Audio Database

AU-D607F
Commentary

This pre-main amplifier is equipped with a newly developed super feed-forward system that transcends the limits of NFB.

In order to supplement the NFB technology used in conventional amplifiers and to further reduce distortion, this circuit is equipped with a newly developed Super Feedforward System. This circuit is based on the feedforward theory devised by H. S. Black in 1928. In 1975, SANSUI explored the possibility of practical use, but it crashed into a wall and was interrupted. In 1978, the research was restarted but failed. In 1980, we obtained a hint that NFB technology could be used in combination, and finally completed this circuit.
This feed-forward circuit takes out only the distortion component from the original signal, combines it with the output in opposite phase, and cancels the distortion. However, this circuit is only theoretically possible and has many problems to overcome, so it was considered a phantom theory. Therefore, the Super Feed-forward system combines the advantages of both NFB and feed-forward.
The NFB mainly works to improve low-frequency distortion and also takes out anti-phase distortion for feed-forward. In addition, an error collection amplifier for feed-forward is installed, and computer technology is used to develop an output summing network capable of canceling distortion even in response to 2-pole compensation, making it possible to eliminate distortion over a wide band.
This super feed-forward system enables designs with low NFB, improves amplifier stability and reduces TIM distortion to almost 0.

It is equipped with the diamond differential circuit adopted in the AU-D series.
The diamond differential circuit is a dual complimentary service differential connection consisting of two pairs of upper and lower differential circuits. It is mounted on the pre-drive stage to deliver the necessary drive current to the power stage accurately even for transient and complex peak inputs such as music signals.
The 2-pole phase compensation circuit extends the operating range of the NFB and realizes excellent high-speed response to input signals.

It is designed to be simple and straight, and the signal flow is very short and simple. At the same time, three dimensional wiring is carried out to create the shortest signal path.
Furthermore, by adopting a heat pipe for heat dissipation, it is possible to develop the pattern from input to output along the flow of the circuit diagram in an ideal portable type for the printed circuit board configuration. Therefore, the power stage and driver stage can be set close to each other, which was difficult with the conventional heat sink. Furthermore, the two transistors constituting the push-pull output circuit can be installed close to each other, eliminating the need to draw wires near the output transistor through which a large amount of power flows.
A twin relay speaker switch is used to switch between speakers A and B to prevent the output line from being routed.

By utilizing the know-how acquired through the AU-D907Limited and using a large amount of wood bonnet, bronze-plated screws, and NM elements, we are thoroughly implementing designs that are less affected by magnetic strain, including the substrate and chassis structure.

The tone amplifier is omitted and the configuration consists of two amplifiers, a high-gain equalizer amplifier and a power amplifier.
The EQ uses a low-noise, high-gm dual FET for the first stage, and a push-pull drive pure complimentary service SEPP output with two differentials and current differentials with a current mirror.
In addition, a DC servo system is employed to remove the output capacitor while maintaining the stability of the DC region, and all signal capacitors from the input to the speaker out are eliminated.

A newly developed linear servo regulator is used for the power supply dedicated to the equalizer.
By supplying a constant bias current in the circuit, this stabilized power supply can provide a stable response to transient loads, enabling a clean and stable power supply at all times.

The MM/M input of the AU-D607F is switched by the gain and input impedance switch of the equalizer, so that even when the MC cartridge is used, the configuration is ICL and OCL.
In addition, MM/MC can be switched with the switch on the front panel, and the current position is indicated by the lighting of the indicator.

The power supply section is a two independent power supply system with a 32,800 μ F custom capacitor.

It is equipped with a simple tone control circuit composed of CR.
Because it is a simple system without an equalizer or power amplifier, it is designed so that the tone control does not work at the volume position of -6dB to 0 db (at full power). Therefore, the saturation does not exceed the amplification of the amplifier at full power unlike the conventional system.

Equipped with a subsonic filter, 2-circuit tape monitor, recording selector / copy function, audio muting, balance control, input selector with encoder, etc.

There were 2 kinds, black model with Rosewood style bonnet and silver model with white oak style bonnet.

Model Rating
Type Integrated amplifier
Power Amplifier Unit
Effective power 75W + 75W (8 ohm, 10 hz to 20 khz, THD 0.005%)
75W + 75W (8 ohm, 1 kz, 0.003% THD)
Total harmonic distortion factor (10 Hz to 20 kHz at effective output) Not more than 0.005%
Intermodulation Distortion Factor (60 Hz : 7 kHz = 4 : 1, SMPTE) Not more than 0.008%
Output Bandwidth (IHF, both channel operation, THD 0.02%) 5 Hz to 70 kHz
Damping factor (new IHF, 20 Hz to 20 kHz) 100 (8 Ω)
Frequency Response (1W) DC ~ 300 khz + 0 -3dB
Signal-to-noise ratio (A network) 110 dB or more
Envelope distortion Below the measurement limit
TIM Strain (Sawtooth method) Below the measurement limit
Slew rate ± 180 v / μ sec (8 Ω)
Inside slew rate ± 300 v / μ sec (8 Ω)
Rise time 0.8 μ sec
Preamplifier Section
Input Sensitivity / Input Impedance (1 kHz) Phono1, 2 mm : 2.5mV/47k Ω
Phono1 MC : 250 μ V/100 Ω
Tuner, AUX, Tape Play1, 2 : 250mV/27k Ω
Phono maximum allowable input (1 kHz, THD 0.01%) MM:200mV
MC:20mV
Output Level / Impedance (1 kHz) Tape Rec : 250 mv (47k Ω) / 600 Ω
Total harmonic distortion factor Phono1, 2 mm : 0.005% or less (20 Hz to 20 kHz, 5 V)
RIAA Deviation (MM) 20 Hz to 20 kHz ± 0.2 dB
Signal-to-noise ratio (A network) Phono1, 2 mm : 88 dB or more
Phono1 MC : 70 dB or more
Phono input equivalent noise
(A network, short circuit)
Phono1, 2 mm : -140dBV
Phono1 MC:-142dBV
Channel separation Phono1, 2 mm : 60 dB or more
Phono1 MC : 50 dB or more
Tuner, AUX, Tape Play : 80 dB or higher
Tone control Bass : + 6 to -8dB at 50 Hz
Treble : ± 6 dB at 10 kHz
Filter Low : 16 Hz (-3dB, 6dB/oct.)
Audio Muting -20dB
<General>
Rated power consumption (Electrical Appliance and Material Control Law) 200W
External dimensions Width 445x Height 163x Depth 403 mm
Weight 12.4kg