20W/8Ω power amplifier based on STK4132

Rohit Balkishan Dubla

Figure 1 shows the amplifier schematic. It is based on the 20 + 20W hybrid power IC STK4132 from Sanyo. The circuit is based on the typical application given in the datasheet but with a few changes as follows:

• 1. The muting feature has been disabled. In order to do this, the pins 6, 7 & 8 are not used and pin 4 is returned to -Vcc via the 100Ω resistor R7 (pin 7 when used, connects to pin 4 via a 100Ω resistor, and is internally connected to -Vcc via a transistor switch).

  2. Voltage gain is reduced from that used by the typical application. The gain resistor R2 is 2.7k instead of 560Ω. Sensitivity is 800mV to 1V with the given component values.

  3. There is no low-pass filter at the input, only the high pass filter formed by R1 and C1.

  4. Bootstrap capacitor C4 is 100µF instead of 47µF.

  5. Input capacitor C1 is 10µF instead of 2.2µF.

The schematic shows only one channel and all components except R3, R7 & C3 have to be duplicated for the other channel (pin nos. shown in brackets). Also, the component labelling is different from that in the datasheet - bear this in mind while comparing this with the datasheet schematic.

The power supply must be between ±22V to ±30V DC at 4A for operation into 8Ω per channel. The supply must be properly decoupled using 100nF decoupling capacitors close to pins 9, 11 and 14.

This amplifier is part of an active 3-way setup. Click here for photos.