2-way active system

Rohit Balkishan Dubla

Note: This system has been upgraded to a 3-way active system

This system is based on the Sanyo STK4132 (salvaged from an old system) and Philips TDA1521 power audio ICs. STK4132 is rated for 20W + 20W into 8Ω and TDA1521 is rated for 12W + 12W into 8Ω (configured for 6W into 8Ω).

The photo shows the complete setup. The grey box contains the two power amplifiers and the pre-amp cum crossover. The power amplifiers are built around the STK4132 and TDA1521 audio power ICs. The crossover is an active 12db/oct 2-way Bessel type with the crossover frequency set to about 3500 Hz. The smaller box sitting over it is the phono pre-amp-cum-RIAA equaliser (see Phono pre-amp version 2). Above the phono pre-amp can be seen my Technics SL-7 turntable. It is a fully automatic direct-drive type with a tangential tone-arm. To the left and right are the speakers bought from a second-hand shop and belonged to a Panasonic component system (SC-PM17), and were meant to be bi-wired. I removed the internal "crossover" which was simply a 4.7µF capacitor in series with the tweeter and re-wired it for bi-amping with a 47µF non-polar cap. This cap is only for DC protection and plays no part in the crossover. Despite the rather modest power ratings, the system packs quite a punch, especially with the turn-table.

Specifications

Amplifier

Power (low): 20 + 20W/8Ω.

Power (high): 6 + 6W/8Ω.

Pre-amp cum crossover

Pre-amp gain: 6db

Crossover type: 2-way active, 12db/oct Bessel alignment.

Crossover frequency: 3.4kHz.

Speakers

Woofer: 8Ω, 7 cm, paper cone.

Tweeter: 8Ω, 4 cm, paper cone.

Schematics

2-way active crossover

20 + 20W amplifier using STK4132

6 + 6W amplifier using TDA1521

Power supply unit