IEC 60268-3:2018

IEC 60268-3 ®
Edition 5.0 2018-04
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Sound system equipment –
Part 3: Amplifiers
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IEC 60268-3 ®
Edition 5.0 2018-04
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Sound system equipment –
Part 3: Amplifiers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.160.10 ISBN 978-2-8322-5644-2

– 2 – IEC 60268-3:2018 RLV  IEC 2018
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and rated values . 7
3.1 Terms and definitions . 8
3.2 Rated values . 8
4 Conditions . 9
4.1 Rated conditions and standard measuring conditions . 9
4.1.1 Overview . 9
4.1.2 Rated conditions . 10
4.1.3 Standard measuring conditions . 11
4.2 Other conditions. 11
5 Classes of operation . 11
6 Interchangeable parts . 12
7 Automatic controls . 12
8 Power supply . 12
9 Position of the volume controls . 12
10 Pre-conditioning for measurements . 13
11 Series of measurements . 13
12 Variable consumption apparatus . 13
13 Marking . 13
14 Operating environment . 14
15 Characteristics to be specified, and their methods of measurement . 14
15.1 Power supply characteristics . 14
15.1.1 Characteristics to be specified . 14
15.1.2 Method of measurement . 14
15.2 Tolerance of (long-term) power supply voltage variations . 15
15.2.1 Characteristic to be specified . 15
15.2.2 Methods of measurement . 15
15.3 Tolerance of power supply frequency variations . 16
15.3.1 Characteristics to be specified . 16
15.3.2 Methods of measurement . 16
15.4 Tolerance of power supply harmonics and ripple . 17
15.4.1 Characteristics to be specified . 17
15.4.2 Methods of measurement . 17
15.5 Input characteristics . 17
15.5.1 Rated source impedance, characteristic to be specified . 17
15.5.2 Input impedance . 17
15.5.3 Rated source e.m.f., characteristic to be specified . 19
15.5.4 Minimum source e.m.f. for rated distortion-limited output voltage . 19
15.6 Output characteristics . 20
15.6.1 Rated load impedance, characteristic to be specified . 20
15.6.2 Output source impedance . 20
15.6.3 Output voltage and power (distortion-limited) . 21
15.6.4 Maximum effective output power (distortion-limited at 10 %) . 22

15.6.5 Regulation . 23
15.6.6 Overload restoring time . 24
15.7 Limiting characteristics . 24
15.7.1 Overload source e.m.f. . 24
15.7.2 Short-term maximum output voltage and power . 25
15.7.3 Long-term maximum output voltage and power . 25
15.7.4 Temperature-limited output power . 26
15.8 Characteristics of protection circuits . 27
15.8.1 General . 27
15.8.2 Protection against potentially damaging combinations of output voltage
and current . 28
15.8.3 Characteristics of d.c. offset protection circuits . 29
15.9 Sustaining-time for rated (distortion-limited) output voltage or power . 30
15.9.1 General . 30
15.9.2 Characteristic to be specified . 31
15.9.3 Method of measurement . 31
15.10 Gain . 32
15.10.1 Voltage gain and e.m.f. gain . 32
15.10.2 Maximum e.m.f. gain . 32
15.10.3 Attenuation characteristic of the volume control . 32
15.10.4 Attenuation characteristic of balance controls for multi-channel
equipment. 33
15.11 Response . 33
15.11.1 Gain-frequency response . 33
15.11.2 Gain-limited effective frequency range . 34
15.11.3 Distortion-limited effective frequency range . 34
15.11.4 Phase-frequency response . 35
15.12 Amplitude non-linearity . 35
15.12.1 General . 35
15.12.2 Rated total harmonic distortion, characteristic to be specified . 35
15.12.3 Total harmonic distortion under standard measuring conditions . 35
15.12.4 Total harmonic distortion as a function of amplitude and frequency . 36
15.12.5 Harmonic distortion of the nth order under standard measuring
conditions . 37
15.12.6 Harmonic distortion of the nth order as a function of amplitude and
frequency . 38
15.12.7 Modulation distortion of the nth order (where n = 2 or n = 3) . 38
15.12.8 Difference-frequency distortion of the nth order (where n = 2 or n = 3) . 40
15.12.9 Dynamic intermodulation distortion (DIM) . 41
15.12.10 Total difference frequency distortion . 43
15.12.11 Weighted total harmonic distortion . 44
15.13 Noise . 45
15.13.1 Characteristic to be specified . 45
15.13.2 Method of measurement . 45
15.14 Hum . 46
15.14.1 General . 46
15.14.2 Characteristics to be specified . 46
15.14.3 Method of measurement . 47
15.15 Balanced inputs and outputs . 47
15.15.1 Balance of the input . 47

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15.15.2 Overload (distortion-limited) peak-to-peak common-mode input voltage . 48
15.15.3 Balance of the output . 49
15.16 Cross-talk and separation in multi-channel amplifiers . 50
15.16.1 Characteristics to be specified . 50
15.16.2 Method of measurement . 50
15.17 Gain and phase differences between channels in multi-channel amplifiers . 52
15.17.1 Gain difference . 52
15.17.2 Phase difference. 52
15.18 Dimensions and mass, characteristics to be specified . 53
Annex A (informative) Balanced interfaces . 60
Annex B (informative) Specification of a multi-channel amplifier. 61
B.1 General . 61
B.2 Example specification of a 5.1 channel amplifier . 61
B.3 Example specification of a 5 channel amplifier . 61
Bibliography . 63

Figure 1 – Example block diagram for multi-channel amplifier . 53
Figure 2 – Connection diagram of equipment for digital input . 54
Figure 3 – Arrangements for the Class D amplifier . 54
Figure 4 – Arrangements for measuring input impedance . 55
Figure 5 – Oscillogram when measuring overload restoring time . 56
Figure 6 – Protection against potentially damaging combinations of output voltage and
current . 57
Figure 7 – Arrangement for combining two input signals . 58
Figure 8 – Frequency spectrum below 30 kHz of the signal for measuring dynamic
intermodulation distortion . 58
Figure 9 – Arrangement for measuring the balance of a balanced input . 59
Figure 10 – Arrangement for measuring the internal impedance balance of a balanced
output . 59
Figure 11 – Arrangement for measuring the voltage symmetry of a balanced output . 59
Figure B.1 – Block diagram for a 5.1 channel surround amplifier . 61
Figure B.2 – Block diagram for a 5 channel surround amplifier . 62

Table 1 – Different rated total harmonic distortion and rated distortion-limited output
power specifications for the same amplifier . 31
Table 2 – Distortion components due to dynamic intermodulation distortion falling in
the frequency range up to 20 kHz . 42

INTERNATIONAL ELECTROTECHNICAL COMMISSION
______________
SOUND SYSTEM EQUIPMENT –
Part 3: Amplifiers
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.

– 6 – IEC 60268-3:2018 RLV  IEC 2018
International Standard IEC 60268-3 has been prepared by IEC technical committee 100:
Audio, video and multimedia systems and equipment.
This fifth edition cancels and replaces the fourth edition published in 2013. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) rated condition of digital input is newly specified;
b) tolerance of rated power supply is changed;
c) maximum effective output power is appended to output characteristics list;
d) "Terms, definitions and rated values" clause is complemented.
The text of this standard is based on the following documents:
CDV Report on voting
100/2960/CDV 100/3069/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60268 series, published under the general title Sound system
equipment, can be found on the IEC website.
This part of IEC 60268 shall be used in conjunction with IEC 60268-1:1985 and
IEC 60268-2:1987.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The “colour inside” logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this publication using a colour printer.

SOUND SYSTEM EQUIPMENT –
Part 3: Amplifiers
1 Scope
This part of IEC 60268 applies to analogue amplifiers, and the analogue parts of
analogue/digital amplifiers, which form part of a sound system for professional or household
applications. It specifies the characteristics that should be included in specifications of
amplifiers and the corresponding methods of measurement.
NOTE The methods of measurement for digital amplifiers and similar equipment are given in IEC 61606 [1] .
In general, the specified methods of measurement are those which are seen to be most
directly related to the characteristics. This does not exclude the use of other methods that
give equivalent results.
In general, the methods are based on the simplest measuring equipment which can provide
useful results. This does not exclude the use of more complex equipment that can give higher
accuracy and/or allow automatic measurement and recording of results.
Rated conditions and standard measuring conditions are specified in order to allow
measurements to be reliably repeated.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60065:2001 2014, Audio, video and similar electronic apparatus – Safety requirements
Amendment 1:2005
Amendment 2:2010
IEC 60268-1:1985, Sound system equipment – Part 1: General
IEC 60268-1:1985/AMD1:1988
IEC 60268-1:1985/AMD2:1988
IEC 60268-2:1987, Sound system equipment – Part 2: Explanation of general terms and
calculation methods
Amendment 1:1991
IEC 60417:2002, Graphical symbols for use on equipment
Available from: http://www.graphical-symbols.info/equipment – 12-month subscription to regularly
updated online database comprising all graphical symbols published in IEC 60417
IEC 60958:2016 (all parts), Series, Digital audio interface
__________
Numbers in square brackets refer to the Bibliography.

– 8 – IEC 60268-3:2018 RLV  IEC 2018
IEC 61000-4-13:2002, Electromagnetic compatibility (EMC) – Part 4-13: Testing and
measurement techniques – Harmonics and interharmonics including mains signalling at a.c.
power port, low frequency immunity tests
IEC 61000-4-13:2002/AMD1:2009
IEC 61000-4-13:2002/AMD2:2015
IEC 61000-4-17:1999, Electromagnetic Compatibility (EMC) – Part 4-17: Testing and
measurement techniques – Ripple on d.c. input power port immunity test
IEC 61000-4-17:1999/AMD1:2001
IEC 61000-4-17:1999/AMD2:2008
IEC 61000-4-29:2000, Electromagnetic Compatibility (EMC) – Part 4-29: Testing and
measurement techniques – Voltage dips, short interruptions and voltage variations on d.c.
input power ports immunity tests
IEC 61606-1:2009, Audio and audiovisual equipment – Digital audio parts – Basic
measurement methods of audio characteristics – Part 1: General
IEC 61883-6:2014, Consumer audio/video equipment – Digital interface – Part 6: Audio and
music data transmission protocol
IEC 61938:1996, Audio, video and audiovisual systems – Interconnections and matching
values – Preferred matching values of analogue signals
IEC 61938:2013, Multimedia systems – Guide to the recommended characteristics of
analogue interfaces to achieve interoperability
3 Terms, definitions and rated values
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
class A
class of operation in which the current in each active device supplying the load current is
greater than zero throughout each cycle of the signal for all values of load current up to, and
including, the value determined by the rated output power or voltage and the rated load
impedance
3.1.2
class B
class of operation in which the current in each active device supplying the load current is
equal to zero for exactly one-half of each cycle of load current
Note 1 to entry: In common usage, the term Class B is extended to the case where current flows for slightly more
than one half-cycle.
Note 2 to entry: Classes G and H are modifications of class B with improved efficiency.

3.1.3
class AB
class of operation in which the current in at least one of the active devices supplying the load
current is zero for some part of each cycle of load current for some range of values of load
current not exceeding the value defined by the rated output power or voltage and the rated
load impedance
Note 1 to entry: At sufficiently low signal levels, a Class AB amplifier usually operates in Class A.
3.1.4
class D
class of operation in which all active power devices are switched between fully on and fully off
at a rate faster than the highest frequency of interest, and where the wanted signal is
encoded in the switching pattern
Note 1 to entry: Other classes of operation have been commercialized but no formal definitions of such classes
have been submitted for standardization.
3.2 Rated values
A full explanation of the term "rated" is given in IEC 60268-2.
The rated conditions for amplifiers are:
– rated power supply voltage;
– rated source impedance;
– rated source e.m.f.;
– rated load impedance;
– rated total harmonic distortion, or rated (distortion-limited) output voltage or power;
– rated mechanical and climatic conditions.
NOTE 1 Total harmonic distortion and (distortion-limited) output voltage or power are interdependent. Both cannot
be taken as rated conditions simultaneously because normally a given sample amplifier produces less than rated
total harmonic distortion at rated output voltage or power.
NOTE 2 If the power supply frequency is critical, it is also a rated condition.
To obtain the correct conditions for measurements, the values for the above-mentioned rated
conditions shall be taken from the manufacturer's specification. These values themselves are
not subject to measurement but they constitute the basis for measuring the other characteristics.
Methods of measurement for these other characteristics are given in this document and the
manufacturer is either required or permitted to state 'rated values' for these characteristics in
the specification of the equipment. These include
– rated voltage gain;
– rated distortion limited output voltage or power (when not adopted as a rated condition);
– rated signal-to-noise ratio;
– rated equivalent noise source e.m.f.
4 Conditions
4.1 Rated conditions and standard measuring conditions
4.1.1 Overview
For convenience in specifying how amplifiers shall be set up for measurement, sets of
conditions are specified in this document, under the titles of "Rated conditions" and "Standard
measuring conditions".
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4.1.2 Rated conditions
4.1.2.1 Analogue input
An amplifier, considered as a four-terminal network with regard to a specified pair of input
terminals and a specified pair of output terminals, shall be understood to be working under
rated conditions when the following conditions are fulfilled:
a) the amplifier is connected to its rated power supply;
b) the source e.m.f. is connected in series with the rated source impedance to the input
terminals;
NOTE 1 Multi-channel amplifiers can be specified with any number of channels driven, or all channels. See
Annex B. The input signal can be applied simultaneously to all inputs of similar channels.
c) the output terminals are terminated with the rated load impedance;
NOTE 2 For the measurement of Class D amplifiers, the low pass filter can be connected between the
analyser and the rated load impedance. The low pass filter (analogue) is given in IEC 61606-1 (see Figure 3).
d) the terminals which are not used during the measurement are terminated, if necessary, as
specified by the manufacturer;
e) the source e.m.f. is a sinusoidal voltage equal to the rated source e.m.f. at an appropriate
frequency. Unless there is a special reason to the contrary, this frequency shall be the
standard reference frequency of 1 000 Hz according to IEC 60268-1.
Such a reason could be that the standard reference frequency is outside or near the limit
of the effective frequency range of the amplifier;
f) the volume control, if any, is set to such a position that the rated distortion-limited output
voltage appears at the output terminals;
g) the tone controls, if any, are set to a specified position to give the specified frequency
response, generally the flat frequency response;
h) the balance control(s), if any, is (are) set to the mechanical central position;
i) the rated mechanical and climatic conditions according to IEC 60268-1 are complied with.
Figure 1 shows block diagrams of amplifiers with some rated conditions stated.
Amplifiers for which the rated distortion-limited output power exceeds the rated temperature-
limited output power are likely to be subject to overheating when operated under rated
conditions for an extended period of time. For these amplifiers, rated conditions shall be
maintained for no longer than can be tolerated by the amplifier.
4.1.2.2 Digital input
The amplifier and measuring instrument is connected as shown in Figure 2. The input signal is
a digital audio signal and the output signal is an analogue signal. All the digital specifications
are described in IEC 61606-1. The digital interface can be according to IEC 60958 or
IEC 61883-6, or other interfaces having the same specification as in 3.1 of IEC 61606-1. The
source e.m.f. for digital input is the signal level of the digital sine signal generator specified in
4.6.2 of IEC 61606-1:2009:
a) the amplifier is connected to its rated power supply;
b) input signal is adjusted to:
– frequency: 997 Hz;
– signal level: full-scale level.
NOTE 1 Multi-channel amplifiers can be specified with any number of channels driven, or all channels. See
Annex B. The input signal can be applied simultaneously to all inputs of similar channels.
NOTE 2 The standard reference frequency of 997 Hz is according to 4.3 of IEC 61606-1:2009.
c) the output terminals are terminated with the rated load impedance;

NOTE 3 For the measurement of Class D amplifiers, the low pass filter can be connected between the
analyser and the rated load impedance. The low pass filter (analogue) is given in IEC 61606-1 (see Figure 2).
d) the terminals that are not used during the measurement are terminated, if necessary, as
specified by the manufacturer;
e) the volume control, if any, is set to such a position that the rated distortion-limited output
voltage appears at the output terminals;
f) the tone controls, if any, are set to a specified position to give the specified frequency
response, generally the flat frequency response;
g) the balance control(s), if any, is (are) set to the mechanical central position;
h) the rated mechanical and climatic conditions according to IEC 60268-1 are complied with.
Amplifiers for which the rated distortion-limited output power exceeds the rated temperature-
limited output power are likely to be subject to overheating when operated under rated
conditions for an extended period of time. For these amplifiers, rated conditions shall be
maintained for no longer than can be tolerated by the amplifier.
4.1.3 Standard measuring conditions
These are obtained by bringing the amplifier under rated conditions (see 4.1.2) and then
reducing the source e.m.f. to a level of −10 dB referred to the rated source e.m.f.
4.2 Other conditions
If supplementary data of the amplifier are presented, applying to other than the rated or
standard measuring conditions, for example at different frequencies or at different settings of
controls, then the conditions shall be fully defined in the presentation. These conditions shall,
if possible, be chosen according to the recommendations made in the relevant clauses of this
document.
The procedures for supplementary measurements may be derived from the measurement
procedures given for the standard conditions. If special precautions are necessary to ensure
accuracy, these shall be indicated together with the measurement procedure involved.
5 Classes of operation
Class A: in which the current in each active device supplying the load current is greater than
zero throughout each cycle of the signal for all values of load current up to and including the
value determined by the rated output power or voltage and the rated load impedance.
Class B: in which the current in each active device supplying the load current is equal to zero
for exactly one-half of each cycle of load current.
NOTE 1 In common usage, the term Class B is extended to the case where current flows for slightly more than
one half-cycle.
NOTE 2 Classes G and H are modifications of class B with improved efficiency.
Class AB: in which the current in at least one of the active devices supplying the load current
is zero for some part of each cycle of load current for some range of values of load current not
exceeding the value defined by the rated output power or voltage and the rated load
impedance.
NOTE 3 At sufficiently low signal levels, a Class AB amplifier usually operates in Class A.
Class D: in which all active power devices are switched between fully on and fully off at a rate
faster than the highest frequency of interest, and where the wanted signal is encoded in the
switching pattern.
– 12 – IEC 60268-3:2018 RLV  IEC 2018
NOTE 4 Other classes of operation have been commercialized but no formal definitions of such classes have
been submitted for standardization.
Amplifier classes are classified according to the operation of an amplifying stage. These
classes are defined as Class A, Class B, Class AB and Class D; detailed definitions are given
in 3.1.
6 Interchangeable parts
For type measurements, interchangeable parts shall have characteristics as close as is
reasonably practicable to the mean characteristics specified for these parts.
For measurements on a particular sample, the interchangeable parts supplied with that
amplifier shall be used.
7 Automatic controls
The amplifier may contain automatic control circuits such as limiters, compressors, expanders
and electronic fader circuits. These circuits make certain characteristics of the amplifier
dependent either on a signal passing through the amplifier itself or on an external control
signal. When measuring the characteristics of such an amplifier, the automatic control circuits
shall be disabled, except when measuring their characteristics.
8 Power supply
Measurements shall be made with the amplifier connected to rated power supply. Care shall
be taken to maintain the power supply voltage at the rated value during the measurement. If
the manufacturer claims power supply voltage tolerances exceeding ±10 %, then the
characteristics to be specified shall also be stated for the upper and lower limits of these
tolerances. The tolerance of the supply voltages should be ± 1 % or less. A tolerance of up to
± 10 % may be allowed if the results of the measurements are not noticeably affected.
Additional measurements may be made at the upper and lower limits claimed as tolerable for
the power supply voltage, the power supply frequency and the a.c. power supply harmonics or
the d.c. power supply ripple.
WARNING – The power supply voltage tolerances specified by the manufacturer shall
not be exceeded.
9 Position of the volume controls
If a characteristic is measured at only one position of the volume control, the control shall be
at the position corresponding to rated conditions (see 4.1.2), unless a maximum or minimum
position of the control is inherent in the characteristic to be measured.
If the characteristic is to be measured for several settings of the volume control, then
the position for rated conditions shall be included, other preferred settings being maximum,
and −3 dB, −6 dB, −10 dB, −20 dB and −40 dB with respect to the setting for rated conditions.
Volume controls belonging to channels not being measured shall, if possible, be put in the
minimum position, unless otherwise stated.

10 Pre-conditioning for measurements
Before beginning measurements on an amplifier, it shall be operated under approximately
standard measuring conditions for a period of 1 h, or as specified by the manufacturer.
Before operating the amplifier the manufacturer's instructions concerning initial operation
should be studied.
The amplifier is then brought under standard measuring conditions (see 4.1.3). Due to internal
heating, the output voltage may subsequently vary with time. Unless excessive, this effect is
ignored during the pre-conditioning period. When the pre-conditioning period is over, the
amplifier shall be brought under rated conditions or standard measuring conditions, as
required.
11 Series of measurements
If a series of measurements is made, the amplifier should preferably be maintained under
standard measuring conditions in the periods between measurements.
If the amplifier has to be put out of operation for an extended period between measurements,
then pre-conditioning according to Clause 10 shall be repeated before each set of
measurements, unless this can be shown to be unnecessary.
12 Variable consumption apparatus
Sound system equipment shall be considered as variable consumption apparatus if it contains
one or more power amplifiers operating in the Class AB, B, or D modes, in which the d.c.
power supply for the output stages is either electronically regulated by means of series control
elements or is not regulated.
NOTE 1 Variable consumption apparatus is defined in IEC 60065:1976 as "apparatus in which the power
consumption can vary by more than 15 % due to changes in load impedances of the output circuit or in signal
parameters", but no definition appears in later editions.
NOTE 2 Where the d.c. supply is regulated by shunt control elements, the power consumption is usually, if not
always, substantially constant. The apparatus, however, behaves in some respects as a variable consumption
apparatus, and, in particular, the text of 15.7.4.1 still applies.
All the measurements contained in this document may be performed on variable consumption
apparatus, in most cases with no special problems. However, certain problems may occur in
the measurement of hum and rated distortion-limited output power, and some additional
measurements are valuable in assessing the performance of such apparatus (see the note of
15.6.3.1 and item c) of 15.14.3).
13 Marking
Principles for marking the terminals and controls are given in IEC 60268-1.
Marking may concern:
– personal safety and prevention of spread of fire, in the sense of IEC 60065;
– safety in case of faulty connections;
– indications relating to normal operation, according to IEC 60417.
__________
IEC 60065:1976, Safety requirements for mains operated electronic and related apparatus for household and
similar general use
– 14 – IEC 60268-3:2018 RLV  IEC 2018
Marking can neither prevent incorrect operation nor provide complete operating instructions. It
therefore has to be considered in conjunction with adequate means for preventing dangerous
or faulty operation, and with the directions for use included in the user's instructions. Care
should be taken that marking is unambiguous and as clearly understandable as possible.
Terminals for the interconnection of equipment, which are inaccessible without the use of a
tool when the equipment has been installed, shall be clearly and unambiguously identified
with respect to the manufacturer's instructions for installation. It may be assumed that t
...

IEC 60268-3 ®
Edition 5.0 2018-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Sound system equipment –
Part 3: Amplifiers
Équipements pour systèmes électroacoustiques –
Partie 3: Amplificateurs
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IEC 60268-3 ®
Edition 5.0 2018-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Sound system equipment –
Part 3: Amplifiers
Équipements pour systèmes électroacoustiques –

Partie 3: Amplificateurs
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.160.10 ISBN 978-2-8322-6243-6

– 2 – IEC 60268-3:2018  IEC 2018
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and rated values . 8
3.1 Terms and definitions . 8
3.2 Rated values . 9
4 Conditions . 9
4.1 Rated conditions and standard measuring conditions . 9
4.1.1 Overview . 9
4.1.2 Rated conditions . 10
4.1.3 Standard measuring conditions . 11
4.2 Other conditions. 11
5 Classes of operation . 11
6 Interchangeable parts . 11
7 Automatic controls . 11
8 Power supply . 12
9 Position of the volume controls . 12
10 Pre-conditioning for measurements . 12
11 Series of measurements . 12
12 Variable consumption apparatus . 12
13 Marking . 13
14 Operating environment . 13
15 Characteristics to be specified, and their methods of measurement . 13
15.1 Power supply characteristics . 13
15.1.1 Characteristics to be specified . 13
15.1.2 Method of measurement . 14
15.2 Tolerance of (long-term) power supply voltage variations . 14
15.2.1 Characteristic to be specified . 14
15.2.2 Methods of measurement . 15
15.3 Tolerance of power supply frequency variations . 15
15.3.1 Characteristics to be specified . 15
15.3.2 Methods of measurement . 16
15.4 Tolerance of power supply harmonics and ripple . 16
15.4.1 Characteristics to be specified . 16
15.4.2 Methods of measurement . 17
15.5 Input characteristics . 17
15.5.1 Rated source impedance, characteristic to be specified . 17
15.5.2 Input impedance . 17
15.5.3 Rated source e.m.f., characteristic to be specified . 19
15.5.4 Minimum source e.m.f. for rated distortion-limited output voltage . 19
15.6 Output characteristics . 19
15.6.1 Rated load impedance, characteristic to be specified . 19
15.6.2 Output source impedance . 20
15.6.3 Output voltage and power (distortion-limited) . 20
15.6.4 Maximum effective output power (distortion-limited at 10 %) . 22

15.6.5 Regulation . 23
15.6.6 Overload restoring time . 24
15.7 Limiting characteristics . 24
15.7.1 Overload source e.m.f. . 24
15.7.2 Short-term maximum output voltage and power . 24
15.7.3 Long-term maximum output voltage and power . 25
15.7.4 Temperature-limited output power . 26
15.8 Characteristics of protection circuits . 27
15.8.1 General . 27
15.8.2 Protection against potentially damaging combinations of output voltage
and current . 27
15.8.3 Characteristics of d.c. offset protection circuits . 28
15.9 Sustaining-time for rated (distortion-limited) output voltage or power . 29
15.9.1 General . 29
15.9.2 Characteristic to be specified . 31
15.9.3 Method of measurement . 31
15.10 Gain . 31
15.10.1 Voltage gain and e.m.f. gain . 31
15.10.2 Maximum e.m.f. gain . 31
15.10.3 Attenuation characteristic of the volume control . 32
15.10.4 Attenuation characteristic of balance controls for multi-channel
equipment. 32
15.11 Response . 33
15.11.1 Gain-frequency response . 33
15.11.2 Gain-limited effective frequency range . 33
15.11.3 Distortion-limited effective frequency range . 34
15.11.4 Phase-frequency response . 34
15.12 Amplitude non-linearity . 34
15.12.1 General . 34
15.12.2 Rated total harmonic distortion, characteristic to be specified . 35
15.12.3 Total harmonic distortion under standard measuring conditions . 35
15.12.4 Total harmonic distortion as a function of amplitude and frequency . 35
15.12.5 Harmonic distortion of the nth order under standard measuring
conditions . 36
15.12.6 Harmonic distortion of the nth order as a function of amplitude and
frequency . 37
15.12.7 Modulation distortion of the nth order (where n = 2 or n = 3) . 37
15.12.8 Difference-frequency distortion of the nth order (where n = 2 or n = 3) . 39
15.12.9 Dynamic intermodulation distortion (DIM) . 40
15.12.10 Total difference frequency distortion . 42
15.12.11 Weighted total harmonic distortion . 44
15.13 Noise . 44
15.13.1 Characteristic to be specified . 44
15.13.2 Method of measurement . 45
15.14 Hum . 45
15.14.1 General . 45
15.14.2 Characteristics to be specified . 45
15.14.3 Method of measurement . 46
15.15 Balanced inputs and outputs . 46
15.15.1 Balance of the input . 46

– 4 – IEC 60268-3:2018  IEC 2018
15.15.2 Overload (distortion-limited) peak-to-peak common-mode input voltage . 47
15.15.3 Balance of the output . 48
15.16 Cross-talk and separation in multi-channel amplifiers . 49
15.16.1 Characteristics to be specified . 49
15.16.2 Method of measurement . 50
15.17 Gain and phase differences between channels in multi-channel amplifiers . 51
15.17.1 Gain difference . 51
15.17.2 Phase difference. 51
15.18 Dimensions and mass, characteristics to be specified . 52
Annex A (informative) Balanced interfaces . 58
Annex B (informative) Specification of a multi-channel amplifier. 59
B.1 General . 59
B.2 Example specification of a 5.1 channel amplifier . 59
B.3 Example specification of a 5 channel amplifier . 59
Bibliography . 61

Figure 1 – Example block diagram for multi-channel amplifier . 52
Figure 2 – Connection diagram of equipment for digital input . 52
Figure 3 – Arrangements for the Class D amplifier . 53
Figure 4 – Arrangements for measuring input impedance . 53
Figure 5 – Oscillogram when measuring overload restoring time . 54
Figure 6 – Protection against potentially damaging combinations of output voltage and
current . 55
Figure 7 – Arrangement for combining two input signals . 55
Figure 8 – Frequency spectrum below 30 kHz of the signal for measuring dynamic
intermodulation distortion . 56
Figure 9 – Arrangement for measuring the balance of a balanced input . 56
Figure 10 – Arrangement for measuring the internal impedance balance of a balanced
output . 56
Figure 11 – Arrangement for measuring the voltage symmetry of a balanced output . 57
Figure B.1 – Block diagram for a 5.1 channel surround amplifier . 59
Figure B.2 – Block diagram for a 5 channel surround amplifier . 60

Table 1 – Different rated total harmonic distortion and rated distortion-limited output
power specifications for the same amplifier . 30
Table 2 – Distortion components due to dynamic intermodulation distortion falling in
the frequency range up to 20 kHz . 41

INTERNATIONAL ELECTROTECHNICAL COMMISSION
______________
SOUND SYSTEM EQUIPMENT –
Part 3: Amplifiers
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60268-3 has been prepared by IEC technical committee 100:
Audio, video and multimedia systems and equipment.
This fifth edition cancels and replaces the fourth edition published in 2013. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) rated condition of digital input is newly specified;
b) tolerance of rated power supply is changed;
c) maximum effective output power is appended to output characteristics list;
d) "Terms, definitions and rated values" clause is complemented.
This bilingual version (2018-12) corresponds to the English version, published in 2018-04.

– 6 – IEC 60268-3:2018  IEC 2018
The text of this standard is based on the following documents:
CDV Report on voting
100/2960/CDV 100/3069/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60268 series, published under the general title Sound system
equipment, can be found on the IEC website.
This part of IEC 60268 shall be used in conjunction with IEC 60268-1:1985 and
IEC 60268-2:1987.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
The French version of this standard has not been voted upon.

SOUND SYSTEM EQUIPMENT –
Part 3: Amplifiers
1 Scope
This part of IEC 60268 applies to analogue amplifiers, and the analogue parts of
analogue/digital amplifiers, which form part of a sound system for professional or household
applications. It specifies the characteristics that should be included in specifications of
amplifiers and the corresponding methods of measurement.
NOTE The methods of measurement for digital amplifiers and similar equipment are given in IEC 61606 [1] .
In general, the specified methods of measurement are those which are seen to be most
directly related to the characteristics. This does not exclude the use of other methods that
give equivalent results.
In general, the methods are based on the simplest measuring equipment which can provide
useful results. This does not exclude the use of more complex equipment that can give higher
accuracy and/or allow automatic measurement and recording of results.
Rated conditions and standard measuring conditions are specified in order to allow
measurements to be reliably repeated.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60065:2014, Audio, video and similar electronic apparatus – Safety requirements
IEC 60268-1:1985, Sound system equipment – Part 1: General
IEC 60268-1:1985/AMD1:1988
IEC 60268-1:1985/AMD2:1988
IEC 60268-2:1987, Sound system equipment – Part 2: Explanation of general terms and
calculation methods
Amendment 1:1991
IEC 60417:2002, Graphical symbols for use on equipment – 12-month subscription to
regularly updated online database comprising all graphical symbols published in IEC 60417
IEC 60958:2016 (all parts), Series, Digital audio interface
__________
Numbers in square brackets refer to the Bibliography.

– 8 – IEC 60268-3:2018  IEC 2018
IEC 61000-4-13:2002, Electromagnetic compatibility (EMC) – Part 4-13: Testing and
measurement techniques – Harmonics and interharmonics including mains signalling at a.c.
power port, low frequency immunity tests
IEC 61000-4-13:2002/AMD1:2009
IEC 61000-4-13:2002/AMD2:2015
IEC 61000-4-17:1999, Electromagnetic Compatibility (EMC) – Part 4-17: Testing and
measurement techniques – Ripple on d.c. input power port immunity test
IEC 61000-4-17:1999/AMD1:2001
IEC 61000-4-17:1999/AMD2:2008
IEC 61000-4-29:2000, Electromagnetic Compatibility (EMC) – Part 4-29: Testing and
measurement techniques – Voltage dips, short interruptions and voltage variations on d.c.
input power ports immunity tests
IEC 61606-1:2009, Audio and audiovisual equipment – Digital audio parts – Basic
measurement methods of audio characteristics – Part 1: General
IEC 61883-6:2014, Consumer audio/video equipment – Digital interface – Part 6: Audio and
music data transmission protocol
IEC 61938:2013, Multimedia systems – Guide to the recommended characteristics of
analogue interfaces to achieve interoperability
3 Terms, definitions and rated values
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
class A
class of operation in which the current in each active device supplying the load current is
greater than zero throughout each cycle of the signal for all values of load current up to, and
including, the value determined by the rated output power or voltage and the rated load
impedance
3.1.2
class B
class of operation in which the current in each active device supplying the load current is
equal to zero for exactly one-half of each cycle of load current
Note 1 to entry: In common usage, the term Class B is extended to the case where current flows for slightly more
than one half-cycle.
Note 2 to entry: Classes G and H are modifications of class B with improved efficiency.
3.1.3
class AB
class of operation in which the current in at least one of the active devices supplying the load
current is zero for some part of each cycle of load current for some range of values of load
current not exceeding the value defined by the rated output power or voltage and the rated
load impedance
Note 1 to entry: At sufficiently low signal levels, a Class AB amplifier usually operates in Class A.
3.1.4
class D
class of operation in which all active power devices are switched between fully on and fully off
at a rate faster than the highest frequency of interest, and where the wanted signal is
encoded in the switching pattern
Note 1 to entry: Other classes of operation have been commercialized but no formal definitions of such classes
have been submitted for standardization.
3.2 Rated values
A full explanation of the term "rated" is given in IEC 60268-2.
The rated conditions for amplifiers are:
– rated power supply voltage;
– rated source impedance;
– rated source e.m.f.;
– rated load impedance;
– rated total harmonic distortion, or rated (distortion-limited) output voltage or power;
– rated mechanical and climatic conditions.
NOTE 1 Total harmonic distortion and (distortion-limited) output voltage or power are interdependent. Both cannot
be taken as rated conditions simultaneously because normally a given sample amplifier produces less than rated
total harmonic distortion at rated output voltage or power.
NOTE 2 If the power supply frequency is critical, it is also a rated condition.
To obtain the correct conditions for measurements, the values for the above-mentioned rated
conditions shall be taken from the manufacturer's specification. These values themselves are
not subject to measurement but they constitute the basis for measuring the other characteristics.
Methods of measurement for these other characteristics are given in this document and the
manufacturer is either required or permitted to state 'rated values' for these characteristics in
the specification of the equipment. These include
– rated voltage gain;
– rated distortion limited output voltage or power (when not adopted as a rated condition);
– rated signal-to-noise ratio;
– rated equivalent noise source e.m.f.
4 Conditions
4.1 Rated conditions and standard measuring conditions
4.1.1 Overview
For convenience in specifying how amplifiers shall be set up for measurement, sets of
conditions are specified in this document, under the titles of "Rated conditions" and "Standard
measuring conditions".
– 10 – IEC 60268-3:2018  IEC 2018
4.1.2 Rated conditions
4.1.2.1 Analogue input
An amplifier, considered as a four-terminal network with regard to a specified pair of input
terminals and a specified pair of output terminals, shall be understood to be working under
rated conditions when the following conditions are fulfilled:
a) the amplifier is connected to its rated power supply;
b) the source e.m.f. is connected in series with the rated source impedance to the input
terminals;
NOTE 1 Multi-channel amplifiers can be specified with any number of channels driven, or all channels. See
Annex B. The input signal can be applied simultaneously to all inputs of similar channels.
c) the output terminals are terminated with the rated load impedance;
NOTE 2 For the measurement of Class D amplifiers, the low pass filter can be connected between the
analyser and the rated load impedance. The low pass filter (analogue) is given in IEC 61606-1 (see Figure 3).
d) the terminals which are not used during the measurement are terminated, if necessary, as
specified by the manufacturer;
e) the source e.m.f. is a sinusoidal voltage equal to the rated source e.m.f. at an appropriate
frequency. Unless there is a special reason to the contrary, this frequency shall be the
standard reference frequency of 1 000 Hz according to IEC 60268-1.
Such a reason could be that the standard reference frequency is outside or near the limit
of the effective frequency range of the amplifier;
f) the volume control, if any, is set to such a position that the rated distortion-limited output
voltage appears at the output terminals;
g) the tone controls, if any, are set to a specified position to give the specified frequency
response, generally the flat frequency response;
h) the balance control(s), if any, is (are) set to the mechanical central position;
i) the rated mechanical and climatic conditions according to IEC 60268-1 are complied with.
Figure 1 shows block diagrams of amplifiers with some rated conditions stated.
Amplifiers for which the rated distortion-limited output power exceeds the rated temperature-
limited output power are likely to be subject to overheating when operated under rated
conditions for an extended period of time. For these amplifiers, rated conditions shall be
maintained for no longer than can be tolerated by the amplifier.
4.1.2.2 Digital input
The amplifier and measuring instrument is connected as shown in Figure 2. The input signal is
a digital audio signal and the output signal is an analogue signal. All the digital specifications
are described in IEC 61606-1. The digital interface can be according to IEC 60958 or
IEC 61883-6, or other interfaces having the same specification as in 3.1 of IEC 61606-1. The
source e.m.f. for digital input is the signal level of the digital sine signal generator specified in
4.6.2 of IEC 61606-1:2009:
a) the amplifier is connected to its rated power supply;
b) input signal is adjusted to:
– frequency: 997 Hz;
– signal level: full-scale level.
NOTE 1 Multi-channel amplifiers can be specified with any number of channels driven, or all channels. See
Annex B. The input signal can be applied simultaneously to all inputs of similar channels.
NOTE 2 The standard reference frequency of 997 Hz is according to 4.3 of IEC 61606-1:2009.
c) the output terminals are terminated with the rated load impedance;

NOTE 3 For the measurement of Class D amplifiers, the low pass filter can be connected between the
analyser and the rated load impedance. The low pass filter (analogue) is given in IEC 61606-1 (see Figure 2).
d) the terminals that are not used during the measurement are terminated, if necessary, as
specified by the manufacturer;
e) the volume control, if any, is set to such a position that the rated distortion-limited output
voltage appears at the output terminals;
f) the tone controls, if any, are set to a specified position to give the specified frequency
response, generally the flat frequency response;
g) the balance control(s), if any, is (are) set to the mechanical central position;
h) the rated mechanical and climatic conditions according to IEC 60268-1 are complied with.
Amplifiers for which the rated distortion-limited output power exceeds the rated temperature-
limited output power are likely to be subject to overheating when operated under rated
conditions for an extended period of time. For these amplifiers, rated conditions shall be
maintained for no longer than can be tolerated by the amplifier.
4.1.3 Standard measuring conditions
These are obtained by bringing the amplifier under rated conditions (see 4.1.2) and then
reducing the source e.m.f. to a level of −10 dB referred to the rated source e.m.f.
4.2 Other conditions
If supplementary data of the amplifier are presented, applying to other than the rated or
standard measuring conditions, for example at different frequencies or at different settings of
controls, then the conditions shall be fully defined in the presentation. These conditions shall,
if possible, be chosen according to the recommendations made in the relevant clauses of this
document.
The procedures for supplementary measurements may be derived from the measurement
procedures given for the standard conditions. If special precautions are necessary to ensure
accuracy, these shall be indicated together with the measurement procedure involved.
5 Classes of operation
Amplifier classes are classified according to the operation of an amplifying stage. These
classes are defined as Class A, Class B, Class AB and Class D; detailed definitions are given
in 3.1.
6 Interchangeable parts
For type measurements, interchangeable parts shall have characteristics as close as is
reasonably practicable to the mean characteristics specified for these parts.
For measurements on a particular sample, the interchangeable parts supplied with that
amplifier shall be used.
7 Automatic controls
The amplifier may contain automatic control circuits such as limiters, compressors, expanders
and electronic fader circuits. These circuits make certain characteristics of the amplifier
dependent either on a signal passing through the amplifier itself or on an external control
signal. When measuring the characteristics of such an amplifier, the automatic control circuits
shall be disabled, except when measuring their characteristics.

– 12 – IEC 60268-3:2018  IEC 2018
8 Power supply
Measurements shall be made with the amplifier connected to rated power supply. Care shall
be taken to maintain the power supply voltage at the rated value during the measurement.
The tolerance of the supply voltages should be ± 1 % or less. A tolerance of up to ± 10 % may
be allowed if the results of the measurements are not noticeably affected.
Additional measurements may be made at the upper and lower limits claimed as tolerable for
the power supply voltage, the power supply frequency and the a.c. power supply harmonics or
the d.c. power supply ripple.
WARNING – The power supply voltage tolerances specified by the manufacturer shall
not be exceeded.
9 Position of the volume controls
If a characteristic is measured at only one position of the volume control, the control shall be
at the position corresponding to rated conditions (see 4.1.2), unless a maximum or minimum
position of the control is inherent in the characteristic to be measured.
If the characteristic is to be measured for several settings of the volume control, then
the position for rated conditions shall be included, other preferred settings being maximum,
and −3 dB, −6 dB, −10 dB, −20 dB and −40 dB with respect to the setting for rated conditions.
Volume controls belonging to channels not being measured shall, if possible, be put in the
minimum position, unless otherwise stated.
10 Pre-conditioning for measurements
Before beginning measurements on an amplifier, it shall be operated under approximately
standard measuring conditions for a period of 1 h, or as specified by the manufacturer.
Before operating the amplifier the manufacturer's instructions concerning initial operation
should be studied.
The amplifier is then brought under standard measuring conditions (see 4.1.3). Due to internal
heating, the output voltage may subsequently vary with time. Unless excessive, this effect is
ignored during the pre-conditioning period. When the pre-conditioning period is over, the
amplifier shall be brought under rated conditions or standard measuring conditions, as
required.
11 Series of measurements
If a series of measurements is made, the amplifier should preferably be maintained under
standard measuring conditions in the periods between measurements.
If the amplifier has to be put out of operation for an extended period between measurements,
then pre-conditioning according to Clause 10 shall be repeated before each set of
measurements, unless this can be shown to be unnecessary.
12 Variable consumption apparatus
Sound system equipment shall be considered as variable consumption apparatus if it contains
one or more power amplifiers operating in the Class AB, B, or D modes, in which the d.c.

power supply for the output stages is either electronically regulated by means of series control
elements or is not regulated.
NOTE 1 Variable consumption apparatus is defined in IEC 60065:1976 as "apparatus in which the power
consumption can vary by more than 15 % due to changes in load impedances of the output circuit or in signal
parameters", but no definition appears in later editions.
NOTE 2 Where the d.c. supply is regulated by shunt control elements, the power consumption is usually, if not
always, substantially constant. The apparatus, however, behaves in some respects as a variable consumption
apparatus, and, in particular, the text of 15.7.4.1 still applies.
All the measurements contained in this document may be performed on variable consumption
apparatus, in most cases with no special problems. However, certain problems may occur in
the measurement of hum and rated distortion-limited output power, and some additional
measurements are valuable in assessing the performance of such apparatus (see the note of
15.6.3.1 and item c) of 15.14.3).
13 Marking
Principles for marking the terminals and controls are given in IEC 60268-1.
Marking may concern:
– personal safety and prevention of spread of fire, in the sense of IEC 60065;
– safety in case of faulty connections;
– indications relating to normal operation, according to IEC 60417.
Marking can neither prevent incorrect operation nor provide complete operating instructions. It
therefore has to be considered
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