Are Aluminum Stomp Box Cases Better Shielded? I think not.

http://www.fillmorepedal.com Superior, noise-free guitar effects pedals are the result of superior design and construction of the circuit, and not whether you use an aluminum case versus a polycarbonate case. My effects are quiet even before I put them in the case. This Demo shows that an aluminum case (whether or not the circuit is grounded to the case) does little to prevent radio waves from entering the case. Choice of case, be it aluminum or polycarbonate, is best left to esthetics, and to the personal preference of the user.

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[sfdog1369]

Right On Bill Ya Get The Good Housekeeping Seal Of Approval Keep On Bro!!!

[wnorcott]

Thanks Dog! Ya know I build my guitar effects real good to make up for my sloppy guitar playing haha. But that will be our little secret!

Bill

[gliderp]

Actually, a series of smaller holes would be better than 1 large hole as far as EMI shielding goes. It's known as a "Waveguide beyond cuttoff". Since your dealing with audio frequencies, the input and output signals and power must some sort of ferrite emi chokes or pi filters. Just dropping a circuit in a metal box is never the end of any shielding job. I design / build / test high power solid state rf supplies in the VHF frequency range. I am quite familiar with the emi beast. LOL!

Cheers...

[wnorcott]

Thanks for the input I use a combination of ferrite bead inductor and/or just series-resitor RC lowpass filtering on the audio input of guitar effects. Yes it was apparent to me you know what you are talking about.

I build in polycarbonate cases frequently and have no problems with RF noise or any kind of noise for that matter. These effects pedals operate on a 9V battery or a filtered ,regulated 9V PS (I also put a filter capacitor in the effect but it is redundant). Thanks.

Bill

[gliderp]

Not a fair test. The lead is sorta' acting like an antenna, and the hole is huge relative to the wavelength. Also, die cast boxes are not naturally real good rf enclosures, especially the slot. Repeat the test with the phone in box that doesn't have a hole, and tape edges with copper tape. You're not "grounding" anything at 1.8 GHz with a lead that has probably 100 nHy of inductance, and wound in a loop.

[wnorcott]

Thanks for the input So to make it a fairer test I should drill 6 more holes and plug in (2) 20 foot guitar cords instead of 1 hole and a 1 foot long alligator clip.

My point is a die cast aluminum case when used to build a guitar effect has more holes in it than a Swiss cheese, on the top of the case and on all sides, not 1 small hole in the bottom like I did in the demo.

So reliance on a die cast aluminum case to 'shield' a guitar pedal from RF from is not the way to go.

Bill

[wnorcott]

If a lead connected to electrical ground sorta acts as an antenna, you are helping make my point. The grounded diecast case itself is an antenna too. So is the 20' guitar cord. The case shields nothing.

Consider a guitar effect case: 5/8" hole for footswitch, (2) 1/4" guitar jack holes with long guitar cables plugged in (antennas?), 2 or 3 holes drilled for 1/4" shaft potentiometers, LED. & 3/8" hole for a DC power jack. Holes everywhere. No copper foil anywhere.

Bill

[wnorcott]

Also check out my video response (above) for an example of a high-gain Fuzz Face fuzz box I guilt over a year ago in a polycarbonate fuzz. Not a trace of noise, hum, radio interference, or any of it.

Bill