IEC 60268-3:2013

IEC 60268-3 ®
Edition 4.0 2013-04
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 4.0 2013-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Sound system equipment –
Part 3: Amplifiers
Équipements pour systèmes électroacoustiques –

Partie 3: Amplificateurs
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XB
ICS 33.160.10 ISBN 978-2-83220-735-2

– 2 – 60268-3  IEC:2013
CONTENTS
FOREWORD . 5

1 Scope . 7

2 Normative references . 7

3 Conditions . 8

3.1 Rated conditions and standard measuring conditions . 8

3.1.1 Overview . 8

3.1.2 Rated conditions . 8

3.1.3 Standard measuring conditions . 9
3.2 Other conditions . 9
4 Classes of operation . 9
5 Interchangeable parts . 10
6 Automatic controls . 10
7 Power supply . 10
8 Position of the volume controls . 10
9 Pre-conditioning for measurements . 11
10 Series of measurements . 11
11 Variable consumption apparatus . 11
12 Marking . 11
13 Operating environment . 12
14 Characteristics to be specified, and their methods of measurement . 12
14.1 Power supply characteristics . 12
14.1.1 Characteristics to be specified . 12
14.1.2 Method of measurement . 12
14.2 Tolerance of (long-term) power supply voltage variations . 13
14.2.1 Characteristic to be specified . 13
14.2.2 Methods of measurement . 13
14.3 Tolerance of power supply frequency variations . 14
14.3.1 Characteristics to be specified . 14
14.3.2 Methods of measurement . 14
14.4 Tolerance of power supply harmonics and ripple . 15
14.4.1 Characteristics to be specified . 15

14.4.2 Methods of measurement . 15
14.5 Input characteristics . 15
14.5.1 Rated source impedance, characteristic to be specified . 15
14.5.2 Input impedance . 15
14.5.3 Rated source e.m.f., characteristic to be specified . 17
14.5.4 Minimum source e.m.f. for rated distortion-limited output voltage . 17
14.6 Output characteristics . 18
14.6.1 Rated load impedance, characteristic to be specified . 18
14.6.2 Output source impedance . 18
14.6.3 Output voltage and power (distortion-limited) . 19
14.6.4 Regulation . 20
14.6.5 Overload restoring time . 20
14.7 Limiting characteristics . 21
14.7.1 Overload source e.m.f. . 21

60268-3  IEC:2013 – 3 –
14.7.2 Short-term maximum output voltage and power . 21

14.7.3 Long-term maximum output voltage and power . 22

14.7.4 Temperature-limited output power . 23

14.8 Characteristics of protection circuits . 24

14.8.1 General . 24

14.8.2 Protection against potentially damaging combinations of output

voltage and current . 24

14.8.3 Characteristics of d.c. offset protection circuits . 25

14.9 Sustaining-time for rated (distortion-limited) output voltage or power . 26

14.9.1 General . 26

14.9.2 Characteristic to be specified . 27
14.9.3 Method of measurement . 28
14.10 Gain . 28
14.10.1  Voltage gain and e.m.f. gain . 28
14.10.2 Maximum e.m.f. gain . 28
14.10.3 Attenuation characteristic of the volume control . 28
14.10.4 Attenuation characteristic of balance controls for multi-channel
equipment . 29
14.11  Response . 30
14.11.1 Gain-frequency response . 30
14.11.2 Gain-limited effective frequency range . 30
14.11.3 Distortion-limited effective frequency range . 31
14.11.4 Phase-frequency response . 31
14.12 Amplitude non-linearity . 31
14.12.1 General . 31
14.12.2 Rated total harmonic distortion, characteristic to be specified . 31
14.12.3  Total harmonic distortion under standard measuring conditions . 32
14.12.4 Total harmonic distortion as a function of amplitude and frequency . 32
14.12.5  Harmonic distortion of the nth order under standard measuring
conditions . 33
14.12.6  Harmonic distortion of the nth order as a function of amplitude and
frequency . 34
14.12.7  Modulation distortion of the nth order (where n = 2 or n = 3) . 34
14.12.8 Difference-frequency distortion of the nth order (where n = 2 or n =
3) . 36
14.12.9 Dynamic intermodulation distortion (DIM) . 37

14.12.10 Total difference frequency distortion . 39
14.12.11 Weighted total harmonic distortion . 40
14.13 Noise . 41
14.13.1  Characteristic to be specified . 41
14.13.2  Method of measurement. 41
14.14 Hum . 42
14.14.1 General . 42
14.14.2  Characteristics to be specified . 42
14.14.3 Method of measurement. 42
14.15 Balanced inputs and outputs . 43
14.15.1 Balance of the input . 43
14.15.2  Overload (distortion-limited) peak-to-peak common-mode input
voltage . 44
14.15.3  Balance of the output . 44

– 4 – 60268-3  IEC:2013
14.16 Cross-talk and separation in multi-channel amplifiers . 46

14.16.1 Characteristics to be specified . 46

14.16.2 Method of measurement. 46

14.17 Gain and phase differences between channels in multi-channel amplifiers . 47

14.17.1  Gain difference . 47

14.17.2 Phase difference . 48

14.18 Dimensions and mass, characteristics to be specified . 48

Annex A (informative) Balanced interfaces . 56

Annex B (informative) Specification of a multi-channel amplifier. 57

Bibliography . 59

Figure 1 – Example block diagram for multi-channel amplifier . 49
Figure 2 – Arrangements for the Class D amplifier . 50
Figure 3 – Arrangements for measuring input impedance . 51
Figure 4 – Oscillogram when measuring overload restoring time . 52
Figure 5 – Protection against potentially damaging combinations of output voltage and
current . 53
Figure 6 – Arrangement for combining two input signals . 54
Figure 7 – Frequency spectrum below 30 kHz of the signal for measuring dynamic
intermodulation distortion . 54
Figure 8 – Arrangement for measuring the balance of a balanced input . 55
Figure 9 – Arrangement for measuring the internal impedance balance of a balanced
output . 55
Figure 10 – Arrangement for measuring the voltage symmetry of a balanced output . 55
Figure B.1 – Block diagram for a 5.1 channel surround amplifier . 57
Figure B.2 – Block diagram for a 5 channel surround amplifier . 58

Table 1 – Different rated total harmonic distortion and rated distortion-limited output
power specifications for the same amplifier . 27
Table 2 – Distortion components due to dynamic intermodulation distortion falling in
the frequency range up to 20 kHz . 38

60268-3  IEC:2013 – 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 fourth edition cancels and replaces the third edition published in 2000. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– rated condition of multi-channel amplifier is expanded;
– arrangement for the D-class amplifier is added;
– method of measurement for output power (distortion-limited) is expanded;
– Annex B is newly added.
– 6 – 60268-3  IEC:2013
The text of this standard is based on the following documents:

FDIS Report on voting
100/2010A/CDV 100/2066/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 publication 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.
60268-3  IEC:2013 – 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 which 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 [4] .
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 which
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 which 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, in whole or in part, are normatively referenced in this document and
are indispensable for its application. 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, Audio, video and similar electronic apparatus – Safety requirements
Amendment 1:2005
Amendment 2:2010
IEC 60268-1:1985, Sound system equipment – Part 1: General
Amendment 1:1988
Amendment 2:1988
IEC 60268-2:1987, Sound system equipment – Part 2: Explanation of general terms and
calculation methods
Amendment 1:1991
IEC 60417, Graphical symbols for use on equipment. Available from: http://www.graphical-
symbols.info/equipment
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
Amendment 1:2009
––––––––––––
Numbers in square brackets refer to the Bibliography.

– 8 – 60268-3  IEC:2013
IEC 61000-4-17:1999, Electromagnetic Compatibility (EMC) – Part 4-17: Testing and

measurement techniques – Ripple on d.c. input power port immunity test

Amendment 1:2001
Amendment 2:2008
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 61938:1996, Audio, video and audiovisual systems – Interconnections and matching

values – Preferred matching values of analogue signals

3 Conditions
3.1 Rated conditions and standard measuring conditions
3.1.1 Overview
For convenience in specifying how amplifiers shall be set up for measurement, sets of
conditions are specified in this standard, under the titles of rated conditions and standard
measuring conditions.
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 standard 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.
3.1.2 Rated conditions
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:

60268-3  IEC:2013 – 9 –
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 2).

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.
3.1.3 Standard measuring conditions
These are obtained by bringing the amplifier under rated conditions (see 3.1.2) and then
reducing the source e.m.f. to a level of –10 dB referred to the rated source e.m.f.
3.2 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
standard.
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.
4 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.

– 10 – 60268-3  IEC:2013
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.
NOTE 4 Other classes of operation have been commercialized but no formal definitions of such classes have
been submitted for standardization.
5 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.
6 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.
7 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.
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.
8 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 3.1.2), unless a maximum or minimum
position of the control is inherent in the characteristic to be measured.

60268-3  IEC:2013 – 11 –
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.

9 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 3.1.3). 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.
10 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 9 shall be repeated before each set of
measurements, unless this can be shown to be unnecessary.
11 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 more than 15 % due to changes in load impedances of the output circuit or in signal
parameters', but no definition appears in the fifth (1985) or sixth (1998) 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 14.7.4.1 still applies.
All the measurements contained in this standard 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
14.6.3.1 and item c) of 14.14.3).
12 Marking
Principles for marking the terminals and controls are given in IEC 60268-1.
––––––––––––
IEC 60065:1976, Safety requirements for mains operated electronic and related apparatus for household and
similar general use
– 12 – 60268-3  IEC:2013
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 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 these
instructions are to be read by adequately skilled personnel.
13 Operating environment
Measurements, especially those including temperature measurements, shall be carried out
with the amplifier mounted in a situation similar to that in which it is to be used. Restrictions
on mounting and special ventilation requirements shall be stated by the manufacturer and
form part of the rated conditions (see 3.1.2). See also IEC 60065 or other appropriate
IEC safety standard.
14 Characteristics to be specified, and their methods of measurement
14.1 Power supply characteristics
14.1.1 Characteristics to be specified
The following information shall (except where indicated as optional) be stated by the
manufacturer in the locations indicated, for each pair of terminals to be connected to the
power supply and for each position of the power supply voltage selector, if any:
a) the type of power supply (d.c. or a.c.); on the equipment and in the specification;
b) the rated power supply voltage (this is a rated condition, see 3.1.2); on the equipment and
in the specification;
c) the power supply frequency or range of frequencies (this may be a rated condition, see
3.1.2); on the equipment and in the specification;
d) the power drawn, under rated conditions, expressed in watts; on the equipment and in the

specification;
e) for variable consumption apparatus (see Clause 11), the power drawn from the power
supply may optionally be expressed as a function of output voltage or power from zero to
the rated value, with specified load impedances, including the rated load impedance. This
characteristic is particularly of value for equipment which may be operated from batteries.
It may be presented as a graph.
If, in items d) or e) above, the apparent power drawn is significantly greater than the true
power, the apparent power should be stated in addition.
14.1.2 Method of measurement
The amplifier is brought under rated conditions. The power drawn from the power supply is
measured in watts by means of a wattmeter:
a) with rated source e.m.f., see 14.5.3;
b) with the source e.m.f. according to standard measuring conditions;

60268-3  IEC:2013 – 13 –
c) for variable consumption apparatus, at various values of output voltage or power from

zero to the rated value.
14.2 Tolerance of (long-term) power supply voltage variations

14.2.1 Characteristic to be specified

The tolerance of power supply voltage variation, such that, for any power supply voltage

within the stated limits:
a) the upper limit of working voltage is not exceeded for any condition of normal operation;

this applies particularly to such components as semiconductor devices and electrolytic

capacitors;
b) the tolerances of the heater voltage of electronic tubes used in the amplifier are not
exceeded;
c) the maximum permissible temperature is not exceeded in any component when the
amplifier works under standard measuring conditions – except as regards power supply
voltage – for an extended period of time;
d) neither output nor gain is subject to excessive variations;
e) the signal-to-hum ratio is not reduced by more than 3 dB with respect to the rated value.
Amplifiers designed to take their power supply from the mains are generally not subject to
power supply variations exceeding ± 10 %. Such variations do not generally require a special
design of amplifier.
Amplifiers designed to take their power supply from batteries or small converters may be
subject to larger variations of power supply voltage, which may be due to changing load, the
temperature of batteries or the gradual decrease of battery voltage during life or discharge.
The rated value shall be stated by the manufacturer in the specification. If the manufacturer
states that the amplifier tolerates power supply voltage variations not exceeding ± 10 %, then
compliance with requirements a), b) and c) is considered to be within the scope of normal
amplifier design. Compliance with requirements d) and e) shall be checked.
If the manufacturer states that the amplifier will tolerate power supply voltage variations
exceeding ± 10 %, the specification shall give details of any special means for compensating
such variations and the proper working of these means shall be checked if possible.
Compliance with requirements a) to e) shall be checked.
14.2.2 Methods of measurement
14.2.2.1 Temperature
The amplifier is brought under standard measuring conditions.
a) If a rated temperature-limited output power is given, the source e.m.f. shall be adjusted so
that this value of output power is obtained.
b) The power supply voltage is adjusted to the upper limit stated by the manufacturer and the
source e.m.f. readjusted, if necessary, to restore the output power to the value specified in
item a).
c) The amplifier shall be capable of working continuously under these conditions for at least
4 h without any component exceeding th
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