YAMAHA A-6a
¥ 69,800 (around 1981)
Commentary
A pre-main amplifier with Yamaha's original technologies such as ZDR circuit and X power supply.
A unique ZDR is used to eliminate distortion generated at the final stage of the main amplifier.
This method detects only the distortion component generated at the final stage of the amplifier and adds it to the input side with the same gain to eliminate the generation of distortion. This makes the absolute amount of distortion generated at the final stage of the amplifier 0.
In addition, harmful distortion such as crossover distortion and thermal distortion are eliminated, and distortion caused by speakers is also canceled.
The equalizer section uses a pure current servo amplifier system.
In this method, the amplifier operation is idealized by preventing signal current (variable current) from flowing into the power supply line and ground line as in the conventional method. Since a constant current is always supplied, there is no adverse effect of noise and impedance change caused by variable current, and pure amplification is possible by combining with the circuit configuration such as ICL method FET differential input stage.
Yamaha's original X power supply is used for the power supply.
The X power supply system is small but has the same power supply capability as a huge power supply, and enables constant voltage power supply.
Equipped with a DISC switch that always selects a DISC (record) regardless of the position of the selector.
It also has a Rec Out selector and a loudness circuit.
Equipped with Listening Level Monitor, it can be checked by lighting of LED when peak output exceeding the set value is met in the range of 0.2W to 150W.
The Main Direct switch is mounted. When turned ON, the signal from the equalizer or tuner is directly connected to the main high-gain DC amplifier.
It is equipped with functions such as muting switch, high filter and tone control.
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Model Rating
| Type | Pre-main amplifier |
| Rated Output (Both Channel Operation, 20 Hz to 20 kHz) | 100W + 100W (8 Ω, strain 0.003%) |
| Power bandwidth | 10 Hz to 100 kHz (8 Ω, 50W, 0.02% distortion) |
| Damping factor | 65 (8 Ω, 1 kHz) |
| Input Sensitivity / Impedance | Phono MM : 2.5mV/47k Ω Phono MC : 160 μ V/100 Ω Tuner, AUX, Tape : 150mV/47k Ω |
| Maximum Allowable Input (1 kHz, Distortion 0.01%) | MM:180mV MC:10mV |
| Output Voltage / Impedance | Rec Out : 150mV/270 Ω |
| Frequency Response (Main Direct On) | Tuner, AUX, Tape → SP Out : 1 Hz to 100 kHz + 0 -2dB |
| RIAA deviation (20 Hz to 20 kHz) | MM → Rec Out : ± 0.2 dB MC → Rec Out : ± 0.3 dB |
| Total harmonic distortion rate (20 Hz to 20 kHz) | MM → Rec Out (5 V) : 0.003% MC → Rec Out (5 v) : 0.006% AUX Others → SP Out (50W, 8 Ω) : 0.003% |
| Intermodulation distortion factor (8 Ω) | AUX and others → SP Out : 0.002% |
| Signal-to-noise ratio (IHF-A) | Phono MM:86dB Phono MC:70dB Tuner, AUX, Tape : 106 dB |
| Input equivalent noise (IFF-A) | Phono MM:-138dBV Phono MC:-142dBV |
| Residual Noise (Main Direct On) | 65 μ V |
| Tone control | Bass : ± 10 dB (20 Hz) Treble : ± 10 dB (20 kHz) |
| High filter | 10 kHz, 12dB/oct. |
| Loudness control | 1kHz:20dB |
| Listening Level Monitor | 0.2W ~ 150W |
| Power supply voltage | 100 VAC, 50Hz/60Hz |
| Rated power consumption | 165W |
| AC outlet | Power switch interlock : 2 systems, 100W Power switch not linked : 1 system, 200W |
| External dimensions | Width 435x Height 112x Depth 365 mm |
| Weight | 9.1kg |