We're all familiar with a guitar or bass that picks up EM noise and produces
a steady buzz through the amp. The noise goes away when the player touches
some grounded piece of metal on the guitar, or the strings if the bridge is
grounded.

My question is why does touching a ground point eliminate the buzz? What is
the player's body adding to the circuit in electrical terms? Is it just like
adding a big capacitor between ground and... what, air? Or could it be that
grounding the player allows the player's body to soak up some of the EMI and
reduce the amount reaching the pickups?

Just curious,
Sean

"Sean Conolly" wrote in message . ..
We're all familiar with a guitar or bass that picks up EM noise and produces
a steady buzz through the amp. The noise goes away when the player touches
some grounded piece of metal on the guitar, or the strings if the bridge is
grounded.

My question is why does touching a ground point eliminate the buzz? What is
the player's body adding to the circuit in electrical terms? Is it just like
adding a big capacitor between ground and... what, air? Or could it be that
grounding the player allows the player's body to soak up some of the EMI and
reduce the amount reaching the pickups?

Just curious,
Sean


Are you sure that the metal being touched is grounded? Maybe it
only gets grounded when touched.
Another theory is that the metal is acting as an antenna and adding
a human body into the circuit changes the resonant frequency so that
it no longer is efficient at whatever frequency (60 Hz?) it was
picking up before.

"Sean Conolly" wrote in message . ..
We're all familiar with a guitar or bass that picks up EM noise and produces
a steady buzz through the amp. The noise goes away when the player touches
some grounded piece of metal on the guitar, or the strings if the bridge is
grounded.

My question is why does touching a ground point eliminate the buzz? What is
the player's body adding to the circuit in electrical terms? Is it just like
adding a big capacitor between ground and... what, air? Or could it be that
grounding the player allows the player's body to soak up some of the EMI and
reduce the amount reaching the pickups?

Just curious,
Sean


Are you sure that the metal being touched is grounded? Maybe it
only gets grounded when touched.
Another theory is that the metal is acting as an antenna and adding
a human body into the circuit changes the resonant frequency so that
it no longer is efficient at whatever frequency (60 Hz?) it was
picking up before.

In article writes:

We're all familiar with a guitar or bass that picks up EM noise and produces
a steady buzz through the amp. The noise goes away when the player touches
some grounded piece of metal on the guitar, or the strings if the bridge is
grounded.

My question is why does touching a ground point eliminate the buzz? What is
the player's body adding to the circuit in electrical terms?

You'd get the same result if you connected
a piece of wire between the strings or bridge (which is usually, but
not always, connected to the shield of the cable to the pickup) and
the amplifier chassis. You might, however, get MORE hum because you've
created another ground path and now you have a dreaded ground loop.
Sometimes, when you touch the strings, the hum gets worse also.

The reason why you can get away with changing the ground path by
touching something is that it's a high impedance circuit, so the
concept of a "direct ground path" can be a bit liberal. The cable
shield is going to ground through the resistance of your body and the
capacitance between your feet and ground. This is quite a high
impedance path as you might imagine, several megohms at power line
frequencies, but not insignificant when compared to the 100K ohms or
greater of a typical instrument amplifier input.

Of course the same current flowing through you to ground that reduces
(or increases) hum can electrocute you if there's enough current
available through that path due to an improper safety ground.



--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

In article writes:

We're all familiar with a guitar or bass that picks up EM noise and produces
a steady buzz through the amp. The noise goes away when the player touches
some grounded piece of metal on the guitar, or the strings if the bridge is
grounded.

My question is why does touching a ground point eliminate the buzz? What is
the player's body adding to the circuit in electrical terms?

You'd get the same result if you connected
a piece of wire between the strings or bridge (which is usually, but
not always, connected to the shield of the cable to the pickup) and
the amplifier chassis. You might, however, get MORE hum because you've
created another ground path and now you have a dreaded ground loop.
Sometimes, when you touch the strings, the hum gets worse also.

The reason why you can get away with changing the ground path by
touching something is that it's a high impedance circuit, so the
concept of a "direct ground path" can be a bit liberal. The cable
shield is going to ground through the resistance of your body and the
capacitance between your feet and ground. This is quite a high
impedance path as you might imagine, several megohms at power line
frequencies, but not insignificant when compared to the 100K ohms or
greater of a typical instrument amplifier input.

Of course the same current flowing through you to ground that reduces
(or increases) hum can electrocute you if there's enough current
available through that path due to an improper safety ground.



--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

"Mike Rivers" wrote in message
news:znr1084973112k@trad...

In article
writes:

We're all familiar with a guitar or bass that picks up EM noise and
produces
a steady buzz through the amp. The noise goes away when the player
touches
some grounded piece of metal on the guitar, or the strings if the bridge
is
grounded.

My question is why does touching a ground point eliminate the buzz? What
is
the player's body adding to the circuit in electrical terms?

You'd get the same result if you connected
a piece of wire between the strings or bridge (which is usually, but
not always, connected to the shield of the cable to the pickup) and
the amplifier chassis. You might, however, get MORE hum because you've
created another ground path and now you have a dreaded ground loop.
Sometimes, when you touch the strings, the hum gets worse also.

The reason why you can get away with changing the ground path by
touching something is that it's a high impedance circuit, so the
concept of a "direct ground path" can be a bit liberal. The cable
shield is going to ground through the resistance of your body and the
capacitance between your feet and ground. This is quite a high
impedance path as you might imagine, several megohms at power line
frequencies, but not insignificant when compared to the 100K ohms or
greater of a typical instrument amplifier input.

I've always thought that the ground side was a much lower impedance than
that, unless it's isolated from the AC ground. A player standing on carpet
in sneakers should be an extremely high resistance, not sure about impedance
at audio frequencies. I can see that I need to draw up the full circuit to
better understand what's going on here. It's been many years since I opened
a guitar amp, so please excuse my ignorance.

Sean

"Mike Rivers" wrote in message
news:znr1084973112k@trad...

In article
writes:

We're all familiar with a guitar or bass that picks up EM noise and
produces
a steady buzz through the amp. The noise goes away when the player
touches
some grounded piece of metal on the guitar, or the strings if the bridge
is
grounded.

My question is why does touching a ground point eliminate the buzz? What
is
the player's body adding to the circuit in electrical terms?

You'd get the same result if you connected
a piece of wire between the strings or bridge (which is usually, but
not always, connected to the shield of the cable to the pickup) and
the amplifier chassis. You might, however, get MORE hum because you've
created another ground path and now you have a dreaded ground loop.
Sometimes, when you touch the strings, the hum gets worse also.

The reason why you can get away with changing the ground path by
touching something is that it's a high impedance circuit, so the
concept of a "direct ground path" can be a bit liberal. The cable
shield is going to ground through the resistance of your body and the
capacitance between your feet and ground. This is quite a high
impedance path as you might imagine, several megohms at power line
frequencies, but not insignificant when compared to the 100K ohms or
greater of a typical instrument amplifier input.

I've always thought that the ground side was a much lower impedance than
that, unless it's isolated from the AC ground. A player standing on carpet
in sneakers should be an extremely high resistance, not sure about impedance
at audio frequencies. I can see that I need to draw up the full circuit to
better understand what's going on here. It's been many years since I opened
a guitar amp, so please excuse my ignorance.

Sean

In article writes:

I've always thought that the ground side was a much lower impedance than
that,

This is exactly the problem. There's already one ground path through
the cable shield that's fairly low impedance (but apparently it's not
doing much good, or the hum you hear isn't from lack of grounding).
When you touch the strings, you're providing a parallel path between
the strings (at ground potential) and the ground (through you). Now
you have a ground loop. Not a very good one, but a ground loop none
the less.


--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

In article writes:

I've always thought that the ground side was a much lower impedance than
that,

This is exactly the problem. There's already one ground path through
the cable shield that's fairly low impedance (but apparently it's not
doing much good, or the hum you hear isn't from lack of grounding).
When you touch the strings, you're providing a parallel path between
the strings (at ground potential) and the ground (through you). Now
you have a ground loop. Not a very good one, but a ground loop none
the less.


--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

"Mike Rivers" wrote in message
news:znr1085068287k@trad...

In article
writes:

I've always thought that the ground side was a much lower impedance than
that,

This is exactly the problem. There's already one ground path through
the cable shield that's fairly low impedance (but apparently it's not
doing much good, or the hum you hear isn't from lack of grounding).
When you touch the strings, you're providing a parallel path between
the strings (at ground potential) and the ground (through you). Now
you have a ground loop. Not a very good one, but a ground loop none
the less.

Hmm. But it happens when I stand on the carpet in my rubber-soled tennies,
which means I'm not making a very good connection to the ground.

Peace,
Paul

"Mike Rivers" wrote in message
news:znr1085068287k@trad...

In article
writes:

I've always thought that the ground side was a much lower impedance than
that,

This is exactly the problem. There's already one ground path through
the cable shield that's fairly low impedance (but apparently it's not
doing much good, or the hum you hear isn't from lack of grounding).
When you touch the strings, you're providing a parallel path between
the strings (at ground potential) and the ground (through you). Now
you have a ground loop. Not a very good one, but a ground loop none
the less.

Hmm. But it happens when I stand on the carpet in my rubber-soled tennies,
which means I'm not making a very good connection to the ground.

Peace,
Paul

In article writes:

Hmm. But it happens when I stand on the carpet in my rubber-soled tennies,
which means I'm not making a very good connection to the ground.

That's when you have an "antenna" problem, not a "ground" problem. How
about introducing hum on to the ground lead when you touch the
strings? If it's mostly in phase with the "natural" hum, you get more
hum. If it's mostly out of phase, you get less. You're still a pretty
high impedance source, though.

--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

In article writes:

Hmm. But it happens when I stand on the carpet in my rubber-soled tennies,
which means I'm not making a very good connection to the ground.

That's when you have an "antenna" problem, not a "ground" problem. How
about introducing hum on to the ground lead when you touch the
strings? If it's mostly in phase with the "natural" hum, you get more
hum. If it's mostly out of phase, you get less. You're still a pretty
high impedance source, though.

--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo