Sanyo M3330 Audio Chip

On this Sanyo M3330 printed circuit board (PCB), there are three Sanyo audio chips in a SIL package. The vertically oriented chip on the left is the stereo preamplifier, whilst the two horizontally oriented chips are the headphone power amplifiers. Interestingly, the Sanyo LA3160 is a car stereo preamplifier chip in an eight-pin package. It has a THD of 0.1 % typically, and crosstalk of -65 dB.

LA4140 Audio Chips

Here are the two headphone power amplifier chips. The Sanyo LA4140 is a mono IC; hence, two are required for a stereo application. This is a remarkable chip because it has a wide operating voltage between 3.5 V to 12 V, and a maximum power output of 0.5-watt, which is a lot for headphones these days.

Power / Regulation

This shows the power supply regulator and motor regulator circuits. The power supply regulator is a single transistor circuit that seems to work very well. I was able to play a 90-minute cassette twice.

The motor regulator circuit consists of three transistors, and they seem to perform adequately regulating the voltage. However, in the last stages, when the batteries are close to depletion, you should hear a whining noise through the headphones.

Controls

The contacts in the headphone socket required cleaning with a good contact cleaner. This robust socket still operates well.

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