YAMAHA A-500
¥ 49,800 (around 1982)
Commentary
A pre-main amplifier developed using Yamaha circuit technology such as the ZDR circuit.
Equipped with Yamaha's original ZDR (0 distortion rule) circuit.
This circuit consists of two circuits, a distortion detection circuit and an addition circuit. At the final stage, only the distortion component is taken out by the bridge configuration and returned to the input side to suppress the generation of distortion. In distortion reduction technologies such as NFB, only the mixed music signal component is fed back, while in ZDR, only the distortion component is fed back, and in principle, the effect of suppressing only the distortion is obtained. In addition, the distortion caused by counter electromotive current generated during speaker driving is also reduced to 0 in real time.
The preamp section consists of FET differential input DC servo system and Yamaha's original pure current dam system.
This pure current dam prevents signal current from flowing into the ground line and power supply line by supplying a constant current from the power supply to the amplifier by the pure current dam. This reduces the adverse effects of non-linear (wiring and dissimilar metal bonding) that inevitably exists in the power supply line and ground line and non-linear inside the power supply (vibration of Chemicon foil, diode, transformer, etc.).
Equipped with an MC equalizer amplifier.
An electrolytic capacitor of 12,000 μ Fx2 is used for the power supply.
Model Rating
| Type | Pre-main amplifier |
| Rated output | 70W + 70W (20 Hz ~ 20 kHz, 8 Ω, 0.007% distortion) |
| Frequency characteristic | 20 Hz ~ 20 kHz -0.2 dB (Phono MM → Rec out) |
| RIAA deviation | + / - 0.2 dB (MM) + / - 0.3 dB (MC) |
| Total harmonic distortion rate (20 Hz to 20 kHz) | MM:0.003% MC:0.005% |
| Signal-to-noise ratio (IHF-A network) | MM:86dB MC:69dB |
| Power bandwidth | 10 Hz to 50 kHz (8 Ω, 35W) |
| Input sensitivity | MM:2.5mV MC : 160 μ V |
| Maximum allowable input | MM:150mV MC:10mV |
| Tone control | Bass : ± 10 dB (350 Hz) Treble : ± 10 dB (3.5 kHz) |
| Accessory circuit | Audio Muting Subsonic filter Continuous loudness Rec Out Selector |
| Pwer | 100 VAC, 50Hz/60Hz |
| Rated power consumption | 130W |
| External dimensions | Width 435x Height 112x Depth 327 mm |
| Weight | 7.3kg |