A pre-main amplifier that pursues circuitry, characteristics, and functions at an affordable price point.
The equalizer circuit uses a two-stage direct-coupled discrete circuit with low-noise transistors.
The SN ratio is improved by not using ICs, which do not allow much freedom in the selection of circuit constants during circuit design. Transient characteristics have also been improved by utilizing data obtained from circuit analysis using computer-aided design (CAD) methods.
In addition, the SN ratio has been prevented by paying attention to the printed pattern routing and wiring, and shielded wires have been eliminated from the input/output circuits.
The tone control circuit is a two-stage direct-coupled discrete configuration almost identical to the equalizer circuit.
The circuit system is a Yamaha CR-NF mixing type, in which the gain of the circuit is increased by the CR in parallel with the NF dividing resistor when boosting, and attenuated by the CR inserted on the output side when cutting. This method allows the CR time constants on the boost and cut sides to be the same, so that a B-type volume curve can be used, which is easy to make precise, and the characteristics without undulation at the midpoint position can be obtained.
The circuit configuration of the main amplifier section is an input differential-emitter grounded-pure complementary all-stage direct-coupled OCL circuit that combines a current mirror circuit. The transistors used in the power and drive stages are carefully selected for their high frequency characteristics, and the use of PNP and NPN transistors with well matched pair characteristics minimizes harmonic distortion and switching distortion.
The meter circuit uses a logarithmic compression circuit with diode negative feedback, allowing a wide output range of 100mW to 50W to be read without switching.
A REC OUT selector is provided to allow recording output of a source other than the one being played.
Furthermore, when the deck connected to REC OUT is not in use, the deck can be disconnected from the signal path by setting the REC CUT OFF position, preventing the effects of shield wires and the negative effects on the amplifier caused by a drop in input impedance when the deck power is turned off.
A loudness circuit is provided to improve characteristics during low volume playback.
The volume uses a high-precision volume with a gang error of no more than ±2 dB over a wide range of -70 dB to 0, resulting in a very small difference between the left and right channel volume even at low volume.
A speaker protection circuit using relays is provided.
If a DC voltage is generated at the output terminals, a relay is used to protect the speakers by disconnecting them. This circuit also serves as a muting circuit to prevent unpleasant clicking noise when the power is turned on.
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