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Hum increases as volume drops on new Sheraton wiring, help please?


vomer

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I've just built a new wiring loom for my Sheraton II with GFS humbuckers, and a Guitar Parts Resource kit with CTS pots, Switchcraft switch & jack, and braided wire.

 

Pickup volume is good. Tone controls work. But two problems: First, hum levels are comparable with my single coil guitars, i.e. not hum-cancelling. Second, when either volume pot is turned down the hum increases dramatically rather than disappearing as the pickup sound does.

 

The loom isn't installed yet, but I did remember to touch the pot where the bridge ground will attach, during my testing. I think I've followed the wiring diagram correctly. I used Stewmac's with his independent volume suggestion, its the second diagram on the link below. So I'm stuck! Very grateful if anyone can help.

 

http://www.stewmac.com/freeinfo/Electronics/Wiring_diagrams/i-1217.html

 

Thanks.

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Sounds like a ground connection is missing somewhere. Can you post a clear picture of the electronics?

 

That wiring diagram shows a non-standard way of connecting the tone caps but it will work. Also make sure you haven't wired the jack in reverse, a lot of people do that.

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Check the diagram that came with the pickups and make sure you have the right wires connected together for humbucking operation (on a 4 conductor pickup) if not it will be noise adding instead of noise canceling,however as Spud says,you may have a bad or missing ground...you should also check for cold or bad solder joints.

 

I built a guitar back during my college days where I had the coils acting as noise adding...once I figured out I had wired it that way,I switched them,and it was waaay quieter.

 

This doesn't sound like it should be too tough to figure out.

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The "THICK" centre lug on the 3 way is for the ground connections. Make sure

you are using shielded wires from the pots to the 3 way and tie ALL the shields

together and solder them to this ground lug.

 

I "peel" the shields back at the signal lugs side of the switch,

then use a solid wire soldered to the shields and then to this ground lug.

The stew-mac diagram does not show a connection to this lug on the first diagram,

but does for the Les Paul wiring diagram.

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Daneman, thanks, they are GFS which come with the single coil wires (red and white) already joined. Then there is a sleeve, and a black to ground and a green hot. I already tried switching the black and the green but no change. I think my soldering is just fantastic :-) but carverman may have a point with the "solid wire soldered to the shields and then to this ground lug." Thanks carverman, I'll try that, it was awkward trying to solder all three sleeves to the ground lug so if there is a weak ground its likely to be there.

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Then there is a sleeve' date=' and a black to ground and a green hot.[/quote']

 

There should also be a bare ground wire in that sleeve that needs to be soldered to the back of the volume pots along with the black wire... I can't confirm this as there are no detailed pix/diagrams on the GFS site but that's the way it's usually done.

 

The trick at the switch end is to twist all three shields together along with a fourth wire and solder that; then attach the other end of the fourth wire to the switch's grounding lug.

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Update- carverman' date=' I tried your method for the switch ground but no change yet. Seems like I will have to re-do all the grounds. [/quote']

 

How about doing it an easier way? Take a ground wire and solder it to the ground

lug of your output jack. Plug the guitar into your amp. Take the loose end of the

"test" gnd wire and touch the spots where the grounds should be...don't forget

to touch the pickups as well...see if the hum goes away when you hit the "right"

spot.

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Good job Dan, I was just about to suggest the same idea,I keep alligator clip leads around to trouble shoot problem circuits the same way. Has helped me with many repair and installs don't know why I didn't suggest before...I picked up a guitar and 2 hours disappeared. I'd thought about this today at work.

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Thanks guys, tried it but no change. I had been thinking along similar lines, and had tried a meter from the jack across all grounds. I've also emailed Stewmac and they said their diagram is correct. I see that Seymour Duncan has a 'how to install pickups' video on his site. I'll have a look and see if I'm doing something basically incorrect, and maybe see if there's a different circuit diagram to try.

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I've had a thought. I think maybe I should have started this thread, "OK, assume I know nothing..." because I think I may have made a basic mistake. Where grounds and hots follow similar routes I've used braided cable, e.g. from the switch to each volume pot, so the grounds are running along the shield of the hot signal. Could this be putting the hum into the circuit? Should all the wiring between pots be individual cables, with grounds and hots running in separate cables? If so, which cable runs should be shielded, I assume the pickup cables as that's how they come, and the cable to the jack socket maybe? In the old loom, which I'm not copying for various reasons, only the jack and switch have braided cable.

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Vomer, I think you need to reverse the hot and ground on your jack. I tried a little scientific experiment,used clip leads to wire 2 cables hot to grnd grnd to hot thereby simulating a bkwrd wired jack. The guitar played but buzzed like a single coil at normal playing levels but when I turned it down,the humming got louder and deeper. So you may want to try this.

I remembered doing that myself some years ago. Took me some time to figure it out back then.

If its backwards tuning down the volume control seems to turn down the grounding instead of the signal. Almost as though you've reversed grounding and signal paths cause as far as your amp is concerned, you have.

If that doesn't fix your problem,then you might have a hot/ground switched somewhere else,I'd doubl check the switch next,and make sure you have the specs on how to wire that specific one,as the internal connections vary, you can't just copy how the old one was hooked up.

Hope some of this helps

Dana

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Thanks Daneman, I've been avoiding switching the hot and ground on the jack as I can see that it is wired correctly. I follow your thinking though. And I considered the earth lift switch on my Peavey Encore, but that seems OK, and the problem is there through my Valve Junior also. I've run seven or eight guitars through these amps so I think thay are OK.

 

As with the jack, with the Switchcraft switch I can see the metal of each signal path so I know that is OK.

 

I found an article in Harmony Central's FAQ about grounding and shielding. At the moment my money is on the problem being that I have used braided wire for the short runs in between the pots, and where there are both hot and ground connections between the pots I've used the braid to carry the ground. Which is all very neat and tidy but I think it's introducing hum into the hot. I disconnected some of these and was amazed at the hum generated by my holding the braid when neither end was connected! The detail of how this all works is still a bit mysterious to me, but tomorrow I will replace the short runs of wire, i.e. between the pots, with non-braided cable. I'll let you know.

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Cool. If that doesn't help,you might try my test with 2 short cables and alligator clip leads. I managed to simulate the exact conditions you said you were experiencing,and I don't think there's enough voltage or current present to cause noise to be induced through the braided shield,just my opinion though.

Good luck and let us know what you figure out.

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Does my thinking make sense guys ? I managed to exactly duplicate the problems Volmer described' date='and would like to hear any other thoughts...kinda fun when you CAN actually help somebody out ya know:-" [/quote']

 

Well it ain't exactly rocket science, but yes, if the sleeve and tip got reversed, the

shield of the guitar cable would be carrying the signal all the way to the frame of

the amp input jack. I think you would see a "short" if that was the case, but...

since the guitar wiring is basically floating, a reversal somewhere between the

input jack and one of the pickups could cause a ground loop.

 

If the two p_ups are two wire (two signals and a ground/shield) then it is a matter of connectiong one of

the wires (white or black) to the shell of the volume controls along with the shield. The tone pots have

one lug open connection and the volume pots have one lug connected to ground. If you have all 3

wires (volume neck. volume bridge and output of 3 way switch shielded and the shields connected

to the ground lug on the 3 way and the volume pot cases AND the frame (sleeve) of the output connector,

that's basically it..you shouldn't have any hum unless one of the p_ups has an open connection inside.

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As with the jack' date=' with the Switchcraft switch I can see the metal of each signal path so I know that is OK.

 

At the moment my money is on the problem being that I have used braided wire for the short runs in between the pots, and where there are both hot and ground connections between the pots I've used the braid to carry the ground. Which is all very neat and tidy but I think it's introducing hum into the hot. I disconnected some of these and was amazed at the hum generated by my holding the braid when neither end was connected! The detail of how this all works is still a bit mysterious to me, but tomorrow I will replace the short runs of wire, i.e. between the pots, with non-braided cable. I'll let you know.[/quote']

 

 

I connect the braided shields to the pot cases all the time and I don't get any hum, and I have rewired a few

guitars in my day. If the braid is connected properly, it will not introduce hum into the signal...disconnecting

the braid at both ends makes the signal conductor act like a antenna of sorts..this is a 500K ohm circuit going

into an amp input impedance of 1 megohm. You can similate the same thing by touching the tip of your

guitar cord while the other end is plugged into the amp's input jack.

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  • 1 month later...

It's been a while since I could look at this, thanks for everyone's input. I fiddled around some more and couldn't get it. So I decided to look at the wiring on my Epiphone EA250, which is quiet and has independant volume controls. And I got to clean out 35 years of muck. I drew out the wiring as a schematic, I hope it might be of interest:

 

EA250 wiring

 

PS I haven't used it for the Sheraton yet, I'll need to get more braided cable. Could be a couple of weeks, I'll let you know how I get on.

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It's been a while since I could look at this' date=' thanks for everyone's input. I fiddled around some more and couldn't get it. So I decided to look at the wiring on my Epiphone EA250, which is quiet and has independant volume controls. And I got to clean out 35 years of muck. I drew out the wiring as a schematic, I hope it might be of interest:

 

PS I haven't used it for the Sheraton yet, I'll need to get more braided cable. Could be a couple of weeks, I'll let you know how I get on.[/quote']

 

I had a look at the schematic drawing. Other than the pickups going to the center tap of

the volume controls, it pretty much looks the same as the standard "2 humbucker, 2 vols. 2 tones

and 3 way" by SD...which has the pickups going to the outer tap of the volumes and the center

tap of the volumes going to the 3 way.

 

What difference does that make as far as hum?

I would surmise..none but it seems to be a more consistent

voltage divider, since the 3 way sees the 500K pot resistance,rather than a portion of it's

500k resistance...and the p_up sees a variable resistor (center tap moves from 500k to zero ohms).

 

With the SD diagrams (the p_pup is hooked to one outer tap of the volume (500k) and

the center tap of the volume is fed to the 3 way. The 3 way sees full output

from the p_up (volume on full), or a decreasing impedance down to gnd ..or 0 ohms on the pot.

 

Maybe other forum members would like to comment on the appreciable differences of the EA250 configuration?

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With the standard wiring method, where the volumes will short each other out at zero, the guitar's output (and the amp's input) is grounded at '0'.

 

normal.gif

 

The 'independent' wiring method leaves the guitar's output 'floating' when the volumes are turned down.

 

alternate.gif

 

...I could see how the latter method could be noisy.

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With the standard wiring method' date=' where the volumes will short each other out at zero, the guitar's output (and the amp's input) is grounded at '0'.

 

The 'independent' wiring method leaves the guitar's output 'floating' when the volumes are turned down.

 

...I could see how the latter method could be noisy.[/quote']

 

Makes sense. but I would think that with the tap connected to the pickups, the

series resistance of the p_up would "pull down" the 500K volume pot, since

the pickup resistance is in parallel with the pot , (depending on the wiper position),

except for "0" where it doesn't matter, and the output is floating at 500k or whatever

the pots resistance is. The output is still terminated (500k) but at that high impedance

there could be a bit of hissing noise, especially on a long guitar cord.

 

I would think that Vomer should try and tackle the standard wiring method

again. Something doesn't make sense in the way it's wired up.

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