Plug in = Buzz; touch it = no buzz ... WHY ?

[ward]

I revisited the Doug Hammond Sweet Thing I made some weeks ago.
It was/is great sounding but too noisy to me.
In the meantime I had learned that some additional PS filtering for noisy pedals is sometimes helpfull.

I added a 470uF cap in parallel and a 200 ohm resistor in series to the circuit.
Result = better.

The buzz that is still there disappears allmost totally when my hand is on the strings.
When I place a finger on the box where the sweet thing is in, it is even better.

So I was wondering, in electronic terms, what am I doing to the device when I touch the box ?
And can I emulate that effect with something ?

[GibsonGM]

That sounds to me like a grounding issue, Ward - your hand on strings/box is acting like a ground path...someone like R.G. or Mark would have more knowledge of what's up, but could it be a ground loop or something causing that?  Did you use star grounding? Maybe shielded input/output lines?

My 1st instinct would be to open it up, hook everything up, get it to buzz...then start touching parts inside the pedal.  Using a pencil eraser for this will show loose stuff..using a finger will show possible ground problem areas.  Of course, only do this on something low-voltage & current!   

Have you included the enclosure in the ground path, via the input jack?

[ward]

I used shielded in- and outputlines to the switch.
The enclosure is grounded via in- and output jack.

I need to read some on stargrounding and ground loops.

[Connoisseur of Distortion]

it's poor form to ground to the box in multiple locations 

i've gotten accustomed to making my ground point at the 9vdc input, because the power supply doesn't much care if its in a noisy environment.

[GibsonGM]

Ya, I generally ground mine at the input jack, since the battery - is there already.  Gnd wire to PC board, where I allow 1 trace to be the board ground, and everything goes there.  Never had a problem this way. Not true "star grounding", but it works. 

From your description, ward, it almost seems like something may NOT be grounded and could be hanging open, a cap or something at the power supply, maybe? I'm not sure where you added your cap/resistor.   Possibly you could try running it off a 9V battery to eliminate the PSU as a source of the trouble (you're on an adapter, right)?
Poke in there and let us know!

[aron]

The buzz that is still there disappears allmost totally when my hand is on the strings.
When I place a finger on the box where the sweet thing is in, it is even better.

Maybe it's amplifying the buzz that's already there in the guitar...  What type of guitar and try it with a battery if you are using an adaptor.

Aron

[ward]

it's poor form to ground to the box in multiple locations 

i've gotten accustomed to making my ground point at the 9vdc input, because the power supply doesn't much care if its in a noisy environment.

How can I ground at just one point if both jacks, and the pots are making contact with the box ?
Do I need to insulate them all from the alu box ?

Stargrounding = is grounding everything at one common point,  Right ??
By grounding you mean 'making contact with the box', Right ?

From your description, ward, it almost seems like something may NOT be grounded and could be hanging open, a cap or something at the power supply, maybe? I'm not sure where you added your cap/resistor.   Possibly you could try running it off a 9V battery to eliminate the PSU as a source of the trouble (you're on an adapter, right)?
Poke in there and let us know!

I'm on adapter.
I've checked all grounds for continuity with a mm.  (black lead touching the box, red lead for poking around, mm on beep testing)
Board ground ok
In- , outputjack ground ok
pot houses are NOT all grounded
neg. on the ps supply input ok

(Power supply is :
tranny
> to bridge rect
> to large cap
> to 7809 regulator
> to large cap
> to output supply connector  (shielded from chassis, nothing in the ps is touching chassis ground.))


The effect is great sounding, and definitly usable but it would be nice to get rid of these final dBs noise.

Maybe it's amplifying the buzz that's already there in the guitar...  What type of guitar and try it with a battery if you are using an adaptor.
Aron

That is part of the problem, I tried first with a tele.
The buzz got much better when further from the amp.
So part of the buzz is from the guitar.
Than I tried with a SeymD HB equipped guitar.  That one is very quiet on other setups, even high gain ones.

[aron]

There must be some build problem. I have the Sweet Thing as well and it's fine. It really does sound like a grounding problem... but where?

[awilson40]

what type of jacks did you use, If they are the plastic "marshal" type, then they dont ground to the case.
I had the same issue with my English Channel and ran a wire from the neg on the board to the case
solved the problem.

[ward]

I think I'm chasing a ghost here.
I checked it again,
the buzz is not bad with my hand on the guitarbridge,
the amount of buzz that goes away is the same whether I touch the bridge or touch the efxbox.
I'm going to compare with another distortion-booster this evening.

[GibsonGM]

Wow, ward...I'm thinking guitar, amp Xformer, light dimmer/monitor nearby....but no Even double-grounding the jacks shouldn't give you THAT much trouble (if any)!!  And, the amp doesn't do it with other boxes, right?   Maybe it's picking up hum from the AC transformer?  I've seen that a lot, even with caps. That's why I pretty much stick to batteries...I'd try it that way, maybe inject your batt voltage after the regulator ckt.  I distrust wall warts, lol.  Provided it's built right, it shouldn't do that hum thing very much at all...

To insulate a jack from the enclosure, you use a little plastic or rubber washer between it and the enclosure.  I don't really bother...I've gone so far as only having the TIP connection on my output jack, and let the box be its ground, always works fine.  Or I just ground both, no biggie.  The theory is only the input jack touches the box...something has to ground the box!    Star grounding = 1 point, yes. Not complicated...the box IS grounded via the input jack, but nowhere else!  I have the input jack switch the ground conn. to the batt, all ground boards go to 1 place, as I wrote above.  Always works.

Good luck with this one!  It really has shades of a short somewhere, missing ground etc., in my humble opinion.

[GibsonGM]

AFTERTHOUGHT....
Try removing the ckt. from the enclosure...if that fixes the problem (reasonably, you'll then have no shielding so it will hum a bit...), your POTS might be SHORTING OUT on the enclosure! Something you said above tripped that in my memory...I always isolate the pots from the enclosure. I actually RUN that ground wire many pots need, don't rely on the box.  If you short across the rows of 'terminal rivets', you can have similar symptoms!   The  BODY of the pot can touch the enclosure, that's fine, but NOT the terminal strip! 
Hope this helps!  It would be great if it's that simple...