Lanzar amplifier original circuit. Tuning a power amplifier lanzar - a schematic diagram of a power amplifier, a description of the circuit diagram, recommendations for assembly and adjustment. Schematic diagram of ULF Lanzar

PARAMETER

ON LOAD

2 Ohm
(4 Ohm bridge)

240

For example, take the supply voltage equal to ± 60 V. If the installation is done correctly and there are no defective parts, then we get the voltage map shown in Figure 7. The currents flowing through the elements of the power amplifier are shown in Figure 8. The power dissipation of each element is shown in Figure 9 (about 990 mW is dissipated on transistors VT5, VT6, therefore, the TO-126 package requires a heat sink).

Figure 7. Voltage map of the power amplifier LANZAR INCREASE

Figure 8. Power amplifier current map INCREASE

Figure 9. Power dissipation map of the amplifier INCREASE

A few words about details and installation:
First of all, you should pay attention to the correct installation of parts, since the circuit is symmetrical, then mistakes are quite frequent. Figure 10 shows the breakdown of details. The regulation of the quiescent current (the current flowing through the terminal transistors when the input is closed to the common wire and compensating for the current-voltage characteristic of the transistors) is performed by a resistor X1. When you turn it on for the first time, the resistor slider should be in the upper position according to the circuit, i.e. have maximum resistance. The quiescent current must be 30 ... 60 mA. It has no idea to put it higher - neither instruments, nor perceptible changes by ear occur. To set the quiescent current, the voltage is measured at any of the emitter resistors of the final stage and set in accordance with the table:

Figure 10 Location of parts on the power amplifier board. The places where the most frequent installation errors occur are shown.

The question was raised about the advisability of using ceramic resistors in the emitter circuits of terminal transistors. You can also use MLT-2, two each, connected in parallel with a nominal value of 0.47 ... 0.68 Ohm. However, the distortions introduced by the ceramic resistors are too small, but the fact that they are interrupted - when overloaded, they are interrupted, i.e. their resistance becomes infinite, which quite often leads to the rescue of terminal transistors in critical situations.
The radiator area depends on the cooling conditions, figure 11 shows one of the options, it is necessary to fasten the power transistors to the heat sink through insulating gaskets ... It is better to use mica as it has a rather low thermal resistance. One of the options for mounting transistors is shown in Figure 12.

Figure 11 One of the options for a radiator for a power of 300 W, provided there is good ventilation

Figure 12 One of the options for attaching the power amplifier transistors to the heat sink.
Insulating spacers must be used.

Before installing the power transistors, as well as in case of suspicion of their breakdown, the power transistors are checked by a tester. The limit on the tester is set for diode testing (Figure 13).

Figure 13 Checking the terminal transistors of the amplifier before installation and in case of suspicion of breakdown of transistors after critical situations.

Is it worth picking up transistors by coffee. gain? There are quite a few disputes on this topic and the idea of ​​selecting elements has been going on since the deep seventies, when the quality of the element base left much to be desired. Today, the manufacturer guarantees the spread of parameters between transistors of the same batch of no more than 2%, which in itself speaks of good quality elements. In addition, given that the terminal transistors 2SA1943 - 2SC5200 are firmly established in sound engineering, the manufacturer began to release paired transistors, i.e. transistors of both forward and reverse conductance already have the same parameters, i.e. the difference is not more than 2% (Fig. 14). Unfortunately, such pairs are not always found on sale, nevertheless, several times we had to buy "twins". However, even with a parsing of coffee. gain between forward and reverse conduction transistors, it is only necessary to ensure that the transistors of the same structure are of the same batch, since they are connected in parallel and the spread in h21 can cause an overload of one of the transistors (for which this parameter is higher) and, as a consequence, overheating and exit from building. Well, the spread between transistors for positive and negative half-waves is fully compensated by negative feedback.

Figure 14 Transistors of different structure, but of the same batch.

The same applies to differential cascade transistors - if they are of the same batch, i.e. bought at the same time in one place, then the chance that the difference in parameters will be more than 5% is VERY small. Personally, we like the FAIRCHALD transistors 2N5551 - 2N5401 more, but the STs sound quite decent too.
However, this amplifier is also assembled on a domestic element base. This is quite realistic, but let's make an amendment to the fact that the parameters of the purchased KT817 and those found on the shelves in their workshop, purchased back in the 90s, will differ quite significantly. Therefore, here it is still better to use the h21 meter available in almost all digital tests. True, this gadget in the tester shows the truth only for low-power transistors. It will not be correct to select the transistors of the final stage with its help, since h21 also depends on the current flowing. It is for this reason that separate test stands are already being made to reject power transistors. from the regulated collector current of the tested transistor (Fig. 15). The calibration of a permanent device for rejecting transistors is carried out in such a way that the microammeter at a collector current of 1 A deviates by half the scale, and at a current of 2 A - completely. When assembling an amplifier only for yourself, you can not make a stand, two multimeters with a current measurement limit of at least 5 A.
To produce the rejection, you should take any transistor from the rejected batch and set the collector current equal to 0.4 ... 0.6 A for the transistors of the penultimate stage and 1 ... 1.3 A for the transistors of the final stage with a variable resistor. Well, then everything is simple - transistors are connected to the terminals and, according to the readings of the ammeter included in the collector, transistors with the same readings are selected, not forgetting to look at the readings of the ammeter in the base circuit - they should also be similar. The spread of 5% is quite acceptable; for arrow indicators on the scale, you can make marks of the "green corridor" during the calibration. It should be noted that such currents do not cause bad heating of the crystal of the transistor, but given the fact that without a heat sink, the duration of measurements should not be stretched in time - the SB1 button should not be held pressed for more than 1 ... 1.5 seconds... Such rejection, first of all, will allow to select transistors with a really similar amplification box, and checking powerful transistors with a digital multimeter is only a check to calm the conscience - in the microcurrent mode, powerful transistors have amplification boxes of more than 500 and even a small spread when checking with a multimeter in real current modes can be huge ... In other words, checking the amplification box of a powerful transistor showing the multimeter is nothing more than an abstract quantity that has nothing to do with the amplification box of the transistor through the collector-emitter junction, at least 0.5 A.

Figure 15 Rejection of powerful transistors by amplification box.

Pass-through capacitors C1-C3, C9-C11 have a not quite typical inclusion, in comparison with factory analogs of amplifiers. This is due to the fact that with such a connection, a rather large capacitor is not obtained, but the use of a 1 μF film capacitor compensates for the not entirely correct operation of electrolytes at high frequencies. In other words, this implementation made it possible to obtain a more pleasant amplifier sound, in comparison with one electrolyte or one film capacitor.
In older versions of Lanzar, 10 ohm resistors were used instead of VD3, VD4 diodes. Changing the element base allowed us to slightly improve the work on signal peaks. For a more detailed consideration of this issue, refer to Figure 3.
Not ideal is modeled in the circuit power supply, and more close to the real, which has its own resistance (R30, R31). When reproducing a sinusoidal signal, the voltage on the supply rails will look like the one shown in Figure 16. In this case, the capacitance of the power filter capacitors is 4700 μF, which is a bit small. For normal operation of the amplifier, the capacitance of the supply capacitors must be at least 10,000 μF per channel, more is possible, but no significant difference is noticeable. But back to Figure 16. The blue line shows the voltage directly on the collectors of the final stage transistors, and the red line shows the supply voltage of the voltage amplifier in the case of using resistors instead of VD3, VD4. As you can see from the figure, the power supply voltage of the output stage has dropped from 60 V and is located between 58.3 V during pause and 55.7 V at the peak of the sinusoidal signal. Due to the fact that the capacitor C14 not only becomes infected through the decoupling diode, but also discharges at the signal peaks, the supply voltage of the amplifier, the voltage takes the form of a red line in Figure 16 and ranges from 56 V to 57.5 V, that is, it has a swing of about 1.5 V.

Figure 16 voltage waveform using decoupling resistors.

Figure 17 Form of supply voltages on terminal transistors and voltage amplifier

Replacing the resistors with diodes VD3 and VD4, we get the voltages shown in Figure 17. As you can see from the figure, the amplitude of the ripple on the collectors of the terminal transistors almost did not change, but the supply voltage of the voltage amplifier acquired a completely different form. First of all, the amplitude decreased from 1.5 V to 1 V, and also at the moment when the peak of the signal passes, the voltage supply of the VN sags only to half the amplitude, i.e. by about 0.5 V, while when using a resistor, the voltage at the peak of the signal sags 1.2 V. In other words, by simply replacing the resistors with diodes, it was possible to reduce the power ripple in the voltage amplifier by more than 2 times.
However, these are theoretical calculations. In practice, this replacement allows you to get a "free" 4-5 watts, since the amplifier occurs at a higher output voltage and reduces distortion at the signal peaks.
After assembling the amplifier and adjusting the quiescent current, make sure that there is no DC voltage at the output of the power amplifier. If it is higher than 0.1 V, then this clearly requires adjusting the operating modes of the amplifier. In this case, the most in a simple way is the selection of the "supporting" resistor R1. For clarity, we will give several options for this value and show the changes in the constant voltage at the output of the amplifier in Figure 18.

Figure 18 Changing the constant voltage at the amplifier output depending on the nominal R1

Despite the fact that on the simulator, the optimal constant voltage was obtained only with R1 equal to 8.2 kOhm, in real amplifiers, this nominal value is 15 kOhm ... 27 kOhm, depending on which manufacturer the transistors of the VT1-VT4 differential cascade are used.
Perhaps it is worth saying a few words about the differences between power amplifiers completely on bipolar transistors and using field workers in the penultimate stage. First of all, when using field-effect transistors, the output stage of the voltage amplifier is VERY strongly unloaded, since the gates of field-effect transistors have practically no active resistance - only the capacitance of the gate is a load. In this version, the amplifier circuitry begins to step on the heels of class A amplifiers, since in the entire range of output powers, the current flowing through the output stage of the voltage amplifier hardly changes. An increase in the quiescent current of the penultimate stage operating on a floating load R18 and the base of the emitter followers of powerful transistors also varies within small limits, which ultimately led to a rather noticeable decrease in THD. However, in this barrel of honey there is also a fly in the ointment - the efficiency of the amplifier has decreased and the output power of the amplifier has decreased, due to the need to apply a voltage of more than 4 V to the gates of field workers to open them (for a bipolar transistor, this parameter is 0.6 ... 0.7 V ). Figure 19 shows the peak of the sinusoidal signal of an amplifier made with bipolar transistors (blue line) and field drivers (red line) at the maximum amplitude of the output signal.

Figure 19 Change in the amplitude of the output signal when using a different element base in the amplifier.

In other words, a decrease in THD by replacing field-effect transistors leads to a "shortage" of about 30 W, and a decrease in the THD level by about 2 times, so it is up to everyone to decide what to set.
It should also be remembered that the THD level depends on the amplifier's own amplification box. In this amplifier the gain box depends on the values ​​of the resistors R25 and R13 (at the used nominal values, the gain box is almost 27 dB). Calculate gain box in dB can be according to the formula Ku = 20 lg R25 / (R13 +1), where R13 and R25 are resistance in Ohms, 20 is a multiplier, lg is a decimal logarithm. If it is necessary to calculate the gain factor at times, then the formula takes the form Ku = R25 / (R13 + 1). This calculation is sometimes necessary when making a preamplifier and calculating the amplitude of the output signal in volts in order to exclude the work of the power amplifier in the hard clipping mode.
Reducing your own coffee. amplification up to 21 dB (R13 = 910 Ohm) leads to a decrease in the THD level by about 1.7 times at the same output signal amplitude (the input voltage amplitude is increased).

Well, now a few words about the most common mistakes when assembling an amplifier yourself.
One of the most popular mistakes is installation of 15 V zener diodes with incorrect polarity, i.e. these elements do not work in the voltage stabilization mode, but like ordinary diodes. As a rule, such an error causes the appearance of a constant voltage at the output, and the polarity can be either positive or negative (usually negative). The voltage value is based between 15 and 30 V. In this case, no cell is heated. Figure 20 shows the voltage map with incorrect installation of the zener diodes, which was issued by the simulator. Erroneous items are highlighted in green.

Figure 20 Voltage map of a power amplifier with incorrectly soldered zener diodes.

The next popular mistake is installation of transistors "upside down", i.e. when the collector and emitter are confused in places. In this case, constant tension is also observed, the absence of any signs of life. True, the reverse switching on of the differential cascade transistors can lead to their failure, but then how lucky. An inverted voltage map is shown in Figure 21.

Figure 21 Voltage map with "inverted" switching on of differential cascade transistors.

Often transistors 2N5551 and 2N5401 are confused in places, and they can also confuse the emitter with the collector. Figure 22 shows the voltage map of the amplifier with the "correct" installation of the transistors tangled in places, and in Figure 23 - the transistors are not only reversed, but also inverted.

Figure 22 Transistors of the differential cascade are messed up in places.

Figure 23 Transistors of the differential cascade are entangled in places, in addition, the collector and emitter are entangled in places.

If the transistors are confused in places, and the emitter-collector are soldered correctly, then a small constant voltage is observed at the amplifier output, the quiescent current of the window transistors is regulated, but the sound is either completely absent, or at the level "it seems to be playing". Before mounting the transistors soldered in this way on the board, they should be checked for operability. If the transistors are swapped, and even the emitter-collector are swapped, then the situation is already quite critical, since in this version for the differential cascade transistors the polarity of the applied voltage is correct, but the operating modes are violated. In this version, there is a strong heating of the terminal transistors (the current flowing through them is 2-4 A), a small constant voltage at the output and a barely audible sound.
It is quite problematic to confuse the pinout of the transistors of the last stage of the voltage amplifier, when using transistors in the TO-220 package, but transistors in the TO-126 package are quite often soldered "upside down", swapping the collector and emitter... In this version, a highly distorted output signal, poor regulation of the quiescent current, and lack of heating of the transistors of the last stage of the voltage amplifier are observed. A more detailed voltage map for this power amplifier mounting option is shown in Figure 24.

Figure 24 The transistors of the last stage of the voltage amplifier are soldered upside down.

Sometimes the transistors of the last stage of the voltage amplifier are confused in places. In this case, a small constant voltage is observed at the output of the amplifier, the sound, if there is, is very weak and with huge distortions, the quiescent current is regulated only upward. An amplifier voltage map with this error is shown in Figure 25.

Figure 25 Wrong wiring of the transistors of the last stage of the voltage amplifier.

The penultimate stage and terminal transistors in the amplifier are rarely confused in places, so this option will not be considered.
Sometimes the amplifier fails, the most common reasons for this are overheating of terminal transistors or overload. Insufficient heat dissipation area or poor thermal contact of transistor flanges can lead to heating of the terminal transistor crystal to the temperature of mechanical destruction. Therefore, before the power amplifier is fully commissioned, it is necessary to make sure that the screws or self-tapping screws that secure the terminals to the radiator are completely tightened, the insulating gaskets between the flanges of the transistors and the heat sink are well lubricated with thermal grease (we recommend the good old KPT-8), as well as the size of the gaskets larger than the size of the transistor by at least 3 mm on each side. If there is not enough heat sink area, and there is simply no other, then you can use 12 V fans, which are used in computer technology. If the assembled amplifier is planned to operate only at capacities above average (cafes, bars, etc.), then the cooler can be switched on for continuous operation, since it will still not be heard. If the amplifier is assembled for home use and will be operated at low powers, then the cooler will already be heard, and there is no need for cooling - the radiator hardly heats up. For such operating modes, it is better to use controlled coolers. Several options for controlling the cooler are possible. The offered cooler control options are based on the control of the heatsink temperature and are turned on only when the heatsink reaches a certain, regulated temperature. To solve the problem of failure of window transistors, you can either install additional protection from overload, or by careful installation of wires going to speaker system(for example, use to connect the speaker to an amplifier of automobile oxygen-free wires, which, in addition to a reduced active resistance, have an increased strength of insulation, resistant to shock and temperature).
For example, consider several options for the failure of terminal transistors. Figure 26 shows the voltage map in the case of the output of reverse terminal transistors (2SC5200) to an open circuit, i.e. the transitions are burnt out and have the maximum possible resistance. In this case, the amplifier maintains operating modes, the output voltage remains close to zero, but the sound quality definitely wants better, since only one half-wave of the sinusoid is reproduced - negative (Fig. 27). The same will happen if the direct terminal transistors (2SA1943) are broken, only a positive half-wave will be reproduced.

Figure 26 Reverse terminal transistors burned out to a break.

Figure 27 Signal at the amplifier output in the case when the 2SC5200 transistors are completely burned out

Figure 27 shows a voltage map in a situation when the terminals are out of order and have the lowest possible resistance, i.e. short-circuited. This version of the malfunction drives the amplifier into VERY harsh conditions and further burning of the amplifier is limited only by the power source, since the current consumed at this moment can exceed 40 A. in that where actually there was a short circuit to the power bus. However, it is this situation that belongs to the easiest diagnostics - it is enough to check the resistance of the transitions between themselves with a multimeter before turning on the amplifier, without even soldering them from the amplifier. The measurement limit set on the multimeter is DIODE CHECK or AUDIBLE RING. As a rule, burnt-out transistors show resistance between junctions in the range from 3 to 10 ohms.

Figure 27 Voltage map of the power amplifier in the event of a burnout of the terminal transistors (2SC5200) for a short circuit

The amplifier will behave in the same way in the event of a breakdown of the penultimate stage - when the terminals are burned off, only one half-wave of the sinusoid will be reproduced, with a short circuit of the transitions - huge consumption and heating.
In case of overheating, when it is believed that the radiator for the transistors of the last stage of the voltage amplifier is not needed (transistors VT5, VT6), they can also fail, and both go to an open circuit and a short circuit. In the case of the VT5 transitions burning out and the infinitely high resistance of the transitions, a situation arises when there is nothing to maintain zero at the amplifier output, and the slightly open terminal transistors 2SA1943 will pull the voltage at the amplifier output to minus the supply voltage. If the load is connected, then the magnitude of the constant voltage will depend on the set quiescent current - the higher it is, the greater the magnitude of the negative voltage at the amplifier output. If the load is not connected, then the output will have a voltage that is very close in magnitude to the negative power bus (Figure 28).

Figure 28 The voltage amplifier transistor VT5 "cut off".

If the transistor in the last stage of the VT5 voltage amplifier fails and its transitions are closed, then with the connected load, the output will have a rather large constant voltage and a direct current flowing through the load, of the order of 2-4 A. If the load is disconnected, then the output voltage the amplifier will be almost equal to the positive power rail (Figure 29).

Figure 29 The voltage amplifier transistor VT5 is "closed".

Finally, it remains only to offer a few oscillograms at the most focal points of the amplifier:

The voltage at the bases of the differential cascade transistors at an input voltage of 2.2 V. The blue line is the VT1-VT2 base, the red line is the VT3-VT4 base. As can be seen from the figure, both the amplitudes and the phase of the signal practically coincide.

Voltage at the junction of resistors R8 and R11 (blue line) and at the junction of resistors R9 and R12 (red line). Input voltage 2.2 V.

The voltage at the collectors VT1 (red line), VT2 (green), as well as at the upper terminal R7 (blue) and the lower terminal R10 (lilac). The voltage breakdown is caused by the load on the load and a slight decrease in the supply voltage.

The voltage across the collectors VT5 (blue) and VT6 (red. The input voltage is reduced to 0.2 V to make it more clearly visible, there is a difference of about 2.5 V in the constant voltage

It remains only to explain about the power supply. First of all, the power of a network transformer for a power amplifier of 300 W should be at least 220-250 W and this will be enough to reproduce even very tough compositions. In other words, if you have a transformer from a tube color TV, then this is an IDEAL TRANSFORMER for one amplifier channel that allows you to easily reproduce musical compositions with a power of up to 300-320 watts.
The capacitance of the power supply filter capacitors should be at least 10,000 uF per arm, 15,000 uF is optimal. By using containers above the specified rating, you simply increase the cost of the structure without any noticeable improvement in sound quality. Do not forget that when using such large containers and supply voltages above 50 V per shoulder, instantaneous currents are already critically huge, therefore it is strongly recommended to use soft-start systems.
First of all, it is strongly recommended to download descriptions of manufacturers' factories (datasheets) on ALL semiconductor elements before assembling any amplifier. This will make it possible to get acquainted with the element base closer and, if any element is not on sale, find a replacement for it. In addition, you will have the correct pinout of the transistors at hand, which will significantly increase the chances of correct installation. Particularly lazy ones are invited to VERY attentively familiarize themselves with at least the location of the terminals of the transistors used in the amplifier: