SIST EN IEC 60268-3:2019

SLOVENSKI STANDARD
01-februar-2019
1DGRPHãþD
SIST EN 60268-3:2013
(OHNWURDNXVWLþQHQDSUDYHGHO2MDþHYDOQLNL
Sound system equipment - Part 3: Amplifiers
Elektroakustische Geräte - Teil 3: Verstärker
Equipements pour systèmes électroacoustiques - Partie 3: Amplificateurs
Ta slovenski standard je istoveten z: EN IEC 60268-3:2018
ICS:
33.160.10 2MDþHYDOQLNL Amplifiers
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60268-3

NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2018
ICS 33.160.10 Supersedes EN 60268-3:2013
English Version
Sound system equipment - Part 3: Amplifiers
(IEC 60268-3:2018)
Equipements pour systèmes électroacoustiques - Partie 3: Elektroakustische Geräte - Teil 3: Verstärker
amplificateurs (IEC 60268-3:2018)
(IEC 60268-3:2018)
This European Standard was approved by CENELEC on 2018-05-30. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,
Switzerland, Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60268-3:2018 E

European foreword
The text of document 100/2960/CDV, future edition 5 of IEC 60268-3, prepared by IEC/TC 100 "Audio,
video and multimedia systems and equipment" was submitted to the IEC-CENELEC parallel vote and
approved by CENELEC as EN IEC 60268-3:2018.

The following dates are fixed:
• latest date by which the document has to be (dop) 2019-02-28
implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2021-05-30
• latest date by which the national
standards conflicting with the
document have to be withdrawn
This document supersedes EN 60268-3:2013.

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Endorsement notice
The text of the International Standard IEC 60268-3:2018 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 61606 series NOTE Harmonized as EN 61606 series.
IEC 60268-5:2003 NOTE Harmonized as EN 60268-5:2003.
IEC 60268-5:2003/A1:2007 NOTE Harmonized as EN 60268-5:2003/A1:2009.

Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60065 (mod) 2014 Audio, video and similar electronic EN 60065 2014
apparatus - Safety requirements
- -  + A11 2017
IEC 60268-1 1985 Sound system equipment -- Part 1: HD 483.1 S2 1989
General
+ A1 1988  - -
+ A2 1988  - -
IEC 60268-2 1987 Sound system equipment - Part 2: HD 483.2 S2 1993
Explanation of general terms and
calculation methods
+ A1 1991  - -
IEC 60417 2002 Graphical symbols for use on equipment - -
IEC 60958 series Digital audio interface EN 60958 series
IEC 61000-4-13 2002 Electromagnetic compatibility (EMC) -- Part EN 61000-4-13 2002
4-13: Testing and measurement
techniques - Harmonics and
interharmonics including mains signaling at
a.c. power port, low frequency immunity
tests
+ A1 2009  + A1 2009
+ A2 2015  + A2 2016
IEC 61000-4-17 1999 Electromagnetic compatibility (EMC) -- Part EN 61000-4-17 1999
4-17: Testing and measurement
techniques - Ripple on d.c. input power
port immunity test
+ A1 2001  + A1 2004
+ A2 2008  + A2 2009
IEC 61000-4-29 2000 Electromagnetic compatibility (EMC) -- Part EN 61000-4-29 2000
4-29: Testing and measurement
techniques - Voltage dips, short
interruptions and voltage variations on d.c.
input power port immunity tests
IEC 61606-1 2009 Audio and audiovisual equipment - Digital EN 61606-1 2009
audio parts - Basic measurement methods
of audio characteristics -- Part 1: General
IEC 61883-6 2014 Consumer audio/video equipment - Digital EN 61883-6 2014
interface - Part 6: Audio and music data
transmission protocol
IEC 61938 2013 Multimedia systems - Guide to the EN 61938 2013
recommended characteristics of analogue
interfaces to achieve interoperability

IEC 60268-3 ®
Edition 5.0 2018-04
INTERNATIONAL
STANDARD
Sound system equipment –
Part 3: Amplifiers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.160.10 ISBN 978-2-8322-5587-2

– 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 . 13
13 Marking . 13
14 Operating environment . 13
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 . 14
15.2.1 Characteristic to be specified . 14
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 . 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) . 21
15.6.4 Maximum effective output power (distortion-limited at 10 %) . 22

IEC 60268-3:2018  IEC 2018 – 3 –
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 . 31
15.10.1 Voltage gain and e.m.f. gain . 31
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 . 34
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 . 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) . 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 . 46
15.15 Balanced inputs and outputs . 47
15.15.1 Balance of the input . 47

– 4 – IEC 60268-3:2018  IEC 2018
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 . 51
15.17.1 Gain difference . 51
15.17.2 Phase difference. 52
15.18 Dimensions and mass, characteristics to be specified . 52
Annex A (informative) Balanced interfaces . 59
Annex B (informative) Specification of a multi-channel amplifier. 60
B.1 General . 60
B.2 Example specification of a 5.1 channel amplifier . 60
B.3 Example specification of a 5 channel amplifier . 60
Bibliography . 62

Figure 1 – Example block diagram for multi-channel amplifier . 53
Figure 2 – Connection diagram of equipment for digital input . 53
Figure 3 – Arrangements for the Class D amplifier . 54
Figure 4 – Arrangements for measuring input impedance . 54
Figure 5 – Oscillogram when measuring overload restoring time . 55
Figure 6 – Protection against potentially damaging combinations of output voltage and
current . 56
Figure 7 – Arrangement for combining two input signals . 57
Figure 8 – Frequency spectrum below 30 kHz of the signal for measuring dynamic
intermodulation distortion . 57
Figure 9 – Arrangement for measuring the balance of a balanced input . 58
Figure 10 – Arrangement for measuring the internal impedance balance of a balanced
output . 58
Figure 11 – Arrangement for measuring the voltage symmetry of a balanced output . 58
Figure B.1 – Block diagram for a 5.1 channel surround amplifier . 60
Figure B.2 – Block diagram for a 5 channel surround amplifier . 61

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

IEC 60268-3:2018  IEC 2018 – 5 –
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.

– 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.
A bilingual version of this publication may be issued at a later date.

IEC 60268-3:2018  IEC 2018 – 7 –
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
IEC 60268-3:2018  IEC 2018 – 9 –
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;

IEC 60268-3:2018  IEC 2018 – 11 –
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.

IEC 60268-3:2018  IEC 2018 – 13 –
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
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