SL414 is combined audio preamplifier and power amplifier IC manufactured by National semiconductors in early days. This amplifier is designed to operate in 10V to 20V range and deliver 3W (R.M.S) audio output power into 7.5Ω load. The frequency bandwidth of this IC is between 30Hz to 18kHz and with 8Ω load it produces 0.5% T.H.D on 3W.

The most uncommon feature of this IC is its EP-10 package. This EP-10 package is common to most of SL4xx series amplifiers and thanks to its inbuilt screw it is really easy to attach heat-sinks to these ICs.

EP-10 package of SL414 audio amplifier IC.
EP-10 package of SL414 audio amplifier IC.

During our prototyping, we try several SL414 amplifiers and most of them give quiet satisfactory results to us. Link to most stable SL414 design is available at the bottom of this article. As per our experiments, to archive best results it is mandatory to build this amplifier on PCB with screened wires. Also to get the good results make sure to drive this amplifier with regulated DC power supply. In our tests we use LM317 base PSU to drive this amplifier.

As per the manufacturer to use the SL414 it is essential to attach 25°C/W or better heat sink to this IC.

SL414 block diagram and pinouts.

To get the maximum output change the resistor between pin 6 and 7 until the output voltage of amplifier is equal or closer to Vcc/2.

As per our experiments in some of the circuits, SL414 drives into high frequency oscillations and to avoid this attach 500pF - 1000pF capacitor to pin 5 (preamplifier output line) and to the ground.

SL414 is quiet hard to find and no longer manufactured by National (or TI).

Project Related Downloads

Schematic and PCB design for SL414 3W power amplifier.