titan 2000 - acoustic psychos · elektor electronics 2/99 it could be argued that most of the...
TRANSCRIPT
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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
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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.
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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
D8
30
V
1W3
D9 3
9V
1W3
D10
1N
40
04
T43 B
F
T44
BF
256A
T45
BC
T46
C31
15n
T47 BD
712
245A
R651
5Ω
R66
15k
R71
330Ω
R69
22Ω
R70
22ΩR68
5k6
R73
12k R72
15k
R67
270ΩT48 B
F24
5A
T49
BF
256A C3
8
15n
T50
BC
T51
D13
1N
40
04
T52BD
711
5k
P5
D11
30
V1W
3C
39
2µ2
63
V
C37
47µ
63
V
D12 3
9V
1W3
C41
470µ
10
0V
C40
220n
C35
470µ
10
0V
C36
220n
25
0Ω
P2
T5 T1
D1
C6
220µ
25
V
T7
BF
R4
22Ω
T3
T9
BF
871
D2
C7
220µ
25
V
T6 R7 470Ω
T8B
F
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
D4
5V
6
0W5
T11
R18
270Ω R19
10k 1W
D5 15
V1W
3
C9
100n
T13 BF
256C
R22
3k3
1W
C2
1n
C1
2µ2
R2 5
62
Ω
Re1
V23
042-
A20
03-B
101
C13
100µ
25
V
C12
100n
D7 15
V1W
3
T14 BF
256C
R23
3k3
1W
C11
100n
C22
100p
D6
5V
6
0W5
C5
2n2
T12
R21
10k 1W R20
270Ω
R8 22Ω1
R9 390Ω
5kP1
JP
1
R10 47
0Ω
C3 1n
R11 47
0Ω
C18
100p
R24
68Ω
T15
T21
R25
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
T28
T27
C15
100n
R33
220Ω R35
220Ω
R34
470Ω
50
0Ω
P3
R32
22kR31
22k
R30 R
C14
C
R55 4
M7
R54 4
M7
OP
90
G
IC1
2 3
6
7 4
1
5
D14
D151
2V
0W5
D16
1N
40
04
D17
1N
40
04
C26
2µ2
63
V
C27
2µ2
63
VC
25
68n
C24 1µ
R53
1M
R38
150Ω
R45
0Ω22
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
100n
C44
100n
C45
100n
C46
100n
C47
100n
C48
100n
245A
245A
JP
2
64
0
2x
63
9
2x
5V
+5
V I
LS
+L
S+
LS-
LS-
2R 1R
70
V
70
V
15
V
15
V
15
V
15
V
P-L
S
85
V
85
V
D3
1N
41
48
P-IN
MU
TE
+7
8V
-78V
9900
01 -
11
T39
...T
42=
2SA
1987
T32
...T
34=
2SA
1930
T35
...T
38=
2SC
5359
T29
...T
31=
2SC
5171
BD BD
14
0
BD
139
E
C
B
BF
256C
GD
S
BD
140
BF
245A
BC
639
CB
E
BC
560
CB
E
BC
550
BC
640
MJ
E3
40
E
C
B
MJ
E3
50
BD
712
0V830V83
2V24
20mV 20mV
38mV 32mV
35V35V
45mV 45mV
1V451V45
53mV 53mV
1V
0V36
39V
39V
1V7 1V7
-30V
-39V
-39V
0V36
1V
53V -53VT
10
8V4
2mA
1
BF
872
13
9
T1,
T4,
T5,
T15
...T
17 =
BC
560C
T2,
T3,
T6,
T18
...T
20 =
BC
550C
T24
...T
26=
MJE
340
T21
...T
23=
MJE
340
BD
711
BE
C
2SC
5359
2SA
1987
E
C
B
2SC
5171
2SA
1930 E
C
B
BF
871
C
EB
BF
872
T27
...T
42 o
n c
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
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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-
61Elektor Electronics 2/99
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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-
62 Elektor Electronics 2/99
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.
63Elektor Electronics 2/99
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
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65Elektor Electronics 2/99
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]
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Elektor Electronics 3/99
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
Design by T. Giesberts
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
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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.
33Elektor Electronics 3/99
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
34 Elektor Electronics 3/99
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-
35Elektor Electronics 3/99
Figure 6. Completed pro-totype of the protectionnetwork.
-
37Elektor Electronics 3/99
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.
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38 Elektor Electronics 3/99
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.
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39Elektor Electronics 3/99
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
-
Elektor Electronics 4/99
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
Design by T. Giesberts
Titan 2000Part 3:
construction and setting up
AUDIO & HI-FI
-
41Elektor Electronics 4/99
990001-1
(C) ELEKTOR
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18 C
19
C20
C21
C22
C23
C24
C25 C
26
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
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
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
R56R57
R58R59
R60
R61
R62
R63R64
R65R66
R67
R68
R69
R70
R71
R72R73 R74R75
R76
R77
R78
R79
RE
1
RE
2
RE
3
RE
4
T1
T2
T3
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
--
++
+-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.
-
42 Elektor Electronics 4/99
99
00
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
43Elektor Electronics 4/99
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-
44 Elektor Electronics 4/99
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]
45Elektor Electronics 4/99
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.
-
Elektor Electronics 6/99
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
Design by T. Giesberts
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
47Elektor Electronics 6/99
C1C2
C3
C4 C
5
C6
C7
C8
C9C10
C11
C12C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
C27
C28
C29
C30
C31C32
C33
C34 C35
C36
C37
C38C39
C40
C41
C42
C43
C44
C45
C46
C47
C48
D1
D2D
3
D4 D5 D6D7
D8
D9
D10
D11
D12
D13
D14
D15
D16
D17 IC1
IC2
JP1
JP2
P1
P2
P3
P4 P5R1
R2
R3
R4R5
R6
R7
R8R9
R10
R11
R12
R13
R14
R15R16 R17
R18
R19
R20
R21
R22 R23
R24
R25
R26
R27
R28
R29
R30
R31 R32
R33
R34
R35
R36
R37
R38R
39
R40
R41
R42
R43
R44
R45
R46
R47
R48
R49
R50
R51
R52
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
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
T32
T33
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
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
C27
C28
C29
C30
C31C32
C33
C34C35
C36
C37
C38C39
C40
C41
C42
C43
C44
C45
C46
C47
C48
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
R52
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]
48 Elektor Electronics 6/99
Figure 18. Test setup for theprototype half-bridge amplifier(centre). Note the large powersupplies at the left and right ofthe amplifier.
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49Elektor Electronics 6/99
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
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33Elektor Electronics 5/99
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.
Design by T. Giesberts
Titan 2000Part 4: wiring and performance
AUDIO & HI-FI
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34 Elektor Electronics 5/99
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18 C
19
C20
C21
C22
C23
C24
C25 C
26
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
D11D12
D13
D14D15
D16D17
IC1
IC2
JP1
JP2
P1
P2
P3
P4
P5
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
R35
R36
R37
R38
R39
R40
R41
R42
R43
R44
R45
R46
R47
R48
R49
R50
R51
R52
R53
R54
R55
R56R57
R58R59
R60
R61
R62
R63R64
R65R66
R67
R68
R69
R70
R71
R72R73 R74R75
R76
R77
R78
RE1
T1
T2
T3
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
--
++
+-0
0
LS+
LS
-
I
T
+5V
mute
T
T
P-L
S
P-IN
99
00
01
-1
B1
C18
C19
C20
C21
C22
C23
C24
C25
C26
D13
F1
IC7
IC8
IC9
K4
R35
R36
TR1
50m
AT
-12V
+12V0
+5V
~
~
C1 C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12C13C14
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
P2P3
R1
R2
R3
R4
R5R6 R7
R8
R9R10
R11R12
R13R14
R15
R16
R17
R18
R19
R20
R21
R22
R23
R24R25
R26R27
R28
R29
R30
R31R32
R33
R34
T1
T2
T3
T4
T5
T6
0
+12V
-12V
intextVre0
0
~~
LSP
inputT
+I
T
+5V
tem
p
T
mute
2R
990001-2
B1
C1
C2
C3
C4
C5
C6
C7
C8
C9
D1D2
D3
D4
D5
D6
D7
F1
IC1
IC2
K1
K2
K3
K4
P1
P2
R1
R2
R3
R4
R5R6
R7R
8
R9R10
R11R12
R13
R14
R15
R16
R17R18
R19
R20R21
R22
R23
R24
R25
T1
T2
TR1
tem
p.
max
.
T
T
~~
63m
AT
-+
ECB
12V
~~
99
00
41
-1
C1
C2
C3
C4
D1
D2
D3
D4
D5
D6
D7
D8
F1
F2
K1
K2
K3
K4
R1
R2
TR1
TR2
990001-3
0-
--
++
+
~~
0.16AT
0.16AT
D18 D19K1 L1
R79
RE2
RE3
RE4
LS+ LS- LS+
T1R
ERROR ON EARLY POWER
MAX.
ON
POWE