LA4570 Audio Chip

The LA4570 is a single-chip dual preamplifier integrated circuit (IC) manufactured by the Sanyo Corporation. The audio head feeds the weak signals to the preamplifier, which performs the first stage of the amplification process. This IC also has built in power amplifiers which drives a pair of headphones.

Sanyo are a world-renowned innovator of monolithic IC, and this one is the best that they made for portable audio applications. This vintage IC is no longer in production, however, amongst electronics enthusiasts, it is very popular for building high quality headphone amplifiers. Even a recycled chip is probably worth something these days. If I can find a recycled chip, I may plan to build a record player preamplifier, to reproduce that 1990s sound quality. It will be a unique piece of audio equipment that nobody else would have.

Circuit Diagram

It is interesting to see that the recommended headphone impedance is 16 Ω, and a "common amp" powers the output ground level (pin 11). Driving an output like this is unique and offers a much better frequency response.

This IC also has a built-in ripple filter, which requires a capacitor at pin 8 and pin 9 to set the cut-off frequency. The preamplifiers have a closed loop gain of 40 dB / 1 kHz NAB, which is very good for a chip that operates on less than three volts. This chip also has a mute function, and the application of +1.5 V to pin 7 activates it. The internal switches cut off the signals from the preamplifiers, however, this function is not used on this player.

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