Hum Debug Procedure

[loos]

Hello all, I've just completed my first assembly of a Tele style guitar and am happy with it saving the question of a lot of hum. I know plenty has been written on this topic but I still don't understand what needs to be done and what is window dressing. Should I have used shielded wire for wiring the control plate? Ought I have put a shielding braid inside the tunnels between the pickups and the control plate? I've been wondering if I could simply wrap the entire body in aluminum foil and alligator clip the foil to a ground such as an output jack screw to see if the problem is one of shielding or if the hum is purely wiring related.

I realize I haven't a clue regarding a proper debug procedure, and don't know where one ought to use shielded wire.

Just to give the layout I have a chambered tele body without any F holes, replacement Fender pots and three way switch, Lace Tele pickups. The pick guard has no shielding, the pickup cavities aren't shielded and there is no shielding paint in the passageways. The wire is 22 gauge Radio Shack stranded hookup wire.

When I touch the bridge plate the hum diminishes as it ought to and the pickups respond to screwdriver taps correctly. I haven't put strings on yet since it rather looks as if I'm going to have to remove components. The same amp plugged into the same socket produces almost no hum with my Lace holy grail pickups. I followed the Lace wiring diagram in both cases. Guidance gratefully accepted.

loos

[Samba Pa Ti]

is the bridge grounded ?

there should be a wire coming from the control plate ground (back of pot) usually it uses the same hole as the bridge pickup wire and then the plastic is removed and the bare wire is squashed between the body and the bridge making contact

eg > http://www.tdpri.com/articles/build_gifs/BIG/1359092.jpg

dont worry about using unshielded wire or shielding the pickup routes, i doubt thats the reason it will be humming unless you have a lot of noisy electronics.

also double check wiring and make sure the output jack is wired up correctly (hot lead to the tip of the jack)

[loos]

is the bridge grounded ?

there should be a wire coming from the control plate ground (back of pot) usually it uses the same hole as the bridge pickup wire and then the plastic is removed and the bare wire is squashed between the body and the bridge making contact

eg > http://www.tdpri.com/articles/build_gifs/BIG/1359092.jpg

dont worry about using unshielded wire or shielding the pickup routes, i doubt thats the reason it will be humming unless you have a lot of noisy electronics.

also double check wiring and make sure the output jack is wired up correctly (hot lead to the tip of the jack)

Yes thanks I did ground the bridge using the technique you mention, squashed bare wire under the plate and then into a mounting screw hole and although I was careful about following instructions I did check to make sure that I hadn't switched the signal and ground wires on the output jack. I've 3.4 Ohms resistance between the bridge plate and the output jack ground. Checking resistance using a short standard cord plugged in I get 6.47 Ω from the neck PU, the middle position measures 4.31Ω and the bridge 12.6 Ω.

I'm interested to note that the buzz is quite loud and hissy when the volume knob is up all the way and almost instantly when turning it down the trebly tone of the buzz goes down a lot. I thought about cleaning the brand new pot but thinking about it didn't since it isn't scratchy.

loos

[guitar101]

is the bridge grounded ?

there should be a wire coming from the control plate ground (back of pot) usually it uses the same hole as the bridge pickup wire and then the plastic is removed and the bare wire is squashed between the body and the bridge making contact

eg > http://www.tdpri.com/articles/build_gifs/BIG/1359092.jpg

dont worry about using unshielded wire or shielding the pickup routes, i doubt thats the reason it will be humming unless you have a lot of noisy electronics.

also double check wiring and make sure the output jack is wired up correctly (hot lead to the tip of the jack)

Yes thanks I did ground the bridge using the technique you mention, squashed bare wire under the plate and then into a mounting screw hole and although I was careful about following instructions I did check to make sure that I hadn't switched the signal and ground wires on the output jack. I've 3.4 Ohms resistance between the bridge plate and the output jack ground. Checking resistance using a short standard cord plugged in I get 6.47 Ω from the neck PU, the middle position measures 4.31Ω and the bridge 12.6 Ω.

I'm interested to note that the buzz is quite loud and hissy when the volume knob is up all the way and almost instantly when turning it down the trebly tone of the buzz goes down a lot. I thought about cleaning the brand new pot but thinking about it didn't since it isn't scratchy.

loos

I don't think you are going to get very far with the pick guard and the cavities unshielded. The shield should be made continuous (tied together) with wire and this shield is tied to the ground wires of your pickups and the ground wire of the output jack. Really with the cavities etc. unshielded you are fighting a losing battle.

[Samba Pa Ti]

I don't think you are going to get very far with the pick guard and the cavities unshielded. The shield should be made continuous (tied together) with wire and this shield is tied to the ground wires of your pickups and the ground wire of the output jack. Really with the cavities etc. unshielded you are fighting a losing battle.

lace pickups (practically noisless) into a telecaster wont need much shielding, only the neck pickup is out in the open, the rest of the electronics are all shielded by design (control plate and bridge being made of steel/brass).

still that doesnt explain where the hum is coming from though.

[Workingman]

Have you checked your cord?

[psw]

Is the OP still having troubles on this?

I suspect the LACE pickups should be quiet, I'm not sure of the type you have...

A tele tends to pretty good shielding wise, if trad, the control cover plate is metal and provides a shield, the pickguard covers mostly wood, unlike a strat, so no real benefit shielding that.

If the pickup wires are shielded, these will cover any of the cavities better than shielded paint ever will...

It's good practice to put a shielded cable to the output jack, but then again on a tele it is so short and covered mainly by the control plate...so generally ok...

Aluminum foil...no, i don't think so!!!

the bridge and so the strings are grounded, it will be better with the strings on, these also provide a little bit of a shield above the pickups...

It could be that you have the pickup covers or something hot..not familiar with the Lace codes and such...does it have a separate bare wire for ground?

Along with the bridge, i take it the pots and so the control plate is grounded, is there a drop in noise when the knobs or control plate is touched?

It's tricky to know exactly what is going on here...do you have a multimeter to check grounds?

The volume pot does sound a bit dodgy...

I'm interested to note that the buzz is quite loud and hissy when the volume knob is up all the way and almost instantly when turning it down the trebly tone of the buzz goes down a lot. I thought about cleaning the brand new pot but thinking about it didn't since it isn't scratchy.

Cleaning it is probably not going to help, but if you have a multimeter, you could check the resistance between the middle tag and the outers to see the value of it, and if there is something strange going on with the volume wide open.

maybe also check that the pickup covers are grounded...just in case, multimeter from cover to ground (say bridge plate)

You might want to try it with strings on it...I suspect there's nothing wrong outside of the control cavity...

I doubt very much if it is a shielding issues, real single coils tend to be noisy you understand, but on a tele, there is so little in there to cause trouble and generally pickups have shielded wires that takes care of the cavity shileds.

best of luck...

[loos]

Thanks for all the ideas, I'm going to see about shielding the run to the output jack, I'll check the pots to see if they are OK and I guess that'll take me through the weekend. The Lace pickups have two covered ground wires each and the hot. All are waxed. The ones I put on the Fernandes Strat sounded so great I didn't hesitate before selecting them for the Tele. But perhaps I've a funky pot, I'll see. My first wiring job I made the mistake of cutting the wires too short and now wonder about either replacing the wire or splicing on some.. I really ought to have thought a wee bit more carefully before cutting.

[Samba Pa Ti]

Thanks for all the ideas, I'm going to see about shielding the run to the output jack, I'll check the pots to see if they are OK and I guess that'll take me through the weekend. The Lace pickups have two covered ground wires each and the hot. All are waxed. The ones I put on the Fernandes Strat sounded so great I didn't hesitate before selecting them for the Tele. But perhaps I've a funky pot, I'll see. My first wiring job I made the mistake of cutting the wires too short and now wonder about either replacing the wire or splicing on some.. I really ought to have thought a wee bit more carefully before cutting.

what sortof lace pickups are they ?

all the sensors are filled with silicone type stuff not wax, are they "powered by lace" pickups the telecaster ones or the holygrail strat pickups ?

[Reinhold]

Or are they alumitones, because I'm getting some weird hum on my new prewired s/s/s set I installed, despite grounding everything correctly, unless one of their wires aren't soldered correctly. My hum also goes away when I touch the strings or the bridge.

[loos]

Thanks again for all the good ideas, here's some sort of response..

My pickups are the Lace Tele Sensor series, and everything really seems grounded correctly, I've checked all the grounds with my multimeter. So I decided to put strings on it and just play for awhile before taking it apart and doing the shielding. There are a few other issues to solve now, a bit of a buzzy tone which may be because two bridge saddle screw springs aren't under much or any tension which may be creating a sympathetic rattle and I think I may see some improvement adding a second string tree for the D and G strings. The neck adjusted well, I did the .010" feeler gauge check and the frets aren't terribly uneven or even more than slightly worn. I do need a new nut, the neck is from a MIM tele I saw at a local shop, looked like a victim of guitar rage in which the poor body took the brunt of some sad sack's poorly managed anger. The neck is fine save a few scratches on the head and really poorly filed nut slots which actually look as if the PO didn't know which side the bass strings went on. I'll get a Tusq nut, they seem to be usually rated as acceptable to very good and aren't expensive.

I like the suggestion of checking resistance on the pots but have a question there, do I need to unsolder them before I can check, It's been a few years since I've done electronic soldering... I really think the last real project was putting together Dynaco kits.

Seems like there are 5 or 6 Ω resistance between the switch plate and the front PU cover. The rear PU has a non conductive cover on it.

It sure is nice having a light guitar, I think once debugged it's going to be a real favorite.

loos

[psw]

OK...

well...there's hum and electronic buzz...and there's mechanical rattles and fret buzz...very different things...

I just installed a Tusq XL nut and found it easy to work and is teflon impregnated (and now comes in white or black) and have been very impressed. Worth to get this kind of slippery nut to help with tuning...

Otherwise, all these kids of set up, nuts and frets, truss rod adjustments and such can be handled elsewhere on the forum...

Electronics wise...

Seems like there are 5 or 6 Ω resistance between the switch plate and the front PU cover. The rear PU has a non conductive cover on it.

There seems to be a problem here...hmmm

Are you sure it's 6 ohm (how do you type the ohm symbol btw?) and not like 6k ohm or 6,000 ohm like the value of a pickup? The multimeter usually has different settings and may be on the 1,000 ohm reding so be saying 6 but meaning 6,000 if you get my drift...check it by reading a pickup...is it the same or similar value?

I ask, because the cover of the pickup should be grounded, there should be no resistance to other ground points like the bridge or the controls and such.

What it may be indicating and will be causing problems is that the cover is "hot" instead of grounded. Does the cover have it's own ground wire, are you sure you have the hot and ground around the right way...could reverse them on the neck pickup and see if this helps.

It's a little tricky to know what's going on here, did you work from a wiring diagram, could you post that?

You can measure the value of a pot, form the middle tag to an outer, remember to turn it, one direction will be the full resistance, the other zero (when 'off')...but I really don't think the pots are at all at fault, rarely introduce noise like described.

Did you do the entire wiring? If so, it might be easier to 'start over' with a good diagram and such, checking everything as you go with a multimeter...but it must be something simple like the neck cover being hot which seems to be a distinct possibility.

This could well be a great guitar, it's nice to hear of things being 'saved' like this. I too am not aware of the actual pickup models used, wire colour codes or specs...do you have links to the specific models we are dealing with?

Traditionally, the tele neck pickup has a chrome cover on it, this is wired to the 'ground' lead internally, to do any phasing or fancy wiring, this needs to have a separate lead. More modern pickups often will have a separate ground lead for grounding the cover separate from the cover...so as well as the two coil leads, there is a third wire. If your pickup has only two wires, one will be connected directly to the cover...you can identify it with a multimeter as there will be zero ohms resistance between one lead and the cover...this MUST be the ground. Another simple test is if you were to touch the cover, does this make the noise worse, or is it the same effect as touching the bridge or the strings and such...all grounded parts should get quieter when touched, if anything is hot, it usually sounds like you touched the tip of an amp or maybe even short out (no sound)...so check all this over carefully, as this may well be the 'simple' problem that's been overlooked.

[loos]

Ah reading the ohm meter. Well I've got a lovely meter, a Fluke 63 and the readings fluctuate wildly unless the leads are clipped on not pressed against. I do like the old analog meters for their lack of sensitivity, way easier for me to read. But there is a bar graph at the bottom of the display and it shows almost no resistance. If I clip the two leads together I get 3.0 Ω . That's one bar. I imagine any wire must have some resistance. So the reading I got shows virtually no resistance. I fear I'm rather clueless on the fine points.

I get the ohm symbol by using the character palette, Mac OS 10.5.8 the one I'm using is Lucida Grande and although I ought to be able to give you the unicode value it's eluding me at the moment but I just click on the symbol I want and it's there on the virtual page.

Regarding the wiring, I simply followed the diagram that came from Lace with the pickups. I'd post it but it's on their site on the web. I've wired three guitars so far, one had push pull center tap pots which were too long for the cutout and kept being OK and then touching something so I just removed all the fancy stuff and wired it according to... I'm not sure, very likely the StewMac site's diagram for standard Tele with three way switch and all went well. Mostly well that is but that is a different guitar with it's own weirdness... a P 90 neck pickup which I gather ought to have a different value pot. I'd love to sort that out but one at a time I think. The second guitar was my Fernandes Strat which I again just wired following the diagram which came with the pickups, Lace Holy Grails and that has been flawless and a real joy, I like the tone a lot.

But here on the Tele everything seems OK, just a lot more hum than I expected based on the Strat and a DeArmond Les Paul type which is almost dead silent, all plugged into the same amp, same cord, same circuit, same lights on etc. When I don't touch the guitar the hum is quite loud and if I touch any of the appropriate things, bridge, strings, control plate, the hum drops to an almost reasonable level. I'd think it reasonable if the Strat and the LP clone weren't so much quieter.

[loos]

Are you sure it's 6 ohm (how do you type the ohm symbol btw?)

I found it, on my keyboard option z gives Ω.

[guitar101]

I don't think you are going to get very far with the pick guard and the cavities unshielded. The shield should be made continuous (tied together) with wire and this shield is tied to the ground wires of your pickups and the ground wire of the output jack. Really with the cavities etc. unshielded you are fighting a losing battle.

lace pickups (practically noisless) into a telecaster wont need much shielding, only the neck pickup is out in the open, the rest of the electronics are all shielded by design (control plate and bridge being made of steel/brass).

still that doesnt explain where the hum is coming from though.

I don't agree I think that shielding will solve your problem.

Try this site

http://www.guitarnuts.com/wiring/shielding/tele.php

[Woodenspoke]

Dont over think this.

There is no reason to worry about readings between two ground points if you are just checking continuity. The beeper on your meter will be just fine.

Every part and ground wire and shielded cable cover needs to be grounded through the pot covers and every pot cover need to be connected. Then it all runs into the ground on the jack. If your control cavity was shieded then adding a ground sheild to the wires on the jack is a waste of time.

So in short you should be able to place your meter on any two objects connected to ground and get a reading or a beep. Its really that simple. Most people who have never had solder experience have issues getting wires soldered properly to the back of the pots.

So I would start by making sure everything is connected to the back of the pot that needs to be; and that all the pot shells are interconnected (grounded). Its a point to point check. If everything reads connected its something else. Then I would start by removing one pickup from the system to isolate which pup the buzz is comming from.

But as was said first make sure its all connected properly according to your wiring diagram.

[guitar101]

Just wondering how you made out with the hum problem.???

[loos]

I took the guitar to have a nut fitted, something I was not ready to do and when I get it back I'm going to shield the switchplate cavity and around the output jack. Also under the pick guard and the wire tunnels. Then I'll report. I perhaps expected it to be quieter than was reasonable but I'm going to continue, I'd like it as quiet as can be expected.

loos

[psw]

Single coil pickups are always susceptible to hum...it's in their nature. Not familiar with yours, but they are never going to be happy near a computer monitor for instance, or fluro lights and such.

A fair bit can be done with shielding, a lot can be done with just shielded cable....for instance, if the neck pickup has shielded leads, that would pretty much cover it. My tele has no shielding other than the metal bridge and control covers and shielded pickup leads...it's deal quiet, but both pickups are noiseless and humbucking...similar my new LP, split the coils and you will get some noise...so the noise is not due to cavity shielding (or in both guitars a lack of it other than shielded cables) but due entirely to the single coil pickups...