Isolating metal 1/4" jacks

[puretube]

at one point...
(i.e.: not one jack @ the left side end of the PCB,
and the other on the right side end of the "rail"-trace on the PCB)


[EDIT] with 1/10"  un-tinned "spaghetti"-traces, i.e. !

I love to have my in/right & out/left coupled by a groundplane...
(but  then again knowing at which side I got my PS cap, and knowing what routes from where to what...)

[mikeb]

I stand admonished, corrected and better educated!

Mike

[zachary vex]

so....
just tie gnd terminals of both jacks to the gnd of the pcb.
that the way boss, dod, ibanez,  
&
(after looking @ the "guts" of the NanoHead)
so does ZVex.
but not Lovetone.
They use plastic sleave  jacks.   wonder why?
cheaper(?) ...not that much diff in $$(mouser)
staywellgrounded
tone

actually, the nano head's output is isloated electrically because it comes from a transformer.  this means there is no ground loop when i ground one side.

[gaussmarkov]

interesting ... i was going to start a thread about this.  must be something in the air.

a survey of my boutique pedals shows that none of the jacks are insulated from the enclosure.  so i infer that ground loops through the enclosure are rarely a problem.  i'd like to hear zach expand on his oblique comment. :?

this is much more interesting than meets the eye.

[Eric H]

actually, the nano head's output is isloated electrically because it comes from a transformer.  this means there is no ground loop when i ground one side.

Anyone care to guess why the input isn't isolated?

-Eric

[gaussmarkov]

So, you can and should isolate a metal 1/4" jack with a pair of plastic washers...

I have not seen consistent support for this approach in effects (amps are
a different matter).   So I have run down as much advice as I could easily
find from the popular sources.  As a newb, I have found the discussion of
this really confusing.   I summarize the experts below.  Here's the bottom
line as I read them:
[list=1]
1.  In general practice, one does not isolate metal 1/4" jacks.
2.  There is no general concern about ground loops from doing this.
3.  In general practice, a metal chassis/enclosure is connected to ground,
via a jack or a lug attached to the chassis.
[/list:o]

This advice is in the FAQ and some authors note that questions about
this are very common.

References:
Electronic Projects for Musicians by Craig Anderton (p. 53)

When dealing with metal cases, putting in a chassis ground lug grounds
anything connected to that lug or touching the chassis.  Therefore,
any pot or switcyh cases that touch the chassis automatically become
grounded, shielding the insides.  You may notice that since the ground
terminals of jacks also touch the chassis, it's technically unnecessary
to run a ground wire from the jack ground to the chassis ground.  Do
it anyway!  Frequently jacks come loose, and when they do, the
ground contact may become intermittant.  A wire prevents this problem.


Ground - Where do the connections that show a ground symbol go to?
http://www.diystompboxes.com/cnews/FAQ.html

Generally speaking, take all the ground points, connect them together,
then connect them to the ground lug of the input or output jack. Take
the power supply (i.e. battery) and connect it to the ground lug as
well. If you want the input jack to switch your battery on and off,
then connect the lug to ground as before, but connect the battery
terminal to the middle connector (i.e. "ring")of a stereo jack. When
a mono jack is inserted, the ground circuit will be complete and the
switch will be on. Note that some circuits connect the + or positive
terminal of the battery to ground, although it is more common to connect
the negative terminal to ground. The sleeves of the input and output
jacks usually go to ground as they are usually connected to the metal
casing and the ground lug - unless they are isolated jacks.


Humming effects - Always powered by a battery
http://www.geofex.com/fxdebug/fxhum.htm

It's probably got a loose ground connection inside the pedal that
is not tying the effect signal grounds together throughout the box.
Open it up and check for broken wires to jacks, pots, the effect board,
and so on. It is also possible that one or the other jack in the
effect has a dirty or contaminated ground ring, and the signal cord's
not making good contact; or that the jack is cracked a bit. If this
is a new pedal you've built, it is possible that all the grounds are
not connected together on the board or that a bad solder joint is
keeping it all from making contact.


Basic Building Instructions: The Wiring
http://www.generalguitargadgets.com/index.php?option=content&task=view&id=169&Itemid=200

Wiring for grounding can vary, whether you bring the ground from each
jack and pot back to the board or "daisy chain" the grounds of the
off-board components together and then bring them back to the board
ground. Either way or combinations of both ways will work and some
of my latest board layouts have enough ground pads on the board so
you don't have to daisy chain off-board grounds if you don't want to.
What I'm trying to say is that the wiring diagrams will work as they
are shown, but you may wire the grounding differently if you like, as
long as all the grounds are somehow connected together.

We recommend that you never use the chassis (enclosure) for ground
connections for the jacks, pots, switches, etc. This will work with
steel and aluminum enclosures, and even though many commercial pedals
do this, I don't believe it is a good practice. If the bolt holding
the part ever works loose from the enclosure you may end up with
unnecessary shorting problems if you don't have ground wires soldered
to the parts.

Comment:  The point here seems to be not to rely on the chassis
for the grounding of jacks.  This does not seem to be a recommendation
to isolate metal jacks.

Q: What do I do with the ground connections?
http://www.muzique.com/qa.htm

A: This is by far the most frequently asked question. On my pc boards,
all grounds are usually tied together to a common point that is labeled
"GND" or maybe just "GR". This is the ground for the board and it should
be connected to the power supply ground.

Usually the metal box for an effect is used as a universal ground. The
input and output jacks' ground lugs will automatically connect to the
metal chassis (unless they are the plastic body Re'an brand). The wire
from the pcb ground connection can then be connected to one of the in/out
jacks' ground lug; it doesn't matter which. The power supply ground ground
also will connect to one of the in/out ground lugs - exception: see next
question.

[object88]

I personally have a slight aversion to plastic jacks and pots... I've stripped quite a few in the past.  

But my past expirience has been with line-level or above signals, so I perhaps any potential hum was lost in the S/N ratio?

[ethrbunny]

I take all my input grounds, tie them together and attach to the pcb at one point. My jacks are not insulated from the chassis.

Is this why I am having trouble learning "little wing"?

But seriously - the problem occurs when attaching to more than one ground point on the PCB? Aren't they all going to be the same potential? Its been a very very very long time since college physics but isn't this against Maxwell's law? Why would grounding at different points on the same conductor cause a problem?

Im going to pore over this thread for a bit.

(Never mind. My cat is telling me that she is very very hungry and that I need to drop everything and tend to her needs immediately!)

[object88]

I think the idea is that ideally, the chassis, jacks, pots, and various ground points on a PCB are at the same potential for lack of any resistance between them, but in actuality, there are minute (or siginificant, in the case of oxidization, for example) resistances.

[robbiemcm]

This just has me confused now. Can someone explain three things to me...


(1) Why does this have to be done?

(B) How I go about getting it done, one jack attatched to ground one not... I assumed they both had to be?

(III) Does it HAVE to be done to any box with a metal enclosure?

[gaussmarkov]

This just has me confused now. Can someone explain three things to me...

(1) Why does this have to be done?

(B) How I go about getting it done, one jack attatched to ground one not... I assumed they both had to be?

(III) Does it HAVE to be done to any box with a metal enclosure?

Man, I totally sympathize. :roll:  The record on this is all over the map.  And for
me part of the confusion comes from not knowing what to pay attention
to and what to let pass by.  I've decided that there's some "best practice"
advice out there that may not be relevant to everyone.

Here's my advice (but remember, i am trying to figure this out, too :?):  
(1) Ground the enclosure because otherwise it
adds hum.  I've actually checked this.  I don't know why it helps to
keep the noise down but it does. (B) You can use insulating washers
mentioned in this thread to insulate all jacks but one, though the impact
of this will often be unnoticeable.  If you want to keep the look of the
jacks the same put only the outside washer on the jack that's grounding
the enclosure.  (III) Yes.

It is not "best practice" to let all of the jacks' grounds touch the metal
enclosure.  But for some of us, this "best practice" is overkill.  If you are
building effects to learn electronics generally, this is a really good thing
to know.  If the input jack on my amp is not insulated, then I get a serious
hum that indicates a "ground loop."  A ground loop happens when there
is more than one route to ground.  For an effect box, the logical ground
is the output ground because that is going to the amp which has the
ultimate ground.  People sometimes refer to the enclosure/chassis as the
ground, but that makes no sense (to me) in an effect.

My 2 cents.  

[robotboy]

So, if I use switchcraft jacks as they're packaged they naturally connect the ground point connected to their sleeve to the metal on the inside of my enclosure? I've been connecting all my ground points together on my PCB and then connecting the sleeves on my jacks to ground as well. -9V goes to the ring on the input jack. I haven't had any humming problems so far. Is this grounding strategy not sufficient enough for "professional quality" effects?

[gaussmarkov]

So, if I use switchcraft jacks as they're packaged they naturally connect the ground point connected to their sleeve to the metal on the inside of my enclosure? I've been connecting all my ground points together on my PCB and then connecting the sleeves on my jacks to ground as well. -9V goes to the ring on the input jack. I haven't had any humming problems so far. Is this grounding strategy not sufficient enough for "professional quality" effects?

Yes, the metal switchcraft jacks without added insulating washers do connect ground to a metal enclosure.  And, yes, do connect the lugs for the sleeves/ground on those jacks to a single ground on your PCB.  That's the recommendation you see most often from the usual authorities.  And, yes, that is what a lot of pro pedal makers do also.  Look at the pics and you don't see any insulating washers.

Nevertheless, a lot of folks recommend insulating washers.  :?

Wiring the jack's sleeve to the pcb ground is recommended for insurance, in case a jack gets loose.  It seems that this is not critical otherwise.

No hum on your pedals?  Excellent!    And, apparently, exactly what a lot of experts predict.    (Gosh, I hope I don't offend somebody. :shock: )