Titan 2000 schematic

Elektor Electronics 2/99

It could be argued

that most of the out-

put amplifiers pub-

lished in this maga-

zine lack power.

Although this is a

debatable point, it

was felt that a true

heavyweight output

amplifier would make

a welcome change for

many constructors.

The Titan 2000 can

produce 300 watts

into 8 Ω, 500 watts

into 4 Ω, and

800 watts into 2 Ω.

For those who believe

that music power is a

reputable quantity, the

amplifier can deliver

2000 watts of this

magical power into

4 Ω.

58

Design by T. Giesberts

Titan 2000

High-power hi-fi and

public-address amplifier

Brief parameters

Sine-wave power output 300 W into 8 Ω; 500 W into 4 Ω; 800 W into 2 Ω
Music power* 2000 W into 4 Ω
Harmonic distortion <0.005%
Slew limiting 85 V µs

–1

Open-loop bandwidth 55 kHz
Power bandwidth 1.5 Hz – 220 kHz

*See text about the validity of this meaningless quantity.

AUDIO & HI-FI

Contents

INTRODUCTION

Amplifier output has been a cause of
argument for as long as there have
been audio power amplifiers. For
domestic use, a power rating of
2× 50 W is more than sufficient. With
the volume control at maximum and
the use of correctly matched good­quality loudspeakers, this will provide

a sound pressure level (SPL) equiva­lent to that of a grand piano being
played forte in the same room.

However, not all amplifiers are
intended for domestic use: many are
destined for discos, small music halls
and other large rooms. But even here,
what power is really required? Since
doubling the amplifier output increases
the SPL by a barely audible 3 dB, it was
felt that 300 watts sine wave power into
8Ωwould appeal to many .

‘ PROGRAMMABLE’

POWER OUTPUT

The amplifier has been designed in
such a manner that its output is ‘pro­grammable’ as it were. With a sine
wave input, it delivers an average
power of 300 W into an 8Ω load,
which should meet the requirements
of all but the power drunk. Compared

with the output of 50 W from a
domestic audio amplifier, this
gives an increase in SPL of

7.5 dB. If even higher outputs are
needed, the load impedance may be
lowered to 4 Ω, which will give an
increase in SPL of 10 dB compared
with a 50 W output.

Although music power is a depre­catory term, since it does not really
give the true power rating of an ampli­fier, readers may note that the Titan
2000 can deliver 2 kW of this magical
power into 4 Ω. (True power is average

power , that is, the product of the r.m.s. volt-

age across the loudspeaker and the r.m.s.
current flowing into the speaker. The term
music power is generally meaningless,
because to some manufacturers it means the
product of the peak voltage and peak cur­rent; to others it means merely double the
true power; and to yet others, even more
disreputable, it means quadrupling the true
power).

However, power is not the only cri­terion of an amplifier. Low distortion,
good slew limiting, and an extended
power bandwidth, as possessed by the
Titan 2000, are also hallmarks of a good
amplifier.

Power bandwidth denotes the fre­quency range over which the power
falls to not less than half its maximum
value. This is much more telling than
the frequency response, which is usu­ally measured at a much lower output
level.

Slew limiting is the maximum input
voltage change that can occur in one

59

Elektor Electronics 2/99

1

Figure 1. Simplified block dia­gram of the Titan 2000. The aux­iliary power supply, protection
networks and thermal control
are discrete circuits built on dis­crete PCBs.

Contents

regulator

± 78V

T43...T52

voltage amplifier

T1...T10

T15...T26

input stages &

cascode amplifiers

± 85V

auxiliary

power supply

2x 15V

current amplifier

T27...T34
T35...T42

drivers & output stages

offset control

main power

supply

± 70V

heat sink

sensor

fan

protection

circuits

UinU

thermal

control

out

990001 - 12

0

60

Elektor Electronics 2/99

Figure 2. Although the circuit diagram gives the impres­sion of a highly complex design, the amplifier is, in
essence, fairly straightforward.

2

Contents

R56

85V

BF871

BD711

BC550

BF245A BC639

R62

R57

15Ω

BF872

BD712

BC560

BC640

BF256C

R26

R25

R24

D4

R18

R13

T47

330Ω

15k

1V

2R

1R

K1

2SC5359

1M

C24

2µ2 63V

1N4004

T24...T26=MJE340

R17

-39V

T51

2x

15n

T50

D11

220n

100V

470µ

2SA1987

2SC5171

MJE340

BD139

1µ

150Ω

R72

BC

640

T48

30V

2SA1930

MJE350

BD140

D14

2

5

7

1

C19

T18 T19 T20

C23

C22

D6

C11

R20

C5

R15

C18

-78V

C39

15k

BF

245A

1W3

0W5

12V

3

IC1

6

68Ω

0V83 0V83

68Ω

68Ω

270Ω

1V45 1V45

1k00

2µ2

63V

R67

I

+5V

2k2

C42

R78

C

EB

5V

C45

100n

C44

100n

C43

100n

T31

T30

BE

E

B

C

BE

C

S

GD

70V

C

T29...T31=2SC5171

T21...T23=MJE340

3k3

R22

T11

2mA1

63V

T46

BC

639

T45

R58

270Ω

0V36

T29

T23

T22

T21

1W

T13

53V-53V

15V

39V

12k

R64

22Ω

R61

C31

15n

22Ω

R60

C29

220n

C28

470µ 100V

C17

100p

68Ω

T17

68Ω

T16

68Ω

T15

C21

100p

C20

100p

5V6

0W5

C8

100n

270Ω

150Ω

R16

C4

2n2

1k00

C16

100p

+78V

D10

1N4004

C32

2µ2

BD712

15k

R63

2x

BF

245A

T43

D8

30V

1W3

R76

10Ω

R41

38mV32mV

10Ω

R40

10Ω

R39

560Ω

R36

BF256C

D5

R19

T9

P2

250Ω

D1

8V4

5k6

R59

39V

1n

R77

100Ω

6

8

IC2

2

T35...T38=2SC5359

C9

10k

C10

BF871

R5

330Ω

C6

1V71V7

C34

C33

P4

T44

BF256A

D9

C30

100Ω

5

7

6N136

3

2Ω2

R79

100Ω

R74

33Ω

R75

0Ω22

25V

100V

1W3

63V

R48

0Ω22

R47

0Ω22

R46

0Ω22

R45

BD

139

T27

220Ω

R33

22k

R31

1n

C3

T3

5k

22Ω

R12

53mV53mV

22Ω

R4

T7

BF

245A

JP2

D3

1N4148

T38

T37

T36

T35

15V

1W3

100n

1W

100µ

T5

220µ

25V

470µ

220n

39V

47µ

MUTE

D18D19

L1

Re4 Re3 Re2

LS+ LS+

0Ω22

R52

20mV20mV

0Ω22

R51

0Ω22

R50

0Ω22

R49

150Ω

R38

R30RC14

C15

100n

2V24

R34

500Ω

470Ω

P3

470Ω

R11

470Ω

JP1

R10

45mV45mV

T1

R2
C1

Re1

390Ω

R9

T2

562Ω

2µ2

5k

P1

22Ω1

R8

22Ω

R14

R6

V23042-A2003-B101

LS1

T39...T42=2SA1987

T39 T40 T41 T42

C

T28

T4

22Ω

T6

T8

BF

245A

47k

R3

C2

1n

1M

R1

P-IN

T27...T42 on common heatsink

LS- LS-

10Ω

R44

10Ω

R43

10Ω

R42

560Ω

R37

BD

140

220Ω

R35

22k

R32

15V

1W3

D7

C12

100n

10k

1W

R21

C13

25V

100µ

T10

470Ω

R7

C7

C41

C40

P5

5k6

R68

39V

D12

C37

220µ

D2

25V

470µ

220n

47µ

C48

C47

C46

BF872

100V

5k

BF256A

1W3

63V

100n

100n

100n

T32 T33 T34

T14

15V

-30V

T49

-39V

70V

P-LS

R53

C26

D16

T32...T34=2SA1930

15V

T24 T25 T26

1W

BF256C

3k3

R23

35V 35V

T12

12k

R73

22Ω

R70

C38

22Ω

R69

C36

C35

D15

4

100p

R29

R28

R27

100p

100p

5V6

100n

2n2

100p

D13

BD711

270Ω

0V36

E

C

B

990001 - 11

E

C

B

B

C

E

B

C

E

C27

2µ2 63V

OP90G

D17

1N4004

15V

4M7

R54

C25

68n

4M7

R55

0W5

T1, T4, T5, T15...T17 = BC560C

T2, T3, T6, T18...T20 = BC550C

1N4004

T52

330Ω

R71

15k

R66

1V

15Ω

R65

85V

microsecond, and to which the ampli­fier can respond.

DESIGN
CONSIDERATIONS

The Titan 2000 is based on the ‘com­pact power amplifier’ published in the
May 1997 issue of this magazine. That
was a typical domestic amplifier with a
power output of 50 W into 8 Ω or 85 W
into 4 Ω. The special property of this
fully balanced design was the use of
current feedback instead of voltage
feedback, which resulted in a fast­responding amplifier with a large
open-loop bandwidth. The amplifier
performed well both as regards instru­ment test and measurements and lis­tening tests. However, to serve as a
basis for the Titan 2000, its output cur­rent and drive voltage range had to be
increased substantially.

For a start, the supply voltage has to
be more than doubled, which means
that transistors with a higher power
rating have to be used in the power
supply . The higher supply voltage also
results in larger potential drops across a
number of components, and this
means that dissipation problems may
arise.

The large output current required
for the Titan 2000 makes a complete
redesign of the current amplifier used
in the ‘compact power amplifier’
unavoidable, since that uses insulated­gate bipolar transistors (IGBTs).
Although these are excellent devices,
the large spread of their gate-emitter
voltage makes their use in parallel net-

works next to impossible. To obtain the
requisite output power, the use of par­allel networks of symmetrical pairs of
transistors is inevitable.

In view of the foregoing, bipolar
transistors are used in the current
amplifier of the Titan 2000. However,
these cannot be driven as readily as
IGBTs, which means that current drive
instead of voltage drive is used. This
entails a substantial upgrading of the
driver stages and the preceding cas­code amplifiers (which also consist of a
couple of parallel-connected transis­tors). The good news is that the power
transistors in the Titan 2000 are consid­erably less expensive than IGBTs: an
important factor when eight of these
devices are used.

Finally, the protection circuits have
been enhanced in view of the higher
voltages and currents. The circuits pro­tecting against direct voltages and
short-circuits are supplemented by
networks protecting against overload
and (too) high temperatures. The latter
is coupled to a proportional fan con­trol.

In short, a large part of the Titan
2000 is a virtually new design rather
than a modified one.

BRIEF DESCRIPTION

The block diagram of the Titan 2000 is
shown in Figure 1. The voltage ampli­fier consists of input stages T

1–T10

, and

cascode amplifiers/pre-drivers T

15–T26

.
The current amplifier is formed by dri­ver transistors T

27–T34

, and output

transistors T35–T42.

The offset control stage prevents
any direct voltage appearing at the
output of the amplifier.

The loudspeaker is linked to the
amplifier by three heavy-duty relays.

The current amplifier operates from
a ±70 V supply, which is provided by
two 50 V mains transformers. To enable
the voltage amplifier to drive the cur­rent amplifier to its full extent, it needs
a slightly higher supply voltage to
compensate for the inevitable losses
caused by inevitable voltage drops.
This is accomplished by superimposing
a ±15 V potential from an external
auxiliary supply on to the main ±70 V
supply and dropping the resulting
voltage to ±78 V with the aid of regu­lator T

43–T52

.

The combined protection circuits
constantly compare the input and out­put voltage of the amplifier: any devi­ation from the nominal values leads to
the output relays disconnecting the
loudspeaker and the input relay
decoupling the input signal.

The thermal protection circuit mon­itors the temperature of the heat sink
and, if necessary, switches on a fan. If,
with the fan operating, the tempera­ture approaches the maximum per­missible limit, the output relays are
deenergized and disconnect the loud­speaker.

CIRCUIT DESCRIPTION

The circuit diagram of the Titan 2000 is
shown in Figure 2. In spite of the large
number of components, the basic cir-

61

Elektor Electronics 2/99

Contents

cuit is straightforward.

As already noted in
the previous para­graph, transistors
T

1–T10

form the input

amplifier, T

11

and T12are buffers, T

13

and T14are current sources, T15–T

26

form the cascode amplifier/pre-driver
stage, T

27–T34

are the driver transistors

in the current amplifier , T

35–T42

are the

output transistors, and T

43–T52

form a

sophisticated supply voltage regulator.

Input amplifier

Strictly speaking, the input amplifier is
formed by transistors T

3–T4

. Cascode

stages T

9–T10

serve merely to enable
the input section handling the high
voltages. These voltages are limited by
zener diodes D

5

and D7, which are part
of the potential divider that also sets
the operating points of T

21–T26

. In
view of the requisite stability, the cur­rent through the zener diodes is held
constant by current sources T

13

and
T

14

. Resistors R22and R23limit the
potential across, and thus the dissipa­tion in, these field-effect transistors.

Otherwise, the input section is vir­tually identical to that of the ‘compact
power amplifier’. The drop across the
emitter resistors of buffers T

1

and T

2

determines the drop across the emitter
resistors of T

3

and T4, and conse­quently the setting of the operating
point of the overall input section. To
eliminate the influence of temperature
variations, T

1

is thermally coupled to

T

3

and T2to T4.

Since the operating point of buffers

T

1

and T2is critical, current sources T

5

and T6have been added. The reference
for these current sources is provided
by light-emitting diodes (LEDs) D

1

and

D

2

. The current through these diodes

is determined by current sources T

7

and T8. In view of the
requisite stability,
diode D

1

is thermally

coupled to T

5

and D

2

to T6.

Any imbalance of the input stages is
compensated by making the current
through T

5

equal to that through T

6

with potentiometer P2.

Cascode amplifiers/pre-drivers

The large output current of the Titan
2000 necessitates a proportionally
large pre-drive voltage, which is pro­vided by three parallel-connected cas­code amplifiers, T

15–T26

. The current
through these amplifiers is arranged at
10–15 mA, but the current feedback
used may cause this level to be appre­ciably higher. This is the reason that the
transistors used in the T

21–T26

posi­tions are types that can handle cur­rents of up to 50 mA when their collec­tor-emitter voltage is 150V.

The input section is linked to the

cascode amplifiers by buffers T

11

and

T

12

, which results in a lowering of the
input impedance. The arrangement
also enables an increase in the values
of R

13

and R15, which results in a 3 dB
increase in amplification of the input
section.

The function of resistors R

19

and

R

21

is threefold: they limit the dissipa­tion of the buffers; they obviate the
need of an additional voltage to set the
operating point of the buffers; they
limit the maximum current through
the buffers, and thus the cascode
amplifiers, to a safe value.

The open-loop amplification of the
Titan 2000 is determined solely by
those of the input section and cascode
amplifiers. The amplification of the
input section depends on the ratios
R

13

:(R12+R8) and R15:(R14+R8) and,

with values as specified is ×10 (i.e., a

gain of 20 dB).

The amplification of the cascode
amplifiers is determined largely by the
ratio of parallel-connected resistors R

31

and R32and the parallel network of
R

24–R26

. With values as specified, the
amplification is about ×850 (remem-
ber, this is a push-pull design), so that
the overall amplification of input sec­tion plus cascode amplifiers is ×8500 (a
gain of close to 80 dB).

Current amplifier

Since one of the design requirements is
that the amplifier is to work with loads
down to 1.5 Ω, the output stages con­sist of four parallel-connected pairs of
transistors, T

35–T38

and T39–T42. These
transistors have a highly linear transfer
characteristic and provide a direct-cur­rent amplification that remains virtu­ally constant for currents up to 7 A.

Like the output transistors, the dri­ver stages need to remain within their
safe operating area (SOA), which
necessitates a threefold parallel net­work. The transistors used in the dri­ver stages are fast types
(f

T

=200 MHz).

Setting the bias voltage for the req­uisite quiescent current is accom­plished by balanced transistors T

27

and

T

28

. These transistors are mounted on
the same heat sink as the output tran­sistors and driver transistors to ensure
good thermal coupling and current
control. Of course, the current rises
during full drive conditions, but drops
again to its nominal level when the
amplifier cools off. The quiescent cur­rent is set to 200 mA with potentiome­ter P

3

.

Owing to the large output current,
the connection between amplifier out­put and loudspeaker is not arranged
via a single relay, but via three. Two of
these, Re

3

–Re4, are controlled in syn­chrony by the protection circuits.
When they are deenergized, their dis­abling action is delayed slightly to give
the contacts of the third relay , Re

2

, time
to open, which is of importance in a
fault situation.

Input relay Re

1

is switched off in

synchrony with Re

2

to ensure that

there is no input signal by the time Re

3

and Re4are deenergized.

Optoisolator IC

2

serves as sensor for
the current protection circuits. The
light-emitting diode in it monitors the
voltage across R

48–R52

via potential

divider R

74–R75

, so that the positive as
well as the negative output currents
are guarded. The use of an optoisola­tor prevents earth loops and obviates
compensation of the ±70 V common­mode voltage. The +5 V supply for the
optoisolator is derived from the pro­tection circuits.

Feedback

The feedback loop runs from the out-

62

Elektor Electronics 2/99

3

Figure 3. Circuit dia­gram of the requisite
auxiliary power supply.

Contents

K1

12V / 1VA5

70V

Tr1

D3

D4

4x 1N4007

K2

D1

C3

100n

160mA T

R1

1M

D2

C1

470µ
100V

K3

F1

85V

70V

4x 1N4007

Tr2

D5

D6

12V / 1VA5

C4

100n

R2

1M

K4

F2

160mA T

990001 - 13

C2

470µ
100V

D7

D8

85V

put of the power stages to the junction
of T

3

and T4via resistors R10and R11.
This is current feedback because the
current through T

3

and T4depends on

the potential across R

8

, which is deter­mined largely by the current through
R

10

and R11. The overall voltage ampli­fication of the output amplifier is deter­mined by the ratio R

8

:(R10+R11).

Compensation

Capacitors C3–C5and resistors R16, R

17

form part of the compensation net­work required for stable operation.

Low-pass filter R

2–C2

at the input is
essential to prevent fast, that is, high­frequency, signals causing distortion.
This filter is also indispensable for sta­bility’s sake.

Coupling capacitor C

1

is needed
because the available offset compensa­tion network merely redresses the bias
current of the input buffers and is not
intended to block any direct voltages at
the input.

Relay Re

1

at the input enables the
input signal to be ‘switched off’. It
forms part of the overall protection
and in particular safeguards the input
section against overdrive. The overall
protection circuit will be discussed in
detail next month.

Network R

9-P1

is intended specifi­cally for adjusting the common-mode
suppression when two amplifiers are
used in a bridge arrangement. It is
needed for only one of these ampli­fiers, and may be interconnected or
disabled by jumper JP

1

as needed.

Offset compensation is provided by

integrator IC

1

, which ensures that if
there is any direct voltage at the output
of the amplifier, the operating point of
T

1-T2

is is shifted as needed to keep the
output at earth potential. The opera­tional amplifier (op amp) used draws
only a tiny current (20 µA) and has a
very small input offset (450 µV).

Supply voltage for IC

1

is taken from
the ±15 V line for the input section via
diodes D

16

and D17. This arrangement
ensures that the supply to the IC is
retained for a short while after the
main supply is switched off so that any
interference is smoothed out.

Diodes D

14

and D15safeguard the

input of IC

1

against (too) high input

voltages in fault conditions.

The values of resistors R

54

and R

55

arrange the level of the compensating
current at not more than 1 µA, which is
sufficient to nullify the difference
between the base currents of T

1

and T2.

Regulation

Although current feedback has many
advantages, it also has a serious draw­back: poor supply voltage suppression.
This makes it essential for the supply
voltage for the voltage amplifier to be
regulated. In view of the requisite high
symmetrical potential and the fact that
the unregulated voltage that serves as
input voltage can vary substantially
under the influence of the amplifier
load, two discrete low-drop regulators,
T

43–T47

and T48–T52are used.

As mentioned before, owing to

inevitable losses through potential
drops, the supply voltage for the input
section and cascode amplifiers needs to
be higher than the main ±70 V line.
Furthermore, the input voltage to the
regulators must be higher than the
wanted output voltage to ensure effec­tive regulation.

Fortunately, the current drawn by
the voltage amplifier is fairly low
(about 70 mA) so that the input voltage
to the regulators can be increased with
a simple auxiliary supply as shown in
Figure 3. This consists of two small
mains transformers,two bridge recti­fiers, D

1–D4

and D5–D8, and the neces-

sary reservoir and buffer capacitors.

The ±15 V output is linked in series
with the ±70 V line to give an unregu­lated voltage of ±85 V.

The 39 V reference is provided by
zener diode D

9

. This means that the
regulator needs to amplify the refer­ence voltage ×2 to obtain the requisite
output voltage.

The zener diode is powered by cur-

rent source T

43

, to ensure a stable ref­erence, which is additionally buffered
by C

30

.

Differential amplifier T

45-T46

, whose
operating point is set by current source
T

44

, compares the output voltage with
the reference via potential divider
R

63-R64-P4

. This shows that the output

voltage level can be set with P

4

.

Transistor T

47

is the output stage of
the regulator. The output voltage
remains stable down to 0.2 V below the
input voltage.

63

Elektor Electronics 2/99

Current-feedback

In an amplifier using voltage feedback (Figure a), the differential voltage at its inputs is multiplied by the open-loop
amplification. The feedback loop forces the output voltage to a level that, divided by network R

1-R2

, is equal to the

input voltage.

Whereas an amplifier with voltage feedback has high-impedance inputs, an amplifier with current feedback (Figure
b) has an high-impedance and a low-impedance input. Its input stage consists of a buffer with unitary gain between
the inverting and non-inverting inputs. Essentially, the inverting input is the low-impedance input. The buffer is fol­lowed by an impedance matching stage that converts the output current of the buffer into a directly proportional out­put voltage.

The current feedback loop operates as follows. When the potential at the non-inverting input rises, the inverting input
will also rise, resulting in the buffer current flowing through resistor R

1

. This current, magnified by the impedance
matching stage, will cause the output
voltage of the amplifier to rise until the
output current flowing through resistor R

2

is equal to the buffer current through R1.
The correct quiescent output voltage can
be sustained by a very small buffer cur­rent. The closed-loop amplification of the
circuit is determined by the ratio
(1+R

2

):R1.

A interesting property of an amplifier
with current feedback is that the closed­loop bandwidth is all but independent of
the closed-loop amplification, whereas
that of an amplifier with voltage feedback
becomes smaller in inverse proportion to
the closed-loop amplification – a relation
known as the gain-bandwidth product.

Contents

U

in

A(s)

ab

U

out

U

in

R2

R1

R2

A

= 1 +

v

R1

R1

R(s)

A

=1

v

I

R2

A

= 1 +

v

R2
R1

990001 - 14

U

out

65

Elektor Electronics 2/99

Resistor R57and diode D8protect T

43

against high voltage during switch-on,
while D

10

prevents current flowing
through the regulator in the wrong
direction.

Capacitors C

31

and C32enhance the

rate of operation of the regulator.

Network R

56-C28-C29

provides
additional smoothing and r.f. decou­pling of the ±85 V lines.

NEXT MONTH

Next month’s second and concluding
instalment of this article will describe
details of the protection circuits, the fan
control, and the construction of the
amplifier. The instalment will also
include detailed specifications and per­formance characteristics.

[990001-1]

Contents

Elektor Electronics 3/99

SIX FUNCTIONS

The integrated protection network con­sists of six sub-circuits:

• power-on delay

• transformer voltage sensor

• temperature sensor

• current sensor

• direct-current sensor

• overdrive sensor
The power-on delay ensures that the

relays in the amplifier are energized
50–100 milliseconds after the supply
has been switched on to prevent
switch-on clicks.

The transformer voltage sensor
reacts to the cessation of the secondary
voltage of the mains transformers to
prevent switch-off clicks and crackles.

The temperature sensor responds to
excessive heat sink temperatures, but it
should be noted that this works only in

This second of four

parts deals primarily

with the protection

network incorporated

in the amplifier. This

indispensable net-

work safeguards the

amplifier and the

loudspeakers con-

nected to it against all

kinds of error that

may arise. The net-

work is an indepen-

dent entity with its

own power supply.

32

Design by T. Giesberts

Titan 2000

Part 2: protection network

INTRODUCTION

As mentioned briefly in Part 1, exten­sive and thorough protection is a must
in an amplifier of this nature. It may
well be asked why this is so: is there
such a likelihood of mishaps arising?
Or is the amplifier so vulnerable? On
the contrary: extended tests on the
prototype have shown that the Titan
2000 is a very stable and reliable piece
of equipment. In fact, unusual means
had to be used to actuate the protec­tion circuits during these tests, since
not any standard test prompted the
amplifier into an error situation.

The extensive protection is neces­sary because by far the largest number
of mishaps occur owing to actions by
the user, not because of any shortcom­ings in the amplifier. For example, the
most robust and reliable amplifier can
not always cope with extremely high
overdrive or overload conditions.

Correction. In last month’s first part
of this article, it was stated erro­neously that the article consists of
two parts, whereas in fact it will be
described in four parts.

AUDIO & HI-FI

Contents

conjunction with the fan drive, which
is reverted to later in this article.

The current sensor monitors the
output current, while the direct-cur­rent and overdrive sensors form a
combined circuit that monitors differ­ences between the input and output
signals, and reacts to excessive direct­current levels or distortion. This circuit
is the most important and ‘intelligent’,
but also the most complex of the six.

All sensors, when actuated, react in
the same way: they cause the output
relays and the mute relay at the input
of the amplifier to be deenergized
immediately. This action causes the

input signal and the
output load to be dis­connected from the
amplifier. After the fault
causing the sensor
action has been
removed or remedied, the relevant
protection circuit is disabled, where­upon the amplifier relays are reener­gized after a short delay.

When the protection network is
actuated, a red LED lights to indicate
an error. When the fault has been
removed or remedied, the red LED
remains on, but a yellow LED flashes
to indicate that the amplifier will be

reenabled shortly. The red LED then
goes out, shortly followed by the yel­low, whereupon a green LED lights to
indicate that all is well.

COMMON SECTION
AND POWER

- ON DELAY

The circuit of the integrated protection
network, including the +5 V and ±12 V
power supplies, is shown in Figure 4.

33

Elektor Electronics 3/99

V

V

4

Figure 4. The protection network con­sists of six sensor circuits each of which
causes the input and output relays of
the amplifier to be deenergized when a
fault occurs.

Contents

LSP

input

C1

100n

R1

R5

680Ω

30µH

2x 100n
250V

100k

IC1

P2

C2

C16

100n

8

4

500Ω

R2

1k05

1n

16

IC3

P1
250Ω

8

C12

100n

C13

100n

R6

820k

K4

P3
500k

12V

12V
12V

12V

C17

100n

C14

100n

C15

100n

D1

2x

BAT82

D2

D3

2x

BAS45A

D4

16

IC4

8

F1

50mA T

Tr1

3

2

5V

2x 15V

8VA

IC2

IC1a

R7

11

6

1M

12V

12V

C3

100n

IC1 = OP249GP
IC2 = LM319

5

IC1b

6

R4

10k0

R3

10k0

1

R14

2M2

R13

470k

C7

470n
R15

1k

D6

EARLY

B80C1500

C26

47n

temp

I

11
12
13

IC2a

IC2b

3
4
5
6
7
8
9

5V

R12

C6

2k2

100n

12

3

7

8

4

5

12

13

5V

7
5
4
6
14
13
15
1
2
3

C8

100n

9

1

12V

R8

47k

4

R9

C4

100n

7

C5

100n

11
10

9

12

12V

RCX
RX
CX

CT=0

IC3

470Ω

R10

470Ω

R11

47k

CTR14

!G

D5

+

5

9

10

1N4148

CT

74HC4060

IC4

74HC175

1D

C1

R

5

4

K1

IC5

4N35

R16

4k7

126

D7

R19

47k

R24

47k

47k

R25

R20
2M7

C9

4µ7
63V

R23

4k7

2k2

R22
R21

2k2

T1

BC

R27

4k7

4k7

R26

T3

BC

547B

547B

T2

T4

R28

BD
140

BD
140

3k9

D9

ON

1N
4148

5V

D8

ERROR

R17

1k

2
3
7
6
10
11
15
14

R18
47k

Vre

12V

JP1

Vre Ext.

K2

K3

int
ext

2R

1R

mute

IC9

12V

+5V

5V

+5V

+12

+12V

4µ7

C18

4µ7
63V

C19

4µ7
63V

C22

63V

+12V

+5V

D13

R35

3k3

+5V

+12V

POWER

50V

50V

D10

D11

C10

10µ
63V

2x

1N4007

R32

15k

R31

15k

R30

3k3

IC6

126

4N35

R29

47k

5

4

5V

C11

47µ 25V

BC

547B

R34

T6

100k

R33

D12

100k

1N4001

T5

2x

7805

R36

C23

22Ω

47µ

C20

1000µ
25V

C21

470µ
25V

25V

IC7

7812

IC8

C24

47n

B1

C25

47n

7912

–12V

–12V

–12V

12V

–12

990001 - 2 - 11

The network is linked to the input
and output of the amplifier via termi­nals ‘input’ and ‘LSP ’ respectively (to
terminals ‘P-IN’ and ‘P-LS’ on the
amplifier board).

Terminals ‘50 V≈’ are connected to
the secondary windings of the mains
transformers.

The three output relays and the
mute relay in the amplifier are linked
to the protection network via K

2

, and

K

3

respectively.

The current sensor is connected to
the output of optoisolator IC

2

in the
amplifier (‘I->’ on the amplifier board)
via K

1

.

The terminals marked ‘temp’ are
intended to be linked to the output of
the fan control circuit.

As mentioned earlier, the action of
each sensor results in the deenergizing
of the output and mute relays in the
amplifiers. This implies that the out­puts of the the various sensor circuits
are interlinked. This is effected by com­bining the open-collector outputs of
these circuits into a wired OR gate with
R

12

functioning as the common pull­up resistance. The combined output
signal serves to reset a number of

34

Elektor Electronics 3/99

-12V

~
~

Parts lists

Protection network

Resistors:
R

1

, R33, R34= 100 kΩ

R

2

= 1.05 kΩ

R

3

, R4= 10.0 kΩ

R

5

= 680 Ω

R

6

= 820 kΩ

R

7

= 1 MΩ

R

8

, R11, R18, R19, R24, R25, R29= 47 kΩ

R

9

, R10= 470 Ω

R

12

, R21, R22= 2.2 kΩ

R

13

= 470 kΩ

R

14

= 2.2 MΩ

R

15

, R17= 1 kΩ

R

16

, R23, R26, R27= 4.7 kΩ

R

20

= 2.7 MΩ

R

28

= 3.9 kΩ

R

30

, R35= 3.3 kΩ

R

31

, R32= 15 kΩ

R

36

= 22 Ω

P

1

= 250 Ω, multiturn preset (upright)

P

2

= 500 Ω, multitun preset (upright)

P

3

= 500 kΩ, multiturn preset (upright)

Capacitors:
C

1

, C3= 0.1 µF

C

2

= 0.001 µF

C

4

, C5, C6, C8, C12–C17=0.1 µF,

ceramic

C

7

= 0.47 µF

C

9

, C18, C19, C22= 4.7 µF, 63 V, radial

C

10

= 10 µF, 63 V, radial

C

11

, C23= 47 µF, 25 V, radial

C

20

= 1000 µF, 25 V, radial

C

21

= 470 µF, 25 V, radial

C24–C26= 0.047 µF, ceramic
Semiconductors:

D

1

, D2= BAT82

D

3

, D4= BAS45A

D

5

, D7= 1N4148

D

6

, D8, D9, D13= 3 mm high-efficiency

LED

(yellow, red, green, green respectively)

D10, D11= 1N4007
D

12

= 1N4001

T

1

, T3, T5, T6= BC547B

T

2

, T4= BD140

Integrated circuits:
IC

1

= OP249GP (Analog Devices)

IC

2

= LM319N

IC

3

= 74HC4060

IC

4

= 74HC175

IC

5

, IC6= 4N35

IC

7

= 7812

IC

8

= 7912

IC

9

= 7805

Miscellaneous:
JP

1

= 2.54 mm pin strip and pin jumper

K

1

, K2= 3-way terminal block, pitch

5mm
K3= 2-way terminal block, pitch 5 mm
K

4

= 2-way terminal block, pitch 7.5 mm

B

1

= bridge rectifier, rectangular, Type

B80C1500
F

1

= fuse, 50 mAT and fuse holder

Tr

1

= mains transformer, 15 VA, with

2×15 V secondary
Heat sink (for IC

7

) = e.g. Fischer

SK104, 50 mm
Mains interference filter

Figure 5. The printed-circuit
board of the overall protec­tion network.

Contents

+12V

0

+5V

D8

+5V

0
Vre

ext
int

+12V

D9

H8

H7

H4

C11

H3

C18

T5

C19

C22

R34

R25

JP1

R28

mute

R17

R24

IC8

IC7

R33

T3

K3

T6

D12

R26

C8

C21

C20

IC6

R18

R27

IC9

C26

T4

R29

R21

R35

B1

R20

C23

IC4

T1

R30

R22

C25

C24

R36

C10

C17

T2

R19

R31

R23

C9

R32

IC3

D13

TR1

~

~

0

R2

D10
D11

C13

C16

D1

R4

R13

R14

C12

C7

C5

D5

R15

IC2

R8

C15

C14

0

T

K2

D6

2R

I

P1

D2

D4

IC1

C3

D3

R3

R10

R9

R11

R12

-12V

+

K1

IC5

R16

C6

T

R1

R6

R7

R5

D7

temp

K4

F1

C4

H5

50mAT

H6

H2

LSP

P3

T

input

C1 C2

P2

990001-2

990001-2

(C) ELEKTOR

H1

990001-2

(C) ELEKTOR

D-type bistables (flip­flops), contained in
IC

4

, which are inter­connected to form a
shift register. Note that D-type bistables
are essential since these can be set and
reset in a defined manner.

The outputs of IC

4

are used to drive

two level converters, T

1-T2

and T3-T

4

respectively, which bridge the differ­ence between the 5 V level of the logic
ICs and the 12 V supply for the relays.
Jumper JP

1

enables a different, external

supply voltage (V

RE

) to be used if 12 V

relays are not employed.

Transistors T

1

and T2drive Re1and

Re

2

, which are the first to be energized
(synchronously). On switch-off, capac­itor C

9

ensures that T2remains on for
some milliseconds longer during
which period Re

3

and Re4are deener-

gized (see Part 1).

The power-on delay, which also
operates after a fault situation, is more
complex than usual. To start with, after
the supply voltage us switched on,
input CLR of IC

4

is held low (active)
for a few seconds by the circuit around
T

6

. When, after this period, CLR is

made high by R

12

–which happens
only when there is no error situation
(any longer)–the internal oscillator of
IC

3

is enabled via D5. This results after
a few seconds in a clock pulse appear­ing at the CLK input of IC

4

, where-

upon Q

4

goes high. The period

between the oscillator being enabled

and the appearance of
the first clock pulse is
not defined since,
owing to the presence

of T

6

, a power-on reset is purposely not
provided. To ensure a minimum delay
in the energizing of Re

1

and Re2in
spite of this, a high level is clocked into
Q

4

after IC3has been enabled. The pre­cise moment at which this happens
varies, therefore, only when the supply
voltage is switched on for the first time.

A period of IC

3/Q3

later, Q1of IC

4

goes high, whereupon Re1and Re2are
energized. After another period, Q

2

of

IC

4

becomes high, whereupon Re3and

Re

4

are energized. At the same time,

IC

3

is disabled since its reset is inter-

linked with Q

2

of IC4.

The red LED, D

8

, in parallel with Q

1

of IC4lights when the relays in the
amplifier are not energized, either
because the amplifier is (not yet)
switched on, or owing to an error .

The yellow LED, D

6

, is linked to the

output of the oscillator in IC

3

, causing

it to flash until IC

4

is clocked.

The green LED, D

9

, is connected in

parallel with Re

3

and Re4, so that it
lights only when the amplifier is fully
switched on.

TRANSFORMER
VOLTAGE SENSOR

The 50 V≈ secondary voltages of the
mains transformers in the amplifier are
rectified by diodes D

10

and D11, and

smoothed by R30-R31-R32-C10. The val­ues of these components ensure that
the LED in optoisolator IC

6

lights suf­ficiently to hold the associated photo
transistor on. This transistor pulls the
base of T

5

to ground, causing T5to cut
off. When the secondary voltages fail,
T

5

is switched on immediately via R29,

whereupon the D-type bistables in IC

4

are reset.

Use is made of an optoisolator pur­posely to avoid any risk of earth loops
between the supply return and the
ground of the protection network,
which is linked to the input ground of
the amplifier.

TEMPERATURE SENSOR

The temperature sensor works in a
manner similar to that of the trans­former voltage sensor . The optoisolator
in this circuit is IC

5

, which, in contrast to

IC

6

, is normally cut off and comes on
only when the heat sink becomes
excessively hot.

The sensor reacts to the fan control
circuit switching the fan speed to max­imum (because the heat sink is getting
too hot). A comparator in the fan con­trol circuit then toggles, whereupon
IC

5

is actuated via the ‘temp’ input and

resets the D-type bistables in IC

4

. This
situation changes only after the heat
sink has cooled down to an acceptable
temperature (although the fans may
still be rotating).

CURRENT SENSOR

To nullify high common-mode voltages
and to prevent any risk of earth loops,
the current sensor also uses an optoiso­lator, IC

2

(Figure 5). However, this is
not located on the protection board,
but directly at the output of the ampli­fier.

The values of the relevant compo­nents cause the sensor to be actuated
when the output current is about 40 A.
This may appear a very large current,
but this is due entirely to the specified
requirement that the amplifier must be
capable of delivering 60 V into a load
of 1.5 Ω without the protection circuit
being actuated. The current level may
be lowered to some extent by increas­ing the value of R

74

in the amplifier.

Output resistor R

78

is in parallel

with R

12

by linking terminals ‘I’, ‘+5 V’
and ground on the amplifier board to
K

1

on the protection board via three
lengths of insulated, stranded circuit
wire twisted together. This arrange-

35

Elektor Electronics 3/99

Figure 6. Completed pro­totype of the protection
network.

Contents

37

Elektor Electronics 3/99

ment ensures a low impedance to any
interference and a high reaction speed.

DIRECT- CURRENT AND
OVERDRIVE SENSOR

The d.c. and overdrive sensor con­stantly compares the input and output
signals of the amplifier and reacts
when the difference between the two
is too great. The comparison is effected
with the aid of operational amplifier
IC

1

which has a very low bias current
and a very low offset. It is, of course,
essential that during the comparison of
the two signals by differential amplifier
IC

1b

the differences in phase and tran­sit times do not lead to error detection.
At the same time, the voltage amplifi­cation (×43) of the amplifier must be
taken into account.

The amplification is compensated

by potential divider R

1-R2-P1

at input
LSP. The potentiometer is a multiturn
type to ensure accurate adjustment.

The phase difference is compen-

sated by the circuit based on IC

1a

. The
transit at high and low cut-off points
is simulated by first-order networks
that can also be adjusted very accu-

rately with multiturn poten­tiometers P

2

and P3.

The inputs of IC

1a

and IC

1b

are protected by diodes. Since any
leakage current of these diodes, com­bined with the high input impedance
(≈ 1MΩ) of IC

1a

, might lead to an
appreciable offset, and therefore to an
unwanted error detection, the diodes,
D

3

and D4, are special types with a

leakage current of only 1 nA.

The output of differential amplifier

IC

1b

is monitored by a window com-

parator formed by IC

2a

and IC2b. The
value of the components used in
potential dividers R

8-R9

and R10-R

11

ensures that the protection circuit is
actuated when the direct voltage
reaches a level of ±5 V or the distortion
becomes 2.5 per cent. Such distortion
will normally be the result of over­drive, but the circuit reacts equally well
to oscillations or other spurious signals
that cause too large a difference to be
detected.

CONSTRUCTION AND
SETTING UP

The integrated protection network is
best built on the printed-circuit board
shown in Figure 5. Populating this
board should not present any undue

difficulties, but it should be noted that
diodes D

6

, D8, D9and D13, are not
located on the board, but are linked to
it via flexible, stranded circuit wire.
They are fitted to the front of the enclo­sure.

Jumper JP

1

will normally be in posi­tion ‘intern’ unless relays with a coil
voltage other than 12 V are used.

A prototype of the completed pro-

tection board is shown in Figure 6.

All input and output terminals of
the board are clearly marked with the
same symbols as shown in Figure 4.
Most interconnections can be made in
thin, stranded hook-up wire to
DEF61-12, but the input and output
links (‘input’ and ‘LSP’) must be
screened audio cable.

Although the power supply for the
protection network can be fitted on the
same board, the relevant section may
be cut off and fitted elsewhere. Of
course, the supply lines must then be
linked to the relevant terminals on the
protection board via insulated,
stranded hook-up wire.

The power supply is straightfor­ward. From the secondary output of
the specified mains transformer, Tr

1

, a
symmetrical ±12 V supply is obtained
with the aid of regulators IC

7

and IC8.
From the same secondary, a +5 V sup­ply for the digital circuits is obtained
with the aid of regulator IC

9

. Since the
relays are fed by the +12 V line, regu­lator IC

7

must be fitted on a heat sink.

To ensure that the protection net­work is not actuated by interference on
the mains supply , it is advisable to pre­cede the power supply by a suitable
noise filter. This may be made from a
30 µH choke and two 0.1 µF, 300 V≈
capacitors as shown in dashed lines in
Figure 4.

The network is set up by maximiz­ing the common-mode suppression

7

Parts lists

Auxiliary power supply

Resistors:
R

1

, R2= 1 MΩ

Capacitors:
C

1

, C2= 470 µF, 100 V, radial

C

3

, C4= 0.1 µF, 100 V, pitch 7.5 mm

Semiconductors:
D

1–D8

= 1N4007

Miscelleneous:
K

1

= 2-way terminal block, pitch 7.5

mm

K

2

= 3-way terminal block, pitch

7.5 mm

K

3

, K4= 2-way terminal block, pitch

5mm

Tr

1

, Tr2= mains transformer, 1.5 VA,

with 12 V secondart

F

1

, F2= fuse, 160 mAT, and fuse

holder

Figure 7. Printed-circuit board
for the auxiliary power supply
described in Part 1.

Contents

H1

990001-3

990001-3

(C) ELEKTOR

K1

~~

H2

(C) ELEKTOR

990001-3

TR1

TR2

H4

D1

D2

F1

0.16AT

C1

D3

D4

D5

D6

C2

F2

D7

D8

0.16AT

C3

+++

K2 K3K4 R1R2

C4

0

---

H3

38

Elektor Electronics 3/99

9

with the aid of an oscilloscope or a
multimeter with sufficient bandwidth.
Measurements need to be made at
1 kHz, 20 kHz, and 20 Hz. The open­circuit amplifier is driven as far as pos­sible by a suitable sine-wave generator
or CD player with a test CD.

With a signal of 1 kHz, set P

1

for

minimum sign al at the output of IC

1b

,
follow this with a signal of 20 kHz and
adjusting P

2

, and finally, with a signal

of 20 Hz, by adjusting P

3

. Since the set­tings influence one another to some
extent, the potentiometers should be
set a couple of times, perhaps also at
some different audio frequencies.

POWER SUPPLY

The auxiliary power supply described
in Part 1 is best constructed on the
printed-circuit board shown in Fig-
ure 7. The mains voltage is linked to
K

1

, the ±70 V to K2and the +85 V and

–85 V lines to K

3

and K4respectively.
Since all currents are low level, the
wiring may be made in thin, insulated,
stranded hook-up wire. A completed
prototype board is shown in Figure 8.

The main supply for the amplifier is
a straightforward, unregulated type,
providing an output of ±70 V. Its cir­cuit diagram is shown in Figure 9.

Since the specified requirements
call for a 2 Ω load, the supply must be
rated at 1000 VA, which necessitates
two toroidal transformers. To prevent
unforeseen equalizing currents, the
dual secondaries are not linked in par­allel, but are individually connected to
a bridge rectifier. The outputs of the
rectifiers can be connected in parallel
without any problem. The rectifiers
need to be mounted on a suitable heat
sink such as a Type SK01.

It should be clear that the wiring of

the power supply must
allow for the large out­put currents of the
amplifier. In the proto­type, the electrolytic
capacitors are linked by 3 mm thick
strips of aluminium. The remainder of
the wiring should be in insulated,
high-current wire to BS6231 with a
conductor size of 50/0.25 mm (2.5 mm

2

)
or better. The use of car-type connec­tors is recommended.

Note that the power supply as

described is intended for use with a

mono(phonic) ampli­fier that can deliver
800 W into 2 Ω and
should remain stable

with loads of 1.5 Ω. If
you are certain that you will always
use 4 Ω or 8 Ωloads, the power supply
requirements may be relaxed to some
extent. A reasonable relaxation is the
use of 2×50V/300 VA transformers and
10,000 µF/100 V smoothing capacitors.
The rating of the primary fuses may
then be reduced to 1.5 AT.

MAINS

- ON DELAY

The use of a mains-on delay is recom­mended when heavy loads are to be
switched on, as in the case of the pre­sent amplifier. Such a delay circuit
switches on the mains to the load grad­ually to ensure that the switch-on cur­rent remains within certain limits and to
prevent the mains fuses from blowing.

The most recently published (in this
magazine) mains-on delay is found in
the July/August 1997 issue (p. 74),
whose circuit diagram is reproduced in
Figure 10. Its printed-circuit board is
readily connected with the primary
windings of the two mains transform­ers. The board is not available ready­made, however, and its diagram is,
therefore, reproduced in Figure 11.

8

Figure 8. The auxiliary
power supply is small
enough to fit in most
enclosures.

Figure 9. The main power supply for
the amplifier is a heavy-duty entity
in which the six capacitors are par­ticularly impressive.

Contents

mains

power-on

delay

2A5 T

e.g. 974078 - 1

mains

power-on

delay

2x 50V
500VA

2x 50V
500VA

200V / 35A

200V / 35A

6x 22000µ / 100V

70V

1000VA

e.g. 974078 - 1

2A5 T

990001 - 2 - 12

70V

39

Elektor Electronics 3/99

The delay arranges for the load,
that is, the Titan 2000, to be switched
on in two stages. In the first of these,
the switch-on current is limited by
series network R

4–R7

. After the delay

determined by capacitors C

2

and C3,
the series network is shorted by a relay
contact, whereupon the full current
flows between K

1

and K2.

Relay Re

1

can switch up to 2000 VA.
Its supply voltage is obtained from the
mains with the aid of rectifier B

1

,

capacitor C

1

and resistor R3.

Since the amplifier power supply
uses two mains transformers, two
mains-on delay circuits are needed.

Fuse F

1

functions as a primary

mains fuse for the amplifier.

Capacitor C

1

is a metallized paper
type intended especially for use with
mains voltage applications.

Bear in mind that the circuit is
linked directly to the mains supply and
thus carries lethal voltages.

Next month’s third instalment of
this article deals with the construction
of the amplifier, a few other practical
matters, and some measurements.

[990001-2]

Figure 10. The mains-on delay ensures that the
switch-on current remains within certain limit. Two of
these delays are required for each Titan 2000.

Figure 11. Printed-circuit board for the mains-on delay
circuit, which is not available ready made.

Parts lists

Mains-on delay circuit

Resistors:

R

1

, R2= 470 kΩ

R

3

= 220 Ω

R

4–R7

= 10 Ω, 5 W

Capacitors:
C

1

= 0.33 µF, 300 V a.c.

C

2

, C3= 470 µF, 40 V

Miscellaneous:
K

1

, K2= 2-way terminal block, pitch

7.5 mm

B1= bridge rectifier, round, Type

B250C1500

Re

1

= relay, coil 12 V, 1200Ω; contact

rating 250 V, 8 A

F

1

= see text

10

11

Contents

R1

K1

470kR2470k

C1

330n

*

250V

zie tekst

*

see text

*

voir texte

*

siehe Text

*

F1

R3

220Ω

*

~

B1

C3

470µ
40V

Re1

B250C1500

Re1 = V23057-B0006-A201

(250V / 8A)

C2

470µ
40V

R4

10Ω

5W

R5

10Ω

5W

R6

10Ω

5W

R7

10Ω

5W

K2

974078 - 11

~~~~

H3

F1

K1

R4

C1

R2

H4

974078-1

R1

R3

974078-1

B1

C3

R5

R6

RE1

H2

OUT

K2

R7

C2

H1

974078-1

Elektor Electronics 4/99

INTRODUCTION

It is clear from the first two parts of this
article that the Titan 2000 is a complex
unit that needs to be constructed and
wired up with with great care to
ensure the specified performance. For
that reason, the construction notes will
be more detailed than is usual with
projects in this magazine. It is assumed
that the protection network and auxil­iary power supply have already been
built and tested.

MOTHER BOARD

It must be borne in mind that in the
case of a fast power amplifier like the
Titan 2000, with a gain/bandwidth
product of about 0.5 GHz, the board

must be an integral part of the circuit.
The mother board is therefore
designed together with the remainder
of the circuit. The length of the tracks,
the area of the copper pads, the posi­tions of the decoupling capacitors, and
other factors, are vital for the proper
and stable operation of the unit. Con­structors who make their own boards
are therefore advised to adhere strictly
to the published layout.

Owing to the power requirements,
the various stages are parallel configu­rations. When these are mounted on
the heat sinks, a fairly large parasitic
capacitances to earth ensue. This is
because for reasons of stability all seven
heat sinks must be strapped to earth. It

This third of four parts

deals primarily with

the construction of the

amplifier and ends

with a brief resume of

its performance and

specifications. Let the

constructor beware,

however: the Titan

2000 is not an easy

project and certainly

not recommended for

beginners in elec-

tronic construction.

40

Design by T. Giesberts

Titan 2000

Part 3:

construction and setting up

AUDIO & HI-FI

Contents

41

Elektor Electronics 4/99

T13 T14

Parts lists

It is regretted that, owing to circum­stances beyond our control, compo­nent codings in the various sections
have been duplicated. Consequently,
the mother board, protection network
board, and auxiliary power supply
board contain many components
with the same identification (R

1-R36

,

C

1-C26

, D1-D12, T1-T6, IC1-IC2, JP1,

K

1

).

Amplifier

Resistors:
R

1

, R53= 1 MΩ

R

2

= 562 Ω
R3= 47 kΩ
R4, R6, R12, R14, R60, R61, R69, R70=

22 Ω
R5, R62, R71= 330 Ω
R7, R34= 470 Ω
R8= 22.1 Ω
R9= 390 Ω
R10, R11= 470 Ω, 5 W
R13, R15= 1.00 kΩ
R16, R17, R38= 150 Ω
R18, R20, R58, R67= 270 Ω
R19, R21= 10 kΩ, 1 W
R22, R23= 3.3 kΩ, 1 W
R24–R29= 68 Ω
R30= see text
R31, R32= 22 kΩ
R33, R35= 220 Ω
R36, R37= 560 Ω
R39–R44= 10 Ω
R45–R52= 0.22 Ω, inductance-free
R54, R55= 4.7 MΩ
R56, R65= 15 Ω
R57, R63, R66, R72= 15 kΩ
R59, R68= 5.6 kΩ
R64, R73= 12 kΩ
R74, R76, R77= 100 Ω
R75= 33 Ω
R78= 2.2 kΩ
R79= 2.2 Ω, 5 W
P1, P4, P5= 4.7 kΩ (5 kΩ) preset
P2= 250 Ω, preset
P3= 500 Ω, preset

Capacitors:
C1= 2.2 µF, metallized polyester

(MKP)
C2, C3, C42= 0.001 µF
C4, C5= 0.0022 µF
C6, C7= 220 µF, 25 V, radial
C8, C9, C11, C12, C15= 0.1 µF
C10, C13= 100 µF, 25 V, radial
C14= see text
C16–C23= 100 pF, 100 V
C24= 1 µF, metallized polypropylene

(MKT)
C25= 0.68 µF
C26, C27, C32, C39= 2.2 µF, 63 V,

radial

Figure 12. The double-sided printed-circuit board is intended to be combined with the
heat sink into a single entity. Before that can be done, however, the section for the output
relay and the inductor must be cut off the main section.

Contents

T

R79

T9

P4 P5

T10

H16

H15

H4

C8

R22 R23

H11 H12

D3

RE1

R1R2R3

P-IN

C11

H3

T49

T44

T

C10

LS+

C16

C9

mute

C18

R68

R59

C31

D4

D5

C25

R55

C2

D7

D6

C38

C32

R19

R54

R4

T1T2T3 T4

R6

C1

C13

C12

R21

C39

D11

D8
R58
R61

D2

R69

R70

R67

R60

1R

L1

K1

T

H14

D18D19

RE4

RE3

RE2

R13

LS-

C30

T43

D9

T45

R62

T47 T48

R63R64

C4

R18

R26

R16 R17

T11

C20

R57

T17

C33

T46

R25

C29

D10

T16

R24

C21

LS+

C17

T15

OUT2

T21T22T23

R56

990001-1

(C) ELEKTOR

C28

C34 C35

990001-1

H13

++

C43

C46

C44

R45

R49

H1

T35

T29

R39

T39

T32

R42

R46

-

R50

+

R47

R51

R48

R52

R38

R36

R40

R37

R43

R41

R44

T36

T30

T40

T37

T33

T41

T31

T38

T34

T42

H2

D16

P2

T7

R5

D1

T5

R12

P1

JP1

R14

T6

C7

R7

T8

C22

T12

C5

R15

R20

R29

R72R73

T52

T51

R71

D12

D17

P3

JP2

R27

C23

C19

R34

T18

C27

D15

IC1

D14

R53

LS+

C41

C42

+5V

R78

I

T27 T28

OUT1

P-LS

T

0 0

C47

H17H18

C45

R74
R75

C48

--

R77

R33

C15

R35

LS-

R11

T24T25T26

IC2

R76

R65

C26

C24

C6

R31 R32

R9

R8

C14

R30

C3

R10

T19

T20

R28

C40

D13

T50

C36

R66
C37

42

Elektor Electronics 4/99

990001-1

Contents

(C) ELEKTOR

is, of course, of paramount importance
that these capacitances are as small as
feasible. For this reason, it is vital that
in the thermal coupling of T

21–T34

1.5 mm thick ceramic—not mica—iso­lating washers are used. Mica washers
may , however, be used with the output
transistors since parasitic capacitances
there are of no significance.

The component and track layouts
of the mother board are shown in Fig-
ure 12. It will be seen that the board
consists of two sections: the mother
board proper and the output-relay
board. The latter must be cut off before
any other work is done. Later, when it
is built up, it is mounted on the mother
board with the aid of four 50 mm long
metal spacers in such a way that the
LS– and LS+ terminals on the two
boards are above each other. The spac­ers also provide the electrical link
between the boards.

The completed relay board is
shown in Figure 13. Inductor L

1

is

made from a doubled-up length of

1.5 mm enamelled copper wire wound
in two layers of eight turns each
around a 16 mm former (such as a
piece of PVC pipe). After the coil has
been wound, the PVC pipe is removed
and the four windings connected in
parallel. See Figure 14.

Ignoring the drivers and output
transistors for the moment, the con­struction of the mother board is tradi­tional. As always, great care must be
taken during the soldering and placing
of components. Do not forget the ther­mal coupling of T

1-T3

, T2-T4, D1-T5,

D

2-T6

, T45-T46, and T50-T51, as already

pointed out in Part 1. Also, T

21–T23

and

T

24–T26

must be mounted on a heat
sink, and isolated from it by means of
a ceramic washer. When this is done, fit
the composite heat sinks on the board,
and link them to earth.

The input signal and the ±85 V
supply lines are linked to the board via
standard solder pins.

For connecting the ±70 V supply
lines and the relay board, 3 mm screw
holes are provided. Metal spacers are
to be fixed to these and cable connec­tors to the top of the spacers.

MAIN HEAT SINK

When the mother board has been com­pleted, and carefully checked, as far as
described, it and the drivers and out­put transistors, T

27–T42

, must be

mounted on the main heat sink. This is

a 150 mm high Type SK157 from Fis­cher with a thermal resistance of

0.25 K W

–1

. This is admittedly a very
tedious job. It is vital that all requisite
fixing holes are drilled accurately in the
heat sink and preferably tapped with
3 mm thread. The template delivered
with the ready-made board is almost
indispensable for this work.

When the holes have been drilled

(and, possibly, tapped) transistors T

27

and T28should be fitted first (this is
important because they become inac­cessible after the board has been fitted).
They must be located as close as possi­ble to the output transistors and not in
the position indicated on the board.
Again, the template makes all this clear.
Their terminals must then be extended
with the aid of short lengths of equip­ment wire, which are later fed through
the relevant holes on the board and
soldered to the board via, for instance,
a three-way pin header.

The terminals of the drivers and
output transistors must be bent at right
angles: those of the former at the point
where they become thinner and those
of the latter about 5 mm from the body
of the device. When this is done, screw
all transistors loosely to the heat sink,
not forgetting the isolating washers. If it
is intended to use fan cooling, the req­uisite temperature sensor—that is, a
Type BD140 transistor— should also be
attached to the heat sink at this stage.
The template does not show a location
for the sensor, but it seems sensible to
fit it at the centre close to T

37

or T40.

The next step is to fit all ten spacers
to the heat sink: these should all be
10 mm long. In the prototype, spacers
with a 3 mm screwthread at one end
were used. Two of the spacers merely
provide additional support for the
relay board and another two form the
electrical link between the negative
supply line and the heat sink.

When all this work is done, the
board should look more or less like that
in Figure 15. Note that because of tests
later on, there are, as yet, no ceramic
isolating washers fitted on the proto­type.

The next, and most tedious, step is
to combine the board and heat sink. It
is, of course, vital that all spacers are
exactly opposite the relevant fixing
holes and—even more tedious—that
the terminals of all transistors are
inserted into the correct mounting
holes. Bear in mind that the metal

43

Elektor Electronics 4/99

C28, C34, C35, C41= 470 µF, 100 V,

radial
C29, C33, C36, C40= 0.22 µF, 100 V
C30, C37= 47 µF, 63 V, radial
C31, C38= 0.015 µF
C43–C48= 0.1 µF, 630 V

Inductors:
L1= see text

Semiconductors:
D1, D2= LED, red, flat
D3, D18, D19= 1N4148
D4, D6= zener, 5.6 V, 500 mW
D5, D7= zener, 15 V, 1.3 W
D8, D11= zener, 30 V, 1.3 W
D9, D12= zener, 39 V, 1.3 W
D10, D13, D16, D17= 1N4004
D14, D15= zener, 12 V, 500 mW
T1, T4, T5, T15–T17= BC560C
T2, T3, T6, T18–T20= BC550C
T7, T8, T43, T48= BF245A
T9= BF871
T10= BF872
T11, T50, T51= BC640
T12, T45, T46= BC639
T13, T14= BF256C
T21–T23= MJE350
T24–T26= MJE340
T27= BD139
T28= BD140
T29–T31= 2SC5171 (Toshiba)
T32–T34= 2SA1930 (Toshiba)
T35–T38= 2SC5359 (Toshiba)
T39–T42= 2SA1987 (Toshiba)
T44, T49= BF256A
T47= BD712
T52= BD711

Integrated circuits:
IC1= OP90G
IC2= 6N136

Miscellaneous:
JP1, JP2= 2.54 mm, 2-way pinstrip

and pin jumper
K1= 3-way terminal block, pitch 5 mm
Re1= relay, 12 V, 600 Ω
Re2–Re4= relay, 12 V, 16 A, 270 Ω
Heat sink for T21–T26= 38.1 mm,

11 K W–1(Fischer Type SK104-STC;

TO220)
Heat sink for drivers/output transistors,

150 mm, 0.25 K W–1, Fischer Type

SK157
Ceramic isolation washers for T21–T34:

Fischer Type AOS220
Mica isolating washers for T35–T

42

PCB Order no 990001-1 (see Readers

Services towards end of this magazine)

Contents

spacers for linking –, +,
LS+, and LS–, are
already on the board.
As the terminals of the
output transistors are
slightly longer than
those of the drivers, it may be possible
to do this work in two stages: output
transistors first and drivers second. It
may prove necessary to turn one or

more of the transistors slightly, which
is the reason that the fixing screws
have not yet been tightened. When all
terminals are correctly inserted, these
screws must, of course, be tightened
firmly.

The final step is to fix the relay
board on the spacers that form the link
for the LS– and LS+ terminals.

SETTING UP

Before the amplifier module can be
taken into use, presets P

2–P5

must be

set as required. Preset P

1

is intended
only for possibly adjusting the balance
in case of a bridge configuration.

Start by turning P

3

(the quiescent­current control) fully anticlockwise and
P

2

, P4, and P5, to their centre position.
Check the outputs of the power supply
and auxiliary power supply and, if
these are correct, link the +70 V line to
pins ‘+’ and ‘0’, the –70 V line to ‘–’
and ‘0’, the +85 V line to ‘++’ and the

-85 V line to ‘--’. For absolute safety, link
the ±70 V lines temporarily via a 10 Ω,
5 W resistor.

Next, set P

4

and P5for voltages of
+78 V and –78 V respectively at the
cases of transistors T

47

and T52respec-

44

Elektor Electronics 4/99

Figure 13. Illustrating
how the relay board is
mounted on the
mother board with the
aid of spacers.

Figure 14. Air-cored inductor L1is formed by lay­ing two windings each of eight turns of doubled­up each on top of one another. The former is a
length of 16 mm diameter PVC pipe as used by
plumbers. The resulting four windings are sim­ply connected in parallel.

Contents

tively (the cases of these transistors are
linked to the output of the relevant
regulator). It is important that the neg­ative and positive voltages are numer­ically identical.

Since the parameters of the n-p-n
and p-n-p transistors in the input stage
are never exactly identical, there may
be a slight imbalance. This may be cor­rected by adjusting the output of cur­rent source T

5

with the aid of preset P

2

to give a potential of exactly 0 V at the
output (pin 6) of IC

1

(when ‘cold’).

Finally, insert an ammeter (set to
500 mA or 1 A range) in the +70 V or
–70 V line, and adjust P

3

carefully for a
quiescent current of 200 mA (cold con­dition—that is, immediately after
switch-on). With a large drive signal,
the quiescent current may increase to
some 600 mA, but at nominal temper­atures, its level will stabilize at
200–400 mA. Note that these fluctua­tions have no noticeable effect on the
performance of the amplifier.

CHECK AND TEST

When the amplifier has been switched
on for about half an hour, the voltages
shown in Figure 2 (Part1) may be ver­ified. Note that voltage levels depend-

ing on the setting of current sources
habitually show a substantial spread:
30 per cent is quite common. All mea­surements should be carried out with
a good digital voltmeter or multimeter
with a high-impedance input.

Other than the test voltages in the
circuit diagram, there are some others
that may be checked. For instance, the
proper functioning of the output tran­sistors may be ascertained by measur­ing the voltage across R

45–R52

. Hold
one test probe against the loudspeaker
terminal and with the other measure
the potential at the emitters of all out­put transistors. The average value
should be about 20 mV, but deviations
of up to 50 per cent occur.

The voltage amplifier operation
may be checked by measuring its cur­rent drain: if this is within specification,
the voltage across R

56

and R65must be
within 0.8–1.1 V (after the amplifier has
been on for at least half an hour).

Finally, the potential drops across
the emitter resistors of differential
amplifiers T

45-T46

and T50-T51must not
differ by more than a factor 2. Too large
a factor is detrimental to the stable
operation of the amplifiers. A too large
difference may be corrected by chang-

ing the value of R62or R71, as the case
may be. If this is unsuccessful, the rel­evant transistor pair will have to be
replaced.

When all is well, the resistors in
series with the ±70 V lines should be
removed. Note that a rectified voltage
of 70 V, let alone one of 140V, is lethal. It
is therefore absolutely essential to
switch off the power supply and verify
that the residual voltages have
dropped to a safe value before doing
any work on the amplifier.

Next month’s instalment will deal
with the wiring up of the amplifier
and its performance, including speci­fications.

[990001-3]

45

Elektor Electronics 4/99

Figure 15. The PCB is
delivered with a tem­plate to ensure that
the transistors are fit­ted at the correct loca­tion on the heat sink.

Contents

101 48,5 0,5

22,7

T39 T40 T41T29 T30T32

300

T36 T42T35

T27

T37

T33

T28

T31

T38

T34

150

22,7 254,5

990001 - 3 - 13

Elektor Electronics 6/99

BRIDGING:
PROS AND CONS

Bridging, a technique that became fash­ionable in the 1950s, is a way of con­necting two single output amplifiers
(valve, transistor,

BJT, MOSFET, push-pull,

complementary) so that they together
control the passage of an alternating
current through the loudspeaker. This
article describes what is strictly a half­bridge configuration, a term not often
used in audio electronics. When audio
engineers speak of bridge mode, they
mean the full-bridge mode in which
four amplifiers are used.

In early transistor audio power
amplifiers, bridging was a means of
achieving what in the 1960s were called
public-address power levels as high as,

In the introduction to

Part 1 it was stated

that the Titan 2000

could deliver up to

2000 watts of ‘music

power’, a term for

which there is no stan-

dard definition but

which is still used in

emerging markets.

Moreover, without

elaboration, this state-

ment is rather misleading, since the reader will

by now have realized that the single amplifier

cannot possibly provide this power. That can

be attained only when two single Titan ampli­fiers are linked in a half-bridge circuit. The true
power, that is, the product of the r.m.s. voltage

across the loudspeaker and the r.m.s current

flowing into the loudspeaker, is then 1.6 kilo-

watts into a 4-ohm loudspeaker.

46

Design by T. Giesberts

Titan 2000

Part 5: half-bridging

two single amplifiers

GENERAL INTEREST

Contents

say 50–80 W into 8 Ω.
Such power levels were
then way beyond of
what the voltage rat­ings of output transis­tors would permit.

Bridging is considered by many to
be a good thing, since it automatically
provides a balanced input (drive).
However, opponents will quickly point
out that it halves output damping,
doubles the circuitry and virtually can­cels even-order harmonics created in
the amplifier.

Opponents also claim that bridging
amplifiers is tedious and requires too
much space. It is, however, not simple
either to design a single amplifier with
the same power output and the requi­site power supply. A single 2 kW
amplifier requires a symmetrical sup­ply voltage of ±130 V, that is, a total of

260 V. The power supply
for this would be quite a
design. And where
would a designer find
the drivers and output

transistors for this? Advo­cates point out that bridging amplifiers
have the advantage of requiring a rel­atively low supply voltage for fairly
high output powers.

Bridging just about doubles the
rated output power of the single
amplifier. Again, opponents point out
that loudness does not only depend on

47

Elektor Electronics 6/99

1

Figure 17. The interlinking required to form a half-bridge
amplifier from two single Titan 2000 units. Note that the
resulting balanced input may be reconverted to an unbal­anced one with the Brangé design (Balanced/unbalanced
converters for audio signals) published in the March
1998 issue of this magazine. The PCB for that design
(Order no. 980026) is still stocked.

Contents

T35

T29

R39

R45

C43

T39

T32

R42

R49

C46

++

C28

C34 C35

R56

C29

T46

R57

C30

D9

T43

D8

R61

R58

C31

R59

T44

T49

R68

D11

R67

R70

D12

C37

R66

T50

C36

R65

--

C48

R52

990001-1

T15

C17

R24

T16

D10

R25

C33

T17

R26

R62

R18

T47 T48

T45

R60

C32

P4 P5

T11

C4

R16 R17

R63R64

R13

R19

D4

C16

C8

R22 R23

1

2

C11

C18

R71

R44

C41

T51

D13

R75

C39

R72R73

T52

R76

R78

IT+5V

R74

T34

D6

R21

R15

C5

R20
R29

C40

R28

R27

C19

R77

C42

R48

T38

C38

R69

T42

T21T22T23

C21

C20

T13 T14

3

D18D19

T12

T

T20

T19

T18

IC2

K1

1R

L1

C45

R41

T31

T36

T30

R36

R40

R46

C44

D14

D15

R53

C27

IC1

D17

C24

C26

P2

D16

D1

T7

R5

R4

D5

T9

T10

C12

C22

C23

R54

C25

C9

mute

C10

T

D7

C13

RE2

RE3

RE4

T24T25T26

R55

D3

RE1

C1

R6

D2

R7

T8

C7

LS+

C3

R10

R30

LS-

R11

*

LS+

C47

R51

R79

T41

R47

R37

R43

T33

T37

T40

R38

R50

T27 T28

C15

R33

R34

P3

R31 R32

C6

R12

T5

T3 T4
T1

R3
R1

T

P-IN

R2

T2

T6

R14

JP1

R9

R8

C14

R35

LS-
LS+

P-LS

+

T37

+

P-LS

LS+
LS-

R35

JP2

C14

R8

R9

JP1

R14

P1

T6

T2

R6

C2

R2

P-IN

T

R1
R3

R55

C2

T1

R4

T3 T4

T5

P1

R12

C6

R31 R32

C24

P3

R34

R33

C15

T27 T28

00

-

R50

R38

T40

-

00

JP2

T41

T33

R37

R43

R47

D2

R53

C47

LS+

R11

LS-

R10

R30

C3

LS+

C7

T8

R7

C1

RE1

D3

T

mute

C25

R54

R5

T7

D1

D16

P2

C26

D17

IC1

C27

D14

D15

T31

R79

T24T25T26

*

RE4

RE3

RE2

C13

C12

D7

T10

C10

C9

R41

R51

L1

C23

1R

K1

C22

T

D18D19

T13 T14

T9

D5

C20

C21

T21T22T23

T38

T34

R48

C45

T12

*
*
*
*

R74

R75

IT+5V

R78

C42

IC2

R76

R77

T18

C19

R27

T19

T20

R21

D13

R28

C40

R29
R20

T52

C5

R72R73

R15

C39

D6

C18

C11

JP2 niet plaatsen
do not use JP2
ne pas implanter JP2
JP2 nicht stecken

R22 R23

C8

C16

D4

R19

R13

R63R64

R16 R17

C4

T11

R18
R26

T17

C33

R25

T16

R24

T15

C17

990001-1

T42

R44

R52

C48

--

C41

R65

C36

T50

R66

R71

T51

R69

C38

P4 P5

C32

R60

T45

T47 T48

R62

D10

C34 C35

C37

D12

R70

R67

D11

R68

T49

T44

R59

C31

R58

R61

D8

T43

D9

C30

R57

T46

C29

R56

C28

++

C44

R46

R36

R40

T30

T36

R42

C46

R49

T32

T39

R39

T29

C43

R45

T35

990001 - 4 - 11

the amplifier, but
also on the loud­speaker. Bear in
mind, they say, that just changing a
loudspeaker with a sensitivity of, say,
90 dB

SPL

per watt per metre to one with

a sensitivity of 93 dB

SPL

per watt per
metre is equal to doubling the ampli­fier power rating.

Clearly , bridging two amplifiers is a
mixture of good and bad audio engi­neering and sonics.

INTERCONNECTING

It is, of course, necessary that two com­pleted single Titan 2000 amplifiers are
available, each with its own power
supply. It should then be possible to
simply interlink the earths of the two
units, use the inputs as a common bal­anced input, and connect the loud­speaker between terminals LS+ on the
two amplifier. However, a few matters
must be seen to first.

Owing to the requisite stability , it is
imperative that the two amplifiers are
juxtaposed with the space between
them not exceeding 5 cm (2 in). They
should, of course, be housed in a com-

mon enclosure.

The inter-

wiring is shown
in Fig-ure 17. Make sure that the
power supplies are switched off and
that the smoothing capacitors have
been discharged before any work is
carried out.

Start by interlinking the negative
supply lines (terminals 0) with insu­lated 40/02 mm wire. Remove the
insulation at the centre of the length
of wire since this will become the cen­tral earthing point for the new (bal­anced) input. Link the ⊥ terminals on
both boards to the new central earth
with 24/02 mm insulated wire.

Connect the loudspeaker terminals
to the

LS+ terminals on the two boards

with 40/02 mm insulated wire.

Link pins 2 and 3 of the

XLR connec-

tor to the input terminals on the boards
with two-core screened cable. Solder
the screening braid to pin 1 of the

XLR

connector and to the new central
earthing point.

Finally, on both boards remove
jumper

JP

2

from the relevant pin strip.

FINALLY

When all interconnections between the
boards as outlined have been made,
the single amplifiers form a half-bridge
amplifier. If all work has been carried
out as described, there should be no
problems.

In the design stages, network R

9-P1

,
inserted into the circuit with pin
jumper

JP

1

(see Part1), was considered
necessary for common-mode suppres­sion. However, during the testing of
the prototype, the network was found
to be superfluous. It may be retained if
the half-bridge amplifier is to be used
with a second half-bridge amplifier for
stereo purposes, when it may be used
to equalize the amplifications of the
two half-bridge amplifiers.

[990001]

48

Elektor Electronics 6/99

Figure 18. Test setup for the
prototype half-bridge amplifier
(centre). Note the large power
supplies at the left and right of
the amplifier.

Contents

49

Elektor Electronics 6/99

Parameters

With a supply voltage of ±70 V (quiescent ±72 V) and a quiescent current of 200–400 mA

Input sensitivity 2.1 V r.m.s.
Input impedance 87 kΩ
True power output for 0.1%

THD 950 W into 8 Ω; 1.5 kW into 4 Ω

True power output for 1%

THD 1 kW into 8 Ω; 1.6 kW into 4Ω

Power bandwidth 1.5 Hz – 220 kHz
Slew limiting 170 V µs

–1

Signal+noise-to-noise ratio (at 1 W into 8 Ω) 97 dB (A-weighted

93 dB (B=22 kHz)

Total harmonic distortion (B=80 kHz)

at 1 kHz 0.0033% (1 W into 8 Ω)

0.002% (700 W into 8 Ω)

0.0047% (1 W into 4 Ω)

0.006% (700 W into 4 Ω)

at 20 kHz 0.015% (700 W into 8 Ω)

0.038% (1200 W into 4 Ω)

Intermodulation distortion

(50 Hz:7 kHz = 4:1) 0.0025% (1 W into 8 Ω)

0.0095% (500 W into 8 Ω)

0.004% (1 W into 4 Ω)

0.017% (500 W into 4 Ω)

Dynamic intermodulation distortion

(square wave of 3.15 kHz and 0.0038% (1 W into 8 Ω)
sine wave of 15 kHz) 0.0043% (700 W into 8 Ω)

0.005% (1 W into 4 Ω)

0.0076% (1200 W into 4 Ω)

Damping (with 8 Ω load) ≥ 350 (at 1 kHz)

≥ 150 (at 20 kHz)
Open-loop amplification ×8600
Open-loop bandwidth 53 kHz
Open-loop output impedance 3.2 Ω

A comparison of these parameters with the specifications given in Part 4 ((May 1999 issue) show that they are gener­ally in line. In fact, the intermodulation distortion figures are slightly better. Because of this, no new curves are given
here other than power output (1 kW into 8 Ω and 1.6 kW into 4 Ω) vs frequency characteristics for 1 per cent total har­monic distortion.

During listening tests, it was not possible to judge the half-bridge amplifier at full volume, simply because there were
no loudspeakers available that can handle this power output. However, up to 200 W true power output, the half-bridge
amplifier sounds exactly the same as the single amplifier. Instrument test figures show no reason to think that the per­formance at higher output powers will be degraded.

Contents

4k

2k

1k

500

200

100

W

50

20

10

5

2

20 20k

50 100 200 500 1k 2k 5k 10k

Hz

990001 - 4 - 12

33

Elektor Electronics 5/99

WIRING UP

How the various board, power sup­plies, controls and terminals are com­bined into an effective and interfer­ence-free unit is shown in Figure 16.

As already mentioned in Part 2, all
wiring carrying the main supply volt­age (±70 V) must be insulated, high­current wire to BS6321 with a conduc­tor size of 50/0.25 (2.5 mm

2

). This wire

should also be used to link the output

terminals of the power transistors and
the loudspeaker terminals. Any wiring
between smoothing capacitors and
the board should not exceed 15 cm
and be preferably much shorter. This
kind of wire is best terminated into
car-type connectors.

Other wiring may be made in
light-duty, stranded, insulated hook­up wire. It is advisable (and may
prove to be very helpful in case of
problems) to use wire with different
colour insulation for dissimilar func­tions.

The connections between the input
socket and board must, of course, be
in screened audio cable. To avoid
earth loops, the socket should be iso­lated from a metal enclosure. Bear in
mind that the supply earth and the
enclosure are linked by metal spacers
between the two ‘0’ terminals and the
heat sink. It is, therefore, essential that
the heat sink is firmly strapped to the
metal enclosure.

This fourth of five parts deals primarily with the

wiring up of the amplifier and ends with a brief

resume of its performance and specifications.

The fifth and final part of the article in a forth-

coming issue will deal with the temperature

control, bridge configuration and some other

practical hints.

Design by T. Giesberts

Titan 2000

Part 4: wiring and performance

AUDIO & HI-FI

Contents

34

Elektor Electronics 5/99

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C21

C22

C23

C24

C25

C26

C27

C28

C29

C30

C31

C32

C33

C34 C35

C36

C37

C38

C39

C40

C41

C42

C43

C44

C45

C46

C47

C48

D1

D2

D3

D4

D5

D6

D7

D8

D9

D10

D11

D12

D13

D14

D15

D16

D17

IC1

IC2

JP1

JP2

P1

P2

P3

P4 P5

R1R2R3

R4

R5

R6

R7

R8

R9

R10

R11

R12

R13

R14

R15

R16 R17

R18

R19

R20

R21

R22 R23

R24

R25

R26

R27

R28

R29

R30

R31 R32

R33

R34

R35

R36

R37

R38

R39

R40

R41

R42

R43

R44

R45

R46

R47

R48

R49

R50

R51

R52

R53

R54

R55

R56

R57

R58

R59

R60

R61

R62

R63R64

R65

R66

R67

R68

R69

R70

R71

R72R73

R74
R75

R76

R77

R78

RE1

T1T2T3 T4

T5

T6

T7

T8

T9

T10

T11

T12

T13 T14

T15

T16

T17

T18

T19

T20

T21T22T23

T24T25T26

T27 T28

T29

T30

T31

T32

T33

T34

T35

T36

T37

T38

T39

T40

T41

T42

T43

T44

T45

T46

T47 T48

T49

T50

T51

T52

--

++

+

-

00

LS+

LS-

I

T

+5V

mute

T

T

P-LS

P-IN

990001-1

B1

C18

C19

C20

C21

C22

C23

C24

C25

C26

D13

F1

IC7

IC8

IC9

K4

R35

R36

TR1

50mAT

-12V

+12V

0

+5V

~
~

C1 C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

C12

C13

C14

C15

C16

C17

D1

D2

D3

D4

D5

D6

D7

D8

D9

D10

D11

D12

IC1

IC2

IC3

IC4

IC5

IC6

JP1

K1

K2

K3

P1

P2

P3

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

R11

R12

R13

R14

R15

R16

R17

R18

R19

R20

R21

R22

R23

R24
R25

R26

R27

R28

R29

R30

R31

R32

R33
R34

T1

T2

T3

T4

T5

T6

0

+12V

-12V

int

ext

Vre

0

0

~

~

LSP

input

T

+

I

T

+5V

temp

T

mute

2R

990001-2

B1

C1

C2

C3 C4

C5

C6

C7

C8

C9

D1

D2

D3

D4 D5

D6

D7

F1

IC1

IC2

K1

K2

K3

K4

P1

P2

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

R11
R12

R13

R14
R15
R16

R17

R18

R19

R20

R21

R22

R23

R24

R25

T1

T2

TR1

temp.

max.

T

T

~

~

63mAT

-

+

E
CB

12V

~

~

990041-1

C1

C2

C3

C4

D1

D2

D3

D4

D5

D6

D7

D8

F1

F2

K1

K2 K3K4 R1R2

TR1

TR2

990001-3

0

---

+++

~~

0.16AT

0.16AT

D18D19

K1

L1

R79

RE2

RE3

RE4

LS+

LS-

LS+

T

1R

ERROR ON EARLY

POWER

MAX.

ON

POWER

FAN

CONTROL

12V 12V

100V

BD140

TEMP.

SENSOR

2x 100n
250V

X2

Contents

The on/off indicator, the functional
indicators, and the mains on/off
switch should, of course, be fitted on
the front panel of the enclosure. The
mains on/off switch must be a 10 A or
15 A type.

If the output power of the ampli­fier is limited to no more than 500 W,
in which case the enclosure does not
need fan cooling, the heat sink may
be mounted at the outside of the
enclosure or even form the sidewall
or back of a home-made enclosure.

For greater output powers, cooling
fans with relevant apertures at the
front and back of the enclosure are a
must. The heat sink must then be
located in the enclosure in such a
position that it is directly between the
two fans, ensuring a continuous sup­ply of cooling air.

PERFORMANCE

The specification and associated com­ments in the box cannot, of course,
give a full impression of the perfor­mance of the amplifier. It is a well­known fact that amplifiers with an
almost identical specification, and
using identical loudspeakers, can
sound quite different.

Particularly at low frequencies, the
amplifier maintains good control over
the loudspeaker, which results in a
clean fast (i.e., taut over the whole
audio range) sound, totally lacking in
reverberation. High and medium fre­quencies were also reproduced with
excellent definition and without any
trace of tizziness.

The overall impression is that the
amplifier has plenty of reserve and is
not strained in any circumstances.

In next month’s final instalment,
the temperature control and possible
bridge configuration will be dis­cussed.

[990001-3]

35

Elektor Electronics 5/99

B1

C1

C2

C3

F1

K1

K2

R1

R2

R3

R4

R5

R6

R7

RE1

974078-1

~~~~

B1

C1

C2

C3

F1

K1

K2

R1

R2

R3

R4

R5

R6

R7

RE1

974078-1

~~~~

250V

10A

35A

200V

35A

200V

2x 50V
500VA

2x 50V

500VA

MAINS

F1 = 2A5 T F1 = 2A5 T

Figure 16. The wiring
diagram clearly illus­trates how the various
parts of the amplifier
are combined into a
single unit.

Contents

ELEKTOR

50Hz240V

~

No. 990001

1000 VA

F = 2 x 2,5 A T
F = 63 mA T
F = 50 mA T

36

Elektor Electronics 5/99

Technical specifications

(Supply voltage = ±70 V; quiescent current = 200–400 mA)

Input sensitivity 1.1 V r .m.s.
Input impedance 47.5 kΩ
Sine-wave power output (0.1% THD) 280 W into 8 Ω; 500 W into 4 Ω; 800 W into 2 Ω
Music power* (1% THD) 300 W into 8 Ω; 550 W into 4 Ω; 1000 W into 2 Ω
Slew limiting 85 V µs

–1

Open-loop bandwidth 53 kHz
Open-loop amplification ×8600
Power bandwidth 1.5 Hz – 220 kHz
Signal-to-noise ratio (1 W into 8 Ω) 101 dB (A-weighted); 97 dB (B = 22 kHz)
Damping factor (at 8 Ω) >700 (1 kHz); >300 (20 kHz)
Output impedance 1.6 Ω
Harmonic distortion (THD) (B = 80 kHz) 8 Ω 4 Ω 2 Ω
at 1 kHz 0.003% (1 W) 0.0046% (1 W) 0.01% (1 W)

0.005% (200 W) 0.0084% (400 W) 0.02% (700 W)
at 20 kHz 0.009% (200 W) 0.018% (400 W) 0.07% (700 W)
Intermodulation distortion (IM)
(50 Hz:7 kHz = 4:1) 0.004% (1 W) 0.01% (1 W) 0.034% (1 W

0.016% (150 W) 0.025% (300W) 0.07% (500 W)
Dynamic IM
(square wave 3.15 kHz with sine wave 15 kHz) 0.003% (1 W) 0.0036% (1W) 0.0055% (1 W)

0.003% (200 W) 0.005% (400 W) 0.0085% (700 W)

*See Part 1 about the validity of this meaningless quantity.

The specified figures were measured after the amplifier
had been switched on for two hours. The figure show that
the Titan 2000 compares favourably with most amplifiers.
The slew limiting is a measure of the speed of the ampli­fier, which is exceptionally good in the Titan 2000.
Figure A shows the total harmonic distortion plus noise
(THD+N) for an output of 1 W into 8 Ω (lower curve) and
for 200 W into 8 Ω. The latter figure corresponds with 70%
of the peak sine wave power and the curve shows that the
distortion increases clearly only above 10 kHz.
Figure B shows the THD+N at 1 kHz as a function of the
drive with an output impedance of 8 Ω. The curve is pur-

posely drawn for a bandwidth of 22 kHz so that the noise
above 20 kHz does not degrade the performance of the
amplifier. From about 2 W, the distortion increases slightly
with increasing drive, which is normal in most amplifiers.
Figure C shows the peak output of the amplifier at a con­stant distortion of 0.1% and a load of 4 Ω (upper curve) and
8 Ω. The bandwidth was 80 kHz.
Figure D shows a Fourier analysis of a reproduced 1 kHz
signal at a level of 1 W into 8 Ω. It will be seen that the 2nd
harmonics are down just about 100 dB, while the 3rd har­monics are down to –114 dB. Higher harmonics lie below
the noise floor of –130 dB.

A B

C D

Contents

1

0.5

0.2

0.1

0.05

%

0.02

0.01

0.005

0.002

0.001
20 20k50 100 200 500 1k 2k 5k 10k

2k

1k

500

200

100

50

W

20

10

5

2

1

20 20k50 100 200 500 1k 2k 5k 10k

Hz

Hz

200W

1W

990001 - 3 - 14a

990001 - 3 - 14c

1

0.5

0.2

0.1

0.05

%

0.02

0.01

0.005

0.002

0.001
1m 2k2m 5m 10m 20m 50m 100m 500m 1 2 5 10 20 50 100 200 500 1k

+0

-10

-20

-30

-40

-50

-60

-70

d

-80

B

r

-90

-100

-110

-120

-130

-140

-150

-160
2k 20k4k 6k 8k 10k 12k 14k 16k 18k

W

Hz

990001 - 3 - 14b

990001 - 3 - 14d