The Sansui AU-717 Integrated Amplifier remains one of Sansui’s most popular units, released from 1977-1979 the AU-717 used some advanced approaches for its day with a clean, modern look and robust quality construction. With low distortion and moderate output featuring a unique DC stabilization stage the AU-717 is one of the more solid built Sansui amplifier designs in our opinion.
F-2663 Regulated PS + Protection
The AU-717 employs are truly monolithic power plant with separate transformers for each supply. The F-2663 is built around two separate bridge rectifiers and a output of regulated -/+33V dual rails
The initial filter capacitor network was significant increase in capacity with the 220MFd increased to 470MFD and 100MFD input and decoupling to a 330MFD and 220MFD capacity, these including remaining capacitors were replaced with a low impedance, high temp (105C) Nichicon PW and Bipolar VP Nichicons with an increase in operating voltage. New high-grade polypropylene bypass films installed as well.
All small signal devices were replaced with TO-92/TO-92L Fairchild devices for better dissipation and new TO-220 voltage regulators installed with Wakefield performance full synthetic thermal compound applied. VD type diodes were all replaced including both 13V zener diodes and all 1A bridge diodes upgraded to a Ultra-Fast, Soft Recovery type axial Vishay diodes.
BEFORE
AFTER
-/+33V Confirmation. Its important to note that the AU-717 has a floating ground network, tied to the grounding scheme of the drivers.
Hardware
As you can see, and this is often seen on the AU-717’s, that at least two of the mains filters have intact failed when tested ESR/LCR…
All of the 15,000MFD filter capacitors were replaced with new CDE type computer grade capacitors and bypassed with high grade MKP polypropylene film capacitors.
F-2720 Tone
The pre-amp stage of the AU-717 has a very very accurate (see report below) output with some minor changes employ in the component topography we can clean up the signal path coupled output. The AU-717 uses a incredibly well made stepped precision attenuator that is sealed as a quality volume control. Like the input and RIAA, the tone amp stage is well shielded.
The initial differential stage was matched including all remaining devices replaced with modern, low noise TO-92 Fairchild devices. All new bypass films including high grade MKP and audio grade WIMA films. Capacitors were replaced with a audio grade KT/KA and low impedance type Nichicon PW with an increase in operating voltage. VD type diodes were replaced with modern Fairchild 4148 type general axial and all 82ohm fusible resistors replaced with carbon film type.
BEFORE
AFTER
TR Diff Stage Mapping
F-2723 RIAA EQ
The RIAA EQ uses a similar differential gain stage and coupled input/outputs. This stage is well shielded like all AF stages in the 717. Like the above AF stage the output coupling components were simplified for a reduction in overall series resistance.
All of the electrolytic were replaced audio grade/BP KT/KA/ MUSE and low impedance PW Nichicons with an increase in operating voltage. New high grade polypropylene films including the 1MFD input installed. All small signal devices were replaced with modern, low noise TO-92 fairchild type and remaining fusible resistors replaced and VD type diodes to general axial Vishay type.
BEFORE
AFTER
TR RIAA Diff Stage Mapping
RIAA Curve Response
F-2721 & F-2722 Drivers
The AU-717, like many Sansui’s uses a dual JFET 2Sk97 device for the initial differential stage to establish the zero drift dc deviation circuit along with a push-pull front end and NPN/PNP Darlington output stage configuration.
Small signal and TO-126 pre-drivers as well as TO-220 type driver devices were all replaced with low noise, modern Fairchild and OnSemi devices, TO-220 type with new performance Wakefield full synthetic compound. Fusible resistors were replaced with carbon film type and new precision Bourns potentiometers installed.
New high grade and audio grade WIMA polypropylene films installed as well as new low impedance, high temp (105C) Nichicon PW with an increase in operating voltage.
BEFORE
AFTER
Bias Confirmation
Audio Notizen
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