Titan 2000 - Acoustic Psychos · 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

Elektor Electronics 2/99

It could be arguedthat most of the out-

put amplifiers pub-lished in this maga-

zine lack power.Although this is a

debatable point, itwas felt that a true

heavyweight outputamplifier would make

a welcome change formany constructors.The Titan 2000 canproduce 300 wattsinto 8 Ω, 500 watts

into 4 Ω, and800 watts into 2 Ω.

For those who believethat music power is a

reputable quantity, theamplifier can deliver

2000 watts of thismagical power into

4 Ω.

58

Design by T. Giesberts

Titan 2000High-power hi-fi and

public-address amplifier

Brief parametersSine-wave power output 300 W into 8 Ω; 500 W into 4 Ω; 800 W into 2 ΩMusic power* 2000 W into 4 ΩHarmonic distortion

I N T R O D U C T I O NAmplifier output has been a cause ofargument for as long as there havebeen audio power amplifiers. Fordomestic use, a power rating of2×50 W is more than sufficient. Withthe volume control at maximum andthe use of correctly matched good-quality loudspeakers, this will provide

a sound pressure level (SPL) equiva-lent to that of a grand piano beingplayed forte in the same room.

However, not all amplifiers areintended for domestic use: many aredestined for discos, small music hallsand other large rooms. But even here,what power is really required? Sincedoubling the amplifier output increasesthe SPL by a barely audible 3 dB, it wasfelt that 300 watts sine wave power into8 Ω would appeal to many.

‘ P R O G R A M M A B L E ’P O W E R O U T P U TThe amplifier has been designed insuch a manner that its output is ‘pro-grammable’ as it were. With a sinewave input, it delivers an averagepower of 300 W into an 8 Ω load,which should meet the requirementsof all but the power drunk. Compared

with the output of 50 W from adomestic audio amplifier, thisgives an increase in SPL of

7.5 dB. If even higher outputs areneeded, the load impedance may belowered to 4 Ω, which will give anincrease in SPL of 10 dB comparedwith a 50 W output.

Although music power is a depre-catory term, since it does not reallygive the true power rating of an ampli-fier, readers may note that the Titan2000 can deliver 2 kW of this magicalpower into 4 Ω. (True power is averagepower, 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 termmusic power is generally meaningless,because to some manufacturers it means theproduct of the peak voltage and peak cur-rent; to others it means merely double thetrue power; and to yet others, even moredisreputable, it means quadrupling the truepower).

However, power is not the only cri-terion of an amplifier. Low distortion,good slew limiting, and an extendedpower bandwidth, as possessed by theTitan 2000, are also hallmarks of a goodamplifier.

Power bandwidth denotes the fre-quency range over which the powerfalls to not less than half its maximumvalue. This is much more telling thanthe frequency response, which is usu-ally measured at a much lower outputlevel.

Slew limiting is the maximum inputvoltage change that can occur in one

59Elektor Electronics 2/99

voltage amplifier

regulator± 78V

main powersupply± 70V

auxiliarypower supply

2x 15V

T1...T10

T43...T52

input stages &cascode amplifiers

T15...T26

current amplifier

protectioncircuits

thermalcontrol

heat sinksensor

fan

offset control

T27...T34

drivers & output stages

990001 - 12

T35...T42

U in Uout

0

± 85V1

Figure 1. Simplified block dia-gram of the Titan 2000. The aux-iliary power supply, protectionnetworks and thermal controlare discrete circuits built on dis-crete PCBs.

60 Elektor Electronics 2/99

R56 1

5Ω

C28

470µ

10

0V

C30

47µ

63

V

C34

470µ

10

0V

C10

100µ

25

V

C29

220n

C33

220n

C32

2µ2

63

V

R62

330Ω

R57

15k

R58

270Ω

R60

22Ω

R61

22Ω R59

5k6

R63

15k R64

12k

R5

330Ω

5kP4

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30

V

1W3

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9V

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C31

15n

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712

245A

R651

5Ω

R66

15k

R71

330Ω

R69

22Ω

R70

22ΩR68

5k6

R73

12k R72

15k

R67

270ΩT48 B

F24

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T49

BF

256A C3

8

15n

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BC

T51

D13

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40

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711

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63

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470µ

10

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25

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P2

T5 T1

D1

C6

220µ

25

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T7

BF

R4

22Ω

T3

T9

BF

871

D2

C7

220µ

25

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T6 R7 470Ω

T8B

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R6

22ΩT2

T4

R3 47k

R1 1M

R16

150Ω

R12

22Ω R14

22Ω

R17

150Ω

R15

1k00R13

1k00

C4

2n2

C16

100p

C8

100n

C20

100p

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6

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270Ω R19

10k 1W

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3

C9

100n

T13 BF

256C

R22

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62

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Re1

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101

C13

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C18

100p

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68Ω

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T21

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68Ω

T16

T22

R26

68Ω

T17

T23

C21

100p

C17

100p

T18

T19

T20

T24

T25

T26

R27

68Ω

R28

68Ω

R29

68Ω

C23

100p

C19

100p

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T27

C15

100n

R33

220Ω R35

220Ω

R34

470Ω

50

0Ω

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R32

22kR31

22k

R30 R

C14

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M7

R54 4

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63

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C27

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R38

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R45

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T35

R46

0Ω22

T36

R47

0Ω22

T37

R48

0Ω22

T38

R49

0Ω22

R50

0Ω22

R51

0Ω22

R52

0Ω22

T39

T40

T41

T42

R36

560Ω R37

560Ω

R39

10Ω

T29

R40

10Ω

T30

R41

10Ω

T31

R42

10Ω

R43

10Ω

R44

10Ω

T32

T33

T34

R74

100Ω

R75 3

3Ω

R76

10

0Ω

R77

10

0Ω

C42

1nR78

2k2

R79

2Ω

2

L1

D18

D19

K1

LS

1

6N13

6

IC2

6 5

2 3

8 7

Re4

Re3

Re2

C43

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C44

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C45

100n

C46

100n

C47

100n

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2

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P-IN

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TE

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9900

01 -

11

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42=

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1987

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1930

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5359

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5171

BD BD

14

0

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BC

640

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0V830V83

2V24

20mV 20mV

38mV 32mV

35V35V

45mV 45mV

1V451V45

53mV 53mV

1V

0V36

39V

39V

1V7 1V7

-30V

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53V -53VT

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1

BF

872

13

9

T1,

T4,

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T15

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17 =

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560C

T2,

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T24

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340

T21

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om

mo

n h

eats

ink

Figure 2. Although the circuit diagram gives the impres-sion of a highly complex design, the amplifier is, inessence, fairly straightforward.

2

microsecond, and to which the ampli-fier can respond.

D E S I G NC O N S I D E R A T I O N SThe Titan 2000 is based on the ‘com-pact power amplifier’ published in theMay 1997 issue of this magazine. Thatwas a typical domestic amplifier with apower output of 50 W into 8 Ω or 85 Winto 4 Ω. The special property of thisfully balanced design was the use ofcurrent feedback instead of voltagefeedback, which resulted in a fast-responding amplifier with a largeopen-loop bandwidth. The amplifierperformed well both as regards instru-ment test and measurements and lis-tening tests. However, to serve as abasis for the Titan 2000, its output cur-rent and drive voltage range had to beincreased substantially.

For a start, the supply voltage has tobe more than doubled, which meansthat transistors with a higher powerrating have to be used in the powersupply. The higher supply voltage alsoresults in larger potential drops across anumber of components, and thismeans that dissipation problems mayarise.

The large output current requiredfor the Titan 2000 makes a completeredesign of the current amplifier usedin the ‘compact power amplifier ’unavoidable, since that uses insulated-gate bipolar transistors (IGBTs).Although these are excellent devices,the large spread of their gate-emittervoltage makes their use in parallel net-

works next to impossible. To obtain therequisite output power, the use of par-allel networks of symmetrical pairs oftransistors is inevitable.

In view of the foregoing, bipolartransistors are used in the currentamplifier of the Titan 2000. However,these cannot be driven as readily asIGBTs, which means that current driveinstead of voltage drive is used. Thisentails a substantial upgrading of thedriver stages and the preceding cas-code amplifiers (which also consist of acouple of parallel-connected transis-tors). The good news is that the powertransistors in the Titan 2000 are consid-erably less expensive than IGBTs: animportant factor when eight of thesedevices are used.

Finally, the protection circuits havebeen enhanced in view of the highervoltages and currents. The circuits pro-tecting against direct voltages andshort-circuits are supplemented bynetworks protecting against overloadand (too) high temperatures. The latteris coupled to a proportional fan con-trol.

In short, a large part of the Titan2000 is a virtually new design ratherthan a modified one.

B R I E F D E S C R I P T I O NThe block diagram of the Titan 2000 isshown in Figure 1. The voltage ampli-fier consists of input stages T1–T10, andcascode amplifiers/pre-drivers T15–T26.The current amplifier is formed by dri-ver transistors T27–T34, and output

transistors T35–T42.The offset control stage prevents

any direct voltage appearing at theoutput of the amplifier.

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

The current amplifier operates froma ±70 V supply, which is provided bytwo 50 V mains transformers. To enablethe voltage amplifier to drive the cur-rent amplifier to its full extent, it needsa slightly higher supply voltage tocompensate for the inevitable lossescaused by inevitable voltage drops.This is accomplished by superimposinga ±15 V potential from an externalauxiliary supply on to the main ±70 Vsupply and dropping the resultingvoltage to ±78 V with the aid of regu-lator T43–T52.

The combined protection circuitsconstantly compare the input and out-put voltage of the amplifier: any devi-ation from the nominal values leads tothe output relays disconnecting theloudspeaker and the input relaydecoupling the input signal.

The thermal protection circuit mon-itors the temperature of the heat sinkand, if necessary, switches on a fan. If,with the fan operating, the tempera-ture approaches the maximum per-missible limit, the output relays aredeenergized and disconnect the loud-speaker.

C I R C U I T D E S C R I P T I O NThe circuit diagram of the Titan 2000 isshown in Figure 2. In spite of the largenumber of components, the basic cir-


cuit is straightforward.As already noted in

the previous para-graph, transistorsT1–T10 form the inputamplifier, T11 and T12 are buffers, T13and T14 are current sources, T15–T26form the cascode amplifier/pre-driverstage, T27–T34 are the driver transistorsin the current amplifier, T35–T42 are theoutput transistors, and T43–T52 form asophisticated supply voltage regulator.

Input amplifier Strictly speaking, the input amplifier isformed by transistors T3–T4. Cascodestages T9–T10 serve merely to enablethe input section handling the highvoltages. These voltages are limited byzener diodes D5 and D7, which are partof the potential divider that also setsthe operating points of T21–T26. Inview of the requisite stability, the cur-rent through the zener diodes is heldconstant by current sources T13 andT14. Resistors R22 and R23 limit thepotential across, and thus the dissipa-tion in, these field-effect transistors.

Otherwise, the input section is vir-tually identical to that of the ‘compactpower amplifier’. The drop across theemitter resistors of buffers T1 and T2determines the drop across the emitterresistors of T3 and T4, and conse-quently the setting of the operatingpoint of the overall input section. Toeliminate the influence of temperaturevariations, T1 is thermally coupled toT3 and T2 to T4.

Since the operating point of buffersT1 and T2 is critical, current sources T5and T6 have been added. The referencefor these current sources is providedby light-emitting diodes (LEDs) D1 andD2. The current through these diodesis determined by current sources T7

and T8. In view of therequisite stability,diode D1 is thermallycoupled to T5 and D2to T6.

Any imbalance of the input stages iscompensated by making the currentthrough T5 equal to that through T6with potentiometer P2.

Cascode amplifiers/pre-drivers The large output current of the Titan2000 necessitates a proportionallylarge pre-drive voltage, which is pro-vided by three parallel-connected cas-code amplifiers, T15–T26. The currentthrough these amplifiers is arranged at10–15 mA, but the current feedbackused may cause this level to be appre-ciably higher. This is the reason that thetransistors used in the T21–T26 posi-tions are types that can handle cur-rents of up to 50 mA when their collec-tor-emitter voltage is 150 V.

The input section is linked to thecascode amplifiers by buffers T11 andT12, which results in a lowering of theinput impedance. The arrangementalso enables an increase in the valuesof R13 and R15, which results in a 3 dBincrease in amplification of the inputsection.

The function of resistors R19 andR21 is threefold: they limit the dissipa-tion of the buffers; they obviate theneed of an additional voltage to set theoperating point of the buffers; theylimit the maximum current throughthe buffers, and thus the cascodeamplifiers, to a safe value.

The open-loop amplification of theTitan 2000 is determined solely bythose of the input section and cascodeamplifiers. The amplification of theinput section depends on the ratiosR13:(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 theratio of parallel-connected resistors R31and R32 and the parallel network ofR24–R26. With values as specified, theamplification is about ×850 (remem-ber, this is a push-pull design), so thatthe overall amplification of input sec-tion plus cascode amplifiers is ×8500 (again of close to 80 dB).

Current amplifier Since one of the design requirements isthat the amplifier is to work with loadsdown to 1.5 Ω, the output stages con-sist of four parallel-connected pairs oftransistors, T35–T38 and T39–T42. Thesetransistors have a highly linear transfercharacteristic and provide a direct-cur-rent amplification that remains virtu-ally constant for currents up to 7 A.

Like the output transistors, the dri-ver stages need to remain within theirsafe operating area (SOA), whichnecessitates a threefold parallel net-work. The transistors used in the dri-ver stages are fast types(fT=200 MHz).

Setting the bias voltage for the req-uisite quiescent current is accom-plished by balanced transistors T27 andT28. These transistors are mounted onthe same heat sink as the output tran-sistors and driver transistors to ensuregood thermal coupling and currentcontrol. Of course, the current risesduring full drive conditions, but dropsagain to its nominal level when theamplifier cools off. The quiescent cur-rent is set to 200 mA with potentiome-ter P3.

Owing to the large output current,the connection between amplifier out-put and loudspeaker is not arrangedvia a single relay, but via three. Two ofthese, Re3–Re4, are controlled in syn-chrony by the protection circuits.When they are deenergized, their dis-abling action is delayed slightly to givethe contacts of the third relay, Re2, timeto open, which is of importance in afault situation.

Input relay Re1 is switched off insynchrony with Re2 to ensure thatthere is no input signal by the time Re3and Re4 are deenergized.

Optoisolator IC2 serves as sensor forthe current protection circuits. Thelight-emitting diode in it monitors thevoltage across R48–R52 via potentialdivider R74–R75, so that the positive aswell as the negative output currentsare guarded. The use of an optoisola-tor prevents earth loops and obviatescompensation of the ±70 V common-mode voltage. The +5 V supply for theoptoisolator is derived from the pro-tection circuits.

Feedback The feedback loop runs from the out-


12V / 1VA5

Tr1

12V / 1VA5

Tr2

D3

D2

D1

D4

D7

D6

D5

D8

K2

C1

470µ100V

C2

470µ100V

C3

100n

C4

100n

R1

1M

R2

1M

K1

K3

K4

160mA T

F1

160mA T

F2

70V

70V

990001 - 13

4x 1N4007

4x 1N4007

85V

85V

3

Figure 3. Circuit dia-gram of the requisiteauxiliary power supply.

put of the power stages to the junctionof T3 and T4 via resistors R10 and R11.This is current feedback because thecurrent through T3 and T4 depends onthe potential across R8, which is deter-mined largely by the current throughR10 and R11. The overall voltage ampli-fication of the output amplifier is deter-mined by the ratio R8:(R10+R11).

CompensationCapacitors C3–C5 and resistors R16, R17form part of the compensation net-work required for stable operation.

Low-pass filter R2–C2 at the input isessential to prevent fast, that is, high-frequency, signals causing distortion.This filter is also indispensable for sta-bility’s sake.

Coupling capacitor C1 is neededbecause the available offset compensa-tion network merely redresses the biascurrent of the input buffers and is notintended to block any direct voltages atthe input.

Relay Re1 at the input enables theinput signal to be ‘switched off ’. Itforms part of the overall protectionand in particular safeguards the inputsection against overdrive. The overallprotection circuit will be discussed indetail next month.

Network R9-P1 is intended specifi-cally for adjusting the common-modesuppression when two amplifiers areused in a bridge arrangement. It isneeded for only one of these ampli-fiers, and may be interconnected ordisabled by jumper JP1 as needed.

Offset compensation is provided byintegrator IC1, which ensures that ifthere is any direct voltage at the outputof the amplifier, the operating point ofT1-T2 is is shifted as needed to keep theoutput at earth potential. The opera-tional amplifier (op amp) used drawsonly a tiny current (20 µA) and has avery small input offset (450 µV).

Supply voltage for IC1 is taken fromthe ±15 V line for the input section viadiodes D16 and D17. This arrangementensures that the supply to the IC isretained for a short while after themain supply is switched off so that anyinterference is smoothed out.

Diodes D14 and D15 safeguard theinput of IC1 against (too) high inputvoltages in fault conditions.

The values of resistors R54 and R55arrange the level of the compensatingcurrent at not more than 1 µA, which issufficient to nullify the differencebetween the base currents of T1 and T2.

Regulation Although current feedback has manyadvantages, it also has a serious draw-back: poor supply voltage suppression.This makes it essential for the supplyvoltage for the voltage amplifier to beregulated. In view of the requisite highsymmetrical potential and the fact thatthe unregulated voltage that serves asinput voltage can vary substantiallyunder the influence of the amplifierload, two discrete low-drop regulators,T43–T47 and T48–T52 are used.

As mentioned before, owing to

inevitable losses through potentialdrops, the supply voltage for the inputsection and cascode amplifiers needs tobe higher than the main ±70 V line.Furthermore, the input voltage to theregulators must be higher than thewanted output voltage to ensure effec-tive regulation.

Fortunately, the current drawn bythe voltage amplifier is fairly low(about 70 mA) so that the input voltageto the regulators can be increased witha simple auxiliary supply as shown inFigure 3. This consists of two smallmains transformers,two bridge recti-fiers, D1–D4 and D5–D8, and the neces-sary reservoir and buffer capacitors.

The ±15 V output is linked in serieswith the ±70 V line to give an unregu-lated voltage of ±85 V.

The 39 V reference is provided byzener diode D9. This means that theregulator needs to amplify the refer-ence voltage ×2 to obtain the requisiteoutput voltage.

The zener diode is powered by cur-rent source T43, to ensure a stable ref-erence, which is additionally bufferedby C30.

Differential amplifier T45-T46, whoseoperating point is set by current sourceT44, compares the output voltage withthe reference via potential dividerR63-R64-P4. This shows that the outputvoltage level can be set with P4.

Transistor T47 is the output stage ofthe regulator. The output voltageremains stable down to 0.2 V below theinput voltage.


Current-feedbackIn an amplifier using voltage feedback (Figure a), the differential voltage at its inputs is multiplied by the open-loopamplification. The feedback loop forces the output voltage to a level that, divided by network R1-R2, is equal to theinput voltage.

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

The current feedback loop operates as follows. When the potential at the non-inverting input rises, the inverting inputwill also rise, resulting in the buffer current flowing through resistor R1. This current, magnified by the impedancematching stage, will cause the outputvoltage of the amplifier to rise until theoutput current flowing through resistor R2is equal to the buffer current through R1.The correct quiescent output voltage canbe sustained by a very small buffer cur-rent. The closed-loop amplification of thecircuit is determined by the ratio(1+R2):R1.

A interesting property of an amplifierwith current feedback is that the closed-loop bandwidth is all but independent ofthe closed-loop amplification, whereasthat of an amplifier with voltage feedbackbecomes smaller in inverse proportion tothe closed-loop amplification – a relationknown as the gain-bandwidth product.

A(s)

R2

R1

U in

Uout R(s)Av=1

R2

R1

990001 - 14

U in

Uout

I

a b

Av = 1 +R2R1

Av = 1 +R2R1


Resistor R57 and diode D8 protect T43against high voltage during switch-on,while D10 prevents current flowingthrough the regulator in the wrongdirection.

Capacitors C31 and C32 enhance therate of operation of the regulator.

Network R56-C28-C29 providesadditional smoothing and r.f. decou-pling of the ±85 V lines.

N E X T M O N T HNext month’s second and concludinginstalment of this article will describedetails of the protection circuits, the fancontrol, and the construction of theamplifier. The instalment will alsoinclude detailed specifications and per-formance characteristics.

[990001-1]


S I X F U N C T I O N SThe integrated protection network con-sists 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 therelays in the amplifier are energized50–100 milliseconds after the supplyhas been switched on to preventswitch-on clicks.

The transformer voltage sensorreacts to the cessation of the secondaryvoltage of the mains transformers toprevent switch-off clicks and crackles.

The temperature sensor responds toexcessive heat sink temperatures, but itshould be noted that this works only in

This second of fourparts deals primarily

with the protectionnetwork incorporated

in the amplifier. Thisindispensable net-

work safeguards theamplifier and the

loudspeakers con-nected to it against all

kinds of error thatmay arise. The net-

work is an indepen-dent entity with its

own power supply.

32


Titan 2000Part 2: protection network

I N T R O D U C T I O NAs mentioned briefly in Part 1, exten-sive and thorough protection is a mustin an amplifier of this nature. It maywell be asked why this is so: is theresuch a likelihood of mishaps arising?Or is the amplifier so vulnerable? Onthe contrary: extended tests on theprototype have shown that the Titan2000 is a very stable and reliable pieceof equipment. In fact, unusual meanshad to be used to actuate the protec-tion circuits during these tests, sincenot any standard test prompted theamplifier into an error situation.

The extensive protection is neces-sary because by far the largest numberof mishaps occur owing to actions bythe user, not because of any shortcom-ings in the amplifier. For example, themost robust and reliable amplifier cannot always cope with extremely highoverdrive or overload conditions.

Correction. In last month’s first partof this article, it was stated erro-neously that the article consists oftwo parts, whereas in fact it will bedescribed in four parts.

AUDIO & HI-FI

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

The current sensor monitors theoutput current, while the direct-cur-rent and overdrive sensors form acombined circuit that monitors differ-ences between the input and outputsignals, and reacts to excessive direct-current levels or distortion. This circuitis the most important and ‘intelligent’,but also the most complex of the six.

All sensors, when actuated, react inthe same way: they cause the outputrelays and the mute relay at the inputof the amplifier to be deenergizedimmediately. This action causes the

input signal and theoutput load to be dis-connected from theamplifier. After the faultcausing the sensoraction has beenremoved or remedied, the relevantprotection circuit is disabled, where-upon the amplifier relays are reener-gized after a short delay.

When the protection network isactuated, a red LED lights to indicatean error. When the fault has beenremoved or remedied, the red LEDremains on, but a yellow LED flashesto indicate that the amplifier will be

reenabled shortly. The red LED thengoes out, shortly followed by the yel-low, whereupon a green LED lights toindicate that all is well.

C O M M O N S E C T I O NA N D P O W E R - O N D E L A YThe circuit of the integrated protectionnetwork, including the +5 V and ±12 Vpower supplies, is shown in Figure 4.


R2

1k

05

R6

82

0k

R3

10

k0

R8

47

k

R9

47

0Ω

R10

47

0Ω

R11

47

k

R12

2k

2

R16

4k

7

R17

1k

R19

47

k

R27

4k

7

R26

4k

7

R24

47

k

R25

47

k

R28

3k

9

R34

10

0k

250ΩP1

500kP3

500Ω

P2

R1

100k

R5

680Ω

R7

1M

R4

10k0

R14

2M2

R13

470k

R20

2M7

R18

47k

5

4

12IC2a

10

9

7IC2b

C3

100n

C4

100n

C5

100n

C6

100n

2

3

1IC1a

6

5

7IC1b

K1

74HC4060

CTR14

IC3

CT=0

RCX10

11

12

15

13

14

11

13

12

CTCX

RX

!G

1

6

4

5

7

9

3

4

5

6

7

8

9

3

2

+

74HC175IC4

1314

15

11

1012

C1

1D

1

9

4

6

7

3

2

5

R

C8

100n

C7

470n

T1

BC

T5 T6

BC

R33

10

0k

R29

47

k

R30

3k

3

R31

15

k

R32

15

k

T3

BC

T4

BD

T2

BD

R21

2k

2

R22

2k

2

R23

4k

7

4N35

IC55

4

1

2

6

4N35

IC65

4

1

2

6

D7

1N

D11 1N4007

D10

C9

4µ763V

C10

10µ63V

R15

1k

K2

C1

100n D4

D3

BAS45A

C2

1n

D2

D1

BAT82

D5

1N4148

C11

47µ 25V

2x

JP1

140

K3

7805

IC9

IC7

7812

IC8

7912

IC1

8

4

IC2

11

6

C12

100n

C13

100n

C14

100n

C15

100n

C25

47n

C26

47n

C24

47n

C20

1000µ25V

C21

470µ25V

C18

4µ763V

C19

4µ763V

C23

47µ 25V

C22

4µ7 63V

2x 15V

Tr1

8VA

R36

22

Ω

B1

D13

R35

3k

3

K4

50mA T

F1 B80C1500

IC3

16

8

IC4

16

8

C16

100n

C17

100n

50V

50V

IC1 = OP249GPIC2 = LM319

I

+5V

+12V

–12V

+5V

+12V

–12V

+5V

+12V

–12V

+5V

+12V

–12V

5V

12V

12V

2x

12V

12V

12V5V

12V

12V

2x

2x

12V

12V

12V

3

8

5V

140

5V

12V

5V

5V

mute

2R

1R

Vre Ext.

int

ext

LSP

input

4148

temp

ERROR

ON

990001 - 2 - 11

D8

D9

D6

Vre

EARLY

547B

547B

D12

1N4001547B

30µH

2x 100n250V

POWER

4

Figure 4. The protection network con-sists of six sensor circuits each of whichcauses the input and output relays ofthe amplifier to be deenergized when afault occurs.

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

Terminals ‘50 V≈’ are connected tothe secondary windings of the mainstransformers.

The three output relays and themute relay in the amplifier are linkedto the protection network via K2, andK3 respectively.

The current sensor is connected tothe output of optoisolator IC2 in theamplifier (‘I->’ on the amplifier board)via K1.

The terminals marked ‘temp’ areintended to be linked to the output ofthe fan control circuit.

As mentioned earlier, the action ofeach sensor results in the deenergizingof the output and mute relays in theamplifiers. This implies that the out-puts of the the various sensor circuitsare interlinked. This is effected by com-bining the open-collector outputs ofthese circuits into a wired OR gate withR12 functioning as the common pull-up resistance. The combined outputsignal serves to reset a number of


990001-2

(C) ELEKTOR

B1

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

D1

D2

D3

D4

D5

D6 D7

D8

D9

D10

D11

D12

D13

F1

H1

H2

H3

H4

H5

H6H7

H8

IC1

IC2

IC3

IC4

IC5

IC6

IC7

IC8

IC9

JP1

K1

K2

K3

K4

P1

P2

P3

R1R2

R3

R4

R5

R6

R7

R8R

9R

10R

11R

12

R13

R14

R15

R16

R17

R18

R19

R20

R21

R22

R23

R24

R25

R26

R27R28

R29

R30

R31

R32

R33

R34

R35

R36

T1

T2

T3

T4

T5

T6

TR1

50m

AT

0

+12V -12V

int

ex

tV

re0

0 ~ ~

LSP

inp

ut

T

+IT

+5V

temp

T

mute 2R

-12V

+12V0

+5V

~

~

99

00

01

-29

90

00

1-2

(C) E

LEK

TOR

Parts listsProtection network

Resistors:R1, R33, R34 = 100 kΩR2 = 1.05 kΩR3, R4 = 10.0 kΩR5 = 680 ΩR6 = 820 kΩR7 = 1 MΩR8, R11, R18, R19, R24, R25, R29 = 47 kΩR9, R10 = 470 ΩR12, R21, R22 = 2.2 kΩR13 = 470 kΩR14 = 2.2 MΩR15, R17 = 1 kΩR16, R23, R26, R27 = 4.7 kΩR20 = 2.7 MΩR28 = 3.9 kΩR30, R35 = 3.3 kΩR31, R32 = 15 kΩR36 = 22 ΩP1 = 250 Ω, multiturn preset (upright)P2 = 500 Ω, multitun preset (upright)P3 = 500 kΩ, multiturn preset (upright)

Capacitors:C1, C3 = 0.1 µFC2 = 0.001 µFC4, C5, C6, C8, C12–C17 =0.1 µF,

ceramicC7 = 0.47 µFC9, C18, C19, C22 = 4.7 µF, 63 V, radialC10 = 10 µF, 63 V, radialC11, C23 = 47 µF, 25 V, radialC20 = 1000 µF, 25 V, radialC21 = 470 µF, 25 V, radial

C24–C26 = 0.047 µF, ceramic

Semiconductors:D1, D2 = BAT82D3, D4 = BAS45AD5, D7 = 1N4148D6, D8, D9, D13 = 3 mm high-efficiency

LED (yellow, red, green, green respectively)D10, D11 = 1N4007D12 = 1N4001T1, T3, T5, T6 = BC547BT2, T4 = BD140

Integrated circuits:IC1 = OP249GP (Analog Devices)IC2 = LM319NIC3 = 74HC4060IC4 = 74HC175IC5, IC6 = 4N35IC7 = 7812IC8 = 7912IC9 = 7805

Miscellaneous:JP1 = 2.54 mm pin strip and pin jumperK1, K2 = 3-way terminal block, pitch

5 mmK3 = 2-way terminal block, pitch 5 mmK4 = 2-way terminal block, pitch 7.5 mmB1 = bridge rectifier, rectangular, Type

B80C1500F1 = fuse, 50 mAT and fuse holderTr1 = mains transformer, 15 VA, with

2×15 V secondaryHeat sink (for IC7) = e.g. Fischer

SK104, 50 mmMains interference filter

Figure 5. The printed-circuitboard of the overall protec-tion network.

D-type bistables (flip-flops), contained inIC4, which are inter-connected to form ashift register. Note that D-type bistablesare essential since these can be set andreset in a defined manner.

The outputs of IC4 are used to drivetwo level converters, T1-T2 and T3-T4respectively, which bridge the differ-ence between the 5 V level of the logicICs and the 12 V supply for the relays.Jumper JP1 enables a different, externalsupply voltage (VRE) to be used if 12 Vrelays are not employed.

Transistors T1 and T2 drive Re1 andRe2, which are the first to be energized(synchronously). On switch-off, capac-itor C9 ensures that T2 remains on forsome milliseconds longer duringwhich period Re3 and Re4 are deener-gized (see Part 1).

The power-on delay, which alsooperates after a fault situation, is morecomplex than usual. To start with, afterthe supply voltage us switched on,input CLR of IC4 is held low (active)for a few seconds by the circuit aroundT6. When, after this period, CLR ismade high by R12 –which happensonly when there is no error situation(any longer)–the internal oscillator ofIC3 is enabled via D5. This results aftera few seconds in a clock pulse appear-ing at the CLK input of IC4 , where-upon Q4 goes high. The periodbetween the oscillator being enabled

and the appearance ofthe first clock pulse isnot defined since,owing to the presence

of T6, a power-on reset is purposely notprovided. To ensure a minimum delayin the energizing of Re1 and Re2 inspite of this, a high level is clocked intoQ4 after IC3 has been enabled. The pre-cise moment at which this happensvaries, therefore, only when the supplyvoltage is switched on for the first time.

A period of IC3/Q3 later, Q1 of IC4goes high, whereupon Re1 and Re2 areenergized. After another period, Q2 ofIC4 becomes high, whereupon Re3 andRe4 are energized. At the same time,IC3 is disabled since its reset is inter-linked with Q2 of IC4.

The red LED, D8, in parallel with Q1of IC4 lights when the relays in theamplifier are not energized, eitherbecause the amplifier is (not yet)switched on, or owing to an error.

The yellow LED, D6, is linked to theoutput of the oscillator in IC3, causingit to flash until IC4 is clocked.

The green LED, D9, is connected inparallel with Re3 and Re4, so that itlights only when the amplifier is fullyswitched on.

T R A N S F O R M E RV O L T A G E S E N S O RThe 50 V≈ secondary voltages of themains transformers in the amplifier arerectified by diodes D10 and D11, and

smoothed by R30-R31-R32-C10. The val-ues of these components ensure thatthe LED in optoisolator IC6 lights suf-ficiently to hold the associated phototransistor on. This transistor pulls thebase of T5 to ground, causing T5 to cutoff. When the secondary voltages fail,T5 is switched on immediately via R29,whereupon the D-type bistables in IC4are reset.

Use is made of an optoisolator pur-posely to avoid any risk of earth loopsbetween the supply return and theground of the protection network,which is linked to the input ground ofthe amplifier.

T E M P E R A T U R E S E N S O RThe temperature sensor works in amanner similar to that of the trans-former voltage sensor. The optoisolatorin this circuit is IC5, which, in contrast toIC6, is normally cut off and comes ononly when the heat sink becomesexcessively hot.

The sensor reacts to the fan controlcircuit switching the fan speed to max-imum (because the heat sink is gettingtoo hot). A comparator in the fan con-trol circuit then toggles, whereuponIC5 is actuated via the ‘temp’ input andresets the D-type bistables in IC4. Thissituation changes only after the heatsink has cooled down to an acceptabletemperature (although the fans maystill be rotating).

C U R R E N T S E N S O RTo nullify high common-mode voltagesand to prevent any risk of earth loops,the current sensor also uses an optoiso-lator, IC2 (Figure 5). However, this isnot located on the protection board,but directly at the output of the ampli-fier.

The values of the relevant compo-nents cause the sensor to be actuatedwhen the output current is about 40 A.This may appear a very large current,but this is due entirely to the specifiedrequirement that the amplifier must becapable of delivering 60 V into a loadof 1.5 Ω without the protection circuitbeing actuated. The current level maybe lowered to some extent by increas-ing the value of R74 in the amplifier.

Output resistor R78 is in parallelwith R12 by linking terminals ‘I’, ‘+5 V’and ground on the amplifier board toK1 on the protection board via threelengths of insulated, stranded circuitwire twisted together. This arrange-


Figure 6. Completed pro-totype of the protectionnetwork.


ment ensures a low impedance to anyinterference and a high reaction speed.

D I R E C T- C U R R E N T A N DO V E R D R I V E S E N S O RThe d.c. and overdrive sensor con-stantly compares the input and outputsignals of the amplifier and reactswhen the difference between the twois too great. The comparison is effectedwith the aid of operational amplifierIC1 which has a very low bias currentand a very low offset. It is, of course,essential that during the comparison ofthe two signals by differential amplifierIC1b the differences in phase and tran-sit times do not lead to error detection.At the same time, the voltage amplifi-cation (×43) of the amplifier must betaken into account.

The amplification is compensatedby potential divider R1-R2-P1 at inputLSP. The potentiometer is a multiturntype to ensure accurate adjustment.

The phase difference is compen-sated by the circuit based on IC1a. Thetransit at high and low cut-off pointsis simulated by first-order networksthat can also be adjusted very accu-

rately with multiturn poten-tiometers P2 and P3.

The inputs of IC1a and IC1bare protected by diodes. Since anyleakage current of these diodes, com-bined with the high input impedance(≈ 1 MΩ) of IC1a, might lead to anappreciable offset, and therefore to anunwanted error detection, the diodes,D3 and D4, are special types with aleakage current of only 1 nA.

The output of differential amplifierIC1b is monitored by a window com-parator formed by IC2a and IC2b. Thevalue of the components used inpotential dividers R8-R9 and R10-R11ensures that the protection circuit isactuated when the direct voltagereaches a level of ±5 V or the distortionbecomes 2.5 per cent. Such distortionwill normally be the result of over-drive, but the circuit reacts equally wellto oscillations or other spurious signalsthat cause too large a difference to bedetected.

C O N S T R U C T I O N A N DS E T T I N G U PThe integrated protection network isbest built on the printed-circuit boardshown in Figure 5. Populating thisboard should not present any undue

difficulties, but it should be noted thatdiodes D6, D8, D9 and D13, are notlocated on the board, but are linked toit via flexible, stranded circuit wire.They are fitted to the front of the enclo-sure.

Jumper JP1 will normally be in posi-tion ‘intern’ unless relays with a coilvoltage other than 12 V are used.

A prototype of the completed pro-tection board is shown in Figure 6.

All input and output terminals ofthe board are clearly marked with thesame symbols as shown in Figure 4.Most interconnections can be made inthin, stranded hook-up wire toDEF61-12, but the input and outputlinks (‘input’ and ‘LSP’) must bescreened audio cable.

Although the power supply for theprotection network can be fitted on thesame board, the relevant section maybe cut off and fitted elsewhere. Ofcourse, the supply lines must then belinked to the relevant terminals on theprotection board via insulated,stranded hook-up wire.

The power supply is straightfor-ward. From the secondary output ofthe specified mains transformer, Tr1, asymmetrical ±12 V supply is obtainedwith the aid of regulators IC7 and IC8.From the same secondary, a +5 V sup-ply for the digital circuits is obtainedwith the aid of regulator IC9. Since therelays are fed by the +12 V line, regu-lator IC7 must be fitted on a heat sink.

To ensure that the protection net-work is not actuated by interference onthe mains supply, it is advisable to pre-cede the power supply by a suitablenoise filter. This may be made from a30 µH choke and two 0.1 µF, 300 V≈capacitors as shown in dashed lines inFigure 4.

The network is set up by maximiz-ing the common-mode suppression

(C) ELEKTOR990001-3 C1

C2

C3

C4

D1

D2

D3

D4

D5

D6

D7

D8

F1

F2

H1

H2 H3

H4

K1

K2

K3

K4

R1

R2

TR1

TR2

990001-3

0-

--

++

+

~~

0.16AT

0.16AT

(C) ELEKTOR990001-3

7 Parts listsAuxiliary power supplyResistors:R1, R2 = 1 MΩ

Capacitors:C1, C2 = 470 µF, 100 V, radialC3, C4 = 0.1 µF, 100 V, pitch 7.5 mm

Semiconductors:D1–D8 = 1N4007

Miscelleneous:K1 = 2-way terminal block, pitch 7.5

mmK2 = 3-way terminal block, pitch

7.5 mmK3, K4 = 2-way terminal block, pitch

5 mmTr1, Tr2 = mains transformer, 1.5 VA,

with 12 V secondartF1, F2 = fuse, 160 mAT, and fuse

holder

Figure 7. Printed-circuit boardfor the auxiliary power supplydescribed in Part 1.


200V / 35A

200V / 35A

2x 50V500VA

2x 50V500VA

2A5 T

2A5 T

990001 - 2 - 12

70V

70V

1000VA

6x 22000µ / 100V

mainspower-on

delay

mainspower-on

delay

e.g. 974078 - 1

e.g. 974078 - 1

9

with the aid of an oscilloscope or amultimeter with sufficient bandwidth.Measurements need to be made at1 kHz, 20 kHz, and 20 Hz. The open-circuit amplifier is driven as far as pos-sible by a suitable sine-wave generatoror CD player with a test CD.

With a signal of 1 kHz, set P1 forminimum sign al at the output of IC1b,follow this with a signal of 20 kHz andadjusting P2, and finally, with a signalof 20 Hz, by adjusting P3. Since the set-tings influence one another to someextent, the potentiometers should beset a couple of times, perhaps also atsome different audio frequencies.

P O W E R S U P P L YThe auxiliary power supply describedin Part 1 is best constructed on theprinted-circuit board shown in Fig-ure 7. The mains voltage is linked toK1, the ±70 V to K2 and the +85 V and–85 V lines to K3 and K4 respectively.Since all currents are low level, thewiring may be made in thin, insulated,stranded hook-up wire. A completedprototype board is shown in Figure 8.

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

Since the specified requirementscall for a 2 Ω load, the supply must berated at 1000 VA, which necessitatestwo toroidal transformers. To preventunforeseen equalizing currents, thedual secondaries are not linked in par-allel, but are individually connected toa bridge rectifier. The outputs of therectifiers can be connected in parallelwithout any problem. The rectifiersneed to be mounted on a suitable heatsink such as a Type SK01.

It should be clear that the wiring of

the power supply mustallow for the large out-put currents of theamplifier. In the proto-type, the electrolyticcapacitors are linked by 3 mm thickstrips of aluminium. The remainder ofthe wiring should be in insulated,high-current wire to BS6231 with aconductor size of 50/0.25 mm (2.5 mm2)or better. The use of car-type connec-tors is recommended.

Note that the power supply asdescribed is intended for use with a

mono(phonic) ampli-fier that can deliver800 W into 2 Ω andshould remain stablewith loads of 1.5 Ω. If

you are certain that you will alwaysuse 4 Ω or 8 Ω loads, the power supplyrequirements may be relaxed to someextent. A reasonable relaxation is theuse of 2×50 V/300 VA transformers and10,000 µF/100 V smoothing capacitors.The rating of the primary fuses maythen be reduced to 1.5 AT.

M A I N S - O N D E L A YThe use of a mains-on delay is recom-mended when heavy loads are to beswitched on, as in the case of the pre-sent amplifier. Such a delay circuitswitches on the mains to the load grad-ually to ensure that the switch-on cur-rent remains within certain limits and toprevent the mains fuses from blowing.

The most recently published (in thismagazine) mains-on delay is found inthe July/August 1997 issue (p. 74),whose circuit diagram is reproduced inFigure 10. Its printed-circuit board isreadily connected with the primarywindings of the two mains transform-ers. The board is not available ready-made, however, and its diagram is,therefore, reproduced in Figure 11.

8

Figure 8. The auxiliarypower supply is smallenough to fit in mostenclosures.

Figure 9. The main power supply forthe amplifier is a heavy-duty entityin which the six capacitors are par-ticularly impressive.


The delay arranges for the load,that is, the Titan 2000, to be switchedon in two stages. In the first of these,the switch-on current is limited byseries network R4–R7. After the delaydetermined by capacitors C2 and C3,the series network is shorted by a relaycontact, whereupon the full currentflows between K1 and K2.

Relay Re1 can switch up to 2000 VA.Its supply voltage is obtained from themains with the aid of rectifier B1,capacitor C1 and resistor R3.

Since the amplifier power supplyuses two mains transformers, twomains-on delay circuits are needed.

Fuse F1 functions as a primarymains fuse for the amplifier.

Capacitor C1 is a metallized papertype intended especially for use withmains voltage applications.

Bear in mind that the circuit islinked directly to the mains supply andthus carries lethal voltages.

Next month’s third instalment ofthis article deals with the constructionof the amplifier, a few other practicalmatters, and some measurements.

[990001-2]

B1

B250C1500

C2

470µ40V

C3

470µ40V

R3

220Ω

R1

470k

R2

470k

C1

330n250V

Re1

F1

R4

10

Ω

5W

R5

10

Ω

5W

R6

10

Ω

5W

R7

10

Ω

5W

K2

K1

* ~*

zie tekst*see text*voir texte*siehe Text*

Re1 = V23057-B0006-A201

974078 - 11(250V / 8A)

Figure 10. The mains-on delay ensures that theswitch-on current remains within certain limit. Two ofthese delays are required for each Titan 2000.

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

974078-1

B1

C1

C2

C3

F1

H1

H2H3

H4

K1

K2

OUT

R1R

2

R3

R4

R5

R6

R7

RE1

974078-1

~~~~

974078-1

Parts listsMains-on delay circuit

Resistors:R1, R2 = 470 kΩR3 = 220 ΩR4–R7 = 10 Ω, 5 W

Capacitors:C1 = 0.33 µF, 300 V a.c.C2, C3 = 470 µF, 40 V

Miscellaneous:K1, K2 = 2-way terminal block, pitch

7.5 mmB1 = bridge rectifier, round, Type

B250C1500Re1 = relay, coil 12 V, 1200Ω; contact

rating 250 V, 8 AF1 = see text

10

11


I N T R O D U C T I O NIt is clear from the first two parts of thisarticle that the Titan 2000 is a complexunit that needs to be constructed andwired up with with great care toensure the specified performance. Forthat reason, the construction notes willbe more detailed than is usual withprojects in this magazine. It is assumedthat the protection network and auxil-iary power supply have already beenbuilt and tested.

M O T H E R B O A R DIt must be borne in mind that in thecase of a fast power amplifier like theTitan 2000, with a gain/bandwidthproduct of about 0.5 GHz, the board

must be an integral part of the circuit.The mother board is thereforedesigned together with the remainderof the circuit. The length of the tracks,the area of the copper pads, the posi-tions of the decoupling capacitors, andother factors, are vital for the properand stable operation of the unit. Con-structors who make their own boardsare therefore advised to adhere strictlyto the published layout.

Owing to the power requirements,the various stages are parallel configu-rations. When these are mounted onthe heat sinks, a fairly large parasiticcapacitances to earth ensue. This isbecause for reasons of stability all sevenheat sinks must be strapped to earth. It

This third of four partsdeals primarily with

the construction of theamplifier and ends

with a brief resume ofits performance and

specifications. Let theconstructor beware,

however: the Titan2000 is not an easy

project and certainlynot recommended for

beginners in elec-tronic construction.

40


Titan 2000Part 3:

construction and setting up

AUDIO & HI-FI


990001-1

(C) ELEKTOR

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

C12

C13

C14

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C18 C

19

C20

C21

C22

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C24

C25 C

26

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C34

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C48

D1

D2

D3

D4

D5

D6

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D10

D11D12

D13

D14D15

D16D17

D18D19

H1

H2H3

H4

H11

H12

H13

H14

H15

H16

H17H18

IC1

IC2

JP1

JP2

K1L1

OUT1

OUT2

P1

P2

P3

P4

P5

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

R11

R12

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R14

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R65R66

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R72R73 R74R75

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R79

RE

1

RE

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RE

3

RE

4

T1

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T21T22T23

T24T25T26

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T41

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T43

T44

T45

T46

T47

T48

T49

T50

T51

T52

--

++

+-0

0

LS+

LS

-

I

T

+5V

mute

T

T

P-L

S

LS+LS-LS+

T

1R

P-IN

99

00

01

-1

Parts lists

It is regretted that, owing to circum-stances beyond our control, compo-nent codings in the various sectionshave been duplicated. Consequently,the mother board, protection networkboard, and auxiliary power supplyboard contain many componentswith the same identification (R1-R36,C1-C26, D1-D12, T1-T6, IC1-IC2, JP1,K1).

Amplifier

Resistors:R1, R53 = 1 MΩ

R2 = 562 ΩR3 = 47 kΩR4, R6, R12, R14, R60, R61, R69, R70 =

22 ΩR5, R62, R71 = 330 ΩR7, R34 = 470 ΩR8 = 22.1 ΩR9 = 390 ΩR10, R11 = 470 Ω, 5 WR13, R15 = 1.00 kΩR16, R17, R38 = 150 ΩR18, R20, R58, R67 = 270 ΩR19, R21 = 10 kΩ, 1 WR22, R23 = 3.3 kΩ, 1 WR24–R29 = 68 ΩR30 = see textR31, R32 = 22 kΩR33, R35 = 220 ΩR36, R37 = 560 ΩR39–R44 = 10 ΩR45–R52 = 0.22 Ω, inductance-freeR54, R55 = 4.7 MΩR56, R65 = 15 ΩR57, R63, R66, R72 = 15 kΩR59, R68 = 5.6 kΩR64, R73 = 12 kΩR74, R76, R77 = 100 ΩR75 = 33 ΩR78 = 2.2 kΩR79 = 2.2 Ω, 5 WP1, P4, P5 = 4.7 kΩ (5 kΩ) presetP2 = 250 Ω, presetP3 = 500 Ω, preset

Capacitors:C1 = 2.2 µF, metallized polyester

(MKP)C2, C3, C42 = 0.001 µFC4, C5 = 0.0022 µFC6, C7 = 220 µF, 25 V, radialC8, C9, C11, C12, C15 = 0.1 µFC10, C13 = 100 µF, 25 V, radialC14 = see textC16–C23 = 100 pF, 100 VC24 = 1 µF, metallized polypropylene

(MKT)C25 = 0.68 µFC26, C27, C32, C39 = 2.2 µF, 63 V,

radial

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


99

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01

-1(C

) ELE

KTO

R

is, of course, of paramount importancethat these capacitances are as small asfeasible. For this reason, it is vital thatin the thermal coupling of T21–T341.5 mm thick ceramic—not mica—iso-lating washers are used. Mica washersmay, however, be used with the outputtransistors since parasitic capacitancesthere are of no significance.

The component and track layoutsof the mother board are shown in Fig-ure 12. It will be seen that the boardconsists of two sections: the motherboard proper and the output-relayboard. The latter must be cut off beforeany other work is done. Later, when itis built up, it is mounted on the motherboard with the aid of four 50 mm longmetal spacers in such a way that theLS– and LS+ terminals on the twoboards are above each other. The spac-ers also provide the electrical linkbetween the boards.

The completed relay board isshown in Figure 13. Inductor L1 ismade from a doubled-up length of1.5 mm enamelled copper wire woundin two layers of eight turns eacharound a 16 mm former (such as apiece of PVC pipe). After the coil hasbeen wound, the PVC pipe is removedand the four windings connected inparallel. See Figure 14.

Ignoring the drivers and outputtransistors for the moment, the con-struction of the mother board is tradi-tional. As always, great care must betaken during the soldering and placingof components. Do not forget the ther-mal coupling of T1-T3, T2-T4, D1-T5,D2-T6, T45-T46, and T50-T51, as alreadypointed out in Part 1. Also, T21–T23 andT24–T26 must be mounted on a heatsink, and isolated from it by means ofa ceramic washer. When this is done, fitthe composite heat sinks on the board,and link them to earth.

The input signal and the ±85 Vsupply lines are linked to the board viastandard solder pins.

For connecting the ±70 V supplylines and the relay board, 3 mm screwholes are provided. Metal spacers areto be fixed to these and cable connec-tors to the top of the spacers.

M A I N H E A T S I N KWhen the mother board has been com-pleted, and carefully checked, as far asdescribed, it and the drivers and out-put transistors, T27–T42, must bemounted on the main heat sink. This is

a 150 mm high Type SK157 from Fis-cher with a thermal resistance of0.25 K W–1. This is admittedly a verytedious job. It is vital that all requisitefixing holes are drilled accurately in theheat sink and preferably tapped with3 mm thread. The template deliveredwith the ready-made board is almostindispensable for this work.

When the holes have been drilled(and, possibly, tapped) transistors T27and T28 should be fitted first (this isimportant because they become inac-cessible after the board has been fitted).They must be located as close as possi-ble to the output transistors and not inthe position indicated on the board.Again, the template makes all this clear.Their terminals must then be extendedwith the aid of short lengths of equip-ment wire, which are later fed throughthe relevant holes on the board andsoldered to the board via, for instance,a three-way pin header.

The terminals of the drivers andoutput transistors must be bent at rightangles: those of the former at the pointwhere they become thinner and thoseof the latter about 5 mm from the bodyof the device. When this is done, screwall transistors loosely to the heat sink,not forgetting the isolating washers. If itis intended to use fan cooling, the req-uisite temperature sensor—that is, aType BD140 transistor— should also beattached to the heat sink at this stage.The template does not show a locationfor the sensor, but it seems sensible tofit it at the centre close to T37 or T40.

The next step is to fit all ten spacersto the heat sink: these should all be10 mm long. In the prototype, spacerswith a 3 mm screwthread at one endwere used. Two of the spacers merelyprovide additional support for therelay board and another two form theelectrical link between the negativesupply line and the heat sink.

When all this work is done, theboard should look more or less like thatin Figure 15. Note that because of testslater on, there are, as yet, no ceramicisolating washers fitted on the proto-type.

The next, and most tedious, step isto combine the board and heat sink. Itis, of course, vital that all spacers areexactly opposite the relevant fixingholes and—even more tedious—thatthe terminals of all transistors areinserted into the correct mountingholes. Bear in mind that the metal


C28, C34, C35, C41 = 470 µF, 100 V,radial

C29, C33, C36, C40 = 0.22 µF, 100 VC30, C37 = 47 µF, 63 V, radialC31, C38 = 0.015 µFC43–C48 = 0.1 µF, 630 V

Inductors:L1 = see text

Semiconductors:D1, D2 = LED, red, flatD3, D18, D19 = 1N4148D4, D6 = zener, 5.6 V, 500 mWD5, D7 = zener, 15 V, 1.3 WD8, D11 = zener, 30 V, 1.3 WD9, D12 = zener, 39 V, 1.3 WD10, D13, D16, D17 = 1N4004D14, D15 = zener, 12 V, 500 mWT1, T4, T5, T15–T17 = BC560CT2, T3, T6, T18–T20 = BC550CT7, T8, T43, T48 = BF245AT9 = BF871T10 = BF872T11, T50, T51 = BC640T12, T45, T46 = BC639T13, T14 = BF256CT21–T23 = MJE350T24–T26 = MJE340T27 = BD139T28 = BD140T29–T31 = 2SC5171 (Toshiba)T32–T34 = 2SA1930 (Toshiba)T35–T38 = 2SC5359 (Toshiba)T39–T42 = 2SA1987 (Toshiba)T44, T49 = BF256AT47 = BD712T52 = BD711

Integrated circuits:IC1 = OP90GIC2 = 6N136

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

and pin jumperK1 = 3-way terminal block, pitch 5 mmRe1 = relay, 12 V, 600 ΩRe2–Re4 = relay, 12 V, 16 A, 270 ΩHeat 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 TypeSK157

Ceramic isolation washers for T21–T34:Fischer Type AOS220

Mica isolating washers for T35–T42PCB Order no 990001-1 (see Readers

Services towards end of this magazine)

spacers for linking –, +,LS+, and LS–, arealready on the board.As the terminals of theoutput transistors areslightly longer thanthose of the drivers, it may be possibleto do this work in two stages: outputtransistors first and drivers second. Itmay prove necessary to turn one or

more of the transistors slightly, whichis the reason that the fixing screwshave not yet been tightened. When allterminals are correctly inserted, thesescrews must, of course, be tightenedfirmly.

The final step is to fix the relayboard on the spacers that form the linkfor the LS– and LS+ terminals.

S E T T I N G U PBefore the amplifier module can betaken into use, presets P2–P5 must beset as required. Preset P1 is intendedonly for possibly adjusting the balancein case of a bridge configuration.

Start by turning P3 (the quiescent-current control) fully anticlockwise andP2, P4, and P5, to their centre position.Check the outputs of the power supplyand auxiliary power supply and, ifthese are correct, link the +70 V line topins ‘+’ and ‘0’, the –70 V line to ‘–’and ‘0’, the +85 V line to ‘++’ and the-85 V line to ‘--’. For absolute safety, linkthe ±70 V lines temporarily via a 10 Ω,5 W resistor.

Next, set P4 and P5 for voltages of+78 V and –78 V respectively at thecases of transistors T47 and T52 respec-


Figure 13. Illustratinghow the relay board ismounted on themother board with theaid of spacers.

Figure 14. Air-cored inductor L1 is formed by lay-ing two windings each of eight turns of doubled-up each on top of one another. The former is alength of 16 mm diameter PVC pipe as used byplumbers. The resulting four windings are sim-ply connected in parallel.

tively (the cases of these transistors arelinked to the output of the relevantregulator). It is important that the neg-ative and positive voltages are numer-ically identical.

Since the parameters of the n-p-nand p-n-p transistors in the input stageare never exactly identical, there maybe a slight imbalance. This may be cor-rected by adjusting the output of cur-rent source T5 with the aid of preset P2to give a potential of exactly 0 V at theoutput (pin 6) of IC1 (when ‘cold’).

Finally, insert an ammeter (set to500 mA or 1 A range) in the +70 V or–70 V line, and adjust P3 carefully for aquiescent current of 200 mA (cold con-dition—that is, immediately afterswitch-on). With a large drive signal,the quiescent current may increase tosome 600 mA, but at nominal temper-atures, its level will stabilize at200–400 mA. Note that these fluctua-tions have no noticeable effect on theperformance of the amplifier.

C H E C K A N D T E S TWhen the amplifier has been switchedon for about half an hour, the voltagesshown in Figure 2 (Part 1) may be ver-ified. Note that voltage levels depend-

ing on the setting of current sourceshabitually show a substantial spread:30 per cent is quite common. All mea-surements should be carried out witha good digital voltmeter or multimeterwith a high-impedance input.

Other than the test voltages in thecircuit diagram, there are some othersthat may be checked. For instance, theproper functioning of the output tran-sistors may be ascertained by measur-ing the voltage across R45–R52. Holdone test probe against the loudspeakerterminal and with the other measurethe potential at the emitters of all out-put transistors. The average valueshould be about 20 mV, but deviationsof up to 50 per cent occur.

The voltage amplifier operationmay be checked by measuring its cur-rent drain: if this is within specification,the voltage across R56 and R65 must bewithin 0.8–1.1 V (after the amplifier hasbeen on for at least half an hour).

Finally, the potential drops acrossthe emitter resistors of differentialamplifiers T45-T46 and T50-T51 must notdiffer by more than a factor 2. Too largea factor is detrimental to the stableoperation of the amplifiers. A too largedifference may be corrected by chang-

ing the value of R62 or R71, as the casemay be. If this is unsuccessful, the rel-evant transistor pair will have to bereplaced.

When all is well, the resistors inseries with the ±70 V lines should beremoved. Note that a rectified voltageof 70 V, let alone one of 140 V, is lethal. Itis therefore absolutely essential toswitch off the power supply and verifythat the residual voltages havedropped to a safe value before doingany work on the amplifier.

Next month’s instalment will dealwith the wiring up of the amplifierand its performance, including speci-fications.

[990001-3]


T27 T28

T36 T42T35 T37 T38

150

990001 - 3 - 13

T39 T40 T41T29 T30T32 T33 T34T31

22,7

101

48,

5 0

,5

22,7 254,5

300

Figure 15. The PCB isdelivered with a tem-plate to ensure thatthe transistors are fit-ted at the correct loca-tion on the heat sink.


B R I D G I N G :P R O S A N D C O N SBridging, a technique that became fash-ionable in the 1950s, is a way of con-necting two single output amplifiers(valve, transistor, BJT, MOSFET, push-pull,complementary) so that they togethercontrol the passage of an alternatingcurrent through the loudspeaker. Thisarticle describes what is strictly a half-bridge configuration, a term not oftenused in audio electronics. When audioengineers speak of bridge mode, theymean the full-bridge mode in whichfour amplifiers are used.

In early transistor audio poweramplifiers, bridging was a means ofachieving what in the 1960s were calledpublic-address power levels as high as,

In the introduction toPart 1 it was statedthat the Titan 2000could deliver up to

2000 watts of ‘musicpower’, a term for

which there is no stan-dard definition but

which is still used inemerging markets.Moreover, without

elaboration, this state-ment is rather misleading, since the reader will

by now have realized that the single amplifiercannot possibly provide this power. That canbe attained only when two single Titan ampli-

fiers are linked in a half-bridge circuit. The truepower, that is, the product of the r.m.s. voltage

across the loudspeaker and the r.m.s currentflowing into the loudspeaker, is then 1.6 kilo-

watts into a 4-ohm loudspeaker.

46


Titan 2000Part 5: half-bridgingtwo single amplifiers

GENERAL INTEREST

say 50–80 W into 8 Ω.Such power levels werethen way beyond ofwhat the voltage rat-ings of output transis-tors would permit.

Bridging is considered by many tobe a good thing, since it automaticallyprovides a balanced input (drive).However, opponents will quickly pointout that it halves output damping,doubles the circuitry and virtually can-cels even-order harmonics created inthe amplifier.

Opponents also claim that bridgingamplifiers is tedious and requires toomuch space. It is, however, not simpleeither to design a single amplifier withthe same power output and the requi-site power supply. A single 2 kWamplifier requires a symmetrical sup-ply voltage of ±130 V, that is, a total of

260 V. The power supplyfor this would be quite adesign. And wherewould a designer findthe drivers and outputtransistors for this? Advo-

cates point out that bridging amplifiershave the advantage of requiring a rel-atively low supply voltage for fairlyhigh output powers.

Bridging just about doubles therated output power of the singleamplifier. Again, opponents point outthat loudness does not only depend on


C1C2

C3

C4 C

5

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C31C32

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C34 C35

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D1

D2D

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D4 D5 D6D7

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D17 IC1

IC2

JP1

JP2

P1

P2

P3

P4 P5R1

R2

R3

R4R5

R6

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R8R9

R10

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R15R16 R17

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R22 R23

R24

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R27

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R31 R32

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R38R

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R54R55

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R70

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R78

RE1

T1 T2T3 T4T5

T6T7T8

T9 T10

T11

T12

T13 T14

T15

T16

T17

T18

T19

T20

T21

T22

T23

T24

T25

T26

T27 T28

T29

T30

T31

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T34T35

T36

T37

T38

T39

T40

T41

T42

T43

T44

T45

T46

T47 T48

T49

T50

T51T52

--++

+-0 0

LS+LS-

I

T

+5V

muteT

T

P-LS

P-IN

990001-1

D18

D19

K1

L1

R79

RE2

RE3

RE4

LS+

LS

-LS

+

T

1R

C1C2

C3

C4C

5

C6

C7

C8

C9C10

C11

C12 C13

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C38C39

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D1

D2

D3

D4D5D6 D7

D8

D9

D10

D11

D12

D13

D14

D15

D16

D17IC1

IC2

JP1

JP2

P1

P2

P3

P4P5R1

R2

R3

R4R5

R6

R7

R8R9

R10

R11

R12

R13

R14

R15R16R17

R18

R19

R20

R21

R22R23

R24

R25

R26

R27

R28

R29

R30

R31R32

R33

R34

R35

R36

R37

R38 R39

R40

R41

R42

R43

R44

R45

R46

R47

R48

R49

R50

R51

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R53

R54R55

R56

R57

R58

R59

R60

R61

R62

R63

R64

R65

R66

R67

R68

R69

R70

R71

R72

R73

R74

R75

R76

R77

R78

RE1

T1T2T3T4 T5T6 T7

T8

T9T10

T11

T12

T13T14

T15

T16

T17

T18

T19

T20

T21

T22

T23

T24

T25

T26

T27T28

T29

T30

T31

T32

T33

T34

T35

T36

T37

T38

T39

T40

T41

T42

T43

T44

T45

T46

T47T48

T49

T50

T51T52

--

++

+ -00

LS+LS-

I

T

+5Vm

ute T

T

P-LS

P-I

N

990001-1

D18

D19

K1

L1

R79

RE2

RE3

RE4

LS+

LS

-LS

+

T

1R

1

23

*

*

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

990001 - 4 - 11

1

Figure 17. The interlinking required to form a half-bridgeamplifier from two single Titan 2000 units. Note that theresulting balanced input may be reconverted to an unbal-anced one with the Brangé design (Balanced/unbalancedconverters for audio signals) published in the March1998 issue of this magazine. The PCB for that design(Order no. 980026) is still stocked.

the amplifier, butalso on the loud-speaker. Bear inmind, they say, that just changing aloudspeaker with a sensitivity of, say,90 dBSPL per watt per metre to one witha sensitivity of 93 dBSPL per watt permetre is equal to doubling the ampli-fier power rating.

Clearly, bridging two amplifiers is amixture of good and bad audio engi-neering and sonics.

I N T E R C O N N E C T I N GIt is, of course, necessary that two com-pleted single Titan 2000 amplifiers areavailable, each with its own powersupply. It should then be possible tosimply interlink the earths of the twounits, use the inputs as a common bal-anced input, and connect the loud-speaker between terminals LS+ on thetwo amplifier. However, a few mattersmust be seen to first.

Owing to the requisite stability, it isimperative that the two amplifiers arejuxtaposed with the space betweenthem not exceeding 5 cm (2 in). Theyshould, of course, be housed in a com-

mon enclosure.The inter-

wiring is shownin Fig-ure 17. Make sure that thepower supplies are switched off andthat the smoothing capacitors havebeen discharged before any work iscarried out.

Start by interlinking the negativesupply lines (terminals 0) with insu-lated 40/02 mm wire. Remove theinsulation at the centre of the lengthof wire since this will become the cen-tral earthing point for the new (bal-anced) input. Link the ⊥ terminals onboth boards to the new central earthwith 24/02 mm insulated wire.

Connect the loudspeaker terminalsto the LS+ terminals on the two boardswith 40/02 mm insulated wire.

Link pins 2 and 3 of the XLR connec-tor to the input terminals on the boardswith two-core screened cable. Solderthe screening braid to pin 1 of the XLRconnector and to the new centralearthing point.

Finally, on both boards removejumper JP2 from the relevant pin strip.

F I N A L L Y

When all interconnections between theboards as outlined have been made,the single amplifiers form a half-bridgeamplifier. If all work has been carriedout as described, there should be noproblems.

In the design stages, network R9-P1,inserted into the circuit with pinjumper JP1 (see Part 1), was considerednecessary for common-mode suppres-sion. However, during the testing ofthe prototype, the network was foundto be superfluous. It may be retained ifthe half-bridge amplifier is to be usedwith a second half-bridge amplifier forstereo purposes, when it may be usedto equalize the amplifications of thetwo half-bridge amplifiers.

[990001]


Figure 18. Test setup for theprototype half-bridge amplifier(centre). Note the large powersupplies at the left and right ofthe amplifier.


ParametersWith 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 kΩTrue power output for 0.1% THD 950 W into 8 Ω; 1.5 kW into 4 ΩTrue power output for 1% THD 1 kW into 8 Ω; 1.6 kW into 4ΩPower bandwidth 1.5 Hz – 220 kHzSlew limiting 170 V µs–1

Signal+noise-to-noise ratio (at 1 W into 8 Ω) 97 dB (A-weighted93 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 ×8600Open-loop bandwidth 53 kHzOpen-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 gener-ally in line. In fact, the intermodulation distortion figures are slightly better. Because of this, no new curves are givenhere other than power output (1 kW into 8 Ω and 1.6 kW into 4 Ω) vs frequency characteristics for 1 per cent total har-monic distortion.

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

2

4k

5

10

20

50

100

200

500

1k

2k

W

20 20k990001 - 4 - 12

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


W I R I N G U PHow the various board, power sup-plies, controls and terminals are com-bined into an effective and interfer-ence-free unit is shown in Figure 16.

As already mentioned in Part 2, allwiring carrying the main supply volt-age (±70 V) must be insulated, high-current wire to BS6321 with a conduc-tor size of 50/0.25 (2.5 mm2). This wireshould also be used to link the output

terminals of the power transistors andthe loudspeaker terminals. Any wiringbetween smoothing capacitors andthe board should not exceed 15 cmand be preferably much shorter. Thiskind of wire is best terminated intocar-type connectors.

Other wiring may be made inlight-duty, stranded, insulated hook-up wire. It is advisable (and mayprove to be very helpful in case ofproblems) to use wire with differentcolour insulation for dissimilar func-tions.

The connections between the inputsocket and board must, of course, bein screened audio cable. To avoidearth loops, the socket should be iso-lated from a metal enclosure. Bear inmind that the supply earth and theenclosure are linked by metal spacersbetween the two ‘0’ terminals and theheat sink. It is, therefore, essential thatthe heat sink is firmly strapped to themetal enclosure.

This fourth of five parts deals primarily with thewiring up of the amplifier and ends with a briefresume of its performance and specifications.The fifth and final part of the article in a forth-

coming issue will deal with the temperaturecontrol, bridge configuration and some other

practical hints.


Titan 2000Part 4: wiring and performance

AUDIO & HI-FI


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C8

C9

C10

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ERROR ON EARLY POWER

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ON

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Documents

Titan 2000 - Acoustic Psychos · 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