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Post by dd842 on Aug 28, 2006 9:33:38 GMT -5
Hi there, Wow! What a helpful bunch of people! Sorry if this has already been discussed - I haven't been able to find it though. I have also refrained from using Smilies, as there doesn't seem to be one that accurately emotes quite how ignorant I am about electronics and wiring! I bought a strat style guitar, with 1 Humbucker, 1 Volume and 1 Tone (no other pickups, pots or switches). The pickup cavity is on the front of the guitar and access to the pots and output jack is from the back (under a removable plastic plate). The current wiring is exactly like this (NOTE THAT THE PICKUP IS THE TWO WIRE VARIETY DESCRIBED IN THE BOTTOM LEFT HAND CORNER OF THE DIAGRAM) www.seymourduncan.com/support/schematics/schematicspdf/1hum_1vol_1tone.pdfI am trying to do the fantastic Guitarnuts Quiet The Beast shield and ground modification , but I am having a problem figuring out how the wiring would work on such a basic guitar. I am wondering if anyone can help (basically, where do the wires go?) Also, the pickup and control cavities are not and will not be electrically connected as there is no pickguard. Do they need to be? If so, how would I do that - attach a wire between the bridge and the aluminum shield in the pickup cavity, and then attach another wire from the shield in the pickup cavity to the shield in the control cavity? Hey! I meant it when I said I was ignorant about this stuff! Any help would be appreciated. Thanks, Dan
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Post by ccoleman on Aug 28, 2006 10:58:18 GMT -5
I am willing to take a shot at this. You want each cavity (pickup and control) to be shielded and install a new wire running directly to your star ground point... in your case this the back of the volume pot.
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Post by dd842 on Aug 28, 2006 11:59:30 GMT -5
Thanks, I am a little lost and appreciate the help.
Where would this wire running directly to the star ground point originate (i.e. do I go from bridge to pickup shield to star ground, from bridge to star ground, or from pickup shield to star ground)?
I had previously attempted this and gave up - but here is what I recall having done: 1) put an aluminum shield in both cavities 2) ran a wire from bridge to pickup shield 3) ran a wire from pickup shield TO CONTROL CAVITY SHIELD* (* my brother-in-law is an electrical engineer and he couldn't understand why I was attaching the ground to the aluminum shield. From what you say, I wasn't supposed to - it should have gone to the star ground, correct?) 4) ring terminal around base of tone pot 5) one cap lead wired to that ring terminal 6) other cap lead wired to another ring terminal that was just pointing up into "mid air" and not in contact with anything else - this was to be the star ground 7) both pickup wires soldered to star ground .....
..... I could not figure out how to get the tone AND volume involved and, once thoroughly confused, I ripped it all out .....
Does the pickup lead itself actually connect to the star ground, and if so, do you know how the pickup then connects from the star ground to the pot ... and how to wire it so both pots are involved by the time the wires reach the output jack? ( ... and is the place where the plug from the amp connects into the guitar an "out"put or and "in"put jack?)
Thanks, Dan
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Post by UnklMickey on Aug 28, 2006 13:07:42 GMT -5
hi Dan,
welcome to Guitarnuts2.
John Atchley had 3 goals in mind with the QTB mod:
1 -- provide additional shielding to reduce hum.
2 -- star grounding to reduce the amount of hum that gets into the signal path.
3 -- isolate as many "touch-points" as possible with a capacitor to reduce the possibility of DC shock if your TUBE amplifier fails.
normally the concept is to connect the "signal" grounds together at a single point. the cases of the pots are NOT signal grounds, they are connected to the shielding ground.
then the frame of the pickup, cavity shielding, and string ground are all connected to a separate point. (shielding ground)
finally, the 2 ground systems are tied together with the protection capacitor.
if you have a HB with a single, shielded connection, you will at best be able to only partially accomplish goals 2 and 3.
i'll assume you are not prepared to modify the internal wiring of your HB.
that means that the frame (and cover, if so equipped) are already connected to the braid of the cable coming from your pickup.
already you have an early connection point for the frame of the pickup that should be connected at a much later point in the circuit.
so, what to do with what you have to work with?
if you have a plastic pickguard and knobs, and no other exposed metal, you might use the following approach.
shield the pickup and control cavities, and allow the shielding to make electrical contact with the pickup and the pots.
the braid will now connect the shielding of the pickup cavity.
the case of the potentiometers will connect the control cavity shielding.
the string ground (wire from the bridge) will connect through the protection capacitor. (the other end of the cap connects to either the back of one of the pots, or to the ground connection of output jack.
this will provide protection if you touch the strings or bridge, but not if you touch the pickup.
unless you modify the pickup, this is as much protection as you can get.
no matter if you do a "complete" job, or the partial one, i just described, the output jack will never be isolated from a DC shock standpoint.
since HBs are inherently quieter than single-coils, and your pickup is already connected through a shielded cable, don't expect a huge reduction in hum.
unk
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Post by dd842 on Aug 28, 2006 14:43:02 GMT -5
Hi Unk,
Thanks for the welcome and the instructions. To help with clarification (i.e. to expose what I don't understand):
If I were to put a thin, flexible copper foil hoop between the plate on the bottom of the HB and the alumimum shield in the pickup cavity - so that it was squished between the two - would that be a good way to electrically contact the pickup cavity with the pickup?
Do I then attach the pickup wire to the star ground, or the shield in the control cavity?
Do I attach the string ground from the bridge to the star ground in the control cavity or to the shield inside the pickup cavity?
Is EVERYTHING supposed to be electrically connected when all is said and done?
If so, does it matter if the star ground is actually touching anything (I thought I had to insulate it)?
FYI - the guitar has no pickguard, just plastic knobs and a plastic panel for access to the control cavity on the back of the guitar.
Based on Atchley's diagram (http://http://guitarnuts2.proboards.com/page/gn1-pages/wiring/shielding/innards.php ) - EXCEPT bearing in mind I have NO switch(es) and only one TONE pot - where do the wires go?
I see the pickup coming into the star ground, but that's where I get confused because the wires start to go all over the place (to the pickup switch, and to the cap between the first and second tone pots). Do you know what is supposed to happen with a very basic layout like mine (1 HB, 1 Volume, 1 Tone).
Thanks again, I really appreciate your time.
Dan
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Post by UnklMickey on Aug 28, 2006 15:52:33 GMT -5
good question about the pickup cavity.
you mentioned there was no pickguard before, but i kinda missed that.
usually the back side of the pickguard is covered with copper foil.
then the springs contact the foil and connect the pickup frame to the foil.
your idea for a hoop sounds okay. what ever you can do to easily make a dependable contact between the shielding and the pickup.
it doesn't make too much sense to have a separate "star" (signal) ground in the control cavity, since the shield ground of the pickup cavity is already connected to the signal ground at the pickup.
you could, but IMHO it wouldn't gain much in hum reduction for your application, and would be extra work.
i would just connect the braid of the pickup cable to the back of the volume pot, as it is now.
for your application, all the grounds, EXCEPT the string ground will be electrically connected together.
because a typical Strat style guitar has both of the wires from the pickup isolated from the frame, it is easy to keep all of the shielding separate from the (-) wires of the pickup coils.
since your pickup frame is already connected to the (-) of one of your HB's coils, i suggested a different approach.
if you want to go the full route, you could modify the wiring in your pickup, keep all the signal grounds separate, unsolder the "low" lug of your volume control from the case of the pot, and connect it instead to a separate signal ground. etc, etc, etc.
but, i think you will be well off to keep it simple.
you don't have a switch, multiple pickups, or multiple tone controls.
so your wiring will look very simple, like the SD diagram.
the only difference will be the shock prevention capacitor in series with the string ground.
unk
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Post by dd842 on Aug 28, 2006 16:41:02 GMT -5
Thanks again, Unk.
I think I am grasping the concept a little better now. I will print your comments and digest them at home.
All the best, Dan
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Post by dd842 on Aug 29, 2006 12:37:27 GMT -5
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Post by UnklMickey on Aug 29, 2006 13:00:11 GMT -5
hi Dan,
yeppers, that's right.
the cap on the tone pot is still needed as part of the tone control.
connecting the shock protection cap, in the way you described, sounds just fine.
cheers,
unk
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Post by dd842 on Sept 5, 2006 15:48:57 GMT -5
Hi Unk, and all,
I just wanted to give a final report on this, as I didn't have a chance to complete it until this past weekend.
In a nutshell, this guitar has now, thanks to CColeman and a Very Special Thanks to Unklmickey, gone
FROM: loud, hissy and hummy, which got worse when I touched the strings, and could only be played while wearing rubber shoes and a copper wire attached from my finger to the bridge, and with no tone (as it made it all worse)
TO: completely silent, regardless or how high the volume and tone are cranked up, and with no special preparation like rubber shoes, etc.
The transformation of this guitar has been nothing short of amazing!
Thank you very much. I simply could not have done it without you, and I look forward to getting to a point where perhaps I can be of assistance some day.
All the best,
Dan
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