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Post by offhand35 on Apr 24, 2008 6:32:19 GMT -5
I am shielding and rewiring an Epiphone Explorer that has a single vol & tone control. I installed a .33uf, 400V cap as recommended, to a ring terminal placed on the shaft of the tone control, and plan to insulate and solder the other end to the star ground before I close it up. I play a tube amp, so I am very interested in setting this up correctly.
Now, the way this is set up, it seems the end from the ring terminal is grounded to the shielding, with the other end grounded to the star ground.
As I understand the way this is supposed to work, a high V jolt from the failed amp would go to the center plug of the jack, to the vol control lug, through the vol pot. to the tone pot, through the 400V cap, to ground.
Doesn't the grounded ring terminal allow it to go to ground and avoid the cap?
I feel as though I am missing something important here......
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Post by D2o on Apr 24, 2008 10:05:02 GMT -5
I am shielding and rewiring an Epiphone Explorer that has a single vol & tone control. I installed a .33uf, 400V cap as recommended, to a ring terminal placed on the shaft of the tone control, and plan to insulate and solder the other end to the star ground before I close it up. I play a tube amp, so I am very interested in setting this up correctly. Now, the way this is set up, it seems the end from the ring terminal is grounded to the shielding, with the other end grounded to the star ground. As I understand the way this is supposed to work, a high V jolt from the failed amp would go to the center plug of the jack, to the vol control lug, through the vol pot. to the tone pot, through the 400V cap, to ground. Doesn't the grounded ring terminal allow it to go to ground and avoid the cap? I feel as though I am missing something important here...... Hi, offhand35, and welcome to the Nuthouze! Good point. You know, I have always just put that cap right in the middle of the wire from the output jack to the bridge ground, on the basis that if there is a catastrophic electrical event I couldn't give a ratz azz about anything other than protecting my own. I don't know if I am correct about my theory, but I feel as if I am most protected by having the cap attached directly to what I am attached directly to the bridge ... sort of like this: bridge _____ __________ jack ssssssssssss| sss| ssssssssssss----- ssssssssssss|400| ssssssssssss----- I hope that helps, and I am sure your question will draw some more comments shortly. |
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Post by pete12345 on Apr 24, 2008 10:35:59 GMT -5
Now, the way this is set up, it seems the end from the ring terminal is grounded to the shielding, with the other end grounded to the star ground. As I understand the way this is supposed to work, a high V jolt from the failed amp would go to the center plug of the jack, to the vol control lug, through the vol pot. to the tone pot, through the 400V cap, to ground. I believe when these amps fail in this way, they put high voltage DC on the 'ground' side of the jack, not to the center terminal. The capacitor blocks this DC voltage, preventing it reaching the shielding and anything attached to it (string ground, metal switches etc.) The shield ground is thus protected from DC shock. Anything connected to the shield ground is similarly protected. In normal use, RF interference picked up by the shielding is passed by the cap (as it is AC) and goes straight to ground. Putting the cap in the connection from the jack ground to the bridge would only protect the strings from shock. The shielding/ switches are still connected to jack ground and could give you a zap in a failure situation. Instead you should isolate the shielding with the cap, and connect the string ground to that. Pete |
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Post by offhand35 on Apr 24, 2008 14:33:23 GMT -5
Thanks to everyone, so far! THIS make a whole lot more sense. With the cap guarding the entry point of the potential High V to all grounded components [and me] I can understand how it is supposed to work. The problem, now, is that the drawings that I have seen don't seem to show anything like what DD842 and pete12345 have just described.
From what has been said so far, it would seem the .33uf/400V cap would do its job if it were placed in the signal ground pathway from the jack to the incoming grounded lug on the vol pot . This is the sole point of entry of ground from the amp.
I will check with my friends at sewatt.com [single ended tube amp forum] to verify the pathway of catastrophic tube failure, whether it be ground or signal path.
My new Seymour Duncan pups arrived today, and I am anxious to assemble this guitar. If more people could confirm/deny this arrangement of the cap, it would be appreciated!
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Post by offhand35 on Apr 24, 2008 14:45:40 GMT -5
You know what, I have to go back and reread the entire article, "Taming the Beast" on guitarnuts 1. I started looking it over again, and it looks like I REALLY misunderstood how to set it up......
Thanks to all for reading this..
P.S. thanks for the welcome! I have been lurking for a while here, but not quite long enough, apparently!
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Post by D2o on Apr 24, 2008 15:17:54 GMT -5
You know what, I have to go back and reread the entire article, "Taming the Beast" on guitarnuts 1. I started looking it over again, and it looks like I REALLY misunderstood how to set it up...... Thanks to all for reading this.. P.S. thanks for the welcome! I have been lurking for a while here, but not quite long enough, apparently! If you are unclear that you have read it correctly, by all means re-read it. I think I'm going to go with Pete here though, and I will point you to a link where this seems to have been dealt with ... if you do a little sifting and keep reading until you get to what ChrisK and sumgai have to say. guitarnuts2.proboards45.com/index.cgi?board=wiring&action=display&thread=1628&page=1It contains such gems as "..... the star ground system is not for safety, it's for noise reduction. The cap is for safety, and so long as all user-accessible metal parts are protected by this cap, then I'm OK with whatever comes after that point in the wiring scheme, star ground or otherwise." and "Placing the cap between the bridge and the cavity shielding is protecting only the bridge/strings. There are other metal parts above the pickguard that the user/player might be touching when the amplifier goes ker-blooey® (ChrisK, 2005). That's the only reason I'm on my high-horse about all this." I have not had time to find other links, but this one seems to back up what Pete is saying. So go back and re-read, and then make sure that anything metal that you can touch is protected ... even if it still confuses you. |
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Post by offhand35 on Apr 24, 2008 18:22:36 GMT -5
Thanks for the link! The key to the whole thing is that the bridge/string ground and shielding are on the far side of the cap, not on the star ground. Somehow I had missed that. Since my Epiphone Explorer has a large part of the metal pup switch exposed, I will put both the bridge and switch ground wires on the same ring terminal and ground them to the copper shielding with a small screw.
This is great! Thanks! Now I can put it all together!
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Post by D2o on Apr 25, 2008 10:31:59 GMT -5
Thanks for the link! The key to the whole thing is that the bridge/string ground and shielding are on the far side of the cap, not on the star ground. Somehow I had missed that. Since my Epiphone Explorer has a large part of the metal pup switch exposed, I will put both the bridge and switch ground wires on the same ring terminal and ground them to the copper shielding with a small screw. This is great! Thanks! Now I can put it all together! No sweat, onehand. Your name indicates that you have had prior experience with tube amp failure without the DC blocking cap. Kidding, of course! Here is another link you can check out to see why some of us consider half-azz shielding to be just fine for most applications (at least from a hum reduction standpoint) and why the DC blocking cap between the strings and jack is just gravy. guitarnuts2.proboards45.com/index.cgi?board=wiring&action=display&thread=1611&page=1BUT, since (you seem to use mainly tube amps - is that right? and) you are ostensibly more interested in retaining your onehand, the lack of complete DC blocking isn't neccessarily going to protect you ... it would be a little like Russian Roulette, depending on when you were touching what. It seems like, in your case, the hum reduction will be the gravy. This is a great place to lurk, but we'd also love to see you around the forums, offhand35.  |
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Post by offhand35 on Apr 25, 2008 18:32:52 GMT -5
Well, again, "Thanks!" I actually do have both hands. I am left handed, and play right hand strung guitar in a left-handed manner. But that is still not the background on my user name. I have a left hand MIA Strat [restrung rt handed] that a previous owner had removed the vol & tone pots, and sent the signal straight out to the output jack. The hum with this guitar in my family room with fluorescent lights is noticeable, and there is a definate ground problem with it as a very strong hum reduces somewhat when I touch the strings. THAT is what 1st led me to eventually land here! That Strat has some very strong tones, and works nicely with a volume pedal, so I am taking my time deciding what to do with it. That will be its own thread. Back to the Epiphone Explorer. I got this at a pawn shop with case for a rediculously low price. It was immediately apparent that this was an urgent candidate for rewiring, shielding, and new pickups. I finished the work last night, with a new Seymour Duncan 59 Model HB Blues Set, strung a set of Daddario Blues/Jazz .011 strings this AM, and almost left home late for work! I could not put it down! This instrument is dead quiet when not being played, but has all the blues tone I could ever want! I have learned much from J. Atchley's site, and may look him up as he suggests, I do get to the Dallas/Ft. Worth area 1-2x / yr., and from this forum! I do plan to participate as time goes by.  |
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Post by ChrisK on Apr 25, 2008 20:35:37 GMT -5
A capacitor does not block DC and pass AC. A capacitor stores a charge. Period. (That there capacity thing is related to charge storage (Q) - it used to be called a condenser, a thing that condensed a charge of electrons.) If the dielectric has a high enough resistance to be a good insulator, it will have a reduced current leakage, and hence appear to block DC (well, have substantially reduce leakage current). Since no insulator is ever perfect/infinite, no leakage current is ever zero.  If the charge storage ability is high enough, the capacitive reactance associated with said capacitance will be low enough to effectively pass a charge-coupled plate potential from one side of the insulator/dielectric to the other, as a function of frequency AND circuit impedance on both sides of the capacitor. While the potential on one plate is varying, the charge-coupling capacity of the capacitor will take substantial (but never complete) precedence over the charging (+/-) of said capacitor (which WILL always occur whenever there is ANY sinking or sourcing charge coupling across the capacitor. This will make it appear to pass (couple) AC. The effect is not perfect. If the charge coupling ability (capacitance) is appreciably slower than the rate of change of the applied potential to the plates, the "wiggling aboot" of the potential on one plate will effect a "wiggling aboot" potential on the other plate. Yes. Indeed. It will do its job. However, it may not be the job that one wants. A 0.33 uF capacitor has a reactance of Zc = 1/(2PiFC) 2Pi is 6.28'ish F is in Hertz C is in Farads At 60 Hz, said 0.33 uF capacitor has Zc = f 1/(6.28*60*0.00000033) = 8 8,038 Ohms (8K38 Ohms) Compared to the low impedance of the cable shield (a few Ohms), this is a fairly large impedance. It will form a nice AC voltage divider in concert with your body. However, it will be less dangerous than a Direct Connection. At 82.4 Hz Zc = f 1/(6.28*82.4*0.00000033) = 8 5,853Ohms (5K853 Ohms) Compared to the high impedance of the typical passive guitar pickup, this sucks putty balls. ;D ;D  This will brighten up the geetar. It might be a good thing. So, it has over 8 K Ohms helping to block 60 Hz and over 5K Ohms helping to block 82.4 Hz (also known in some circles as the low "E" string). DANG!  A switched DC voltage (that might occur when/as the amp fails) WILL BE COUPLED across any capacitor (and ALL points in the known universe are capacitively coupled to ALL other points - it may not be much, but it's there) UNTIL the charge equalizes across the capacitor. Any switched DC potential applied to a plate of a capacitor will effect charging (+/-) across said capacitor as a function of the effective potential, capacitance, and circuit impedance on both sides of the capacitor. Until said switched DC potential has effected nearly complete equalization, it is effectively NOT a DC event, but an AC event described by the Fourier Transform of said signal, made up of increasing effective DC components and decreasing effective AC components, as the events existence approaches steady-state. It's a transient event, known as an electrical transient! If you "come late to the party" (one touches something after the charges have equalized) all is fairly better than those prophylacticly challenged (snickering is not permitted, while a condom is a prophylactic, a prophylactic is not a condom). If one arrives early (one is touching something as it is affected), one gets to form a capacitively coupled voltage divider in concert with the capacitor, to help that transient settle into a steady job. All is not good, but those prophylacticly challenged get to be the fuse in the long-term DC kind of way. (That WILL leave a mark.) And, it's NOT low voltage.......................................... I reiterate. I use RF. Only lightning can jump that gap (Sparky). |
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Post by ashcatlt on Apr 25, 2008 21:42:36 GMT -5
C'mon, a little snickering can't hurt anybody! Aw well, when the mod says...
The strat is likely working normally. The noise goes away when you touch the strings because the closest source of RF interference (you) is being grounded. Shield it, leave out the V/Ts and you'll be in tone heaven.
I think that Explorer probably looks pretty cool played left-handed. Makes me think that I might be able to stomach playing a left-handed explorer. Which makes me think I'd ought to have a lefty strung guitar for party tricks, bar bets...oh, and leftys that might stop by.
And I use virtual tube amplifiers. I can handle any voltage as long as its imaginary.
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Post by ChrisK on Apr 25, 2008 22:12:41 GMT -5
Yeah, well I can really play, virtually.
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Post by pete12345 on Apr 26, 2008 4:27:57 GMT -5
I know it's not as simple as block DC, pass AC (the effective resistance of the cap changes with frequency) but I wanted to put it in simpler terms so non-physics students would get it After all, we are guitarists first, amateur electricians second  Pete |
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Post by offhand35 on Apr 26, 2008 9:54:32 GMT -5
ChrisK's point is well taken: I will not allow the presence of that capacitor to give me a false sense of security, but understand that it MAY help in the event of an amp failure. So far though, my [only] tube amp is a Valve Jr. head, which has a solid state rectifier. I will be aware of potential problems though should I acquire or play through an amp with a tube rectifier.... Meanwhile, I am STILL enjoying the tone from all that work I put into this Explorer, thanks to the help from all of you on this forum, both directly and indirectly! My other amp is a Kustom Sienna solid state acoustic amp for my classical guitar...this is what I actually gig with, the blues/rock and tube amp are for fun only, so far.....I did make the cats want to leave the house this morning..  ashcatlt, I had looked at Flying V's to play ala Albert King, but did not want to shell out a whole bunch of money and still get tone that I was not thrilled with. The stock Explorer's are wired the same, though they are easier to play sitting down, and still give a southpaw full access to the upper scales. Most Explorer's seem to have a compensated stop tailpiece, and would make it very hard to set up with left hand stringing. The one I found is a 1993 Korean made, with a through body tremelo tail, similar to that on a Strat, and intonation would be very easy to set up for either hand, although I don't actually need this feature.... This guitar probably does have a unique look to it, though I have not played in front of a mirror with it yet.... The Explorer is actually a left hand body, and just feels right to me played left handed. Add to that, for this one the final cost was about 1/3 of a Gibson Explorer, is now fully shielded, and has the tone I wanted. |
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Post by ChrisK on Apr 26, 2008 22:08:46 GMT -5
No intention to scold afoot, I occasionally break out into a spate of electronics or physics. Sometimes the hidden detail is important, since little is as simple as we thing (due primarily to things actually being simple, with complex results and interactions).
Many things get lost as "derivatives" are taken. While at university, I concentrated on the first principles, and not the derived equations. When one knows the models, one inherently knows the derivatives.
We were all taught that there are 180 degrees in a triangle, 360 in a rectangle, and other stupid numbers to remember for the degrees in them other polygons (dang, there's a clue).
ALL polygons, including that there infinite-sided one known in some circles as the circle, have only and exactly 360 degrees of outside angle progression.
So, most "instructors" in elementary school (hmmm, perchance another clue) were either lazy or just plain/playing dumb. After all simple concepts are obviously too complex for simple elementary school minds.
All is physics,
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Or marketing,
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Or religion!
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