Shielding on a Fender Jazzmaster

[randyc]

Bill, it's very clear that one of us is "simply misunderstanding". Regarding your science background, this statement (as well as three or four others) seems to contradict that assertion:

"Copper foil is non-magnetic? It's expressly designed to shield EMI (electromagnetic interference). That is the ONLY foil recommended for this purpose."

You might want to try attracting a copper object with a magnet and then tell me about your science background, OK?

[billkath]

Perhaps diamagnetic and conductive would have been a better words-Mea Culpa. We are not talking Ferromagnetism, though-we are talking about the EM field, and it's shielding ability to said field.

[randyc]

Bill, dang it man, you continue to modify your original statements like a politician.

Please make your point clearly, state the facts that support your point clearly and be taken seriously and respectfully. I'll go through this one more time and then I'm DONE.

The wavelength of a 60 Hz radiated signal would be approximately 3,103.96 MILES or 4995.3 kM (in air). In order for a RADIATED signal to have appreciable signal strength, the effective antenna length needs to be an appreciable fraction of one wavelength (somewhere around 1/16 wavelength, perhaps, depending on the radiated signal strength - which would be fairly trivial).

1/16 of a wavelength would suggest that the internal wiring of the guitar needs to be 194 MILES or 312.2 kM long. The point is that RADIATION is UNLIKELY - though not impossible - to be the problem for Drew's guitar (amplifier assumed to be hum-free). Therefore non-magnetic shielding useful in suppressing RADIATION has negligible effect in suppressing MAGNETIC signals.

As I mentioned before, if it was as easy as you suggest, manufacturers would have been shielding in this manner for eight DECADES or more, cost concerns or no cost concerns !

The problem is most probably (99.9%) MAGNETIC coupling from the magnetic field that surrounds all wiring in which current is flowing (every building in the western world, for our purposes). To shield against MAGNETIC coupling, one needs shielding material that is MAGNETIC - copper, aluminum and ALL other NON-ferrous materials are not acceptable.

Additionally, even with FERROUS material, a certain amount of thickness is required to suppress strong magnetic fields to minimal levels. That is impractical. Which brings us back to the invention of the humbuckiing pickup - the only PRACTICAL and economical way of obtaining MAGNETIC suppression to date.

RADIATION shielding (foils, conductive paint and so forth) is effective against higher frequency NOISE and RFI products (light dimmers, fluorescent lighting, sparking, radio transmitters, lightning and so forth). Won't do a thing to shield against 60 Hz susceptibility.

The standard reference on this topic is U.S. Military Standard 461, which the U.K. MOD always references in it's specifications for military electronic hardware.

cheers,
randyc

PS: and U.S. Military Standard 462

[billkath]

Bill, dang it man, you continue to modify your original statements like a politician.

Bit harsh, Randy-calling me a politician Got to remember the time differential-I get a bit punchy at 3 in the morning.

Please make your point clearly, state the facts that support your point clearly and be taken seriously and respectfully. I'll go through this one more time and then I'm DONE.

The wavelength of a 60 Hz radiated signal would be approximately 3,103.96 MILES or 4995.3 kM (in air). In order for a RADIATED signal to have appreciable signal strength, the effective antenna length needs to be an appreciable fraction of one wavelength (somewhere around 1/16 wavelength, perhaps, depending on the radiated signal strength - which would be fairly trivial).

1/16 of a wavelength would suggest that the internal wiring of the guitar needs to be 194 MILES or 312.2 kM long. The point is that RADIATION is UNLIKELY - though not impossible - to be the problem for Drew's guitar (amplifier assumed to be hum-free). Therefore non-magnetic shielding useful in suppressing RADIATION has negligible effect in suppressing MAGNETIC signals.

It's all just frequencies in the EM spectrum. Copper foil, of this thickness doesn't shield against tons of things in the EM spectrum, and it shields somethings better than it shields other things-but that is irrelevant. Whether the copper foil shields against "magnetic" signals (Here, I presume you are talking about 50/60 cycle hum) is neither here or there. What it DOES do is shield against the thing we are talking about-"normal" noise and hum. Ambient stray radiation, of radio frequencies,dimmer hash, flourescent light fittings etc, and "softens" A/C 50/60 cycle hum.

However-for it to be effective in this sheilding, it must be done correctly, and the original poster has not done this.

As I mentioned before, if it was as easy as you suggest, manufacturers would have been shielding in this manner for eight DECADES or more, cost concerns or no cost concerns !

I'd say you were wrong-dead wrong. To back that up-Did Fender design locking tuners for the Statocaster? No they didn't, until someone else came up with the idea that a locking tuner would solve tuning issues when using the trem. Fender couldn't have given a hoot up till then, and only went into that market when they realized that others were making money they could be making. Did Fender address the instabilities of the trem system? No-not until after Floyd ~Rose invented their system. Same with the roller nut. Fender, and other big companies, often think-"it is what it is-people will buy it". And people did. They don't make improvements unless they can make money on the improvements-use it as a selling tool.
The Fender Strat that Should be is the Fender Strat Pro. Fitting a foil shielding and star grounding system is something Fender believe people will do if they want to. Not everyone cares about noisy guitars. It's something that is costly and labour-intensive. They HAVE, however,upgraded their pickup and wire shielding since the old days, and have introduced SNC pickups.

The problem is most probably (99.9%) MAGNETIC coupling from the magnetic field that surrounds all wiring in which current is flowing (every building in the western world, for our purposes). To shield against MAGNETIC coupling, one needs shielding material that is MAGNETIC - copper, aluminum and ALL other NON-ferrous materials are not acceptable.

Additionally, even with FERROUS material, a certain amount of thickness is required to suppress strong magnetic fields to minimal levels. That is impractical.

I don't believe that magnetic coupling crosstalk is his main problem. Part of the problem-sure. But you can only do what you can do-in other words shield for RFI and ESI and use as small an area of properly shielded cable as humanly possible to reduce the EMI. It has to be done properly, though, treat the whole-not just parts. From reading his post, it doesn't seem like he's done it all correctly, and the mods he has made could be exacerbating the problem-making a "bigger" antenna.

Which brings us back to the invention of the humbuckiing pickup - the only PRACTICAL and economical way of obtaining MAGNETIC suppression to date.

Absolutely. However-single-coils can have a similar noise performance, but it takes a LOT more work.

RADIATION shielding (foils, conductive paint and so forth) is effective against higher frequency NOISE and RFI products (light dimmers, fluorescent lighting, sparking, radio transmitters, lightning and so forth).

Yes.

Won't do a thing to shield against 60 Hz susceptibility.

It won't eliminate it. But shielding can lessen it's effect. Just as having the absolutely smallest area of shielded wiring in the circuit does. With shields attached to the star ground. And by the circuit, I'm also including a short , well shielded guitar cable.
We are not talking about eliminating that part of the general interference, just getting it down to a very low level. For it to be effective, however, all exposed areas of the circuit must be shielded. That's between the jack socket and the pickup wirings, and also the trem bay.

[randyc]

I sure give you credit for stubbornness, Bill, that's a valuable characteristic in many situations. In this situation, your stubborness is causing you to make the same errors, again and again.

The OP mentioned the word "hum" about a half-dozen times. You might want to forget about all of the other frequencies that AREN'T causing a problem and focus on the one frequency that IS causing a problem: the A.C. power line frequency. You haven't yet suggested one thing that will eliminate that problem except agreeing with me about humbucking pickups. The rest of that stuff is internet urban legend NOT solid engineering based on centuries-old theory and fact.

And Drew, you know that you shouldn't rely on your ears to determine whether performance is improved or degraded. It's a simple test, just connect your DVM (adjusted for a low A.C. voltage setting) across the speaker leads and MEASURE the danged hum voltage at worst conditions and with guitar/amplifier setting noted.

After making changes, you can make the same measurement to see if things are better or worse.

cheers,
randyc

PS: leave the strings off the guitar - they are not necessary for tracking down hum problems and you can then crank all volumes up for max sensitivity without worrying about feedback.

[SamBooka]

Ok.. it WONT be today..
decided to do something fun instead (pics to come .. Randy wont like it but he never was an Epi fan

I will do the baseline you suggested for the pickups but I have tried that before with an error of +/- 30% so take any findings with as much salt as your blood pressure will allow (I am blaming my multimeter).

[randyc]

I've found that analog meters are more reliable for that type of measurement (even the cheap Radio Shack meters if they have a low enough AC voltage scale). The indicator needle is steady because it mechanically averages variations that digital meters cannot. Unhappily they are a rarity these days. I hung on to my old Triplett 630 and it's very useful for certain measurements.

Oh, but I AM an Epiphone fan - I owned a '53 that I still think about with sadness. I'm just not a Samick fan. The workmanship is OK externally, not OK internally and the materials are always sort of questionable.

Back to your photos, I like good workmanship, regardless of what it is performed on (recall that I complimented you on that Epi pickup installation last year). If you have pictures of your work, be assured that I'll enjoy looking at them.

OK, just checked to see if I have a spare analog meter I could lend you. I do but it is (unfortunately) one of those cheap Radio Shack meters and the AC voltage scale only goes down to 15 volts. That suggests that you could make 5 volt readings accurately. With strings removed and all volume/tone controls on "10" that might work.

Since the measurements will always be made from a low impedance AC source (the speaker terminals) I can likely jury-rig a transformer to make the thing more sensitive. Will let you know tomorrow - it's a tiny meter and would cost peanuts to ship. I have no immediate need for it so you could keep it until your project is satisfactorily concluded.

[SamBooka]

Thanks Randy. If it is something that I can use I will go and buy one. Out of curiosity why do you find the analog ones work better?

When I say I use my ears.. well.. I get a little help from an OD pedal. I will take a look tonight and see what I can find.

[randyc]

The analog meters act like a lowpass filter - the mechanical inertia of the movement can't follow transient events, the meter movement averages out the response and provides what many feel to be a "truer" RMS voltage reading.

Here's a great example of why analog meters are more useful than digital meters for certain applications. Let's say that you want to re-bias the Epiphone Galaxie 25 that someone brought you. After downloading the schematic and checking out the instructions that the manufacturer suggests to perform this procedure, you have concluded that not only are the instrucions useless but DANGEROUSLY useless.

So you decide to measure individual plate currents and adjust the bias potentiometers to obtain equal and correct bias conditions. There are three or four different ways of doing this but for the sake of the illustration, let's just assume that you are going to temporarily install 100 ohm, 1%, 1/4 watt resistors in series with the plates and then measure the voltage drop across the resistors.

The idea would be to adjust the grid bias potentiometers for about 35 mA plate current (EL-84 tubes) which would be a measured 3.5 volt drop across the 100 ohm resistors. So after observing all safety precautions, you clip the leads of your DIGITAL multimeter across the 100 ohm resistor and power the amplifier up.

Now, with your insulated adjustment tool you prepare to rotate the 10 turn pot to obtain that 3.5 volt drop across the plate resistor. You tentatively rotate the pot about 1/4 turn, watching your DVM ... it flickers (recall that it takes about 1/2 a second to update the reading) and just as you are ready to take the reading you smell something and notice that the resistor is smoking and poof, the fuse blows.

Why? Several reasons ...

(1) the manufacturer's schematic and adjustment procedure noted a ten-turn pot but the thrifty Chinese manufacturer used a ONE turn pot instead.

(2) before the digital multimeter could update it's reading, the resistor was fried and the fuse blew.

The analog meter provides real-time feedback for sensitive/critical adjustments like this - no digital updating time is required.

cheers,
randyc

PS: if you decide to buy an analog multimeter be very careful about the specifications - usually the DC voltage is specified with impressive numbers but the AC voltage sensitivity is considerably less as is the AC input impedance. A good passive (no batteries) meter, like my Triplett, will go down to 1.5 volts AC full scale with an input AC impedance of 10k. Meters with built-in FET amplifiers (need batteries) have greater sensitivity and higher input impedance - both very desirable if not too expensive.