Crown SZ-31 Circuit Design

The Crown SZ-31 uses the LAG665 integrated circuit (IC), manufactured by the Mitsumi Corporation. This is an interesting IC because it contains the preamplifiers, power amplifiers, and motor regulator within one package. The external component count is very small, resulting in a clean minimalist design. This IC does not require any inter-stage decoupling, and consequently the wires from the stereo playback head connect directly to the op amps.

The preamplifiers and power amplifiers are directly connected, hence pin 24 and pin 23 join together, and pin 5 and pin 6 join together. However, as an electronic engineer you may wish to mod your unit by separating the pins and installing an inline graphic equaliser.

The output from the power amplifier drives the headphone coil directly, and there is no requirement for a capacitor here either. All of this simplicity results in a player that faithfully reproduces the sound without changing it too much. If you need a player that reproduces the sound exactly as it is on the cassette, then this would be it.

This IC also has a built-in constant current circuit, which drives the motor controller. It regulates the speed of the Mitsumi R-141111 motor keeping the rpm constant.

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