How to use LM3886 DIY Gainclone power amplifier

What is Gainclone?

As early as 1999, the manufacturer 47-Labs issued the "Gain card", which was well-received. It immediately aroused controversy, because its power amplifier IC (integrated circuit) for $5, while the finished product costs about $3,300. On the other hand, Gainclone refers to a DIY amplifier that uses LM3875/LM3886 as the main component.

What is special about Gainclone?

Gainclone only takes up a small amount of space, it is made with the fewest parts, but it has an excellent HiFi effect. It beats those modern HiFi amplifiers and produces 2x68 watts of power with a total harmonic distortion of 0.03% THD.

How to use the LM3886 DIY Gainclone power amplifier? Please see the specific steps below.

Step 1: Prepare parts, materials, and tools

• LM3886 amplifier chip (2 pieces)

• 25V, dual-winding transformer (toroidal/IE)

• Rectifier diode 6 amperes (4 pieces)

• 2×3 PCB board (2 pieces)

• Large radiator (2 pieces)

• Cooling fan (1 pc)

• Plastic/metal case (1pc)

• Terminal

• RCA socket

• AC cable

Resistor:

• 20k 1/4 watt resistors (4 pcs)

• 10k 1/4 watt resistors (2 pcs)

• 15k 1/4 watt resistor (2 pcs)

• 1k 1/4 watt resistor (4 pcs)

• 2.2k 1/4 watt resistor (2 pcs)

Capacitor:

• 10,000uF 25v electrolysis (2 pcs)

• 10uF 25v electrolysis (4 pcs)

• 2.2uF 25v electrolysis (2 pcs)

• 470nF polyester film/ceramic (2 pcs)

• 150nF polyester film/ceramic (2 pieces)-100nF polyester

• Film/ceramic (2 pcs)

Step 2: Parse LM3886

The LM3886 is an improved version of M3875. There is higher output power, and a mute function is also added.

There are two types of LM3886 IC. One of them is LM3886T without insulation, and the other is LM3886TF with insulation. Be careful not to mess up. The heat sink and negative pole of LM3886T are the same. When the two are installed on one heat sink, mica and insulating screw pads should be added to isolate them.

LM3886 is a high-performance audio power amplifier that can provide 68W of continuous average power to 4Ω load and 38W of power to 8Ω at 20%-20kHz 0.1% THD + N. The signal-to-noise ratio of LM3886 is greater than 92dB, and the typical low noise floor is 2.0μV.

Step 3: Schematic diagram (amplifier and power supply)

As you can see, the negative feedback line has been modified. In this way, an increase of about 7dB can be obtained in the 30Hz-70Hz frequency band, and it reaches about 34db at the peak of 30Hz.

When using a 26v DC power supply in a given design, if the speaker load is 4 ohms and the input signal is 2Vp-p, it can provide 65W RMS power. For users who want to use 8 ohms, I recommend using +/- 38V. Of course, a value smaller than this value can also be applied.

The power supply circuit is also very simple. There are two KBU series (6A) bridge diodes and 2x10000 uF capacitors.

Step 4: PCB layout (for LM3886 amplifier)

This is the PCB layout of the amplifier.

The DIY circuit board (PCB production)

Step 5: Soldering the parts (PCB components)

As you can see, small tantalum and metal film capacitors are soldered under the PCB.

Step 6: Install the parts in the plastic case

Transformer/power supply:

Try to save space. My filter capacitor is installed in the core of the toroidal transformer.

Radiator with a fan:

Since the applied voltage is 25 volts, the fan only needs 12 volts, so I used a 7812 voltage regulator chip.

Terminal and RCA plug:

Simply drill holes in the terminal and RCA jacks to be tightly fixed on the rear panel. I used a thin shielded coaxial cable for the RCA input and a No. 16 (99% oxygen-free) speaker cable for the terminal output.

The final assembly is complete!

Only 6 steps are required to make Gainclone. I assure you that its sound effect is beyond your expectations.

Тег: LM3886

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