Elliott Sound Products

Earthing Your Hi-Fi - Tricks and
Techniques

Copyright (c) 1999 - Rod
Elliott (ESP)
Page Created 30 Dec 1999

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Introduction

It is not uncommon to see hi-fi equipment with the earth (ground)
disconnected from one piece of equipment or another, usually to prevent a hum
loop which ruins the listening experience. However, there is nothing quite like
being electrocuted to really ruin the experience should something go
wrong!

Electrocution
First, a quick word on electrocution. It is not fun,
and electricity kills a great many people worldwide every year. A current of
50mA (barely enough to make a low wattage lamp even glow) is sufficient to send
your heart into a state called 'ventricular fibrillation', where the heart
muscles are all working out of synchronisation with each other. Little or no
blood is pumped, and you will die within about 3 minutes unless help is
immediately at hand.

Sometimes (but less often), your heart will simply stop. If this happens, it
is possible that with external heart massage that it might re-start, and
occasionally it might even re-start by itself - rare, but it can happen. The
result of fatal electrocution is that you will no longer be able to enjoy the
hi-fi that you have spent so much time and money putting together, and all other
earthly activities are similarly curtailed   .

This article has been prompted by many e-mails I have received asking about
hum, earthing and what should be done to ensure that equipment is safe, and does
not hum. There are other causes of hum in a sound system other than electrical
(safety) earthing issues, but I will contain this particular article to the
basic issues of safety and eliminating hum loops while maintaining a high degree
of safety.

The regulations regarding safety earth connections vary from one
country to the next, and I do not have the details for each case. This
article is general, and if unsure, you should consult the appropriate
electrical supply authority in your country to obtain the rules that apply
to you.

I have used the terminology I am familiar with - the live
conductor is called the 'active' and the return conductor is called
'neutral'. The safety conductor is called 'earth' or sometimes 'earth
ground' (particularly in the US). These terms differ, so make sure that
you know what they are called where you live.

How The Safety Earth Works

The basic idea of an electrical safety earth (or ground) is pretty much the
same everywhere, but the details can vary widely. The case (chassis) of the
equipment (and except for special situations, the internal electronics) is
connected to an earth pin on the mains outlet. This is then connected through
the house wiring and switchboard to an electrically solid earth point, which is
commonly a copper water pipe (no longer allowed in Australia or NZ), or an
approved earth stake buried deep into the ground.

In some systems used elsewhere, the earth wire is separate back to the
distribution transformer, and in others the neutral is also the earth up until
the household switchboard. Australia and New Zealand use the 'Multiple Earth
Neutral' (MEN) system, where there is a bond between neutral and earth at each
household (or unit complex) main switchboard. The maintains the lowest possible
impedance for the safety earth. Other countries have different regulations and
systems - look it up for your location or ask an electrician if unsure.

Should a fault develop within the equipment that causes the active (live)
conductor to come into contact with the chassis, the fault current will flow to
earth, and the equipment or main switchboard fuse or circuit breaker will blow.
This protects the user from electric shock, bypassing the dangerous current
directly to earth, rather than through the body of the unsuspecting poor bastard
who just touched it. If this experience does not kill, it will invariably enrich
the vocabulary.

Earth leakage circuit breakers (RCD - residual current detectors - see below)
measure the current in the active and neutral conductors. If these differ by
more than a few milliamps, the circuit is disconnected. The principle is simple
- if the current in the two wires differs, some of it must be going somewhere
that is undesirable, so the supply is interrupted almost instantly. While these
are mandatory in some countries (or under some circumstances), it is best not to
rely on any advanced technique, but provide a system that is intrinsically safe
- this is extremely difficult in reality.

There are exceptions to the basic earthed equipment method of protection.
Some equipment is designated 'Double Insulated', and usually has a symbol of two
concentric squares that indicates that the equipment is double insulated, and
that an earth connection is not needed (or in some cases must not be
used). The common plug-pack (wall-wart) power supply is nearly always double
insulated, and such equipment has reinforced insulation, designed to ensure that
it is not possible for the live AC connection to connect to the secondary
electronics in any event - including a complete meltdown. The electrical safety
tests to verify that a product meets the Double Insulation standards are
rigorous and expensive, and are very difficult to meet with high powered
equipment, and even more so when the equipment has a metal case. Nearly all
power amplifiers (for example) are not double insulated, and require an
earth connection.

Colour Codes

The common colour codes for mains wiring are shown in Table 1, below. The
Active (or Line) is the 'hot' conductor, and carries the full AC supply voltage.
The Neutral conductor is not live, but is intended to be the return path for all
current in the active lead. The neutral is always considered to be a 'live'
conductor and must be insulated accordingly, and it must not be used for
anything other than the return path for current from the active. Although this
has caused great confusion to a great many people, it is sensible and logical (I
will not go into the reasons here). The safety earth (or ground) conductor is
intended to provide protection against electrocution, and where fitted, must not
be disconnected.

Conductor

IEC

US

Alternative

Active (Line)

Brown

Black

Red

Neutral

Blue

White

Black

Earth

Green/Yellow

Green

Green

Table 1 - Common Mains
Colour Codes

These colour codes are not standardised, and some variations may be found in
different countries. The column headed 'Alternative' refers to an old code that
used to be used in Australia and several other countries prior to the IEC codes
being adopted. The one common theme of these codes is that they have been
designed so that colour-blind people will not get the wires mixed up. The use of
green with yellow stripes for the earth makes this even more secure. I have no
information on the history of the determination of the colours used, but it is
of little consequence since we can't change it.

Note that in the US, the neutral is sometimes referred to as the
groundED conductor, and earth/ earth ground called the groundING
conductor. These terms are not intuitive and are easily mixed up if you don't
understand the difference. Make sure that you fully understand all terms
that are used where you live.

Earth Loops/ Ground Loops

Figure 1 shows a typical connection of two hi-fi components, and includes the
house wiring and main earthing point. As can be seen, there is a loop (indicated
by the dotted line), which includes the interconnect cable, power leads, and a
small part of the house wiring. Such loops are a major cause of hum in systems,
and it is not uncommon for people to remove an earth wire from one or the other
mains connectors to break the loop and stop the hum. The situation is much worse
if different wall outlets are used for different parts of the sound system. In
this case, the loop may extend all the way back to the main switchboard, making
it longer, and more likely to have a significant voltage between individual
earth connections.

Figure 1 - The Formation of an Earth Loop

Also note that the neutral (return) conductor is attached to earth at the
main switchboard. This is called the MEN system and is standard in Australia
and some other countries, but might not be the case where you live. Check with
an electrician who can tell you how this is done (if you really want to
know).

What happens if the amplifier develops an electrical fault that allows the
live AC conductor to come into contact with the chassis? The current will flow
from the chassis, through the earth connection, and the fuse/ circuit breaker
will blow in the switchboard (or in the equipment if a mains fuse is
fitted).

Should the safety earth be disconnected from the power amp (for example), if
a fault occurs in the amp, the only earth return is now via the interconnects
(assuming that the source is earthed). Interconnects are not designed to
withstand the fault current that can occur with a major electrical fault, and
may disintegrate before the fuse. You now have a live chassis on the amplifier -
just waiting for someone to touch it and possibly die!

Residual Current Detectors

Many new installations use a safety switch, specifically an 'Earth Leakage'
or 'Residual Current' detector (aka GFI - ground fault interrupter, etc.), a
device that will disconnect the AC supply if the current flowing in the active
(live) conductor is not exactly matched by that in the neutral. Any imbalance
means that current is going somewhere it should not be, and the device will
trip.

These safety circuit breakers are very fast acting, and have saved many lives
since their introduction. The 50mA that will kill you is detected by the
breaker, and the power is disconnected - fast! Most of these type of breakers
will operate on as little as 20mA, so you are not only protected against major
faults, but also against excessive AC leakage caused by faulty insulation or
moisture.

This does not mean that you can now go around disconnecting earth connections
to stop hum - the safety devices that may be fitted to your house wiring are
designed to trigger on a fault before you find it the hard way. In many
countries, it is illegal to tamper with electrical (mains) wiring unless you are
licensed - but in all countries, if it can be proven that you disconnected an
earth that allowed a fault to kill someone else, you are liable, and may be
subject to criminal charges !  Is that scary?

What Causes Earth (Ground) Loops?

It is generally accepted that an earth loop conducts a current from one piece
of equipment to the next, and imposes a voltage across the connection. A good
question is where does the current come from, and why doesn't it trip the safety
switch? Contrary to common belief, earth loops are not caused by leakage
current or some other mysterious current that flows in the earth lead back to
the switchboard. If this were the case, it would have to be coming from an
active connection via a leakage path, and this would trip the safety switch
instantly.

The loop is mostly entirely local, and (again) contrary to some claims,
connecting equipment to separate mains outlets will almost certainly make the
situation much worse. Current in the local loop is created by the stray magnetic
field of transformers in the connected equipment. Traditional (EI) laminated
transformers are almost always worse in this respect than toroidal transformers,
but all mains frequency transformers are capable of generating a circulating
current if given the opportunity. These currents are made worse if there is
metal chassis work in close proximity to the transformer laminations. Thick
panels simply mean lower resistance, so a higher current flows for a given
induced voltage.

Another source is a signal lead running parallel to a mains power lead.
Although the conductors of mains leads are twisted, the twist is usually fairly
basic, so balancing of the magnetic field is rather poor compared to the tight
twist of Cat-5 communications cable for example. The magnetic coupling is poor,
and the greatest problems are likely to be caused by capacitive coupling. Since
this favours high frequency noise, the sound is completely different from an
earth loop, and it's a good idea to try to familiarise yourself with the
different sounds made by the various issues that may plague hi-fi setups. If
signal cables and mains wiring must cross each other, ensure they cross at right
angles, and if possible separate the two as far as practicable. Capacitive
coupling can also be an issue with transformer windings, where mains noise is
coupled through to the secondary by inter-winding capacitance, or from Y-Class
caps from mains to chassis.

It is not at all uncommon that multiple earth loops may exist, but in the
vast majority of cases a transformer is the root cause of the problem. The loop
created by the mains safety earth and the various interconnects can be quite
large, and it may not seem possible that cables so far from a transformer could
possibly generate enough current to cause a problem. However, the cables might
well be separated, but what about the equipment chassis? Any metal panel that
passes close to the transformer becomes part of the problem too, depending on
how the internal earthing connection is arranged. It's not uncommon to see the
mains safety earth connected near the mains inlet, and the signal earth
connected somewhere else on the chassis. In isolation, this will never cause a
problem. Once the equipment is connected to something else that's also earthed,
an instant earth loop is created.

While disconnecting the mains earth from one of the offending pieces of kit
may well break the loop, it also renders the setup unsafe if there is an
internal fault. In some countries, it may be illegal to disconnect a safety
earth, and if someone is killed or injured you may be held liable.

Figure 2 - Transformer Induced Earth Loop Current Waveform

The waveform shown above was not simulated. It was captured on a PC based
oscilloscope, using a single loop of thin wire (loosely) around the outside of
an E-I core transformer. No special attempt was made to optimise the signal, and
the loop was terminated by a resistor of 0.22 ohms. The voltage was changed only
very slightly regardless of whether the resistor was connected or not, showing
that it is not unreasonable to expect that the current may be very large indeed
if the impedance of the loop is low enough. Note that the primary frequency is
50Hz, but the waveform shows that there is a very high level of 150Hz ... the
third harmonic.

Remember that any metalwork, including that of another piece of equipment
sitting above that which uses the transformer, becomes part of this loop.
Increasing the size (effective diameter) of the loop does reduce the problem
slightly, but the larger loop may also be more sensitive and need less magnetic
flux to generate a potentially troublesome voltage and current.

Although the measured voltage of the waveform in Figure 2 is only about
20mV, compare this with the signal voltage at a typical listening level.
Assuming speakers at around 90dB/W/m and a power amp gain of 27dB, the hum is
only 15.7dB below a listening level of 1W (90dB SPL at 1 metre). This will be
very audible indeed.

Main Earth Connection

For those who build amps (as is the case with many of the readers of these
pages), a common question is "How should I connect the mains safety earth to the
chassis?". As I stated above, the regulations change from one country to the
next, but the principles are the same. Figure 3 shows a view of the basic
connection, which is very safe. The lug used should be an approved earth lug (or
one that meets any standards that exist where you live). Most are crimped, but
soldering ensures the most reliable connection for safety.

Figure 3 - Safe Method Of Connecting The Safety Earth

Any paint (or anodising, in an aluminium chassis) must be scraped away to
expose bare metal, and the tooth washer ensures that there is a good 'bite' into
the metal itself. The use of two nuts is strongly recommended, since the second
one acts as a locknut, and prevents the first nut from loosening. The flat
washers shown are optional, but highly recommended. They may be a requirement in
some countries.

Do not use the earth connection as mounting for any other panel or component
- it must be dedicated to the task of providing a safety earth point. If a
component mounting bolt is used, at some stage it may be disconnected by a
service (or other) person, which means that the apparatus is unsafe until
everything is (hopefully) put back where it belongs - this does not always
happen.

Make sure that the electrical connection between metal panels is also very
well made. Some chassis are available in a kit form, and when screwed together,
may not make good electrical contact with each other. Should the mains come in
contact with a panel that has a flaky connection with the one that is earthed
properly, the same potential for disaster is still present. All exposed metal
must be properly and securely earthed.

The internal electronics of an amplifier should also be earthed, but now we
have the problem of the hum loop again. There are two possibilities here ...

Don't earth the internal electronics, or use a simple 'loop breaker'
circuit to allow the case to act as a shield for radio frequency interference,
but no solid connection is made (this is a common approach). This provides
protection should there be a failure from the incoming mains to chassis, but
provides none at all if the transformer were to develop a fault between
primary and secondary windings. Such faults are uncommon, but they can (and
do) occur.

Use a high current loop breaker circuit, ensuring that even major fault
currents will be bypassed to the safety earth conductor. Such a circuit was
described as a part of the 100W Guitar Amp project, but is shown again below.
Be warned that this circuit (while safe) may not be legal where you
live.

Use Of Loop Breaker Circuits

While very effective (and safe), as mentioned above such a circuit might not
be legal where you live. If this is the case and hum is causing you grief, the
use of balanced interconnects might solve the problem - but at some cost,
and will require balancing circuitry at each end of all the interconnects. While
not a panacea, this is the approach taken in all professional equipment, and is
usually highly effective, allowing all safety earth connections to remain
exactly as they are to prevent electrocution of the artists or road crew.
Suitable circuits for home (or professional) use are shown in the projects
section.

Note that there is an ongoing debate about the proper connection of pin 1 of
all XLR connectors, and if not done appropriately for the equipment, the "pin 1
problem" may either defeat any benefit from balancing or even make matters
worse. In nearly all cases, transformers are more effective than electronically
balanced circuits, but good ones come at high cost, and cheap ones may seriously
affect the frequency response of the equipment.

Figure 4 - A High Current Safety Loop Breaker Circuit

I have simply shown all internal electronics as a box, with the only
connection to the loop breaker being the zero volt line. This is most commonly
taken directly from the centre tap of the main amplifier filter capacitors, but
should always be connected to a point where there is high current wiring back to
the transformer. It is the transformer that provides isolation from the mains,
and the possibility of an internal transformer fault must be catered for.
Ideally, the mains earth connection and the loop-breaker's earth end should
connect to the same point on the chassis (as shown). Depending on the installed
transformer, there may be a significant circulating current within the chassis
itself.

The only exception is if a double insulated mains transformer is used, but
these are rare. Should the transformer be of 'conventional' construction (not a
toroidal), then the transformer body - the steel core - must be connected to
chassis directly. Do not use any loop breaker circuit to isolate the
transformer core, as it is unnecessary and dangerous to do so.

The loop breaker works by adding a resistance in the earth return circuit.
This reduces circulating loop currents to a very small value, and thus breaks
the loop. The capacitor in parallel ensures that the electronics are connected
to the chassis for radio frequency signals, and helps to prevent radio frequency
interference. Finally, the diode bridge provides the path for fault currents.
The use of a large chassis mounting (35A) type is suggested, since this will be
able to handle the possibly very high fault currents that may occur without
becoming open circuit. Note the way the bridge is wired, with the two AC
terminals shorted, and the two DC terminals shorted. Other connection
possibilities are dangerous, and must be avoided.

In the event of a major fault, one (or more) of the diodes in the bridge will
possibly fail. Semiconductors (nearly) always fail as short circuit, and only
become open circuited if the fault current continues and 'blows' the
interconnecting wires. High current bridge rectifiers have very solid conductors
throughout, and open circuit diodes are very rare (I have never seen a high
power bridge go open circuit - so far at least). Use of the bridge means that
there are two diodes in parallel for fault current of either polarity, so the
likelihood of failure (to protect) is very small indeed.

When a loop breaker is used, it is vitally important that all input and
output connectors are insulated from the case. If not, they will instantly
defeat the loop breaker by providing a direct connection from the zero Volt
point to chassis, and no benefit is obtained. (Electricity has an annoying - but
perfectly logical - tendency to travel along the path of least resistance, and a
direct short circuit will always have less resistance than the loop
breaker.)

It is not uncommon to have an induced voltage of perhaps 1V RMS between the
earth connections of power outlets that are wired separately back to the
switchboard. This small voltage, with a total resistance of perhaps 0.2-0.5 Ohm,
will cause a loop current of 2 to 5 Amps, all of which flows in the shield of
the interconnect. This is sufficient to cause a voltage difference across the
interconnect, which the amplifier cannot differentiate from the wanted signal.
By breaking the loop with the 10 Ohm resistor, the current is now less than
200mA, and the voltage across the interconnect will be very much smaller,
reducing the hum to the point where it should no longer be audible.

Never route an earth wire to the main (star) earthing point on a chassis in
such a way that it forms a partial (or full) turn around a transformer. It is
better to relocate either the star earth point or the transformer to ensure that
no earth conductor can create a partial turn. There may often be conflicting
requirements, but there is usually no reason that proper earthing for minimum
hum and maximum safety should be mutually exclusive. Both are important, and
both must be accommodated in the final design.

An earth loop will typically inject either a 50Hz or 60Hz hum
into the signal, or in the (common) case of a transformer induced current,
a somewhat mangled mains frequency as shown in Figure 2 - if you have a
100Hz or 120Hz buzz (which generally has a hard edge to the sound), you
have done something wrong in the wiring of the power supply, and the
techniques described here will not help. Refer to the article on power supply wiring.

Mains Filters

The core of the transformer (only for C-core or EI types - it's not
accessible with toroidal transformers) should also connect to the chassis and
mains earth. In the unlikely event of a primary to core leakage or short
circuit, the current will be diverted to the protective earth and will trip the
safety switch or circuit breaker. In some cases, a transformer may be fitted
with an electrostatic shield, but these are lamentably uncommon in hi-fi
transformers. Where provided, these too must be connected directly to the main
earth point, and not via a loop breaker (if used).

The purpose of the electrostatic shield is to intercept (and earth) any
interference on the incoming mains. It does this by preventing any signal from
being capacitively coupled from the primary to secondary windings, so the only
form of coupling in the transformer is via the magnetic field in the transformer
core. Most mains transformers have relatively poor high frequency response and
this helps to further reduce interfering signals.

This can dramatically reduce extraneous noises (clicks, pops, whirring
sounds, etc.) that might get into the system via the house and supply company
wiring. This has great potential to pick up noise, since there may be 50 to
100km (or more) of cable (including high voltage feeders and substations)
involved between your amplifier and the generating plant.

In some cases, a mains filter might be fitted to amplifiers or other
equipment (such as specially designed mains leads or 'black boxes') to reduce
any interference. Where fitted, if an earth connection is provided, it must be
connected to the safety earth and chassis - never to the amp's zero volt line.
Typical filters will use Metal Oxide Varistors (MOVs) to cut off any high
voltage spikes, and a capacitor and inductor network to filter out anything that
is not at the mains frequency.

A true 50Hz (or 60Hz) tuned filter will be a large unit indeed, so most line
filters only work at frequencies above a few kHz. This is generally enough to
get rid of most interference, since a well designed power supply should be able
to filter out the majority of noise from the mains. Mains filters usually use
the mains earth as a reference, so it must be present for the units to work
correctly. Not using the safety earth as a reference is extremely dangerous,
since the filters may have capacitors that can (and do) become short circuited
if a high voltage spike manages to get through and punctures the insulation.

Conclusion

Electrical safety cannot be over emphasised. Hum is damn annoying, and
everyone wants it gone. There is no good reason to sacrifice one for the other,
since safety and hum-free operation can peacefully co-exist with care and the
right techniques. Use of a separate earth stake just for hi-fi equipment is
probably unlawful in most countries, as the integrity of the safety earth may be
suspect at best, useless at worst.

As I have said several times, make sure that you find out the legal
requirements in your country, and don't do anything that places you at risk -
either from electrocution or legal liability. Neither is likely to be a pleasant
experience.

Where the mains is noisy (apparently a common occurrence in the US), use of a
dedicated mains filter may be useful to prevent mains noise from entering the
system. This will generally be unnecessary if the supply is well designed
(especially if an electrostatic shield is used on the transformer), but this is
often the exception, rather than the rule.

The use of 'specialty' mains leads (unless fitted with a proper filter which
will be in the form of a box in line with the cable) is unlikely to solve the
problem - regardless of claims made by the manufacturers or reviewers (see The Truth About Cables,
Interconnects and Audio in General for my comments on these - this article
made a lot of audiophiles very unhappy, but advertising hype does not
negate the laws of physics).

The (relatively) recent trend to use switchmode power supplies in consumer
equipment, along with double insulation, has created new problems. All SMPS use
small (and allegedly) 'fail-safe' Y-Class capacitors to the chassis, which is
not earthed. Use of these caps means that the chassis floats at roughly half the
mains voltage, but the impedance is very high. This poses two risks ...

Equipment input circuits may be damaged if double insulated appliances
with an SMPS are connected while switched on. This is covered elsewhere on the
ESP site. Such failures are the result of (typically) half mains voltage
being present on the chassis (and therefore the internal circuitry).
Connection to earthed equipment may cause a large instantaneous current to
flow.

Switchmode supply noise and any high frequency noise on the mains now
flows in the shield of the interconnect. This is not really an earth loop as
such, and the result is more likely to be a harsh (grating) hissing sound. It
is quite distinctly different from normal thermal noise, and is also more
intrusive.

It might be possible to reduce this noise by installing a heavy earth
strap that joins each chassis. Strictly speaking, this may be completely
illegal, but the rules for double insulated appliances in many countries are
often stupid, and fail to address reality. Almost all modern systems will have a
mixture of earthed and double insulated equipment, and any rule that states (for
example) that "double insulated appliances must not be earthed" is instantly
broken when the interconnects are installed. Needless to say, without the
interconnects there is no point having the gear in the first place, because
there's often no other way to get the signal from one unit to the other. Optical
fibre is one method of course, and completely eliminates any possibility of an
earth loop. This is not always a viable option.

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Copyright Notice. This
article, including but not limited to all text and diagrams, is the
intellectual property of Rod Elliott, and is Copyright © 1999.
Reproduction or re-publication by any means whatsoever, whether
electronic, mechanical or electro- mechanical, is strictly prohibited
under International Copyright laws. The author (Rod Elliott) grants the
reader the right to use this information for personal use only, and
further allows that one (1) copy may be made for reference. Commercial use
is prohibited without express written authorisation from Rod
Elliott.

Page created and copyright © 30 Dec 1999./ Updated Dec
2014