Anyone tried shielding their Strat?

[tubeswell]

I found this article this morning.

http://www.guitarnuts.com/wiring/shielding/shield3.php

I would be interested to know if anyone has done this sort of mod and what values they might've used for the DC blocking cap. The article suggests anything from .1 to .5uF, but I'm curious whether anyone has any comment about the tonal differences (other than .5uF sounds bassier).

I like the brightness of my strat, but dislike the noiseyness.

Also any comments on carbon-based paint, and aluminium or copper based conductive paint for shielding the guitar body cavity?

[dai h.]

there should be at least a thread on this (maybe not the specific article but on grounding the bridge) and some additional (interesting) discussion IIRC. Adding extra shielding should help reduce buzz (through electrostatic shielding which materials such as alu and copper provide). (Also, think about the "perpetrator", or noise sources such as lights, monitors, etc. etc. as well as the "victim", or gtr.) Not really sure if the star grounding would be necessary (seems just keeping ground connections low resistance to each other should be fine since currents are extremely tiny--well, more if active electronics are used).

[tubeswell]

Thanks for your comments dai h.

I did the shielding mod this afternoon.

Its definitely quieter. Almost dead silent on the the hum-cancelling positions and noticeably quieter on the other three p'up positions. I used .2uF for the DC blocking cap (2 x .1uF in parallel) to ground. If I go to .1uF, should that theoretically lift the treble response a bit?

[dai h.]

sorry I'm not quite seeing the logic of getting more treble by reducing the cap value there. Could you explain that? I gather the cap goes to the shielding plus bridge (so the noise couples to DC ground via the cap and the cap helps prevent a lethal amount of current)? Normally I'd expect to see a low value R plus maybe some diodes, maybe a smaller cap but of course sticking a low value R and diodes would totally defeat any shock reducing effect. I wonder if layering of shields can be done like that (only capacitively connected).

[David Schwab]

The cap is just to block DC current from flowing, such as in a shock situation.

Changing the value of that cap has no effect on the tone of the guitar. If it did than something's not right with that circuit, or with your wiring.

If you wrapped your pickups with foil, that can dull their tone. The trick is to not wrap a closed loop around the pickup. You have to keep the ends from touching.

I said it in the other thread... I don't believe you can have a ground loop in a guitar, so besides being neat a tidy, star grounding shouldn't change anything at all.

[tubeswell]

Thanks David and dai h. I didn't wrap the p'ups with foil - I left them stock.

I put foil tape right around the body cavities and right across the back of the faceplate - all the foil edges are folded back and taped down to contact the layer(s) below and I tested the resistance with my meter to make sure I got the R as low as I could (about 2-3 Ohms max) anywhere on the shield. The only wires touching this foil shield are the tremolo bridge wire (screwed via a ring terminal to the back of the body cavity so that there isn't a 'loop' from this), and the grounded side of the DC blocking cap, which is soldered to another ring terminal under one of the selector mounting bolts).

The .2uF DC blocking setup I have going to the foil shield is between the ground side of the p'ups (and all the rest of the -ve returns, including the grounds of the .22uF caps that are on both tone controls) and the foil shield. The non-grounded side of the DC blocking cap also takes the p'up returns and the vol pot wiper ground.

The strat is an '89 model with a "TBX" bridge tone control, in which the bridge (mid) tone has a double-ganged pot with the bottom gang wiper going to the selector. The top gang wiper goes to the bottom gang input. The bottom gang input goes to ground via a resistor. The top gang input goes to the same ground via a .22uF cap. (I shifted this common cap/resistor ground from the back of the pot to the non-grounded side of the .2uF DC blocking cap I installed)

I have attached some photos of the guts of it prior to the rewiring so you can see what I am trying to describe.

I removed all the ground wires going to the back of the pots in accordance with the 'star grounding' system described in the mod. Apart from the different setup on the Bridge tone control (derived from the stock setup I described), everything in my rewiring is as per the Shielded wiring mod described on the guitarnuts website.

[dai h.]

if the .33uF cap is connected only to the bridge, then that just looks like it's just meant to AC ground the (human) body plus block DC (as David mentions above). If the signal return and shield are tied together, then it would seem star connecting points could be a bit counterproductive from the point of increasing distances between ground points (maybe there isn't enough to matter though since currents are ultra-miniscule). (With signal return tied to shield/enclosure, seems like it would be better the lower you made the ground impedance/resistance, therefore connecting all points in the shortest physical way possible and the thicker and more conductive the wires the better--i.e. the lower the resistance the less the difference will be between all the ground points and the closer to zero the better the effectiveness as shield.) Something that sounded interesting in the other thread was where David mentioned something about tying the shield at the output--I think basically having a strict separation of shield/signal return up to that point. Maybe you could go further with a pseudo-balanced shield to the amp or something.

[tubeswell]

Sorry I didn't explain properly, in the mod the .33uF cap is between the shield and every -ve return in the guitar (except for the bridge/tremolo/string wire, which goes directly to the shield). See picture.

In explaining this just now, I have just clicked that this puts the bridge/temolo/string wire on the other side of the .33uF cap from the -ve return to the amp, so therefore the .33uF cap can't have any effect on the tone pot caps.

[David Schwab]

I was looking at that on the site. I haven't had the time to sit and look at it better, but I don't think I would wire my grounds that way.

Everything is tired together where the ground goes to the jack, but then he has the cap on the shields, by way of one of the pots.

I would use a cap and resistor on the bridge wire, just for shock protection, but the shields need to be connected to ground, not through the cap.

As dai h. said, start grounding on a guitar can actually make some ground paths longer... there's nothing wrong with having a ground plane, such as the pot cans/foil shield, and grounding everything to that. Then each element has a short path to ground.

When I get a chance I'll try this out, but so far i think most of the info on that site is quite suspect. The bottom line is that single coil pickups hum... shielding wont get rid of that.

[tubeswell]

Well it does quieten down some of the noise I was getting before when I wasn't touching the strings/chassis. So it definitely does something to reduce noise.

[tubeswell]

The Acid test

Well last night my zep tribute band did a set on a fully lit up stage with a zillion possible sources of signal interference, and I'll be danged, the gueetar was a quiet as a mouse. :-)

[martin manning]

I've done this too, and the hum reduction was indeed quite dramatic in high interference environments.

What would have been interesting is to have done it in two steps to separate the effects of improving the shielding vs. the wiring change.

MPM

[dai h.]

I would guess the improvement was primarily due to the addition of electrostatic (capacitive) shielding and the star grounding had little or no effect. I wouldn't bother to change the wiring to confirm though (unless you want to be a total science nerd! ).

[fogonero]

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?

[Guitarist]

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.

If I want, I can stay "balanced" (TRS male) until the amp input and there the cord is soldered "fixed" mono. A good way to use up some mic cable. Label the ends, < Guitar or Amp >. Does this actually help? I don't know for sure. I guess you might be able to go into the balanced In of a firewire mixer for Amplitube modelling or Guitar Rig (requiring both ends to be balanced).
If you try this with hifi triple insulated cable you might get lots of cable noise ;(.

The Strat Lovers Strat is worth the extra time and PP switch. Great for jazz with the series sounds: loud and dark.