The STR-K740P is an FM Stereo / FM-AM Receiver Amplifier; with 5.1 surround sound providing a home theatre experience. This amplifier has Dolby Digital Theatre System (DTS) decoder as well as the Dolby Pro Logic decoder to resolve the surround channels.
This amplifier was part of the Sony HTDDW740 Home Cinema System comprising of surround sound speakers and cables. Currently discontinued, this excellent entry-level system provided a good home theatre experience for anyone new to the technology.
This amplifier came in two versions. The STR-K740P has five 80-watt channels, whilst the STR-K840P has five 100-watt channels. Although both amplifiers are identical, the latter model has a greater output due to the higher specification of the power output stage.
In the 740 version, the power output stage, for all the channels, is a Class AB push-pull configuration, consisting of MP1620 and MN2488 pair of Japanese transistors made by the Sanken Electric Company. The 1620 is a PNP type whilst the 2488 is an NPN type of silicon bipolar transistor. Internally they are the equivalent of Darlington pairs, within a single LF100 / MT100 package.
These are hardy transistors with collector current (Ic) rated at 10 A. It would require a hard short across the speaker terminals in order to damage them. This together with a state-of-the-art Japanese electronic protection mechanism ensures that they will survive in the hands of one us Brits...
The familiar UPC2581 chip drives the power output transistors. Two of these are required for the front and rear speakers, whilst the STK-350 is for driving the centre channel transistors.
The main audio processor is the familiar Mitsubishi M61511FP Analogue Sound Processor chip, providing volume level, tone, and bass for each of the inputs to the amplifier. This chip was utilised in many Sony amplifiers, which is why those amplifiers sound very much alike.
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