NIKKO M-204
¥ 120,000 (around 1976)
Commentary
DC stereo power amplifier with class-A operation in all stages.
The operation mode of the circuit is class A operation to eliminate the notching distortion and crossover distortion caused by class B operation. In addition, the DC amplifier configuration eliminates harmful capacitors from the signal path and suppresses the phase shift in the low-frequency range.
A dual FET with excellent temperature characteristics is used in the first stage to suppress DC fluctuation of output due to temperature change, and at the same time to achieve DC amplifier.
2SA872A PNP transistor with high ft (120 mhz), low Cob (1.8 pf) and excellent linearity is used as a differential amplifier with a current mirror circuit in the next stage to improve bare characteristics. Furthermore, by thermally coupling each element, it is combined with the differential amplifier in the first stage to extract drive voltage without distortion and to suppress direct current fluctuation of output.
The power amplifier stage is a 2-stage Darlington connection with a pre-drive stage with sufficient drive current, and it is a triple push-pull configuration with pure complimentary service connection so that the power transistor of the last stage operates with less distortion and excellent linearity.
The power supply supply stable power to the output stage, the power supply section uses a power transformer with good regulation and sufficient core volume, a high-capacity electrolytic capacitor of 15,000 μ Fx2 per channel, and a high-capacity diode. In addition, the drive stage draws out the merits of A-class full-scale stabilized power supply.
It is equipped with a relay type protection circuit, and the output circuit is disconnected when DC imbalance of the output stage is detected.
Model Rating
| Type | Stereo power amplifier |
| Rated output | 40W + 40W (8 Ω, 20 Hz to 20 kHz, both channel drive, THD0.08%) |
| Total harmonic distortion factor | 20 kHz : 0.08% or less (at 40W output) 1 kHz, 20 Hz : 0.03% or less (at 40W output) 20 Hz ~ 20 kHz : 0.03% or less (at 20W output) |
| Frequency characteristic | 5 Hz ~ 60 kHz (at 20W Output) |
| Input sensitivity | 1 Vrms (at rated output) |
| Residual noise | 0.2mV |
| Damping factor | 50 |
| Pwer | 100 VAC, 50Hz/60Hz |
| Power consumption | 280VA |
| External dimensions | Width 483x Height 175x Depth 300 mm |
| Weight | 18.5kg |