Definitive Shielding method?

[newfish]

Hi All,

After several searches, it looks like there are several ways to shield your signals from RF / Hum etc.

I still have a couple of questions though...

Is it neccesary to shield *all* ins / outs, or just the runs from the sockets to the switch?

I've currently got drains going from all 4 shielded in / out / switch in / switch out cables - and it looks messy - like an Octopus on heat...

If you have an aluminium enclosure - is it neccesary to use shielded cable at all?

I'm making a couiple of simple one-tranny treble boosters - and am about to box up.  There *is* radio pickup with the board sat on my amp in its naked (boxless) state (the PC board, not the amp) - but that's only to be expected, right?

Any suggestions gratefully received.

Cheers,

Ian.

[GibsonGM]

Hi Ian,

I also get RF when my circuits are on the breadboard...but have not had any real issues once they are fully enclosed in a metal enclosure (aluminum).  I've read that some people use shielded cable from input jack to switch....I'm guessing this is to prevent radiation into the circuit, and if you route the input line correctly you can keep it away from the sensitive parts of the board. 
Another way to fix RF is a very small cap from input to gnd, on the order of 10pF or so.  This will bleed those high freq's to ground. 

Rule of thumb...I use input jack switching, so that jack is electrically connected to the chassis.  For the output jack, I do not include a ground wire - it makes its own ground at the sleeve, where it passes thru the enclosure. This avoids ground loops.   Use a common ground bus on the PCB, and that should keep things relatively quiet!  Not quite star grounding, but close....

Shielding effects is something I do after I've assembled everything into the enclosure, since it is so rarely a problem (for me anyway).  The only one that was an issue was an Easyvibe...I picked up LFO tick into the signal path - not RF tho.  The cure was a 1000uF cap across the power supply with a 100 ohm resistor in-line with the power input. 

Hope this is informative, good luck!
~Mike

[newfish]

Thanks Mike.

I've just discovered the joys (!) of making your own PCBs - and have in / out socklets both mounted on the board - all going to a common ground connection.

Am also using those Neutrik / Marshall switching jacks for both in and out. 

I have a common ground trace thick enough (in one or two places) for a new connection to the pot / enclosure.

May give this a go this evening.

I'm starting to try to tidy up my building - and this is one of those areas that always ends up looking like a real mess.

Thanks for your comments Mike.

[soulsonic]

For the output jack, I do not include a ground wire - it makes its own ground at the sleeve, where it passes thru the enclosure.

I disagree; I always connect a wire from the output jack back to the input jack. If you don't do this, you're risking a faulty signal ground connection if the jack ever gets loose (and they always get loose).
Maybe I'm paranoid, but I just can't trust the enclosure to make this crucial connection reliably. I've never experienced a ground loop problem in any pedal I've ever built - even the early ones when I had no idea what I was doing!

Now, as far as shielding the input and output wires is concerned; if the wires are less than about 2 inches long, I don't shield them. But if they are longer, I almost always shield the input and output wires - especially if it's a high gain circuit, and ESPECIALLY if the output is the same polarity of the input and the wires are in any proximity to each other.

[selectortone]

I disagree; I always connect a wire from the output jack back to the input jack. If you don't do this, you're risking a faulty signal ground connection if the jack ever gets loose (and they always get loose).
Maybe I'm paranoid, but I just can't trust the enclosure to make this crucial connection reliably. I've never experienced a ground loop problem in any pedal I've ever built - even the early ones when I had no idea what I was doing!

I'm sure that's good advice in theory. In practice, I traced a Distortion+ circuit off a pedal a customer brought into the guitar store I worked in back in 1978 and built a clone. It's still going strong and the output jack relies on the enclosure for its earth.

On that basis, any pedal I build today is going to see me out with no problems (although I couldn't guarantee it after 2038) .

[petemoore]

   Good thing I wired that output jack [actually all of them] with a ground wire last weekend.
  It's easy enough to have a jacknut strip right out [just have 'dummy' step on the plug once], having a wire on that ground proved to failsafe the performance.
  I used chassis for many of the jack grounds, but I was glad I had the foresight to ground that output jack...one good jerk or wrong step can smooth over a jacks threads.

[newfish]

So now I'm tempted to re-do my PC layout to incorporate the 3DPDT switch too - so there are no leads going off-board.

Once the layout is correct, this should make things much simpler - or am I missing something?

It's going to be tight - since the boxes I have are roughly 6cm x 10cm.

This started off as a simple build, but has now grown to be a full-on PCB-fest.

Can't believe how much I've learned - and how craziness-inducing this layout job is...

[GibsonGM]

Wow, I didn't mean to start a controversy, he he.  By having 2 ground connections to the output jack (a wire, and the enclosure), by definition a ground loop is created. Better to use a nylon washer & isolate the output jack in that case.  BUT, I have done it both ways, and NEVER have had any issues; stompboxes are very forgiving IMHO.   I use lock washers and don't beat the hell out of my stuff, but some guys do.   So everyone is right, LOL. 

Incorporating the switch could be cool, Ian...I haven't done that in case - same thing as the output jack thing - something happens to the switch, causing you to stomp the PCB into the ground!  But it's done a lot. 

[soulsonic]

Oh, I wasn't really trying to be controversial, sorry if I came off that way - I'm just a reliability freak, and with all the jacks wired together it can still function outside the enclosure if it's being serviced or modded and you want to mess try it without having to put it back in the box.
I actually used a brass plate for grounding in a pedal once - it worked pretty good. I was using nylon jacks, so that's how I made the chassis ground. Probably more work than necessary, though.

[newfish]

Hmm - re-drew my layout last night - and will make this weekend.

Photos *will* follow - as will soundclips when it's all boxed up.

Am now tempted to re-do the Optical Trem I've still got cooking - since I have an intense dislike of off-board wiring.

It's just so messy, you know?

[GibsonGM]

No offense taken, Soul.  My way actually isn't true star grounding anyway!  But close enough for stompers.  Losing that output jack and its ground can be UGLY, LOLOL.  Would be a bummer at a gig - I always check mine while I'm setting up.

Good luck with the switch on the board thing!  Experimenting with this stuff is what its all about...