ROTEL RA-2020
¥ 65,000 (around the late 1970 s?)
Commentary
Pre-main amplifier using DC method.
DC system is adopted for the power amplifier section.
In the first stage of the DC-power amplifier section, a dual-FET with the same characteristics is adopted, and it is combined with a pure complimentary service OCL circuit to realize excellent sound quality. In addition, regarding the drift of the midpoint potential, which is a problem in DC-amplifiers, the power fluctuation is suppressed in each stage, and the pair characteristics are improved to improve stability.
Taking advantage of the good sound quality of class A amplifier, it adopts class AB operation system which can obtain large output.
Normal operation is class A operation, and it is automatically switched to class B operation when a large signal requires a large power.
We have achieved a low distortion rate by focusing on materials and parts as well as printed circuit board design and shielding cord placement.
As protection circuits, an Electro-Carry Control ASO (Safe Operating Area) circuit and a DC feedback power limit circuit are mounted. The electro-carry control ASO circuit operates as a relay to protect the amplifier transistors and speakers, and the DC feedback power limit circuit operates quickly against overload to protect the transistors.
Equipped with an LED-based peak indicator. With 13 LEDs per channel, the power is replaced by digital for quick display.
The indicator display is equipped with a sensitivity switching mechanism (- 20 20 dB) and an OFF switch, it is easy to read even when the volume is low, and the indicator can be turned off when it is not necessary.
Equipped with MC head amplifier.
The head amplifier used in the RA 2020 uses a 3-stage parallel coupled circuit with a low-noise FET at the input.
The equalizer amplifier section uses an IC circuit with class A differential for the first stage and push-pull output for the output stage.
A DC amplifier is used for the tone control circuit, and a tone defeat switch can be used to cancel the tone circuit and operate as a flat buffer amplifier.
Equipped with a subsonic filter and a supersonic filter.
Uses gold-plated terminals.
The front panel is an EIJ standard rack mount type.
Model Rating
| Type | Pre-main amplifier |
| Power Amplifier Unit | |
| Rated Output (Both channel drive) | 85W/ch (4 Ω, 1 kHz) 60W/ch (8 Ω, 20 Hz to 20 kHz) |
| Total harmonic distortion factor | 0.02% (20 Hz to 20 kHz at rated output) |
| Cross modulation distortion factor | 0.02% (8 Ω at rated output) |
| Frequency Characteristics (1W/ch, 8 Ω) | 2 Hz ~ 160 kHz + 0 -3dB |
| Input Sensitivity / Impedance | 1V/50k Ω |
| Damping factor (8 Ω) | 50 (20 Hz to 20 kHz) 80(1kHz) |
| S/N ratio (IHF-A network short) | 100dB |
| Crosstalk (10 kHz) | 57dB |
| Equalizer Section | |
| Harmonic distortion factor | Phono MAG:0.006% Phono MC:0.008% |
| RIAA deviation (20 Hz to 20 kHz) | ± 0.5 dB |
| Input Sensitivity / Impedance | Phono1 MAG : 2mV/50k Ω Phono2 mc : 200 μ V/150 Ω |
| Maximum Allowable Input (1 kHz, 0.5% THD) | Phono MAG:200mV Phono MC:5mV |
| Preamplifier Section | |
| Harmonic distortion factor | 0.01% (20 Hz, 20 Hz to 20 kHz) |
| Frequency characteristic | 5 Hz to 120 kHz |
| S/N ratio (IHF-A network) | Tuner, Aux : 92 dB Tape monitor:92dB |
| Residual noise (volume minimum) | 8 μ V, 100 dB |
| Input Sensitivity / Impedance | Tuner, Aux : 150mV/50k Ω Tape monitor : 150mV/50k Ω |
| Maximum Allowable Input (1 kHz, 0.5% THD) | Tuner, Aux : 15 v Tape monitor:15V |
| Slew rate | 30 V / μ S |
| Square wave rise time | 3 μ S |
| <Control Characteristics> | |
| Control Width | Bass : ± 10 dB (100 Hz) Treble : ± 10 dB (10 kHz) |
| Supersonic filter | 24 kHz, 12dB/oct. |
| Subsonic filter | 15 Hz, 12dB/oct. |
| <General> | |
| Maximum Power Consumption | 450W |
| External dimensions | Width 482x Height 143x Depth 328 mm |
| Weight | 13kg |