YAMAHA A-7a
¥ 96,000 (released in 1982)
Commentary
Pre-main amplifier equipped with newly developed ZDR (0 distortion rule).
In order to reduce all distortion in the final stage of the amplifier to 0, it is equipped with ZDR which is Yamaha's original cancellation technology.
In principle, it 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 reduce the generation of distortion to 0.
An original pure current servo amplifier is used for the equalizer amplifier.
This protects the equalizer from nonlinear effects caused by current changes, such as L, C and R components of the power supply and wiring. It consists of the first stage of low-noise Hi-gm dual FET differential Darlington connection → cascode amplification, pre-drive stage of constant current load → output stage of SEPP output.
In addition, the 47k Ω position of the Phono switch is equipped with capacity switching of 220 pf and 330 pf, and it can be used for exact matching with the cartridge and for enjoying the change of sound quality.
The main amplifier section consists of a low-noise dual FET at the first stage and a differential two stage circuit at the second stage → a cascode-connected emitter-grounded amplifier circuit with a constant current load → a bootstrap power supply, and a constant V as in the case of the cascode operation.CELow-impedance pre-drive circuit for push-pull emitter-follower output voltage → Highf with ZDRTIt is a DC servo amplifier configuration called 3-stage Darlington drive output stage of Tr configuration.
The power supply section is equipped with Yamaha's original X power supply.
This X power supply is a constant-voltage power supply that applies high-speed feedback from the secondary side to the primary side of the power supply and keeps the supply voltage exactly constant without being affected by load fluctuations or voltage fluctuations on the primary side. It is highly efficient because it controls the energization time and enables high power transmission.
It also has a feature that the transimpedance can be taken small.
It uses carefully selected high-quality parts. It uses phase-corrected QP capacitor, FET mica capacitor, styrene capacitor, RIAA high-precision metal-coated resistor, polypropylene film capacitor, plastic case Chemi-capacitor for power supply and other parts. oxygen-free copper wire is also used for wire.
Also, a brass EQ sheet holder is adopted.
Equipped with a turnover frequency switching tone control.
It is also equipped with functions such as continuous loudness, disc switch, main direct switch, automatic muting, and listening level monitor.
.JPG)
.JPG)
.JPG)
.JPG)
Model Rating
| Type | Pre-main amplifier |
| Rated Output (Both Channel Operation, 20 Hz to 20 kHz) | 120W + 120W (8 Ω, 0.003% strain) |
| Power bandwidth | 10 Hz to 100 kHz (8 Ω, 60W, 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, 0.003% Distortion) | MM:250mV MC:15mV |
| 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:87dB Phono MC:71dB 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 ~ 200W |
| Power supply voltage | 100 VAC, 50Hz/60Hz |
| Rated power consumption | 215W |
| AC outlet | Power switch interlock : 2 systems, 100W Power switch not linked : 1 system, 200W |
| External dimensions | Width 435x Height 132x Depth 365 mm |
| Weight | 10.6kg |