[OT] Grounding

[Skeleton Man]

Hi,

I have a fairly old (circa 1980) marantz stereo receiver, which has an
annoying humm to it.

I reduced a lot of the hum by replacing a couple of large caps in the power
supply, but it still humms and the only time it doesn't is if I firmly hold
the heatsink attacked to the amplifier chip.. (huge big chip probably 4 -
6" wide bolted to a fairly solid heatsink).

I'm wondering, as the unit is not grounded (2 wire power cord), would
grounding it in some way have any effect on the humming ? (and if so, what
is the best way to do this, as I don't have anything metal going to ground
in my room)

Regards,
Chris

 

[Jan Alter]

Quite often you can reduce humming by turning the plug around and plug in
again. However, to your question you might consider running a wire attached
to the chasis of the Marantz to something in another room that is grounded
and see if you get any satisfaction. Cheap enough experiment.

 

[w_tom]

Does hum disappear when amp is only connected to AC and
speakers - no other peripheral connections? If hum is
eliminated by grounding chassis to AC safety ground, then
there are still problems inside the Marantz.

Amps usually have a single point ground lug so that all
peripheral components can be grounded to same point. Connect
that ground lug to AC receptacle safety grounded screw (at
center of cover plate). This assumes the outlet is a three
wire outlet. That plug reversal test is also strongly
recommended.

 

[P.M. Groen]

Quite often you can reduce humming by turning the plug around and plug in
again. However, to your question you might consider running a wire
attached to the chasis of the Marantz to something in another room that is
grounded and see if you get any satisfaction. Cheap enough experiment.

Or very expensive. When the "0" of the power supply is attached to the case,
grounding it will put another 125V on the amp which can damage the
amplifier. ( Difference between 0 and Ground is app. 125 Volts. Between "0"
and "live" is 110 / 220V)

Greetz,

Peter

 

[Skeleton Man]

Quite often you can reduce humming by turning the plug around and plug in

Or very expensive. When the "0" of the power supply is attached to the case,
grounding it will put another 125V on the amp which can damage the
amplifier. ( Difference between 0 and Ground is app. 125 Volts. Between "0"
and "live" is 110 / 220V)

By "0" do you mean neutral ?


Regards,
Chris

 

[Skeleton Man]

Quite often you can reduce humming by turning the plug around and plug in

again. However, to your question you might consider running a wire attached
to the chasis of the Marantz to something in another room that is grounded
and see if you get any satisfaction. Cheap enough experiment.

Turning the plug around reduced the humming, now I'm curious how that works
?

Regards,
Chris

 

[w_tom]

Electronics have line filters. Those filters may be unique
in design. Some may assume one wire will be neutral and be
designed accordingly. But if your electricity reverses
neutral and hot wire, then currents will flow through the
filter in directions not originally intended.

It is also possible that a component is that filter has
failed (ie capacitor). When you reversed the plug, the
current goes through the twin component that has not been
damaged. Whereas the line filter was once designed for either
plug polarity, now with one failed component, the filter only
works with one plug polarity.

These are just wild examples to demonstrate how plug
polarity could cause or eliminate hum. Many other reasons
exist. Without details, no one can provide you a 'real'
answer. However we do know that by changing polarity, you
changed how electric currents pass through the electronics.
You changed a voltage relationship of wires inside the
electronics with other wires connected to that electronics.
You probably changed a voltage relationship between one AC
wire and electronics ground.

 

[Ken]

Electronics have line filters. Those filters may be unique
in design. Some may assume one wire will be neutral and be
designed accordingly. But if your electricity reverses
neutral and hot wire, then currents will flow through the
filter in directions not originally intended.

It is also possible that a component is that filter has
failed (ie capacitor). When you reversed the plug, the
current goes through the twin component that has not been
damaged. Whereas the line filter was once designed for either
plug polarity, now with one failed component, the filter only
works with one plug polarity.

These are just wild examples to demonstrate how plug
polarity could cause or eliminate hum. Many other reasons
exist. Without details, no one can provide you a 'real'
answer. However we do know that by changing polarity, you
changed how electric currents pass through the electronics.
You changed a voltage relationship of wires inside the
electronics with other wires connected to that electronics.
You probably changed a voltage relationship between one AC
wire and electronics ground.

http://www.hut.fi/~then/mytexts/ungrounded_pc.html

 

[w_tom]

Excellent URL from Ken that (BTW) also describes reason why
those printer switches between a computer and multiple
printers could cause damage to HP LaserJet II printers.
Citation does not specifically cite this example, but this
citation entitled "Dangers and problems of ungrounded PC"
describes why that damage occurred.