagnetic material might also produce a permanent magnetic field. Permanent magnets might have a low or high permeablity. The very strong magnets, neodymium, samarium colbalt, and some ceramics, have low permeabilties. All the little magnetic domains are pretty much flipped in the same direction and cannot be easily changed. That is why they are so strong. Alnico is a weaker magnet, but has a significant permeability. FEMM is most accurate when the permeablity of the permanent magnetic material is low (generally a very strong magnet), and the permeabilty of the other magnetic material in the circuit (cores, etc.) is high. So Robert's left plot is probably more accurate than his right plot. The permeabilities of Alnico and the steel cores are similar, and so the effect of the magnet coupling the two pole pieces together is probably significant, but ignored in the plot. Probably the field lines are more closely confined to the cores than shown, and the field above the cores is a bit stronger.

Good answer Lovekraft. I am an audiophile type, but as for cables, you have it right!

John, series, as you say. But you need to be carefull with more than one pickup. For example, the Gibson Blueshawk uses a dummy in series with either selected single pickup, but switches out the dummy when using both pickups and instead uses the pickups RWRP.

That ought to work, have not done it myself. I have always assumed that it was better to use pole pieces with a larger diameter, more like the slugs used in standard humbuckers rather than the screws, but I do not really know. Your idea is a way to make a unique pickup without any machining. Sounds good.

Robert, I do not drill out the magnets, just use them as they are. They go on the end of the steel pole piece away from the string, one little magnet on each pole piece. I drilled out and tapped the steel pole pieces, and then used allen cap screws cut off so that were just a bit shorter than the pole piece, so they could not come through and hit the magnet.

Robert You should not try to cut or machine it, but rather just use the small magnets of various sizes that you can buy nickel plated and ready to pop onto a pole structure. Neodymium does not demagnetize easily except from heating, so just use it the way it comes.

I second Jester, but just add that the easiest way to make the dummy is as much like the pickup as possible, especially for a "one of a kind" project where the "engineering time" to design a different dummy could get pretty large.

Robert, that sounds like a good idea; I have not tried it. On the last pickup with Neodymium magnets that I made, I drilled and tapped the steel polepices and put in allen cap screws for adjustment. Bill Lawrence has a lot of interesting things on his web site. Under "magnets", he says that it is not the type of magnet (alnico, cerramic, etc.) that matters, but rather how you use it. That is what I have found, too. I can see why Neodymium might be hard to work with in a production environment, although most of them are now sold with a nickel plating that makes them pretty convenient. I think they are ideal for making special one of a kind pickups of any size or for any use.

Neodymium magnets are really pretty cheap. The correct strength to get enough signal but avoid string pull can be determined by experimentation. If you use steel rod pole pieces you can put a small magnet on the back of each. Try different sizes for different compromises between sound and output level. I have gotten as much as about 4 volts peak to peak, but with so much string pull the two modes (horizontal and vertical) of the string vibration are shifted apart in frequency and beat against each other horrendously. So with little magnets about 1/8" deep and about the diameter of a polepiece, they sound really good and give the usual level. So there is not that much to gain except convenience in getting different sounds. One more thing. You should not use neodymium magnets as the poles peices themselves; they are way too strong!

You might want read up on compensated nuts to get an idea of what can cause this.

All strong glues use the electrical forces between molecules. There is no other way. You can call it chemistry if you want; chemistry could be defined as the study of the many many ways the electrical forces among atoms and molecules behave. Epoxy is not designed to be used only in situations where you have to fill a gap. Its mechanical strength is great enough so that you can use it this way. It works fine with very thin layers, too. How could it not? The adhesion is molecule to molecule. A thick layer filling a space requires the glue to have mechanical strength as well as adhesion.

Another possibility is that all three pickups have the same output, and the one with the different colors is "reverse (magnetic) polarity, reverse wound". This is common in the "strat" world. In this case, the different one is for the middle and M-B and M-N will be humbucking.