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Cassette Recorder Sanyo Chip LA 4160


Figure 7.8 shows a typical old-fashioned cassette recorder input circuit. This includes time constants that provide equalization to correct for the characteristics of tapeheads and tape. In addition to these ‘standard’ corrections, individual tape decks may need further corrections, a multiplex filter may be included to remove FM stereo sub carrier signals, and noise reduction circuits such as Dolby or dbx may be used. At the last count, equalization frequencies being used on replay were 3180 µs for all tapes, and either 70 µs or 120 µs for chrome and for ferric tapes respectively, with ferrochrome and pure iron tapes replayed at 70 µs. Equalization needed for recording amplifiers is too specialized to include here partly because recording equalization time constants depend much more on individual needs. The use of discrete components in such circuits is vanishing except for specialized units intended to form part of a hifi system. Consumer cassette




recorders are much more likely to use ICs, and Figure 7.9 shows a one-chip solution using the Sanyo LA4160. This chip contains a preamplifier stage, automatic level control (ALC) and power amplifier with about 1W output power using a supply voltage of 6 V and a loudspeaker of 4 W impedance. Only a few external passive components are needed. Figure 7.10 shows the passive portion of the Baxandall tone control circuit, which is virtually the standard method of tone control used in audio systems. This was originally (about 1952) used in thermionic valve preamplifiers, but the principles have survived the transition, first to discrete transistors, and latterly to op-amps, proving the good design and durability of this circuit. There is very little interaction between the treble and the bass controls, low distortion, and a good range of control amounting to 20 dB or boost or cut.


Figure 7.9  A complete cassette recorder circuit using the Sanyo LA4160 chip.