Help: volume up=quiet, rolled back=loud hum

[legierk]

Sorry for the strange title...had to get someones attention. I have 4 Les Pauls that I completely rewired. I must be doing something wrong or I have bad parts.

At any rate, the subject line says it all. I have gutted various guitars at one time or another to try and fix this, to no avail. I keep thinking I have a ground loop somehow. I basically solder a wire around the pots in a "U" shape (not connecting the last two to each other). Is this correct?

While I'm here, may I ask you guys a few questions?

Is there a "definitive" Les Paul wiring diagram (that shows the grounds also...not just some symbol going to an imaginary spot?)
(I do have two wired for independent volume, but I think I will change those back to the standard volume...I think it sounds better...go figure)

I have read conflicting info on audio (A500k) and Linear (B500k) pots being used for volume and/or tone. What is the recommended use of these (or better yet, what gives the most control and/or subjectively sounds better?

All the guitars, BTW, have stock (496?) Gibson neck buckers and Dimarzio Super Distortions in the bridge. (My other guitars have these SD's in there too, with no hum)

The hum problem is driving me crazy. Is there a brand of pot I should try and stick with? IS there a gauge/type of wire I should try? I'm desperate for some wisdom here....Thanks.

[legierk]

I was quite hoping someone would offer some assistance...I pulled all my Pauls out and have my jumper leads ready and am going to try some troubleshooting that way...bypassing grounds, caps etc.

I bought all the Pauls used BTW which is why I immediatley changed all the electronics to "upgrade" them with new pots and Sprague caps. I shielded the cavities with copper tape also.

Once again, guitars are dead quiet when volume is maxed, but when I roll it back just a tad (and all the way to 0) it develops a hum that is annoying. The hum is loudest at about mid rotation.

Thanks for any advice.

[ChrisK]

I basically solder a wire around the pots in a "U" shape (not connecting the last two to each other). Is this correct?

I don't have any idea as to what you're describing here, especially regarding "not connecting the last two to each other".


You might find folks somewhat slow to respond at this time of the year 'cuz it's like Christmas or sumpthin'.


While I'm not aware of wiring diagrams that explicitly show all of the ground (signal return) wiring, they may exist. The "imaginary spot" that you allude to is common practice amongst those that practice electronics.

Do you have a wiring diagram AND digital pictures of the wiring that you're trying to effect?

[legierk]

Thank Chris. Yeah, I'm off work with nothing to do except try and fix this problem.

You'll notice a wire connecting the backs of the pots. That's what I was referring to regarding in a "U" shape. At any rate, I just soldered a star ground to the copper tape in the middle, but it's still the same. I wrapped copper tape around the hot going to the jack also...still the same. I ran jumpers across everything I could think of, and even to the bridge, but nothing. Very frustrating.

I added a photo of the factory wiring (on the one I haven't messed with) for reference, but they are so different it's really not worth comparing the two. The factory wiring is quiet though...maybe I should just start all over....

This is the schematic I used....http://www.guitarelectronics.com/product/WDUHH3T2202

[http://www.guitarelectronics.com/product/WDUHH3T2202]

hmmm, not sure how to do that...

[/C:\Users\Keith\Pictures\2006-12-26 guitar wiring]

not sure how to upload an image either...

[JohnH]

Hi legierk

Welcome to GN2. First, on posting links, just put the whole link on its own line, including the http bit, but without the square brackets.

To post pictures, you have to upload them somewhere to the internet, such as photobucket etc (Your picture seems to be just a reference to a file on your hard drive). Then post the entire URL address to the photo as above. Preferably, at each end put IMG and /IMG each inside a pair of square brackets , to make it appear on the post. Always preview your post before submitting it, to check the links work.

Haven't seen your picture yet. But on grounding and hum:

The first thing is to screen the cavity with foil, and also the inside of the cover plate at the back (thinking LP here), so that when the cover is screwed down, it overlaps and connects to the cavity foil for a complete screened enclosure.

All of the pot bodies and shafts will be connecting to the foil, because they are placed against it. However, the pot bodies are not automatically connected to the signal ground. You need just one (and no more) connection to the cavity screen from the signal grounds. Usually, one volume pot case is nominated as 'star ground', and all the ground points as shown in the diagram are taken to it, including the shields that cover the pickup wires, the pickup signal ground wires, the wire to the bridge, the ground lugs of the four pots and the ground wire from the output jack.

This star arrangement ensures tha there is only one route from any grounded point, to ground. I also think though, that your description of a 'U' that links up several points, without making a loop, is OK. I have done that several times too.

The key is one connection to the cavity shielding, one route only from any point to ground.

Now to the circuit. This is just my personal opinion. I think those reverse-wired volume controls are a crime against electronics. Sure they stop one pup from shunting the other when turned down with both on. But by the time they are turned down enough to reduce the volume, they wreck the tone of the pickups by putting a big resistance in series with the output, and shunting the pickup coil. This causes several ways in which the treble is lost. And also, that high resistance when turned down will make the signal more sensitive to hum downstream.

For an LP, I think forwards-wired volumes are best, and just don't turn them all the way down when you want to mix pickups. All the useful mixes are are at higher settings. I prefer linear forwards-wired volume controls on LPs, because it is easier to set a mix.

I have an LP copy, on which I've been trying various arrangements. My current set-up, which is the best I've found without active electronics, has two 500k lin volume pots, with 'treble bleed' components (a 1nF cap and a 220k resistor in parallel, from each volume hot outer lug to center lug). These parts help to reduce the loss of treble as you turn down the volume. Theres quite a gradual reduction in volume as you turn down from 10 to 5, and the main mixes are found between 7 and 10. The interaction where one volume reduces both pups seems to only be significant below about 2, on a mixed setting ie, outside the useful range so not a problem.

Thats for passive wiring - however, what I prefer even better is a small preamp built into the guitar - solves all the tone and mix problems. My LP will be going back to that arrangement when I've finished testing the passive circuit.

On tone controls, I think log pots give a better control.

On volume and tone pots, log or lin makes no difference to the sound range that you can achieve, only the position on the knob where each setting occurs.

I hope that helps a bit!

cheers

John

[legierk]

OK Trying this again. I can certainly take more pics, and this wiring looks rough to me, even though I thought I took great pains to make it neat.

I put a star ground in the middle soldered to the copper tape...I wrapped the hot wire to the jack with copper tape...I used jumpers to bypass everything I could, and yes I changed cables just to make sure. Problem still exist.




Stll can't seem to post a photo from myspace...

[zamzara]

I had this problem on my LP copy and also on my bass. When you turned the volume down, it hummed a lot more. WIth the stock LP controls it even did it with one volume on zero and the other on 10.

My solution was to use a single master volume, but wired as follows: instead of using all three pot lugs and passing the signal through the pot, I wired the signal output direct to the jack output, and wired the volume pot in parallel going to ground (exactly as with a tone control, but with no cap). This allows the volume control to bleed off the signal as the pot is adjusted.

There is now no hum and it doesn't seem to affect tone that I can detect. The only quirk is that the taper works a bit differently, it reaches about 40% volume at 1 on the dial and then very quickly goes silent below 1, but that's fine for me.

The other advantage on the LP is that it freed up the other now unused voume position for a rotary switch (with a stock control knob) for spliiting the humbuckers.

[ang3lus]

maybe your amp is doing it ?
check the ground connection in the jack outlet that goes into the wall.

[zamzara]

My idea above was for a linear volume pot btw. Doesn't work too well with audio taper... just tried it and it's far too fiddly.

[zamzara]

I've just had anotehr look at both guitars that had this problem: in both cases it turned out to be ground loops. In the Les Paul the selector switch case was grounded twice and the pot shells were connected together one time too many. I star grounded the bass too and it fixed the problem there too. Volume pots are now back to standard 'master volume' wiring.