Johnny B Good wrote:

---------------------



The one and only item of Hi-Fi kit that remains vulnerable to such hum
induction is the old fashioned TT cartridge wired directly into a remote
RIAA equalisation pre-amp located a metre or two away in the main
amplifier.


** Hum induction into what ?

The mag PU itself or the coaxial cable ?

Mag PUs are sensitive to the fields of power transformers and motors - so the TT must be located sensibly to prevent that.

Co-axial cable rejects external hum fields very well, better in fact than twisted pair cable do.


The proper way to deal with this problem is simply to install
the RIAA pre-amp within the TT itself


** Bad idea fraught with risk of hum induction from the TT's AC wiring, motor and or power tranny. It can be done, but the RIAA stage would need to be built inside a steel box and carefully located PLUS be fed by a remote PSU.

TT's have been working hum free without such lengths for long enough to prove there is no need for such elaborations.

You do post some strange nonsense, based on your own particular and isolated experience.


..... Phil

So, how do we feel that buzz on exposed metal. Its obviously electrostatic
in nature as my aluminium white canes exposed metal parts do it I walk close
to any pylons for example.
Brian

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"Dave Plowman (News)" wrote in message
...
In article ,
Johnny B Good wrote:
I have a dedicated AV radial circuit here. With the earth for that
going
light back to the house earth. Not sure that bit makes any difference,
though, but no big deal when installing it.

It shouldn't. Assuming you only have a single safety earth connection to
the common signal ground return, the whole thing could be left to float
at whatever induced mains voltage happens to occur (including half mains
from filters or even a full contact to the live). It won't make any
difference although I'd be rather leery of actually touching any of the
kit if bringing your hand to within close proximity generates even the
slightest hint of mains hum.

Can you run that by me again? You can obviously get a potential difference
between two earths when any current flows. Like say between the earth to a
socket and the one to a light switch in the same room.

--
*WHERE DO FOREST RANGERS GO TO "GET AWAY FROM IT ALL?"

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 1 Dec 2017 09:31:35 -0000, "Brian Gaff"
wrote:

So, how do we feel that buzz on exposed metal. Its obviously electrostatic
in nature as my aluminium white canes exposed metal parts do it I walk close
to any pylons for example.
Brian

The buzz on exposed metal is easy. It requires that the item is not
earthed, and has a pair of small anti-EMC capacitors from live to
chassis, and neutral to chassis. They form a capacitive potential
divider which will put the chassis at half mains voltage when it is
not attached to anything grounded.

The capacitors have a high impedance (about 3 Megohms) at 50Hz, so you
won't feel anything more than a slight tingle when you touch the
chassis. Once the earth is established by the signal cables the
voltage disappears completely.

d

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In article , Dave Plowman (News)
scribeth thus
In article ,
Don Pearce wrote:
It shouldn't. Assuming you only have a single safety earth connection to
the common signal ground return, the whole thing could be left to float
at whatever induced mains voltage happens to occur (including half mains
from filters or even a full contact to the live). It won't make any
difference although I'd be rather leery of actually touching any of the
kit if bringing your hand to within close proximity generates even the
slightest hint of mains hum.

These days most grounds are heavily compromised by EMC from switching
power supplies coupled in through the Y1 capacitors. Hang enough of
those on a single circuit and eventually you can even trip the RCD
breaker.



Which was the theory behind running my AV ground right back to the house
earthing point, rather than CU earth.


Sort of "technical" earth;?..
--
Tony Sayer

..

In article ,
tony sayer wrote:
Which was the theory behind running my AV ground right back to the house
earthing point, rather than CU earth.


Sort of "technical" earth;?..

Yup. If good enough for studios, good enough for me. Given it didn't
really cost any extra, as part of a house re-wire.

Not got a buzzer fitted to tell when the house earth gets connected to the
tech one, though. ;-)

--
*Never test the depth of the water with both feet.*

Dave Plowman London SW
To e-mail, change noise into sound.

In article , Dave Plowman (News)
scribeth thus
In article ,
tony sayer wrote:
Which was the theory behind running my AV ground right back to the house
earthing point, rather than CU earth.


Sort of "technical" earth;?..

Yup. If good enough for studios, good enough for me. Given it didn't
really cost any extra, as part of a house re-wire.



Not got a buzzer fitted to tell when the house earth gets connected to the
tech one, though. ;-)


Was that a BBC practice?..
--
Tony Sayer

Yes but this does not apply to my mobility cane. The capacitance has to be
really lower than low and hence it has to be the ac field from the very hi
voltage wires above me that does it.
Brian

--
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This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Don Pearce" wrote in message
...
On Fri, 1 Dec 2017 09:31:35 -0000, "Brian Gaff"
wrote:

So, how do we feel that buzz on exposed metal. Its obviously electrostatic
in nature as my aluminium white canes exposed metal parts do it I walk
close
to any pylons for example.
Brian

The buzz on exposed metal is easy. It requires that the item is not
earthed, and has a pair of small anti-EMC capacitors from live to
chassis, and neutral to chassis. They form a capacitive potential
divider which will put the chassis at half mains voltage when it is
not attached to anything grounded.

The capacitors have a high impedance (about 3 Megohms) at 50Hz, so you
won't feel anything more than a slight tingle when you touch the
chassis. Once the earth is established by the signal cables the
voltage disappears completely.

d

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

In article ,
tony sayer wrote:
Not got a buzzer fitted to tell when the house earth gets connected to the
tech one, though. ;-)


Was that a BBC practice?..

Yup. To alert you of a problem when rigging the studio.

--
*(on a baby-size shirt) "Party -- my crib -- two a.m

Dave Plowman London SW
To e-mail, change noise into sound.