R. Pontow Sansui AU-717 Integrated Amplifier

Sansui AU-717 Integrated Amplifier

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

C. Nettles Marantz 4300 Quadradial Receiver

Marantz 4300 Quadradial Receiver

The Marantz 4300 was a impressively built 40W/100W Stereo+Quadradial receiver manufactured from 1972 to 1978 (est.) and encompassing the proprietary "Vari-Matrix" which allows for two to four channel emulation and output. (Customer purchased a Black Replica Faceplate for unit shown in both original Silver and Black)

P800 Regulated PS

The 4300 PS is designed quite a bit differently than the lower series 42XX quads, with a regulated 35V and 14Vdc output with two full wave rectifiers. 

Uniquely Marantz mounted C803 on the P800 to  the chassis as a large axial 1000MFD component, as I always try to avoid any axial capacitor this was replaced by a high temp (105C) low impedance PW capacitors 1000MFD on the actual footprint of the PCB removing long runs of wire an unnecessary connects. 

Both NPN TO-220 regulators were replaced with a robust modern TIP variant with new full synthetic thermal compound as well as remaining small signal devices with new low noise TO-92L Fairchild devices with better dissipation. A new adjustment precision Bourns potentiometer was added. All electrolytic were replaced with high temp (105C) low impedance PW capacitors and high grade WIMA/Polypropylene film capacitors with an increase in operating voltage.

BEFORE

 AFTER

35Vdc SE Confirmation

The 20,000MFD filter capacitors were replaced with a computer-grade Nippon Chem Con type

P700 Drivers

The 4300 has very robust and heavy built driver assemblies with a unique parallel mounting pattern. With a differential front end and tied PP output stage the P700 routes through the phase inverting stage and the BTL (Balanced Transformer-less Connection).

Unlike the original diff pairs, new matched beta differential were installed and then thermally coupled together for better DC stability. 

Differential Boding

The Pre-driver and biasing/regulating devices were all replaced with modern low noise TO-92’ Fairchild devices and a high-speed ZTX TO-92 devices, new TO-220 KSA was also installed. All VD diodes replaced with modern Vishay axial diodes and new precision Bias potentiometers installed, the original offset closed frame plastic pots were removed and proper cleaned.

All new low impedance Nichicon PW and high grade WIMA/Polypropylene film capacitors installed with an increase in operating voltage. 

BEFORE 

AFTER

Bias Confirmation

PE01 Pre-/Buffer

The 4300 has a different approach to the gain stage here, with a tiered input/output gain stages including additional tone control pickup.  The PD01 and PE01 are mounted perpendicular tongue/grove fit which soldered versus wire leaded. 

In the PE01 stage all the initial input .22MFD and other 1FMD< were replaced with a high grade WIMA polypropylene film capacitors, remaining electrolytics/tantalum were all replaced with a audio grade KT/KA Nichicon with an increase in operating voltages. The Decoupling was increased in MFD with a low impedance Nichicon PW.  All small signal devices were replaced with low noise, modern TO-92 Fairchild devices.

BEFORE

 AFTER

PD01 Tone

The PD01 tone buffer stage electrolytics and tantalums, like above were all replaced with audio grade KA/KT and low impedance PW, Bipolars were replaced with a audio-grade Nichicon MUSE type, all  with an increase in operating voltages. All small signal devices were replaced with low noise, modern TO-92 Fairchild devices.

BEFORE

 AFTER

PM01 Inverter

The distal stage phase inverter had all of the electrolytic capacitors replaced with audio grade KA/KT Nichicon capacitors with an increase in operating voltage. All new small signal devices were installed with TO-92/L modern low noise Fairchild devices.

BEFORE 

AFTER

P400 Phono

The gain stage NPN’s were all replaced with low noise modern Fairchild TO-92 devices matched to 1% BETA. The 100MFD decoupling electrolytic was increased to a 220MFD for better filtering and replaced with audio grade KA/KT with an increase in operating voltages along with remaining electrolytic. The ceramics and 1MFD were all upgraded to WIMA polypropylene film capacitors. New Bourns precision clipping potentiometers installed.

BEFORE 

AFTER

RF & P500 Vari-Matrix / 400Hz Oscillator

Dolby and associated RF stage electrolytic and tantalum capacitors were replaced with a low impedance Nichicon PW with an increase in operating voltages.

The vars-matrix, which takes a stereo input and converted to quadraphonic output. All of the electrolytic here were replaced with a low impedance and audio grade KA/KT Nichicons with an increase in operating voltages. New high-grade WIMA PP films and all associated small signal devices were replaced with TO-92/L low noise Fairchild devices. 

BEFORE 

AFTER

New custom 8V SMD LED's installed in both meters and dial display with new Vellum paper to replace the old stained parchment.