Noise Again

[exztinct01]

Can anyone please tell me why everytime I touch my grounded body to any common point of my ungrounded breadboarded preamp, there comes a noise, a hiss I think. I know that grounding was supposed to remove noises but this one actually amplifies when being grounded. There won't be any ground loop as it's not originally grounded.

Also, even when I don't touch the circuit, just hovering my hands near the breadboarded preamp, a noise appears. What's my body's role in this noise?

[Vinnie500]

I was having a similar problem which I got some got tips on what to do about it here
http://www.diystompboxes.com/smfforum/index.php?topic=115895.msg1071205#msg1071205

[GibsonGM]

Your body is one plate of a capacitor if that is occurring (when hovering, not contacting).   Frequently, this IS a ground issue...not always, tho. If the ckt is not in an enclosure, you can get those effects, which would be minimized by a grounded (shielded) enclosure.

If the preamp 'floats', and you ground something w/your body, you are providing an arbitrary 'ground' to the ckt, which may be operating in such a way that the "REAL GROUND" would be 3V, or some such thing.    So, you are really 'plugging in power' in a way, ha ha...

Just another way to show that 'ground' is what we define it as...it does not HAVE to be ZERO volts.  Some point there MUST be common (schematic, please?). 

[PRR]

> my grounded body

How is it grounded?

[exztinct01]

  I'm standing barefooted on concrete 
Don't think it's true ground now though
I connected it with a wire to the soil outside and pour water on the soil and the noise was gone

[FiveseveN]

Well, you learned an important lesson: concrete is not (very) conductive.

[PRR]

Concrete is more conductive than body-through-skin. At least when you have grabbed a live wire and are being electrocuted.

I _would_ expect barefoot on concrete on dirt to be a fairly good audio ground for guitar-chain purposes. Surprised it wasn't for you. Possibilities: sometimes concrete is laid on a poly-plastic sheet so damp does not rise into the building. Or your soil may be very un-conductive; I can't get a single dirt-rod ground below 100 Ohms here on thin fill over bedrock. Electrical wires in/on/near the concrete may be exciting it more than the dirt is grounding it.

[anotherjim]

Long ago I heard that to "activate" a ground rod, you have to pee on the surrounding soil.

Here in the UK, it's been mandatory for a long time to have a damp proof membrane under concrete floors. More recently, there is also a layer of thermal insulation block.
Also, you might have a screed layer on top of the concrete, which may be quite a good insulator. It can have similar colour to concrete.

[PRR]

Yeah, with your foam over poly sheet, your cellar floor is totally floating.

It will *tend* toward ambient ground AC potential because of large area and capacitance, but an inch of foam is significant separation so it may not be close-coupled for AC/Audio potential.

That might change my mind about working barefoot on concrete.

It happens that this house's cellar floor is solid to damp dirt, never dry, so it conducts. Another house I am looking into, water rose 3 feet last spring and even in this drought there's no doubt it is wet and conducty.