Motorola Hi-Fi Power Amplifier
Source: InternetPublisher:公子李 Keywords: Power amplifier power amplifier circuit HIFI Updated: 2024/06/28
This is a very simple, low cost, hi-fi quality power amplifier. You can implement it in 5 ways, as indicated in the diagram (from 20W to 80W RMS).
Some explanations:
- The first thing you should do is to test the gain factor hfe or β of the final power tubes. If their difference is greater than 30%, the amplifier will not give you a clear sound. I used MJ3001 and MJ2501 transistors and their difference was within 5%.
- Before turning on the power, you must short-circuit the input terminals, connect an ammeter in series with the output of the amplifier, then turn on the power supply and adjust R13 so that the ammeter current reaches the microampere level. If you are lucky enough, you may be able to reach 0. It is easy to achieve an ammeter current of 10 microamperes.
Power amplifier circuit diagram:
Power circuit:
Component and property table:
20 / 35 W | 25 / 40 W | 35 / 60 W | 50 / 80 W | 80 / 125 W | |
T1 | BC546 | ||||
T2 | BC556 | ||||
T3 (PNP Darlington) | BD898, BD678 | BD896, BD676 | BDX34 | MJ900G | 2N6052, MJ2501 |
T4 (NPN Darlington) | BD897, BD677 | BD895, BD675 | BDX33 | MJ1000G | 2N6059, MJ3001 |
C1 | 10 to 12 pF | ||||
C2 | 4.7 to 5.6 nF | ||||
C3 (non-polarized capacitor) | 1~10uF | ||||
C4, C5 | 2200 uF / 35 V | 4700 uF / 35 V | 4700 uF / 35 V | 4700 uF / 50 V | 4700 uF / 50 V |
R1, R2, R9, R12 | 10 kΩ | ||||
R3, R4, R5, R6, R14, R15 | 3.3 kΩ | ||||
R7, R8 | 680 Ω | ||||
R10 | 100 kΩ | ||||
R11 | 47 kΩ | ||||
R13 (Trimming resistor) | 10 kΩ | ||||
F1 (Fast) | 1,2 A | 1,6 A | 2 A | 2,2 A | 4 A |
BR1 | B40C1500 | B40C2000 | B40C2800 | B40C3200 | B40C5000 |
Cooler | 4,5 | 2,7 | 2,0 | 1,7 | 1,5 |
Transformer secondary voltage (± 20 %) | 20 + 20 V | 20 + 20 V | 20 + 20 V | 22 + 22 V | 22 + 22 V |
Transformer secondary current | 0,8 A | 1,2 A | 1,3 A | 1,5 A | 2,5 A |
Power (RMS) | 20 W | 25 W | 35 W | 50 W | 80 W |
Music Power | 35 W | 40 W | 60 W | 80 W | 125 W |
Minimum speaker impedance | 8Ω | 8Ω | 8Ω | 8Ω | 4Ω |
Supply voltage (± 20 %) | ± 25 V | ± 25 V | ± 25 V | ± 30 V | ± 30 V |
Maximum current | 0,54 A | 0,85 A | 1,0 A | 1,15 A | 2,0 A |
Required input voltage at maximum power | 1,8 V | 1,5 V | 1,7 V | 1,95 V | 1,7 V |
input resistance | 10 kΩ | ||||
Bandwidth (-3 dB) | 0 C 100.000 Hz | ||||
THD at ½ P | 0,04 % | ||||
THD at Psin | max 0,18 % | ||||
Frequency Response | 93 dB |
I am quite happy with this amp, it has a nice sound quality. Have fun with it!
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