"Single difference, the simplest OCL amplifier, Simple OCL AMPLIFIER
Keywords: power amplifier circuit, power amplifier, power amplifier, power amplifier circuit, amplifier production, OCL power amplifier
With the continuous improvement of performance, the circuit structure is increasing, this is the problem of amateur makers, especially beginners, here, introducing you the simpler power circuit, see what extent that can be simplified What can achieve, this is also an interested issue. Circuit Principles and Performance (1) Circuit Analysis Figure 1 is a scheduling of this active power, only 20 of the amplifier part of the component, and the transistors. I look at a schematic diagram, but it is indeed a practical amplifier, and it provides an output power of ≥50W (120W) at a lower harmonic distortion to 8Ω (4Ω) load. It uses a typical OCL circuit, but it is necessary to improve the design according to the practice situation.
Be
Be
The input stage BG1-2 is used in a convention to use differential magnification, but it is slightly different from the general common circuit to adopt a PNP tube, which is easy and consistency than the two tube pairs compared to the NPN tube. The noise is low. For simple circuit structures, this is to consider as much as possible. The second stage BG3 is the main voltage amplifier, which provides most of the voltage gain, but does not use common "bootstrap" circuits. High-power amplifiers use the "bootstrap" circuit to increase the output power, and can save an electrolytic capacitance that affects the sound quality, and favorable reducing components simplified circuits. C2 is a phase compensation capacitor. The end-level complementary output stage made from BG4-7 in the simplest mode, and the components are less adjustable, so that the push tube BG4-5 with less power is also sufficient to meet the requirements of the push end-level output 100W. The setting of the final static current is mainly based on the decrease of the divergence of the low output power, usually 40-50mA. As for the large output power, the danger is not obvious because of the "masking" effect. The static current is not hot compensation, and the temperature rise is also rising as the temperature rise, but it has not been out of control. This makes it simplifies the installation process, reducing the debugging procedures, in addition, slightly large static currents can reduce the cross-distortion when some big output is. C3 is a high frequency decoupling of a power supply. This machine adds a general negative feedback after the gain of approximately 20 times (26dB), but it can also work with the overall negative power output waveform is still symmetrical, and there is no waveform distortion with an oscilloscope, and use a distortion instrument test. Harmonic distortion, the increase is not larger than the negative feedback (only about 0.2%). It can be seen that the open loop performance of this unit is good. The purpose of negative feedback is mainly used to compensate for the BG3 parameter discrete to ensure the stability of the whole machine gain, rather than mainly used to reduce distortion. Since the vast majority of the front-level amplifier output is separated, the native input is separated by direct capacitance. When the current-stage (or CD player) is designed with a DC output of the output, it can also be directly coupled to this active. Just pay attention to whether there is 300mV in the output of the local output after the front and rear connection, and the performance and work reliability will not be affected. Modern CD has been recorded as low as a few Hz. Ultra-low frequency signal, if you do not want these signals to be lost in playback, it is necessary to consider using direct coupling problems. (2) Performance indicators Figure 1 The circuit looks very inconspicuous, but its performance is impressive. The actual measurement of the prototype is as follows: BG6, 7 Select different complementary high power tubes, its rated output power (RMS): 2N3055 / MJ2955 (Soil 35V, 8Ω) 50W, MJ802 / MJ4502 (Soil 35V, 4Ω) 75W MJ802 / MJ4502 (Soil 37.5V, 8Ω) 62W MJ802 / MJ4502 (Soil 37.5V, 4Ω) 112W MJ802 / MJ4502 (stabilizing soil 35V , 4Ω) 131W Total harmonic distortion: Rated output power 1 kHz 0.35% 10W (RMS) LKHz 0.015% signal-to-noise ratio 115dB power bandwidth (1W, soil 1DB) 2Hz 1 110 kHz damping coefficient (8Ω) 90 It is difficult to see that the motor circuit has strong versatility, as long as the corresponding output tube and power supply capacity are applied, 50-100 W output power can be obtained without changing the circuit. The circuit is simple to reduce the point of one component, but performance is in general. It is satisfactory to some commercially available high-end power amplifiers. Such a simple circuit has a lower distortion and good sound quality, the author has not been relentant, preliminary speculation is due to the fact that the circuit structure is characterized, the front-rear distortion compensates for cancellation, so the open loop of this unit The distortion is low, laying the foundation for obtaining good sound quality. If this is not wrong, then in a simple amplifier circuit, you can do some attempts on the front and rear devices, which may be a road to the open-loop distortion, and interested readers do not prevent further try.
2) Main devices
(1) The power supply portion at different output power of the power supply is the same circuit. (See Figure 1), only the capacity of the power transformer and the filter capacitor is different, Table 1 is the recommended supply capacity and filter capacitance size. The value of the table refers to the power condition that should have when the single road amplifier is used, such as the use of stereo, the secondary current capacity of the power transformer and the filter capacitance value should be doubt. For example, 050WX 2 power transformer secondary capacity should be 28Vx 2 / 4.5-5A1100WX2, and the power amplifier power transformer secondary capacity should be 28Vx2 / 7-8A. If the current capacity is not increased accordingly, the output power does not reach the original rated value in the same time, of course, it is best, preferably a power transformer and corresponding rectifier filtering per channel. The circuit, which is also conducive to reducing the across the channel. Table 1
rated power
Transformer power
Filter capacitor (minimum)
No-load voltage
50W
28V × 2 / 2A
5600μF / 40V
± 40V
100W
28V × 2 / 3A
1000μF / 40V
± 40V
(2) Two complementary high power tubes in other devices are shown in Table 2. Table 2
Output Power
NPN / PNP
ICM
VCEO
PCM
HFE (IC)
50W
2N3055 / MJ2955
15A
60V
115W
20 ~ 70 (4A)
100W
MJ802 / MJ4502
40A
100V
200W
25 ~ 100 (7.5A)
These two pairs of high power tubes ft approximately 2.5 MHz, but since the current is large and the switching power tube, the audio power amplifier use has a good performance, especially the 2N3055 / MJ2955 is a 50W level of high-fidelity, the first choice, the preferred pipe, It is a "free-proof tube" that is very high. The tube VCEO specification is low, and the actual is often more than 100V, and there is no problem in use under soil 40V voltage. However, the dealer is often selected to supply VCEO to 60V or 100V to supply, do not buy 60V. The PCM of BG1-5 (BC557 / 546) was 0.5W, ICM was 100mA, where BG3 required VCEO ≥ 50V, BG4-5 asked VCEO ≥ 100V. FT is ≥ 100 MHz, HFE is 110 ~ 220. BC557, BC546 is more difficult to purchase, and the corresponding high frequency small power tube can be selected as required. In order to improve the open loop linearity, differential tubes and complementary tubes should be paired, which can also reduce the trouble of debugging and do it in mind. The pairing requirements are roughly as follows: Differential tube BGL-2 requires 0.5 mA to differ from 5%, while two tubes VBE are <20 mA. HFE is higher, try to ≥ 100. The complementary push tube BG4-5 requires that two tube HFEs are as close as possible within 1 ~ 80mA. If you can't, you can basically select the HFE at 60 mA. The end-level BG6-7 requires two tube HFEs in the 100mA to 3A (50W amplifier) and 100mA to 4A (for 100W amplifier). If it is not possible, the HFE at 3A or 4A can be selected for basically consistently selective. The main voltage amplifier BG3 requires that the HFE is not less than 60 at 10 to 15 mA. Of course, the BG3 of the two channel amplifiers can be substantially consistent with the HFE. D1-2 is a switching diode 1N914, and the maximum forward current is 75 mA, and the pressure drop is about 1V when 10 mA. Can be converted with 1 N4148. R7-8 uses an amplifier for 2 to 5W carburized resistors, or two 0.68 Ω (1 ~ 2W) metal film resistance in parallel. The rest are 0.5W metal film resistance. C1-3 selects CBB polyester gasless capacitance, C1 can also be used in general electrolytic capacitance, C2-3 requires a pressure ≥100V. The heat sink is selected from the thermal resistance (the boss amplifier) is not inferior to 8 ~ 10 ~ c / w. It is recommended to use a larger heat radiator as much as possible, as the service life and reliability of the power amplifier and the end of the tube have a big relationship.
3) Installing and debugging (1) The components of the mounting process amplifier portion are installed on the 2 printed board. It is important to note that Figure 2 shows the front element mounting surface, do not forget to reverse the replication when the self-made plate is copied. In addition, since each person's selection component size is not consistent, it is necessary to make the active in the figure on the figure, and the wiring interval is appropriately adjusted to make a uniformity between the components. The post-text work is produced together. The end-level BG6-7 is mounted on the printed board through a L-shaped aluminum bracket (60 × 45 × 85 mm). The installation requirements are shown in Fig. 3A, it should be noted that the housing and the L-shaped bracket must be a heat insulating sheet, and the housing is only in contact with the corresponding copper foil on the printed plate (preferably welding), fastening screw B should not have any electrical contact with the copper foil of the printed plate. The heat sink can be directly fastened to the L-shaped bracket, preferably to silicone oil at the heat transfer contact surface. There are not many components of the power supply rectifier filter portion, and the bracket can be installed directly on the chassis. Figure 3b is a schematic diagram of a channel, which means that the "land" line on the printed board should be directly connected to the power transformer. The secondary center tap and two filter electrolytic capacitors are on the common contacts of the electrolytic capacitor, which can be directly welded to the metal chassis or otherwise in other suitable places to communicate with the chassis, that is, "a little" grounding. The grounding end of the speaker does not pass directly from the "land" on the plate. 2 Signal input ground terminal and amplifier output ground should be insulated from the installation of the metal chassis. 8 The wiring of the power supply section is short and thick. It is recommended to connect φ0.2mm × 32-fold plastic lines. The speaker terminal is connected to a special feeder for the sound box between the printed board and the public. (2) Prevent the primary device before debugging debugging. Whether the installation and welding are right and reliable. Particularly pay attention to the diode, triode, and electrolytic capacitance, and whether the high power tube and the heat dissipation bracket are good. After hot, check the power part alone, if there is no problem, then access the power amplifier debug. Pressing the power loaded situation: 1 End-load commissioning In order to reduce the possibility of instant damage, it is not loaded. After the power is turned on, you should take a width in the end-level tube, or a tube is hot, and another tube is cold, and there is no other abnormality, and there is no other abnormally, you can measure the voltage, adjust the voltage and quiescent current. The output midpoint voltage is measured with a digital multimeter DC voltage (200mv) gear, which is generally not considered to be normal below 50mV below. If it is too high, it can increase R2, and then reduce R2, as long as the difference tube is optionally selected, it is often easy to control within 50m. Then the voltage drop on both ends of R7 or R8 is tested. Since the load is not loaded, the two resistance pressure drop is the same. The static current is 40 to 50 mA, the corresponding pressure drop in R7 or R8 should reach 13 to 17 mV, and the voltage of the BG4-5 base is about 2 V. If there is no voltage drop or less than 13 to 17 mV on R7 or R8, the D1 and D2 pressure drop can be tested, and the diode welded in which the pressure drop is small (should be disconnected), and then the larger diode is changed. Repeat, if there is no corresponding diode, it can be used with 220Ω fine-tuning resistance and fine-tuning to R7 or R8 up to 13 to 17 mV. Conversely, if R7 or R8 is lowered, the 220Ω fine-tuning resistor can be used in parallel with D1 or D2 and fine-tuned to R7 or R8 to reach 13 to 17mV, and the midpoint voltage and adjust the R2 to reach the midpoint voltage. Within 50mV. 2 Pure resistance load debugging power amplifier 8 ~ 10Ω 1 / 4W resistance, then measure R7 and R8 voltage drop, at this time, since the BG6, 7 forms respective DC circuits, R7, R8 may drop Inconsistency, at this time, the re-adjusted R2 allows the two resistance to pressure drop, and the midpoint voltage is close to 0V. Such as R7, R8 is the same but not up to 13 ~ 17mv, then D1, D2 or fine-tun the above 2200 fine-tuning resistance, repeated 1 to 2 times, in short, to reach R7, R8 is the same as 13 ~ 17mv, The midpoint voltage is generally adjusted. 8 The actual load commission can be adjusted to the sound box debugging after debugging. The feeder of the connection box and its length is as close as possible to the actual use of the future. When power is turned on, it will not be sent to the signal, and there is no obvious heterogeneous vocalizer, and simultaneously touch the end-level housing, such as the speaker has a heterogeneous and the housing is hot. At this time, it can be installed in parallel networks, L1, R2 in parallel network, and L1, R2 in series, L1, R2, in parallel network, and other brackets are mounted close to the printed board. Generally, R1, Cl, such as unable to completely eliminate the self-excite L1, R2. L1 can be used in a 12mm skeleton with a φ1.0mm enamel line to take a deeper. It is generally eliminated after the above measures. Finally, the addition signal is slightly higher than that of the normal listening level (at any time pay attention to the end-level housing temperature), the output midpoint voltage and the static current are completed. Generally, the medium voltage is 100mv, the static current <100mA and there is no continuous rise. It can be considered that the debugging of this step is best carried out in the case of the summer gas temperature. If it is installed in the winter, I hope to recover in the summer. Test
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