Mains hum...

[Phil Allison]

DecadentLinux...@decadence.org wrote:
================================

** Huh ? 100Hz ?

Think is is just simple capacitive coupled injection of the AC
supply voltage wave. The bane of many poorly shielded electric
guitars .

Yes, and it typically sounds off at twice the line frequency.

** No it does not.

> So, 60Hz gets 120Hz noise and 50Hz gets 100Hz noise.

** The AC supply has a fair amount of 3rd and 5th harmonics that are often more audible that the fundamental.
But SFA 2nd.
Magnetic hum fields radiated from transformers is mostly 3rd to.

...... Phil

 

[whit3rd]

On Thursday, April 7, 2022 at 2:58:46 PM UTC-7, palli...@gmail.com wrote:

DecadentLinux...@decadence.org wrote:
================================

** Huh ? 100Hz ?

Think is is just simple capacitive coupled injection of the AC
supply voltage wave. The bane of many poorly shielded electric
guitars .

Yes, and it typically sounds off at twice the line frequency.

** No it does not.
So, 60Hz gets 120Hz noise and 50Hz gets 100Hz noise.
** The AC supply has a fair amount of 3rd and 5th harmonics that are often more audible that the fundamental.
But SFA 2nd.
Magnetic hum fields radiated from transformers is mostly 3rd to.

Second harmonic is the acoustic (magnetostriction) output from transformers,
and the light from fluorescent fixtures (or used to be; ballasts are more
frequency-rich nowadays). Ripple voltage on a fullwave rectifier, also.

If you apply enough gain, you\'ll see lots of sneaky signal inputs. Microphonic tubes
are /were a major concern, and that\'s why old HiFi preamps were on a different chassis
than the power stages.

 

[Ricky]

On Wednesday, April 6, 2022 at 7:37:40 PM UTC-4, Cursitor Doom wrote:

On Wed, 6 Apr 2022 16:06:28 -0700 (PDT), Ricky
gnuarm.del...@gmail.com> wrote:

On Wednesday, April 6, 2022 at 2:21:53 PM UTC-4, Tauno Voipio wrote:
On 6.4.22 19.51, Ricky wrote:
On Wednesday, April 6, 2022 at 4:59:35 AM UTC-4, Tauno Voipio wrote:
My guess is that the hum is coming from your patient / target.

The capacitance of an average person is about 20 pF to the
active phase line and 200 pF to ground. You can assume that
the patient has about 10% of the line voltage through a pretty
high impedance voltage divider.

When we made ECG equipment in the early 1970\'s, the solution
was to make the input of the amplifier differential and as
high impedance as possible, including guard bootstrapping the
shield braids of the input cables. The impedance of the
connection electrodes are hardly ever identical, and this creates
voltage dividers with the amplifier input impedances. The
imbalance works directly to convert the common-mode hum into
differential input.

That would make sense if each measurement was relative to ground. These measurements only make sense relative to each other. Treating the body as a capacitor to the power line is not of much use. Noise can be introduced when the different parts of the body have different levels of noise. The displayed signals are either one electrode relative to a \"reference\" electrode, or multiple electrodes are averaged together to form a virtual reference which is the reference for each electrode.

I don\'t know for sure, but I expect the body is a relatively low impedance voltage source. I\'m willing to bet the best way for removing power line noise is a simple notch filter in the amplifier. The noise amplitude is low, so no worry about over driving the amps. Just filter it out, best with a digital filter as the design is not complex and the frequency is not subject to drift with component tolerance, temperature, etc., so high Q can be used.
That is true, but we do not have contacts to the low impedance
source. The electrodes can have impedances of tens of kohm,
with mismatch between the electrodes. We do not hit contact
spikes through the skin.

The body is still low impedance with respect to the amplifier inputs. They use paste and a large contact area to minimize skin resistance. Given the high input impedance of the amp, the mismatch in impedance is of little consequence.


A notch filter is not a good idea, as much of the interesting
frequency components are in the mains frequency range. The
ECG signal is spiky by its very nature, and narrow band filters
will spoil the information looked for.


You seem to be confusing a notch (band reject) with a narrow band-pass filter. An adequately narrow band reject filter would have virtually no impact on the signal of interest. It only need be wide enough to accommodate the normal variations in mains frequency.
Leaving aside that the problem has now been resolved, I would have
thought Tauno was right in what he said. The wanted and unwanted
components of the waveform are just too close together to target one
without degrading the other to some meaningful extent.

That\'s simply not true. You can design a filter to satisfy the requirements. It\'s not like the signal of interest has a critical component at 50/60 Hz. Look at the waveform, or better yet, look at the frequency spectrum. There\'s nothing important at that frequency. Tauno also spoke of it incorrectly, referring to \"narrow band filters\". What is called for is narrow band reject which is not at all the same thing and will not disturb the signal overall, unless there is a critical component at the same exact frequency, which is not the case.

--

Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209

 

[Ricky]

On Thursday, April 7, 2022 at 4:44:28 AM UTC-4, palli...@gmail.com wrote:

erichp...@hotmail.com wrote:
========================


My guess is that the hum is coming from your patient / target.

The capacitance of an average person is about ...

I think that when OP tried battery power he was still examining the
output on a mains connected scope? Interesting would be what is seen
with a battery powered scope and the whole system free of any connection
to mains ground.

** That is my contention too, posted 2 days ago.

The ECG amp will probably be heavily low pass filtered
somewhere along the chain so the HF interference won\'t be seen at the
output but it\'s 100Hz modulation rate will be?

** Huh ? 100Hz ?

Think is is just simple capacitive coupled injection of the AC supply voltage wave.
The bane of many poorly shielded electric guitars .



Yes, but later on the OP said he solved the problem with ferrite beads.
** Should have tried Hippy beads or Rosary beads.

He hasn\'t said how many beads he used ...

** Nor how much weed he smoke daily.
but it seems unlikely he used
enough ferrite to attenuate mains frequencies directly so the theory now
is that he instead attenuated some higher frequency pickup that was
itself power line modulated?
** I can see what looks like 50Hz in that slow ECG trace.

Try counting the wiggles.

You can count as much as you like. Without knowing the time base of the capture, there\'s no way to turn a count into a frequency.

--

Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209

 

[Phil Allison]

Ricky wrote:
===============

Tauno Voipio wrote:
Phil Allison wrote:


An adequately narrow band reject filter would have virtually no impact on the signal of interest.

** Shame you have never looked at the phase and amplitude curve of such a filter.

Right!

A narrow notch rings as badly as a narrow peak when fed with
a spiky signal.

At what frequency does it ring?

** Ringing (as seen on a scope) is at the same frequency as the notch minimum.
But you will not find it in a spectrum analysis.


...... Phil

 

[Ricky]

On Thursday, April 7, 2022 at 9:31:47 PM UTC-4, Ricky wrote:

On Thursday, April 7, 2022 at 1:29:01 PM UTC-4, Tauno Voipio wrote:
On 7.4.22 2.52, Phil Allison wrote:
Ricky wrote:
==========

An adequately narrow band reject filter would have virtually no impact on the signal of interest.

** Shame you have never looked at the phase and amplitude curve of such a filter.


It only need be wide enough to accommodate the normal variations in mains frequency.

** About 0.1Hz is all the AC supply varies by.


...... Phil
Right!

A narrow notch rings as badly as a narrow peak when fed with
a spiky signal.
At what frequency does it ring?

The reason I ask, is because if the ringing is high enough frequency, it is out of band and can be filtered out. I\'m willing to bet there is an inverse relationship between the half bandwidth of the notch and the ringing frequency. If it is narrow enough (which is what is desired) it will produce ringing that is far out of band and easily filtered. I believe I read the ECG bandwidth is 150 Hz. I expect it would not be too hard to push the ringing frequency up to a range that is easily filtered.

On doing a bit of research on the matter, it seems to be a much discussed topic, but with no definitive solution. However, here is a paper that seems to say the solution is really in the way the electrodes are attached.

https://www.aami.org/docs/default-source/bi-t/bit/2012-bit-nd-ecg.pdf

--

Rick C.

-++ Get 1,000 miles of free Supercharging
-++ Tesla referral code - https://ts.la/richard11209

 

[Ricky]

On Thursday, April 7, 2022 at 10:01:41 PM UTC-4, palli...@gmail.com wrote:

Ricky wrote:
===============
Tauno Voipio wrote:
Phil Allison wrote:


An adequately narrow band reject filter would have virtually no impact on the signal of interest.

** Shame you have never looked at the phase and amplitude curve of such a filter.

Right!

A narrow notch rings as badly as a narrow peak when fed with
a spiky signal.

At what frequency does it ring?
** Ringing (as seen on a scope) is at the same frequency as the notch minimum.
But you will not find it in a spectrum analysis.

Let\'s construct a mind experiment to analyze that idea. If you stimulate a notch filter with an impulse, a signal containing all frequencies in equal amplitude, what will emerge from the notch filter is a ring at the frequency at which the filter is supposed to have a null?

Is that logically consistent with the frequency response of the filter?

--

Rick C.

+-- Get 1,000 miles of free Supercharging
+-- Tesla referral code - https://ts.la/richard11209

 

[server]

Phil Allison <pallison49@gmail.com> wrote in
news:70523b25-2f3e-45b5-994f-23abc24669e1n@googlegroups.com:

DecadentLinux...@decadence.org wrote:
================================

** Huh ? 100Hz ?

Think is is just simple capacitive coupled injection of the AC
supply voltage wave. The bane of many poorly shielded electric
guitars .

Yes, and it typically sounds off at twice the line frequency.


** No it does not.

So, 60Hz gets 120Hz noise and 50Hz gets 100Hz noise.

** The AC supply has a fair amount of 3rd and 5th harmonics that
are often more audible that the fundamental.
But SFA 2nd.
Magnetic hum fields radiated from transformers is mostly 3rd
to.

..... Phil

But if it gets rectified, the ripple on a badly designed supply
exhibits noise at f*2.

 

[Phil Allison]

DecadentLinux...@decadence.org wrote:
================================

** The AC supply has a fair amount of 3rd and 5th harmonics that
are often more audible that the fundamental.
But SFA 2nd.
Magnetic hum fields radiated from transformers is mostly 3rd
to.

But if it gets rectified, the ripple on a badly designed supply
exhibits noise at f*2.

** Well yes,

the hum you hear from an amp with bad filter electros is 100 or 120Hz.


....... Phil

 

[Phil Allison]

Ricky wrote:
============

A narrow notch rings as badly as a narrow peak when fed with
a spiky signal.

At what frequency does it ring?

** Ringing (as seen on a scope) is at the same frequency as the notch minimum.
But you will not find it in a spectrum analysis.

Let\'s construct a mind experiment to analyze that idea.
If you stimulate a notch filter with an impulse,
a signal containing all frequencies in equal amplitude,
what will emerge from the notch filter is a ring at the frequency
at which the filter is supposed to have a null?

** But will not show up on a spectrum analysis.
That will look as expected, ie missing a chunk.

> Is that logically consistent with the frequency response of the filter?

** The \" ringing\" seen on a scope is an *artefact* - created by missing
and phase shifted components of the input signal.
Same goes for square wave inputs.
All components must be there in the right amounts and phase relationships to get a square looking result.

Brilliant example for \" cognitive dissonance\" for most people.


....... Phil

 

[Tauno Voipio]

On 8.4.22 5.18, Ricky wrote:

On Thursday, April 7, 2022 at 9:31:47 PM UTC-4, Ricky wrote:
On Thursday, April 7, 2022 at 1:29:01 PM UTC-4, Tauno Voipio wrote:
On 7.4.22 2.52, Phil Allison wrote:
Ricky wrote:
==========

An adequately narrow band reject filter would have virtually no impact on the signal of interest.

** Shame you have never looked at the phase and amplitude curve of such a filter.


It only need be wide enough to accommodate the normal variations in mains frequency.

** About 0.1Hz is all the AC supply varies by.


...... Phil
Right!

A narrow notch rings as badly as a narrow peak when fed with
a spiky signal.
At what frequency does it ring?

The reason I ask, is because if the ringing is high enough frequency, it is out of band and can be filtered out. I\'m willing to bet there is an inverse relationship between the half bandwidth of the notch and the ringing frequency. If it is narrow enough (which is what is desired) it will produce ringing that is far out of band and easily filtered. I believe I read the ECG bandwidth is 150 Hz. I expect it would not be too hard to push the ringing frequency up to a range that is easily filtered.

On doing a bit of research on the matter, it seems to be a much discussed topic, but with no definitive solution. However, here is a paper that seems to say the solution is really in the way the electrodes are attached.

https://www.aami.org/docs/default-source/bi-t/bit/2012-bit-nd-ecg.pdf

So, you\'re approaching the beef now.

The kilo-ohm impedances of electrodes are there *after* cleaning
the skin and removing the dear chest hair. There was also electrode
paste between the siver plate of the electorode and the skin.

You did not respond to my question about a reference electrode.

--

-TV

 

[bitrex]

On 4/7/2022 4:19 AM, Phil Allison wrote:

erichp...@hotmail.com wrote:
=======================

My guess is that the hum is coming from your patient / target.

The capacitance of an average person is about ...

I think that when OP tried battery power he was still examining the
output on a mains connected scope? Interesting would be what is seen
with a battery powered scope and the whole system free of any connection
to mains ground.

** That is my contention too, posted 2 days ago.

The ECG amp will probably be heavily low pass filtered
somewhere along the chain so the HF interference won\'t be seen at the
output but it\'s 100Hz modulation rate will be?

** Huh ? 100Hz ?

Think is is just simple capacitive coupled injection of the AC supply voltage wave.
The bane of many poorly shielded electric guitars .


...... Phil

You can tell a guitarist it\'s a good idea to shield the cavity, 7/10
times he won\'t listen though and if you start talking about \"capacitive
coupled injection\" he\'s even less likely to.

 

[Joe Gwinn]

On Fri, 8 Apr 2022 16:14:53 -0400, bitrex <user@example.net> wrote:

On 4/7/2022 4:19 AM, Phil Allison wrote:
erichp...@hotmail.com wrote:
=======================

My guess is that the hum is coming from your patient / target.

The capacitance of an average person is about ...

I think that when OP tried battery power he was still examining the
output on a mains connected scope? Interesting would be what is seen
with a battery powered scope and the whole system free of any connection
to mains ground.

** That is my contention too, posted 2 days ago.

The ECG amp will probably be heavily low pass filtered
somewhere along the chain so the HF interference won\'t be seen at the
output but it\'s 100Hz modulation rate will be?

** Huh ? 100Hz ?

Think is is just simple capacitive coupled injection of the AC supply voltage wave.
The bane of many poorly shielded electric guitars .


...... Phil


You can tell a guitarist it\'s a good idea to shield the cavity, 7/10
times he won\'t listen though and if you start talking about \"capacitive
coupled injection\" he\'s even less likely to.

Some years ago, I was the unofficial chief (and only) engineer of a
local guitar maker (the owner is a friend of mine).

You don\'t try to convince the guitarist (who just wants low noise),
you talk to the guitar maker (who just wants to know exactly how to do
that). And few guitar makers are electronic engineers.

The remedy for capacitive injection was to electro statically shield
the routed cavity, originally by carefully fitted brass foil shielding
tubs, then (after I arrived) by nickel-dust based shield paint sprayed
thickly on the walls of the cavity. The DC resistance between any two
points on the cavity wall was about 20 ohms. The underside of the
pick guard had an aluminum foil layer glued on. These shields were
all grounded to the shield of the coax wire from guitar to amp. The
strings were also grounded.

The remedy for magnetic interference, chiefly at power frequencies and
harmonics, is various kinds of humbucking construction.


Joe Gwinn


PS: What I also did was to invent various kinds of jigs and fixtures,
and introduce them to various kinds of tool not found in luthier tool
catalogs. This collectively had a large impact on their manufacturing
costs. JMG

 

[Ricky]

On Friday, April 8, 2022 at 7:47:21 AM UTC-4, Tauno Voipio wrote:

On 8.4.22 5.18, Ricky wrote:
On Thursday, April 7, 2022 at 9:31:47 PM UTC-4, Ricky wrote:
On Thursday, April 7, 2022 at 1:29:01 PM UTC-4, Tauno Voipio wrote:
On 7.4.22 2.52, Phil Allison wrote:
Ricky wrote:
==========

An adequately narrow band reject filter would have virtually no impact on the signal of interest.

** Shame you have never looked at the phase and amplitude curve of such a filter.


It only need be wide enough to accommodate the normal variations in mains frequency.

** About 0.1Hz is all the AC supply varies by.


...... Phil
Right!

A narrow notch rings as badly as a narrow peak when fed with
a spiky signal.
At what frequency does it ring?

The reason I ask, is because if the ringing is high enough frequency, it is out of band and can be filtered out. I\'m willing to bet there is an inverse relationship between the half bandwidth of the notch and the ringing frequency. If it is narrow enough (which is what is desired) it will produce ringing that is far out of band and easily filtered. I believe I read the ECG bandwidth is 150 Hz. I expect it would not be too hard to push the ringing frequency up to a range that is easily filtered.

On doing a bit of research on the matter, it seems to be a much discussed topic, but with no definitive solution. However, here is a paper that seems to say the solution is really in the way the electrodes are attached.

https://www.aami.org/docs/default-source/bi-t/bit/2012-bit-nd-ecg.pdf

So, you\'re approaching the beef now.

The kilo-ohm impedances of electrodes are there *after* cleaning
the skin and removing the dear chest hair. There was also electrode
paste between the siver plate of the electorode and the skin.

You did not respond to my question about a reference electrode.

That should be addressed to the OP. It\'s not my setup.

I\'ve already mentioned that current practice either uses a single reference electrode, or combines the signals from all electrodes to use as a common reference for all electrodes. This gives N signals for N leads rather than N-1 signals.

What are you looking for with the question?

When you mention kilo-ohm impedances, that is low relative to the amplifier input. It\'s also low enough for stray coupling to only produce a relatively low voltage in the signal. That is what the OP is seeing, a low voltage \"hum\" on his signal. It actually would not take much filtering to make that noise virtually invisible.

You didn\'t answer my question about the frequency of the notch filter ringing.

I believe the required characteristics of the notch filter in this application would not produce noticeable ringing.

--

Rick C.

+-+ Get 1,000 miles of free Supercharging
+-+ Tesla referral code - https://ts.la/richard11209

 

[Phil Allison]

Joe Gwinn wrote:
==============

Think is is just simple capacitive coupled injection of the AC supply voltage wave.
The bane of many poorly shielded electric guitars .

...... Phil


The remedy for capacitive injection was to electro statically shield
the routed cavity, originally by carefully fitted brass foil shielding
tubs, then (after I arrived) by nickel-dust based shield paint sprayed
thickly on the walls of the cavity. The DC resistance between any two
points on the cavity wall was about 20 ohms. The underside of the
pick guard had an aluminum foil layer glued on. These shields were
all grounded to the shield of the coax wire from guitar to amp. The
strings were also grounded.

The remedy for magnetic interference, chiefly at power frequencies and
harmonics, is various kinds of humbucking construction.

** All these things were well known and adopted by makers like Gibson in the 1950s.
But they were a luxury brand sold to professionals.
A radio repair man called Leo Fender began making similar things, very cheaply.
https://en.wikipedia.org/wiki/Leo_Fender#Early_life

Working at a time when triac dimmers were unknown and likewise safety earthing - he gave almost no attention to ES shielding.
His famous Stratocaster guitar has only a token effort at such and is a first class receiver of hum and buzzing from the AC supply.
Nearby fluoro lighting drives one crazy.

https://insounder.org/under-hood-9-evolution-stratocasters-electronics-wiring

Note the use of plastic covered pickups, unshielded wiring and no cavity shielding at all.
Fender relied on the player earthing themselves via the steel strings to proved any measure of shielding.
AFAIK even recent examples are little better.
The instrument is considered to be is \'\"sacred\" by players and must not be changed.


........ Phil

 

[Cursitor Doom]

On Thu, 7 Apr 2022 19:23:40 -0700 (PDT), Ricky
<gnuarm.deletethisbit@gmail.com> wrote:

On Thursday, April 7, 2022 at 10:01:41 PM UTC-4, palli...@gmail.com wrote:
Ricky wrote:
===============
Tauno Voipio wrote:
Phil Allison wrote:


An adequately narrow band reject filter would have virtually no impact on the signal of interest.

** Shame you have never looked at the phase and amplitude curve of such a filter.

Right!

A narrow notch rings as badly as a narrow peak when fed with
a spiky signal.

At what frequency does it ring?
** Ringing (as seen on a scope) is at the same frequency as the notch minimum.
But you will not find it in a spectrum analysis.

Let\'s construct a mind experiment to analyze that idea. If you stimulate a notch filter with an impulse, a signal containing all frequencies in equal amplitude, what will emerge from the notch filter is a ring at the frequency at which the filter is supposed to have a null?

Is that logically consistent with the frequency response of the filter?

Might I suggest a variation of Jan\'s idea?

1. Digitize the waveform
2. Feed a 50Hz signal of equal amplitude into a mixer together with
the digitized waveform.
3. Adjust the phase of the 50Hz signal until the interference is
cancelled out.

I believe this method will have the least detrimental effect on the
desired trace.
In fact it might be possible to use an app like Audacity to do all the
above with just a few mouse clicks, as I\'m pretty sure there\'s a spot
frequency filter somewhere in the software.

 

[Phil Allison]

Cursitor Dope wrote:

====================

1. Digitize the waveform
2. Feed a 50Hz signal of equal amplitude into a mixer together with
the digitized waveform.
3. Adjust the phase of the 50Hz signal until the interference is
cancelled out.

** Huh ???

Makes no sense at all.

In fact it might be possible to use an app like Audacity to do all the
above with just a few mouse clicks, as I\'m pretty sure there\'s a spot
frequency filter somewhere in the software.

** FYI Mr Dope

The AC mains wave drifts in frequency and phase and changes amplitude in the ECG trace with a host of external factors.



........ Phil

 

[Ricky]

On Friday, April 8, 2022 at 7:56:53 PM UTC-4, Cursitor Doom wrote:

On Thu, 7 Apr 2022 19:23:40 -0700 (PDT), Ricky
gnuarm.del...@gmail.com> wrote:

On Thursday, April 7, 2022 at 10:01:41 PM UTC-4, palli...@gmail.com wrote:
Ricky wrote:
===============
Tauno Voipio wrote:
Phil Allison wrote:


An adequately narrow band reject filter would have virtually no impact on the signal of interest.

** Shame you have never looked at the phase and amplitude curve of such a filter.

Right!

A narrow notch rings as badly as a narrow peak when fed with
a spiky signal.

At what frequency does it ring?
** Ringing (as seen on a scope) is at the same frequency as the notch minimum.
But you will not find it in a spectrum analysis.

Let\'s construct a mind experiment to analyze that idea. If you stimulate a notch filter with an impulse, a signal containing all frequencies in equal amplitude, what will emerge from the notch filter is a ring at the frequency at which the filter is supposed to have a null?

Is that logically consistent with the frequency response of the filter?
Might I suggest a variation of Jan\'s idea?

1. Digitize the waveform
2. Feed a 50Hz signal of equal amplitude into a mixer together with
the digitized waveform.
3. Adjust the phase of the 50Hz signal until the interference is
cancelled out.

I believe this method will have the least detrimental effect on the
desired trace.
In fact it might be possible to use an app like Audacity to do all the
above with just a few mouse clicks, as I\'m pretty sure there\'s a spot
frequency filter somewhere in the software.

Sure, that will work for an amateur setup like what is discussed here... as long as nothing moves during the recording. That will only work for a stationary signal.

--

Rick C.

++- Get 1,000 miles of free Supercharging
++- Tesla referral code - https://ts.la/richard11209

 

[Joe Gwinn]

On Fri, 8 Apr 2022 16:14:36 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

Joe Gwinn wrote:
==============

Think is is just simple capacitive coupled injection of the AC supply voltage wave.
The bane of many poorly shielded electric guitars .

...... Phil


The remedy for capacitive injection was to electro statically shield
the routed cavity, originally by carefully fitted brass foil shielding
tubs, then (after I arrived) by nickel-dust based shield paint sprayed
thickly on the walls of the cavity. The DC resistance between any two
points on the cavity wall was about 20 ohms. The underside of the
pick guard had an aluminum foil layer glued on. These shields were
all grounded to the shield of the coax wire from guitar to amp. The
strings were also grounded.

The remedy for magnetic interference, chiefly at power frequencies and
harmonics, is various kinds of humbucking construction.


** All these things were well known and adopted by makers like Gibson in the 1950s.
But they were a luxury brand sold to professionals.
A radio repair man called Leo Fender began making similar things, very cheaply.
https://en.wikipedia.org/wiki/Leo_Fender#Early_life

That\'s my understanding too.

Working at a time when triac dimmers were unknown and likewise safety earthing - he gave almost no attention to ES shielding.
His famous Stratocaster guitar has only a token effort at such and is a first class receiver of hum and buzzing from the AC supply.
Nearby fluoro lighting drives one crazy.

https://insounder.org/under-hood-9-evolution-stratocasters-electronics-wiring

Note the use of plastic covered pickups, unshielded wiring and no cavity shielding at all.
Fender relied on the player earthing themselves via the steel strings to proved any measure of shielding.
AFAIK even recent examples are little better.

All true.


>The instrument is considered to be is \'\"sacred\" by players and must not be changed.

Also true.

One thing that people do is to put a larger coil in the bottom of the
routed-out tub, and use that to humbuck the old-school singlecoil.
With good ES shielding and grounding of everything, this can help a
lot. There is a patent on this, but I don\'t recall the number
offhand.

Joe Gwinn

 

[Phil Allison]

Joe Gwinn wrote:
===============

Think is is just simple capacitive coupled injection of the AC supply voltage wave.
The bane of many poorly shielded electric guitars .



The remedy for capacitive injection was to electro statically shield
the routed cavity, originally by carefully fitted brass foil shielding
tubs, then (after I arrived) by nickel-dust based shield paint sprayed
thickly on the walls of the cavity. The DC resistance between any two
points on the cavity wall was about 20 ohms. The underside of the
pick guard had an aluminum foil layer glued on. These shields were
all grounded to the shield of the coax wire from guitar to amp. The
strings were also grounded.

The remedy for magnetic interference, chiefly at power frequencies and
harmonics, is various kinds of humbucking construction.


** All these things were well known and adopted by makers like Gibson in the 1950s.
But they were a luxury brand sold to professionals.
A radio repair man called Leo Fender began making similar things, very cheaply.
https://en.wikipedia.org/wiki/Leo_Fender#Early_life
That\'s my understanding too.
Working at a time when triac dimmers were unknown and likewise safety earthing - he gave almost no attention to ES shielding.
His famous Stratocaster guitar has only a token effort at such and is a first class receiver of hum and buzzing from the AC supply.
Nearby fluoro lighting drives one crazy.

https://insounder.org/under-hood-9-evolution-stratocasters-electronics-wiring

Note the use of plastic covered pickups, unshielded wiring and no cavity shielding at all.
Fender relied on the player earthing themselves via the steel strings to proved any measure of shielding.
AFAIK even recent examples are little better.
All true.
The instrument is considered to be is \'\"sacred\" by players and must not be changed.
Also true.

One thing that people do is to put a larger coil in the bottom of the
routed-out tub, and use that to humbuck the old-school singlecoil.
With good ES shielding and grounding of everything, this can help a
lot. There is a patent on this, but I don\'t recall the number
offhand.

** There is no huge problem with players standing a few metres away from any AC transformers in the vicinity.
The mag field from an AC transformer is purely short range.
The need for humbucking PUs arose from those who sit next to or even on top of their amps.

As it happens, nearly all humbucking PUs have full ES shielding too, so are dead quiet.


........ Phil