shielding - how important?

[ethrbunny]

Im looking into enclosures for my next few builds. To this point Id been using plastic electrical boxes as they are easy to cut into and cheap for if/when I mess up.

Im wanting something more interesting for my next few builds. Ive not had any problem with external 'noise' to this point but now after reading past postings about shielding Im wondering if I should be. Are certain types of circuits more prone to external noise? If the circuit is properly grounded can this be avoided? Or should I switch to metal boxes immediately and count my blessings for being spared filtering issues to this point?

[Paul Marossy]

High gain distortion circuits are the most likely candidates for giving you trouble with noise. It is possible to have RFI problems, but that can be fixed by adding a small cap to the input to ground to shunt any RF signals.

[niftydog]

Ive not had any problem with external 'noise' to this point

you've been lucky. Obviously you do not play underneath flourescent lights!

Are certain types of circuits more prone to external noise?

yes, but ALL circuits are prone to some extent. Pre-empting your next question, it's not easy to tell which circuits will be more noisey than others. It can depend on a number of factors including PCB layout and the environment in which the effect is being used.

Generally, high gain stages in effects can be very noisey.

If the circuit is properly grounded can this be avoided?

no. EMI and/or RFI will get into even the most carefully designed circuit. Shielding is absolutely the best option, just ask Faraday! (Google "Faraday Cage" if you're bored one day!)

Or should I switch to metal boxes immediately and count my blessings for being spared filtering issues to this point?

Personally, I would. Also from the "ruggedness" perspective it makes good sence. But, if you will continue to use the effects in the same manner as the ones so far, I suppose it's unlikely that noise will become a problem.

BUT, the second you go to play somewhere else it's a whole new ball game.

Why not initially build them into plastic boxes, and when you're 100% happy with something, go the extra effort and expense of putting it in a metal box!?

[bigjonny]

...or put copper foil in the inside of your plastic cases?

http://diystompboxes.com/sboxforum/viewtopic.php?t=26328

[RDV]

Ive not had any problem with external 'noise' to this point

you've been lucky. Obviously you do not play underneath flourescent lights!

Or those awful neon beer advertisements!

RDV

[petemoore]

Theres' commercail stuff with only a ground plane under the board.
  Definitely depends on what it depends on which is always changing.
 Shielding eliminates trying to figure all that out !!!
 I noticed not too much noise differences [ a little more 'maybe...hard to really tell] for the most part running unshielded boxes.
 Although I got a high amplitude "Pete's your box's firing' and 'breaker 19' coming through the 'reciever' and guitar amp at a gig...pretty comical at first..local guy talking to me through my amp with his CB. I shield Everything these days though.
 FF's can pick up the wierdest radio stations.

[ethrbunny]

..fixed by adding a small cap to the input to ground to shunt any RF signals.

How small?

[Paul Marossy]

Check out the FAQ section at this site. It's in there.  

[ethrbunny]

Im there. Thanks!

[DDD]

Shielding is vitally important.
Maybe today it seems to be useless, but change your location or buy a new fluorescent lamp...who knows?

[niftydog]

Or those awful neon beer advertisements!

which they seem to LOVE putting right behind the band risers!!

[KORGULL]

petemoore wrote:

I shield Everything these days though.
FF's can pick up the wierdest radio stations.

I always seem to get the religious stations.
Setting up for a recording session once, some preaching came through the amp. I recorded it and (at a later date) used samples in a song. -Worked out really well.

[Mark Hammer]

One of the strangest electronic experiences I've ever had happened some 35 years ago.

Lacking a component stereo and wanting to have louder listening levels, I rerouted the wires from my little dinky record player (with a "good" Philips crystal cartridge) to my tube reel-to-reel tape deck's mic input and then to my guitar amp.  Having no good cable to stretch the whole distance, and not enough desk space to have everything together, I found myself one day holding the end of a cable from one device and unable to reach the loose cable dangling from the other device.

I called my dad into my room and asked him if he could hand me the other cable.  In one of those all-too-common slips, he picked up the cable with one hand and extended the *other* hand to me by accident.  For a brief instant, I was holding the plug from the cable to the tape deck, he was holding the plug from the cable coming out of the turntable, and I was holding his hand.  Miraculously the volume was *louder* than normal.  I called my sister into the room.  She held my dad's hand and mine, and the volume went up again.  Damnedest thing, and I have no explanation.  Bear in mind that none of us was "shielded" in any sense, so the signal was passing through three bodies, over a distance of some 10 feet or more, and nary a trace of interference came about.  The change in volume from standard connections I had done before was clear, and on the order of about 25-40%  So, not huge, but more than enough to be certain it wasn't my ears playing tricks.

What happens when you DON'T have shielding remains a mystery to me.  As far as I know, none of my family members possess any supernatural abilities.

[DDD]

Wonderous!
Mark, maybe some kind of resonance? More bodies = more capacitance = closer to the resonant peak? Or additional antenna element?

[ethrbunny]

From the FAQ

misc - I am picking up radio stations, how can I stop this?

From Eric Hensel:A 47pf cap to,ground, after the input cap will probably do it --you can adjust this up or down --higher values will start to cut treble. use the lowest value that works.

It sounds (no pun intended) like I need to fix some of my older projects. Im not seeing "after the input cap" - is there a better way to describe where to put this filter cap?

Im not picking up radio but am concerned about interference from lights, etc - all that stuff posted in this thread.

[petemoore]

The first capacitor of a a circuit is often used to let the signal in, and keep DC out.
 USually you'll see these at the far left of the schematic and they feed a gain stage or buffer stage.
 Anyway they're talking about a smaller ish-er [ should probably sample and taste and adjust the value] capacitor from inside the input cap to ground. Larger values cut more highs.

[crawler486]

I used aluminum tape to shield my plastic enclosures.

Go to Wurth Electronics site cause they are giving free samples.
I just got a roll of shielding tapes from them.

Regards