Amplifier Circuit Diagrams

LOW COST REAL 20W QUALITY AMPLIFIER SCHEMATIC CIRCUIT DIAGRAM

LOW COST REAL 20W QUALITY AMPLIFIER: A perfect choice for beginners, this amplifier showcases the superiority of a medium transistor design over its inexpensive integrated counterparts.

Allow me to present a straightforward and affordable circuit I discovered on a foreign forum.

SCHEMATIC CIRCUIT DIAGRAM 1

SCHEMATIC CIRCUIT DIAGRAM 2

This schematic is quite dated, tracing its origins back to 1974. If accurate, it suggests that the design belongs to FAIRCHILD. While it doesn’t promise Hi-end or Audiophile-level results, it doesn’t imply the sound it produces is subpar either.

SCHEMATIC CIRCUIT DIAGRAM 3

I can affirm that it offers superior sound quality compared to integrated amplifiers like TDA2030 and TDA2050, particularly at lower volumes where the bass is notably robust. However, individual assessments may vary.

On the forum where I discovered this circuit, opinions about its sound are divided; some users appreciate it while others don’t. Additionally, using the “HP333 distortion analyzer” from the same forum, measured distortion values were obtained. It’s important to note that I cannot guarantee the absolute accuracy of these results.

Distortion vs frequency

1kHz 0.07%
10kHz 0.08%
20kHz 0.1%
30kHz 0.12%

Distortion vs power output at 1 kHz

0.5 watts 0.17%
1.5 watts 0.12%
4 watts 0.05%
12 watts 0.16%
17 watts 0.5%
20 watts 4%

I believe this amplifier will captivate both novice users and experienced enthusiasts. In this circuit, I employed counterfeit TIP142 and TIP147 transistor pairs instead of genuine ones, although TIP122 and TIP127 are equally suitable and cost-effective alternatives.

The use of FR302 on the feeder floor is optional; I utilized it momentarily. You can select a rectifier diode rated at least 3 Amps and 50 Volts, such as 1N5408, etc.

To cool the output stage transistors effectively, all you need is an aluminum heatsink. Pay close attention to the 32mm gap between the output transistors. This distance is crucial. We placed the transistors in this manner and designed the PCB accordingly because we devised a distinct and economical solution for cooling. As an aluminum heatsink, we repurposed a double-layered curtain rod from our homes, ensuring a budget-friendly approach.

After cutting, we smoothed the edges with files, and the entire surface was polished using sandpaper. Although these heatsinks are currently made of plastic, they are easily procurable from scrap materials. The length you see in the circuit diagram is about 20 cm. If you plan to run the amplifier at full capacity for extended periods, consider opting for a longer curtain rod to enhance the cooling process.

LOW COST REAL 20W QUALITY AMPLIFIER SCHEMATIC CIRCUIT DIAGRAM 4

To prevent short circuits underneath the circuit due to pressure and stretching, it’s crucial to insulate this specific area. We achieve this by covering the region with a suitable biodegradable material, like a thin tarpaulin or plastic sheet. Alternatively, finding a thermal pad is a better choice. In the middle of the curtain rod, there’s a 15cm gap where a piece of rubber is placed to prevent the motor from bending.

Now, we can proceed to test the finished power by supplying 30 volts AC from the orange wires.

LOW COST REAL 20W QUALITY AMPLIFIER SCHEMATIC CIRCUIT DIAGRAM 5

LOW COST REAL 20W QUALITY AMPLIFIER SCHEMATIC CIRCUIT DIAGRAM 6

LOW COST REAL 20W QUALITY AMPLIFIER SCHEMATIC CIRCUIT DIAGRAM 7

LOW COST REAL 20W QUALITY AMPLIFIER SCHEMATIC CIRCUIT DIAGRAM 8

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