Anyone tried shielding their Strat?

[martin manning]

I have done that too -and used a stereo output jack. There the single and shield ground points meet. Thanks to the guitar cord barrel.

So, your signal ground goes to the ring terminal of a stereo output jack, while a wire from the shield ground goes to the sleeve, is that right? Pretty clever.

A standard mono cable plug will then connect the shield and signal grounds at the guitar jack, which will short the cap isolating them. I tested the effect of this earlier by running a clip lead from the trem claw to the jack plate to see if the hum would increase... it didn't. This makes me tend to agree with Dai- most of the improvement is due to the more complete shielding around the PU coils.

I'm wondering what the capacitance of the mic cable you are using is. Is it comparable to a good guitar cable?

MPM

[R.G.]

I know this gets a little far from the main topic, but the site states that using a smaller cap value shunted with a resistor will protect you from AC shocks too. I don't see how. What do you think?

The impedance of a cap rises as frequency decreases. You want to limit current at power line frequency - 50 or 60 Hz - while letting signal through. The resistor "grounds" bridge and strings at power line frequency, the small cap "grounds" it for RF. Done properly, the current that can flow at power line frequency is low enough to only mildly tingle not kill.

I shielded my Strat years ago, and now do it to every guitar I get. It is a major improvement in hum. Nothing is perfect.

However, if you fell into a cactus plant, would you refuse to pull out 98% of the thorns because you knew you couldn't get them all?

[David Schwab]

I have done that too -and used a stereo output jack. There the single and shield ground points meet. Thanks to the guitar cord barrel.

Why not just connect them to the same ground lug where they attach to the jack? You aren't really improving anything since it all connects together when the plug is in. It doesn't matter when the plug isn't in, so putting them on separate lugs on the jack serves no purpose. It doesn't cause any harm though of course, unless you plan on using the jack to turn on a battery.

[David Schwab]

The impedance of a cap rises as frequency decreases. You want to limit current at power line frequency - 50 or 60 Hz - while letting signal through. The resistor "grounds" bridge and strings at power line frequency, the small cap "grounds" it for RF. Done properly, the current that can flow at power line frequency is low enough to only mildly tingle not kill.

I shielded my Strat years ago, and now do it to every guitar I get. It is a major improvement in hum. Nothing is perfect.

However, if you fell into a cactus plant, would you refuse to pull out 98% of the thorns because you knew you couldn't get them all?

Nice explanation R.G. You need to come to the TalkBass forum and dispel some of the myths over there... they just wont listen to me!

[dai h.]

re: the "pseudo-balanced" wiring, was wondering what the benefit is(or is supposed to be). Maybe like a an added capacitive layer from outer shield to inner signal return/ground(my understanding was added layers of shielding was better than thickening)? Pete Cornish (who generally doesn't seem to spout BS/mojo/hype and seems solid technically) sells pseudo-balanced cables (IIRC--also something I vaguely recall about the correct orientation for the cable). Wonder if it's just the extra layer of shield or something else as well. Say if the other side was terminated with a R and C.

(okay, had a quick google and apparently his cables are pseudo--his term is semi-balanced--balanced...)

We have found our system of semi-balanced wiring to be most effective in reducing the amount of radio frequency interference collected by the guitar cable when in an area of high field strength.

http://www.petecornish.co.uk/hdgtr_bass.html

[fogonero]

Thank you very much for the explanation R.G. Does it still protect you from DC Shocks?

[dai h.]

The cables are Uni.-directional i.e. they are designed to use with the end marked with a green cap and "AMP" label connected to the amplifier,

trying to picture the pseudo-balanced wiring conceptually, sort of like adding a metal tube over the hot and ground (hot and signal return/shield/ground) which is sort of like having two conductors on a ground plane (except it's not flat). So there will be a small capacitance from the two inner conductors to the ground plane/tube. So far as I can rationalize the logic seems to be the added "cap"'s ground should be connected back to the amp since the ground area is bigger and thus impedance is lower and if connected to safety ground and it has a good (low-Z) connection to physical earth all the better(the RF that sees the shield takes the path of least resistance towards the amp instead of the signal source, i.e. gtr.). And the electrostatic layer (capacitor layer--assuming copper) lessens the RF to the inner conductors. Seems like capacitive loading would be worse but since putting two conductors on a ground plane is supposed to decrease their mutual capacitance that helps(??). Sorry for going off on a tangent but something earlier about the shielding and mention of "TRS" set my mind off.

(also, I don't actually know if the Pete Cornish cable does have the outer shield connected to the amp end plug but that way seems to make sense)

[R.G.]

Thank you very much for the explanation R.G. Does it still protect you from DC Shocks?

Where are you going to find DC shocks, just out of curiousity?

The cap is an open circuit at DC, and the resistor is quite large, so it takes a lot of DC to get enough current to hurt you.

Notice that none of these completely prevent you from even feeling shocks. What they do is keep you from getting hurt. "Getting hurt" generally means less than 10ma or so across your chest. The resistor is big - I don't have it in front of me, but wasn't it 330K?

If so, V = 0.010*330K = 3300V. So you'd need 3300V DC to be in the dangerous range. If the resistor value was lower, like 100K, that's still 1000Vdc to get to dangerous currents.

AC voltages are much more common and much commoner killers.

[David Schwab]

If so, V = 0.010*330K = 3300V. So you'd need 3300V DC to be in the dangerous range. If the resistor value was lower, like 100K, that's still 1000Vdc to get to dangerous currents.

I measured 85 volts once when I got a bad shock from a mic. That was probably AC? I don't remember and it was before digital multimeters.

But still a long way off from 1000 V!