Ground the poles? Ground to cavity shielding?

[David King]

Don't make this detail harder than it needs to be. Getting the back of the magnet hot enough to silver solder is going to make a mess of the bobbin, tape insulation etc -inviting more problems. A can of MG supershield works every time and seems to last forever even after wax potting.
Now you could get press-fitting copper or brass washers and solder to those or just a strip of brass drilled along with your flatwork and pressed on after assembling your armature.

[Joe Gwinn]

Now you could get press-fitting copper or brass washers and solder to those or just a strip of brass drilled along with your flatwork and pressed on after assembling your armature.

Too complicated. Just put narrow strips of 0.001" brass shimstock in the holes before pressing the magnets in, and solder a thin wire to the brass. Do this before lacquering or potting.

[rjb]

Getting the back of the magnet hot enough to silver solder is going to make a mess of the bobbin, tape insulation etc -inviting more problems.

You're right, of course. I was free-associating and thinking of a different, bobbin-less configuration.

Here is the magnet I tried to solder a ground wire to (see Fig 4):
First Rebuild- Electromuse Eye-Beam (for lap steel)

-rb

[jason lollar]

old emmons pickups just took a braided lead wire used for ground ran it up through a hole in the bottom plare between the magnets and wraped the braid around each magnet before soldering the inner coil wire to it and winding over it. Seems to do a reasonable job of grounding the rods even 40 years later. Kind of a mess to do. The other solution is dont ground them and dont touch the magnets. I can never understand why someone would be touching the magnets while they play anyway unless they stick way up above the cover but even then..... Ground them and you wont get that capacitance thing going if you do touch them.

[RedHouse]

No. You only have one ground which is at your output jack. Everything else is pretty much at the same ground potential.

Here's how Bourns shows to wire grounds.

In the pic, the bridge ground should be connected to the same spot as the other grounds, not off the daisy chain.

Regarding the shielding paint mentioned earlier, you need to paint it and test it with a multimeter to see the answer to your question. It's not uncommon for that stuff to have several hundred Ohms per inch of coating.

In fact a Strat came through my shop lately the user complained it was picking up "all kinds of stuff" at gigs (radio, McDonalds drive through etc). When I took off the scratchplate I noticed someone had used that black shielding paint (ala Stew-Mac) to shield it, and noticed the builder/modder relied on the jackplate to connect the shielding paint to the ground via physical contact.

Measuring from the jackplate area with one lead of my DMM (using piercing test leads) and touching the other lead to the neck pickup area (longest run in the cavity) it measured over 2.3K Ohms.

Resistance like that doesn't make for good shielding. You don't want to see more than a couple hundred Ohms (max) for decent shielding action.
(which is why I tend toward copper foil)

To remedy the poor conductivity, I ran a piece of pre-tinned #26 wire on the floor of the neck pickup cavity rout (glued down the wire to the floor with a drop of CA every 2 inches or so to keep it in place firmly), right down the center of the route, and over into the control cavity, across the floor, up in through the connecting hole to the jackplate and soldered directly to the jack ground, then applied another two coats of shielding paint (I do keep some on hand) over the wire and cavity area.


After the new coats of shielding paint dried, I got less than 300 Ohms doing the same measurement/test.

When one thinks of shielding (some call it screening) one tends to think of "blocking out stuff" which is kinda what it does ...but... for RF and other positive interference, it does it in a way not so self evident. When we make a shield or shielding connection/box/etc, we're actually trying to make the ground plane (zero volts level) a bigger antenna than the positive rail, that causes RF/static/whatever to tend toward that level in the circuit, which is not amplified by our stuff.

One other problem I see a lot in guitars is when folks shield the back plates of the cavities (or back side of scratchplates) and only rely on a mechanical connection to the rest of the ground circuit (ala; copper on both touching/pressing together via backplate screws). After a while humidity gets to the connection and it turns brown/green, at which point the shield is no longer at ground potential, but has been raised up several hunderd Ohms and becomes a nusance noise antenna.

Regarding the grounding of poles (alnico single coils) that can be a bugger because of the construction of the bobbins. What I do is just as David said, wind to the inner lead is the ground lead, but before I wind I wrap a couple turns of #28 un-insulated copper wire around the magnets and shoot the lead out the bottim hole in the center between the D and G string poles. Then wrap the inner bobbin with something like teflon seal tape, then wind the bobbin. After you are done you will have a nice convienient ground lead sticking out the bottom of the pickup to ground the poles. Note that eventually that connection will get some funk into it because of the dis-similar metals in contact with each other but that will take years if you pot the pickup.

Grounding the poles makes a single coil noticably quiter IMHO.

[RedHouse]

...The other solution is dont ground them and dont touch the magnets. I can never understand why someone would be touching the magnets while they play anyway unless they stick way up above the cover but even then...

I was of the same opinion until I came across a Strat who's pickups had really sharp edges on the pickup poles, playing it for a night I noticed when doing a string change it had a bunch of skin-flecks in the covers holes near each pole.
(apparently my skin)

The darn magnets were rubbing the skin of the fingers, specially when played ala Albert King style (no pick). Made me realize how a players fingers actually do reach down through the strings and touch the poles, on Fender Strat pickups in particular. Check out nearly any Les Paul (with covers) that has any miles on it, one can see where the fingers touch the pickup top getting smooge (not spooge) between the strings. If it was just plastic from the picks/plectrums, there wouldn't be any tarnish marks.

[David Schwab]

In the pic, the bridge ground should be connected to the same spot as the other grounds, not off the daisy chain.

Why? The daisy chain is ground. Any grounded part is ground.

[RedHouse]

Why? The daisy chain is ground. Any grounded part is ground.

Proper technique.

[David Schwab]

Proper technique.

Care to elaborate?

Proper for tube amp maybe. Nothing wrong with it in a guitar. I solder my string ground to the back of whichever pot is closest to that wire. The shielding also goes to a pot.

I use a single ground wire to the jack.

[RedHouse]

... Nothing wrong with it in a guitar...

Now don't get yer knickers in a twist David, I'm not criticising it or you. What's "proper" and what "works" are two different aspects of a notion, that's all.

When a guitar is plugged into the amp, the control cavity is effectively an extension of the amplifier, the "sensor" end of an amp chassis, so it it good to take care with your own layout and graound schema, but as you say, "it works".

Remember back to the 50/60's, your Chevy/Ford used to ground the tail lights, dashboard, and other circuitry to local points (dash/frame) then when the ground connections get weak the lighting system worked wonkey, bulbs dimmed etc. In the 70's the Japanese came along and cleaned our clocks with the Datsun's/Toyota's/Honda's where their electrical systems using proper wiring harneses which included a negative lead in each circuit branch that terminated at the battery's chassis connection, no more wonkey electrical problems. Now all the car brand use the "proper" grounding practice in vehicles sold in the US. Ok sure it's not guitars, but it's an example of "it works" vs "proper technique".

Another aspect which can certainly be dismissed if inconvienient, and be clear that I'm making a general statement here (nothing to with you or your work directly David) is that things done properly are IMHO a reflection of a builder's attention to detail. 90% of the time it takes the same amount of time/effort to wire things properly, as to do otherwise, but doing it properly shows one's work better while doing it the other way shows one is just like any other run-o-the-mill builder out there. Excellent work stands out.

For instance (tone discussion excluded here) an good example is looking inside a Mesa/Boogie and say modern Fender amps, the attention to detail is remarkable in the Mesa, proper ground planes, proper circuit layout, proper parts, connections, lead dress, everything clearly shows they take their idea of a product to the next level and reflects the notion of "done properly". The modern Fender's certainly also have a PCBs, modern circuit layout, parts, assembly, but the implementation reflects the notion of get it done, by unskilled labor, as cheap as possible, it reflects the notion of doing it in the way than "it works".

Just my opinion, certainly nothing to get a big forum argument going on, and my post has nothing to do with you or your work David, you can certainly wire your products as you feel appropriate for your business, I have no opinion about your practices.

[Mike Sulzer]

When a guitar is plugged into the amp, the control cavity is effectively an extension of the amplifier, the "sensor" end of an amp chassis, so it it good to take care with your own layout and graound schema, but as you say, "it works".

For that to really be true you would need two wires inside the shielded guitar cable. The shield of the guitar cable would connect the amp chassis to equivalent metal in the guitar. Signal current would not flow in the shield, but in the low side signal wire which would go directly to the low side of the cathode resistor of the first stage. That is, pickups and terminals of pots would not go to metal parts in the guitar, but only over to the amp on the low side signal wire. Then you could have no shield currents (flows of charge necessary to maintain the shield at near ground potential) resulting in voltage in series with the input.

But this is not the way it works; you have just the shield to carry both signal and shielding currents. Thus how you do the "grounding" inside the guitar has little effect: all the current ends up in the guitar cable shield in any case.

[RedHouse]

No doubt, you always see an argument opportunity Mike.

It's no surprise that you could look at the picture I commented on above, see the multiple star grounds (both Vol and one Tone), see they all have ground lugs, and are daisy chained together, and instead want to start a debate the comment I made about treating an ctrl cavity as an extension of the amp front end.

I'll not bother to engage in debate with you about proper wiring technique Mike, I've see the picks you posted of your guitar (and wiring work) they certainly speak for you.

[Mike Sulzer]

It's no surprise that you could look at the picture I commented on above, see the multiple star grounds (both Vol and one Tone), see they all have ground lugs, and are daisy chained together, and instead want to start a debate the comment I made about treating an ctrl cavity as an extension of the amp front end.

Did not understand a word I wrote, did you? So here it is once more: As long as you have a common path for signal and ground currents in a 10 or more foot long cable, the details of the grounding inside the guitar do not matter much at all. Guitars are not much of a problem in this regard because they do not plug into power independently from the amp, and so you are making a big issue of out nothing.

David is right; but when you argue with David, it is not arguing. But if I disagree with you, it is, of course.

[RedHouse]

...David is right; but when you argue with David, it is not arguing. But if I disagree with you, it is, of course.

David IS right, as he said, and I also reiterated ..."it works".

If you think the picture is right, you are entitled to your opinion. In my opinion the picture above is not proper wiring technique.

I mentioned to David (not argued) that it's good to think of the control cavity as an extension of the amp, saying that that because of David's remark about "proper in an amp, but not a guitar". I was trying to point out that there shouldn't be a line drawn in one's work between proper wiring (when inside an amp) relative to wiring a guitar, proper is proper on both/either.

In the pic is a good example of bad wiring technique in the context of this thread.

The context of this thread established early on that the control cavity was to be shielded, to elaborate on that, in the picture there are ground connections that are both irrelevant and locations poorly chosen for inside a shielded control cavity, my point.

In a shielded ctrl cavity there is no need/use for all the lugs around the bushings of the pots, the bodys of the pots do not need any ground connection when inside a shielded control cavity. Moving forward, with the absence of lugs and/or soldering to backs of pots, one would solder the connections to either a point on the shileding itself or even the jack lug or other single point in the cavity, and the bridge ground would attach there likewise.

The picture would be acceptable (but still not "proper") in an un-shielded stock control cavity such as a production guitar, oh but wait, we don't do that here so whats the point in arguing about that?.

When I say "proper" I don't mean doesn't work, or degrades the signal, I mean proper as in if you follow that pic your guitar control cavity wiring will look like sloppy work, without thought, like as if a noob tried to connect all grounds, to all parts, for the sake of completeness regarding the circuits necessity.

When you turn from the threads context because of the paraphrase I chose you effectively skipped my point to debate (typical M-O). My point was, and still is, the ground connections shown in the picture show poor wiring technique when used in the context of this thread, inside a shielded cavity.

You can argue/debate all day long (as you likely will), but it is, what it is.

[Mike Sulzer]

You can argue/debate all day long (as you likely will), but it is, what it is.

Yes, it is what it is. I agree completely about the benefits of good workmanship, despite my poor technical skills. We are not all good at everything.

But it is natural to think that you are talking about functionality as well as workmanship because, well, you are. Right after your "extension" analogy, you mentioned the poor functionality of using a car chassis as a ground current return system, and so bringing up the differences in functionality between an amplifier chassis and a guitar does not seem off topic to me. In the former we have large chassis currents from the power transformer, as well as heater wires and wires with highly amplified signals that might get near wires with low level signals, etc. In a passive guitar, we have none of that. The first places more requirements on the grounding system than the second.