The STK4197mk2 was introduced at a time when Home Theater was the rage. It’s a 3-channel module, comprising of three power amplifiers of 50W each. One for Left, the other for Right and finally the last one for the Center speakers. According to the datasheet, it’s sometime in 1997 that they appeared. The STK ICs were popular with some Japanese manufacturers of that time, one of which was Onkyo.
Inside the STK4197mk2
Fig 1 – Simplified schematic of STK4197mk2
Fig 1 is a simplified schematic of the STK4197mk2. The circuit is quite conventional. There’s the input differential, the VAS and the current outputs. Output transistors are in Quasi-Complementary. Unlike the preceding STK4241mk2, this STK4197mk2 uses a current source in the VAS, so no bootstrapping is needed. It also means there’s no way to change the idling current in the VAS. All three power amps are identical. So what works for one will work for the other two.
Making it work
Fig 2 – Circuit of STK4197mk2
The circuit for the STK4197mk2 is straight-forward. There’s the input and feedback networks. That’s it. It can’t get simpler than this.
Fig 3 – STK4197mk2 pcb
The STK4197mk2 pcb is slightly larger than the STK4241mk2. Length is still 4″ but the width is now 3″, half an inch more. Reason being that I managed to squeeze in two 10,000uF power supply capacitors on board. That’s a total of 20,000uF. Nice and beefy. All that’s needed is a power transformer and a bridge rectifier. The output of the bridge goes to the +V and -V on the pcb. Center tap of the power transformer to the 0V. As with the STK4241mk2, I’m awaiting delivery of this pcb.