A single ICwhere the source is powered by a battery.. zero.
Two IC's connected to one source chassis battery powered..Each shield carries half of it's signal current, the other half being the other channel's return current.
Two IC's with both source and amp chassis bonded to safety ground.. Almost no current at low audio frequencies, half of each at higher frequencies.
For a single coax, there should be zero external magnetic field. This falls apart if two coax cables connect two chassis.
jn
Bill Whitlock would say 316 uA.
-----------------------------------
Leakage Current Effect - A Calculated Example
• A 25-foot cable (foil shield, #26 AWG drain wire) has an end-to-end
shield resistance of 1 Ω
• Measured leakage current between the ungrounded devices is 316
μA (well under the UL limit of 750 μA)
• From Ohm’s law, noise voltage E = I x R = 316 μA x 1 Ω = 316 μV
• Consumer −10 dBV reference level = 316 mV
• Signal to Noise ratio = 20 x log (316 mV⁄316 μV) = 60 dB
• This is 35 dB worse than an audio CD!
• Same length of Belden #8241F cable, with its shield resistance of
only 0.065 Ω, makes S⁄N 84 dB, an improvement of 24 dB!
Bill Whitlock, 9/4/2012 Overview of Audio System Grounding & Interfacing 63
I wonder ----
some people have concrete for a structural floor. Makes a nice ground plane to earth.... Seems like you could have ground effects (C?) and noise coupling --- thru the currents running thru the rebar in concrete. Lay a cable on that floor and measure noise pickup. Then do same after raising it up away from that building's floor.
THx--RNMarsh
jet lagged.
some people have concrete for a structural floor. Makes a nice ground plane to earth.... Seems like you could have ground effects (C?) and noise coupling --- thru the currents running thru the rebar in concrete. Lay a cable on that floor and measure noise pickup. Then do same after raising it up away from that building's floor.
THx--RNMarsh
jet lagged.
I'm planning to build a concrete house with a dedicated room for music. Should I avoid metallic rebar? Is there any substitutes?
//
I once switched from tantalum to back to back tantalum ....
Seemed to sound better, but no measurements ...
Also found that most amps use too low of value in that position ..
My personal preference is to make the system in itself interference bulletproof - stands tall in the strongest winds, 
. Otherwise, it's bound to become undone at the worst moment, you can't beat ol' Murphy's Law - just when you want to show it off to someone, he brings along a bit of electronic kit, unbeknowst to you, and - egg on face!
My ideal is to have the system totally transportable - take it anywhere, minimal setup, and it always fires first up with close to optimum quality.
. Otherwise, it's bound to become undone at the worst moment, you can't beat ol' Murphy's Law - just when you want to show it off to someone, he brings along a bit of electronic kit, unbeknowst to you, and - egg on face!My ideal is to have the system totally transportable - take it anywhere, minimal setup, and it always fires first up with close to optimum quality.
1) reduce or eliminate EMI at the source. Always better than at the device.
2) Shielding is not really difficult to understand just difficult to implement with no holes.
3) Steel for low frequencies, conductive for high frequencies (5-10 KHz up).
I can see hum induced from a power cord under my bench. Lift a DUT and the hum changes. However if you have significant current through the rebar, enough to generate an interferor, I would be worried about much more serious issues that hum in the audio. The Rebar may have problems from electrolysis and corrosion if there are currents passing through it. At least you aren't building a $14B bridge with corrosion problems. New Bay Bridge shows signs of rust in critical areas - Bay Bridge - The Sacramento Bee
There are now composite rebar materials that are non metallic. The problem is has your local building code kept up with these developments. Just as Demian has pointed out the steel in a concrete construction has lead to many structural failures due to the corrosion of the steel. The rebar can be coated with a non conductive material but this would raise the cost. I have friends in construction and they will no longer build houses using slab construction, long term the plumbing in the slab can be a real problem.
What happens in the shielded differential case? Especially if there are two differentials in a common shield? The most extreme case in the consumer arena is an HDMI cable with 4 double shielded twisted pair inside an overall shield. (in some cases more. . .) Usually the shields are all tied together at the connectors.
Thomas Edison used Bamboo . At your location is not the floor insulated from the earth for thermal reasons ? If so the styrofoam or what ever should decouple the slab from the earth. Measure some other's floor to see if the slab is coupled and what field the rebar presents. If all the rebar is tied together then if the wall and ceiling are concrete a fariday cage is a thought.
Differential tries to NOT use the shield as a return path. However, if the shield completes a loop, shield currents can induce voltages along the current path.
The best aspect of diff is the return currents are controlled by design, so untoward currents and lack of path control are not a design feature, rather a secondary effect.
jn
- Status
- Not open for further replies.