SANSUI AU-D55F
¥ 49,800 (released in 1981)
Commentary
Pre-main amplifier with super FF (feed-forward) system.
The Super FF system is an original system adopted in the AU-F Extra series, and is a technology that was born by combining the feedforward theory invented by Dr. H. S. Black with NFB.
The NFB is primarily responsible for reducing distortion in the audible band and also for extracting anti-phase distortion for feed-forward. As a result, the NFB is dominant in the audible band and the feed-forward is dominant outside the audible band to cancel distortion. This theoretically reduces any distortion that occurs in the power stage.
This system consists of an error collection amplifier for amplifying the distortion cancellation signal and a symmetrical two pole output summing network utilizing the latest computer technology.
The Super FF system is adopted in the power amplifier section, and all stages are composed of differential amplification DC amplifiers.
Low-noise FET is used for the first stage and cascode bootstrap connection is used for the third stage.
In the power supply section, we have developed and adopted a dual-bridge method that enhances the power supply by increasing the energy utilization factor. Compared with the conventional method, which uses two positive and two negative diodes for rectification, the dual-bridge method uses four diodes for each, improving the rectification effect by 30%.
In addition, since there is no ground at the midpoint of the power transformer and the ground point is isolated from the chassis via a diode, no stray current flows into the chassis more than necessary and does not adversely affect the signal ground point.
In addition, a one point grounding system has been adopted for all grounding systems, and the LED circuit and protector circuit are independent power sources to improve sound quality.
The equalizer amplifier section uses a high-precision equalizer with an emphasis on disc quality.
As a result, the frequency characteristics have been expanded to 100 kHz and high SN and low distortion have been achieved.
In addition, an MC/MM compatible equalizer is used that supports MC and MM by changing the gain.
In addition, the built-in subsonic filter suppresses waviness and distortion in the ultra-low range caused by the warping of the record.
In addition to minimizing the signal path, the equalizer and power section are completely separated, and the pre-drive stage and power stage are separated by a large heat sink to promote the flux-free concept.
A tone control circuit is incorporated into the NF circuit of the power section.
It uses a direct access input selector that can select all inputs with one touch.
The main volume is made of machined pure aluminum.
Equipped with loudness and high filter.
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Model Rating
| Type | Super FF & DC amplifier |
| Power Amplifier Unit | |
| Effective output (10 hz to 20 khz, THD 0.004%) | 50W + 50W (8 Ω) |
| Total harmonic distortion factor (20 Hz to 20 kHz at effective output) | 0.004% or Less (8 Ω) |
| Intermodulation Distortion Factor (60 Hz : 7 kHz = 4 : 1, SMPTE) | 0.006% or Less (8 Ω) |
| Damping factor (new IHF, 1 kHz) | 40 (8 Ω) |
| Frequency Response (1W) | DC ~ 300 khz + 0 -3dB |
| TIM Strain (Sawtooth method) | Below the measurement limit |
| Slew rate | ± 150 v / μ sec (8 Ω) |
| Rise time | 0.9 μ sec |
| Preamplifier Section | |
| Input Sensitivity / Impedance (1 kHz) | Phono1, 2 mm : 2.5mV/47k Ω Phono1, 2 mc : 250 μ V/100 Ω Tuner, Aux, Tape Play1, 2 : 200mV/47k Ω |
| Phono maximum allowable input (1 kHz) | Phono MM:170mV(THD 0.01%) Phono MC:12mV(THD 0.1%) |
| Output Voltage / Impedance (1 kHz) | Tape rec (Pin) : 200 mv (47k Ω) / 600 Ω |
| Total Harmonic Distortion Factor (1 kHz at 6 V output) | Phono MM : not more than 0.0025% |
| RIAA Deviation (MM, Rec out) | 20 Hz to 100 kHz + 0. 2-0. 5 dB |
| Signal-to-noise ratio (A network, short circuit) | Phono MM : 84 dB or more Phono MC : 65 dB or more Tuner, Aux, Tape play1, 2 : 105 dB or higher |
| Channel Separation (1 kHz) | Phono : 72 dB or more Tuner, Aux, Tape play1, 2 : 90 dB or more |
| Tone control | Bass : ± 10 dB (50 Hz) Treble : ± 10 dB (10 kHz) |
| High filter | 10 Hz (-3dB, 6dB/oct.) |
| Loudness | 100 Hz (+ 8 dB), 10 kHz (+ 5 dB) |
| Audio Muting | -20dB |
| <General> | |
| Rated power consumption | 130W |
| External dimensions | Width 430x Height 112x Depth 334 mm |
| Weight | 7.3kg |